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The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is a destructive pest that causes damage to rice crops worldwide. The olfactory system is critical for host or mate location by weevils, but only limited information about the molecular mechanism of olfaction-related behaviour has been reported in this insect. In this study, we conducted SMRT-seq transcriptome analysis and obtained 54,378 transcripts, 38,706 of which were annotated. Based on these annotations, we identified 40 candidate chemosensory genes, including 31 odorant-binding proteins (OBPs), six chemosensory proteins (CSPs) and three sensory neuron membrane proteins (SNMPs). Phylogenetic analysis showed that LoryOBPs, LoryCSPs and LorySNMPs were distributed in various clades. The results of tissue expression patterns indicated that LoryOBPs were highly abundant in the antennae, whereas LoryCSPs were highly abundant not only in the antennae but also in the abdomen, head and wings. Our findings substantially expand the gene database of L. oryzophilus and may serve as a basis for identifying novel targets to disrupt key olfactory genes, potentially providing an eco-friendly strategy to control this pest in the future.

Herbivores use plant chemicals for host plant selection to maximize their own and/or offspring performance. Since host plants that are optimal for mother and offspring are often different and spatially/temporally separated, it remains unclear how plant chemicals are associated with trade-offs between adult preference and larval performance. We found that adults of the rice water weevil (Lissorhoptrus oryzophilus), one of the most important pests on rice in the world, preferred volatiles from barnyard grass over rice and tended to feed and oviposit on barnyard grass compared with rice. In contrast, larvae performed better on rice roots than on barnyard grass roots. Chemical analyses further showed that rice roots had higher nitrogen and soluble protein but lower lignin and cellulose contents than barnyard grass. Together, these results suggest that volatile emissions, specific non-volatile nutritive and defensive chemicals may have close correlations with trade-offs of the adult preference and larval performance between these two hosts. As developing chemical-based technology is one of the main approaches for the control of pest insects, our findings may also contribute to the future efforts for management of the rice water weevil.

Plant structural traits can act as barriers for herbivore attachment, feeding, and oviposition. In particular, epicuticular waxes (EWs) on the aerial surfaces of many land plants offer protection from biotic and abiotic stresses. In rice (Oryza sativa L.), mutations that reduce EWs have been previously reported. However, whether such mutations affect rice water weevil (Lissorhoptrus oryzophilus Kuschel) and fall armyworm (Spodoptera frugiperda Smith) performance has not been investigated yet. These pests cause significant economic problems in important rice-producing areas of the United States. The aim of our study was to characterize the EWs of EW mutants and wild-type rice plants by gas chromatography–mass spectrometry and compare the resistance of mutant and wild-type plants against rice water weevil and fall armyworm. We hypothesized that mutants with reduced EWs would have weaker resistance to pests than wild-type plants. Three mutant lines (6-1A, 7-17A, and 11-39A) and their wild-type parent (cv. ‘Sabine’) were used to test this hypothesis. Levels of EWs were significantly lower in mutant lines than in the wild-type, and qualitative differences in EW composition were also observed. Reduction in EWs significantly affected performance of insects in experiments conducted under greenhouse conditions. Experiments with rice water weevils were conducted in arenas in which females were given a choice of the mutants and the wild-type for oviposition. Number of first instars emerging from the three EW mutants (an indication of oviposition preference) was higher on the three EW mutants than on wild-type plants with normal wax levels. Similarly, in no-choice experiments using whole plants or detached leaves, weight gains of armyworms on leaves were higher on the mutant lines than on the wild-type. These results indicate that EW traits are involved in rice resistance to weevils and armyworms. Understanding the plant traits that contribute to resistance to rice pests will be helpful for the development of resistant varieties for reducing pest insect damage.

Water conservation is an important factor for production of rice in the United States because of declining aquifer levels, but little research has been done to evaluate insect management in rice systems integrating water conservation practices. Rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important insect pest of rice in the U.S. Rice water weevil is a semiaquatic species that relies on flooded conditions to complete larval development, so water conservation practices are likely to impact their pest status. The study was conducted across the Mississippi River alluvial floodplain to compare rice water weevil population densities in different zones of a furrow irrigated rice field to a conventionally flooded rice field. All locations were sampled at 3, 4, and 5 wk after the initial irrigation. Larval densities were greatest in the lower end of furrow irrigated fields and in the adjacent flooded rice field compared with the upper and middle sections that did not hold standing water when averaged across three sample dates. Also, rice water weevil densities were greater during week five than week three. In terms of rice yields, the top third of furrow irrigated rice fields, the section that remained mostly dry, produced lower rough rice yields than all other sections and the flooded field. These results suggest that rice water weevil populations can be lower in a furrow irrigated rice system. As a result, more research is needed to determine whether a spatial management plan can be developed based on soil moisture zones in furrow irrigated rice.

Associations with arbuscular mycorrhizal (AM) fungi can increase or decrease plant resistance to herbivory in different crop systems, but the effects of AM fungi on plant tolerance to pests remain largely unknown. We investigated whether inoculation of rice (Oryza sativa) with AM fungi stimulates plant growth, yield, and/or tolerance to rice water weevil (Lissorhoptrus oryzophilus) injury. Rice plants were exposed to natural infestations of herbivores during early and mid-to-late season over four field experiments. The experiments followed a 2 × 2 factorial design consisting of two AM fungi seed treatments (inoculated or non-inoculated with AM fungi) and two insecticide seed treatments (treated or untreated). Inoculation with AM fungi increased root colonization in all four field experiments in rice. Inoculation with AM fungi increased densities of weevil larvae and whiteheads resulting from stemborer infestations, while insecticidal seed treatments significantly reduced densities of weevils and marginally reduced whiteheads. Inoculation with AM fungi increased rice biomass before and after flooding, and a clear but not always significant increase in yield was observed in plants inoculated with AM fungi. However, inoculation with AM fungi did not reduce percent yield losses after herbivory injury. Analyses of nutrient contents in roots and shoots revealed inconsistent effects of inoculation with AM fungi. This study highlights for the first time the potential for AM fungi seed treatments to increase rice tolerance to insect pests by influencing plant biomass and yields.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important early-season pest of rice in the U.S. Additionally, lepidopteran stem-boring pests particularly the invasive Mexican rice borer, Eoreuma loftini (Dyar), are increasingly becoming problematic in Louisiana rice. Although insecticidal seed treatments have been widely adopted and have proven highly effective against weevils and stemborers, alternative management tactics are needed. This study was conducted to evaluate the effects of flood timing and rice cultivar on rice water weevil and stemborer infestations. Field experiments were conducted in Crowley, Louisiana, from 2019–2020. In each year, early- and late-planted trials were established according to a split-split-plot randomized block design. Four commonly grown rice cultivars were selected and were either treated or not treated with a chlorantraniliprole seed treatment. Permanent flood was established at normal timing (approximately the five-leaf stage) or delayed by 2 weeks. Seed treatment reduced weevil densities and stemborer injury by 70–84% and 87–94%, respectively, across planting dates, years, cultivars, and flood timings. The rice cultivar ‘Jupiter' consistently supported the highest numbers of immature weevils, whereas low levels of stemborer injury were observed in ‘Jazzman-2'. Weevil densities were 72 and 20% lower in plots subjected to delayed flood compared to normal flood timing in the 2019 and 2020 late-planted trials, respectively. Reductions of 79 and 93% in stemborer injury in the 2019 early- and late-planted trials, respectively, were observed in delayed flooded plots. Weevil and stemborer infestations negatively affected rice yields, with losses among cultivars ranging from 14 to 49%. Yield losses were generally lower in plots subjected to delayed flood compared to normal flood timing but the difference was only significant in the 2020 late-planted trial. Our data suggest that the combination of cultivar resistance and delayed flooding can serve as a valuable component of an integrated pest management program for both rice water weevil and stemborers.

When applied exogenously to plants, jasmonates [i.e., jasmonic acid (JA) and methyl jasmonate (MeJA)] increase plant resistance against herbivores, and their use in pest management has been suggested. For integration into pest management programs, the benefits of the resistance induced by jasmonates must outweigh the costs of jasmonates on plant growth and yield. A previous field study in rice found that seed treatment with MeJA reduced densities of the rice water weevil, Lissorhoptrus oryzophilus, but also reduced plant growth. Yields from MeJA plots were similar to yields from control plots. Because this study was conducted under field conditions with natural levels of pest populations, it was unclear whether effects on growth and yield were due to direct effects of MeJA treatment on the plant or due to lower reductions in rice water weevil densities. Therefore, the present study was designed to characterize the effects of JA and MeJA seed treatment on rice plant growth and yield in a pest-free environment under greenhouse conditions. Seed treatment with 2.5 mM JA and 2.5 mM MeJA enhanced resistance in rice plants to rice water weevils when plants were exposed to weevils 30 days after planting. Seed treatment with MeJA reduced seedling emergence and plant height at 4 and 14 days after planting, respectively, compared to JA and control treatments. However, numbers of tillers per plant at 45 days after planting and days to heading were unaffected by jasmonate seed treatment. Of four yield components (panicles per plant, filled grains per panicle, percent unfilled grains, and filled grain mass) that were measured, only filled grain mass was reduced by seed treatment. Plants grown from MeJA-treated seeds showed 31% lower grain masses compared to plants grown from control-treated seeds. Thus, the effects of seed treatment with MeJA on plant growth were stronger immediately post-treatment and subsided over time, such that plant growth mostly recovered 6 weeks after treatment. At maturity, MeJA may reduce one but not all components of yield. Despite similar effects on rice water weevil resistance, the negative effects of JA seed treatment on plant growth and yield were smaller compared to MeJA seed treatment.

The rice water weevil Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) is a worldwide agricultural pest that causes serious damage to rice. The olfactory and gustatory behaviors of L. oryzophilus in locating host plants and oviposition sites mostly rely on the detection of chemical stimuli in the environment. To reveal such olfactory and gustatory systems, we performed a systematic analysis of major chemosensory receptor genes. The antennal transcriptome of adult female L. oryzophilus was sequenced and assembled using the Illumina sequencing platform. A total of 60 candidate chemosensory receptor genes were ultimately identified, including 41 putative odorant receptors (ORs), 10 ionotropic receptors (IRs) and 9 gustatory receptors (GRs). Relatedness with other species was predicted based on phylogenetic results, and specific chemosensory receptor genes were analyzed, including Orco, carbon dioxide receptors and sugar receptors. Furthermore, qRT-PCR analyses of chemosensory receptor genes showed 59 genes to be antenna-biased genes, whereas only 1 gene was predominantly expressed in non-olfactory tissues. Our research provides insight for understanding olfactory and gustatory systems in the antennae of L. oryzophilus and facilitating the discovery of novel strategies for controlling this pest.

Background For the past decade, insecticidal seed treatment has been the most widely used control tactic against insect pests of rice (Oryza sativa L.) in the USA. Seed treatments are used primarily to control the most economically important early-season pest of rice, the rice water weevil (Lissorhoptrus oryzophilus Kuschel). This study was conducted to evaluate the efficacy of reduced rates of chlorantraniliprole seed treatment against the rice water weevil, fall armyworm (Spodoptera frugiperda J.E. Smith), and sugarcane borer (Diatraea saccharalis F.) under field and laboratory conditions. Concentrations of chlorantraniliprole in plant tissues were determined at vegetative and reproductive developmental stages of rice plants. Results Chlorantraniliprole seed treatment reduced the densities of rice water weevil larvae relative to non-treated controls even at rates 75% lower than the label rate. Increased mortality of fall armyworm larvae was observed at reduced seed treatment rates relative to a non-treated control. Chlorantraniliprole seed treatment increased the mortality of sugarcane borer larvae at all rates relative to controls and the mortality was consistently higher in larvae that were fed stems from treated plants at the vegetative developmental stage than larvae that were fed stems from plants at the reproductive stage. Concentrations of chlorantraniliprole in plant tissues increased with seed treatment rate and decreased with plant age. Conclusion This study has shown that reduced chlorantraniliprole seed treatment rates can provide adequate control against the rice water weevil, fall armyworm, and sugarcane borer, particularly at early developmental stages of rice plants. © 2019 Society of Chemical Industry.

Rice water weevil (RWW) is divided into two types of population, triploid parthenogenesis and diploid bisexual reproduction. In this study, we explored the meiosis of triploid parthenogenesis RWW (Shangzhuang Town, Haidian District, Beijing, China) by marking the chromosomes and microtubules of parthenogenetic RWW oocytes via immunostaining. The immunostaining results show that there is a canonical meiotic spindle formed in the triploid parthenogenetic RWW oocytes, but chromosomes segregate at only one pole, which means that there is a chromosomal unipolar division during the oogenesis of the parthenogenetic RWW. Furthermore, we cloned the conserved sequences of parthenogenetic RWW REC8 and Tws, and designed primers based on the parthenogenetic RWW sequence to detect expression patterns by quantitative PCR (Q-PCR). Q-PCR results indicate that the expression of REC8 and Tws in ovarian tissue of bisexual Drosophila melanogaster is 0.98 and 10,000.00 times parthenogenetic RWW, respectively (p &lt, 0.01). The results show that Tws had low expression in parthenogenetic RWW ovarian tissue, and REC8 was expressed normally. Our study suggests that the chromosomal unipolar division and deletion of Tws may cause parthenogenesis in RWW.

Herbivores use plant chemicals for host-plant selection to maximize their own and/or offspring performance. Since host plants that are optimal for mother and offspring are often different and spatially/temporally separated, how plant chemicals affect trade-offs between adult preference and larval performance remains unclear. We found that adults of the rice water weevil (Lissorhoptrus oryzophilus), one of the most important pests on rice in the world, preferred volatiles from barnyard grass over rice, tended to feed and oviposit on barnyard grass compared with rice. In contrast, larvae performed better on rice roots than on barnyard grass roots. Chemical analysis further show that rice roots had higher nitrogen and soluble sugar but lower lignin and cellhouse contents than barnyard grass. Together, these results suggest that violate, nutritive and defensive chemicals could jointly determine trade-offs of the adult preference and larval performance on these two hosts. As developing chemical-based technology is one of the main approaches for control of pest insects, our findings may also contribute to the future efforts for management of the rice water weevil.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important economic pest of rice in the United States with the ability to substantially reduce rice yields. Stem borers, including the Mexican rice borer, Eoreuma loftini (Dyar), are emerging as more consistent pests in Louisiana and Texas, but the relationship between blanked panicles (whiteheads) caused by stem borer feeding and yield loss is not well understood. A series of field trials was conducted in Louisiana from 2019 to 2020 to determine the relative yield loss by manipulating infestations of both pests with selective insecticides. Results indicate losses from L. oryzophilus infestations are greater than those for E. loftini in early planted rice. In contrast, relative yield losses were approximately equal in later planted rice in 2019, in which E. loftini infestations were high. Additive impacts of the root-feeding L. oryzophilus and the stem-feeding E. loftini were not observed in our study. Linear regression revealed that each increase of one whitehead per square meter is associated with a 1.7% loss in yield. Results from ratoon rice suggest that protection from L. oryzophilus in the main crop also improves yield in the second crop. Collectively, results demonstrate the continued need for effective L. oryzophilus management programs to prevent economic losses. Conversely, findings suggest that benefits of E. loftini control may be minimal in many instances. Control of E. loftini is most likely to be economical under conditions where high populations are anticipated such as in late-planted fields or regions that previously had high infestations.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. We face an increasing global food security challenge as the human population continues to grow across the globe. As agricultural production rises to keep up with food demand, so too does the expansion of crop detrimental pest species. Early detection can be crucial to control their damage and relies on the use of accurate and dependable techniques. We report the first record of rice water weevil (Lissorhoptrus oryzophilus) in the Iberian Peninsula. The distribution range expansion of this invasive rice pest weevil is confirmed through traditional sampling and through natural sampling by bats combined with DNA metabarcoding, a non-invasive technique with strong potential for early detection of pests in agricultural areas. Presence of rice water weevil was confirmed genetically from bat faecal samples collected from a Pipistrellus pygmaeus bat roost in the Ebro Delta (Catalonia, Spain). The known distribution of this rice pest, native to North America, now includes four of the top five rice-producing European countries. To date, the economic damage caused by this pest in Europe is minimal and concentrated in small areas, but chemical and agronomic controls are implemented to control their populations. The nature of this record highlights the potential of insectivorous bats as natural samplers to detect (and possibly control) pest species in crops. Further studies are required to determine the full extent of the rice water weevil's spread, and to investigate integrated pest management systems, including biological control to suppress their populations.

An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS during 2017 and 2018 to determine whether removal of the flood is an economical method of control for rice water weevil, Lissorhoptrus oryzophilus Kuschel. This experiment compared a continuous flood production system to draining a rice field completely and reestablishing a flood for the remainder of the growing season. In addition, two insecticide seed treatments, thiamethoxam and chlorantraniliprole, were compared with an untreated control within each system. Rice water weevil densities were measured prior to draining at 3 wk after flood and again after the flood was reestablished in drained plots. Rice water weevil densities were greater in 2017 than 2018. Chlorantraniliprole at the predrainage and postdrainage sample timing reduced larval numbers compared with the untreated control. The plots where water was removed until soil cracking then re-flooded had significantly lower weevil populations than plots that were continuously flooded during 2018 only. Draining of plots resulted in lower yields in 2018, but not in 2017. Additionally, both of the insecticide seed treatments resulted in greater yields and economic returns than the untreated control. Draining of flooded rice when rice water weevil larvae were present did not provide a consistent benefit, and may result in yield and economic penalties. Insecticide seed treatments consistently provided greater yield benefits in flooded rice. Based on these results, draining of flooded rice is not recommended to manage rice water weevil and insecticide seed treatments should be used to minimize economic losses.

Adaptations to low temperature play a critical role in restricting the geographical distribution of insects. Decreasing day lengths and temperatures trigger seasonal cold adaptations in insects. These adaptions include changes in expression at the miRNA, mRNA and protein levels. The rice water weevil (RWW), Lissorhoptrus oryzophilus, introduced from the Mississippi River, is a globally invasive pest of wetland rice that can survive at the northern border of China. To investigate the changes in expression at the protein level in overwintering female RWW adults, 6-plex tandem mass tags (TMTs) were used in overwintering and summer adults. By using a proteome database available for Curculionidae, 1077 proteins were quantified, 183 of which differed significantly between the overwintering and summer samples. To further understand these differentially expressed proteins (DEPs), bioinformatics analyses such as gene ontology (GO) enrichment analyses were performed. DEPs associated with the terms binding, structural molecule activity, catalytic activity, multicellular organismal process, extracellular region, chitin binding, metabolic process, intracellular part and organic cyclic compound binding were altered by selection during winter. The changes in the expression of these proteins suggest that the proteins are important for RWW survival in winter.

The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel, is one of the most destructive pests causing heavy rice yield loss worldwide. In the present study, amplified fragment length polymorphism (AFLP) was used to analyze the genetic differentiation and transmission routes of 26 RWW geographical populations from Guizhou and 6 other provinces in China. The genetic distance between the 26 populations ranged from 0 to 0.693; the genetic distance between Guizhou and 6 other provinces populations varied from 0.043 to 0.693, with an average of 0.382. There was higher genetic variation among the populations from Guizhou and 6 other provinces compared with populations within Guizhou. The Mantel test showed no correlation between the genetic and geographical distances of the 26 populations. According to genetic distance, clustering, and time that RWW was found in these regions, we deduced that the pest entered Guizhou and spread in this province most likely via three routes: (1) from Hebei to Zunyi and southward to the south-central regions; (2) from Sichuan to Bijie and eastward to the central regions; and (3) from Yunnan through Anshun to the central regions and Qiandongnan prefecture. RWW spread in a natural manner, including flight, crawling, swimming, and by human-associated mechanisms, comprising dissemination through paddies and hay and hitchhiking on human transportations.

Neonicotinoid seed treatments are widely used in agriculture. In rice, Oryza sativa L., in the southern United States, neonicotinoid seed treatments are used to manage early-season populations of the rice water weevil, Lissorhoptrus oryzophilus Kuschel. In addition to their effects on pests, neonicotinoid seed treatments may benefit crop plants directly by increasing plant growth or altering plant responses to stresses. As part of an effort to assess the overall benefits of thiamethoxam seed treatment in rice, rice emergence, growth, and yield were evaluated. In a growth chamber, rice emergence from the soil was 1-2 d more rapid from treated than untreated seeds. These laboratory results were supported by field experiments that revealed higher stand counts from thiamethoxam-treated plots than from untreated plots. Yields from thiamethoxam treatments were no higher than those from untreated plots under conditions in which weevil larvae were absent, a result inconsistent with the hypothesis that thiamethoxam imparts direct yield benefits. In a series of field experiments conducted to compare the relationship between weevil larval densities and rice yields in plots treated with several rates of thiamethoxam or chlorantraniliprole (another widely used seed treatment insecticide), the relationship between weevil density and yield did not differ markedly among both seed treatments. Overall yields from both seed treatments did not differ significantly, despite more effective control in chlorantraniliprole-treated plots. These results provide strong support for effect of thiamethoxam on early-season growth of rice, but only weak support for its direct effect on rice yields.

BACKGROUND In California, rice fields are flooded over the winter months (November through March) to facilitate degradation of post-harvest rice straw and to provide temporary habitat for migratory waterfowl. Prior research showed that winter flood rice fields had fewer rice water weevil (Lissorhoptrus oryzophilus), larvae and pupae during the rice production season than fields that were left unflooded in the winter. A series of experiments were conducted to provide further support for these trends under controlled conditions and to find a mechanism for this phenomenon. RESULTS Under winter flooded conditions there was a 50% reduction in populations of weevil immatures compared with the untreated control (no straw or winter flood). These same conditions corresponded with a 20% increase in the amount of silicon found in plant tissues in 2014 and a 39-90% decrease in methane production in the soil from 2013–2014. CONCLUSION Evidence from previous field research and these controlled studies provides support for the idea that winter flooding is an appropriate tactic for controlling L. oryzophilus populations in following the spring. However, the mechanism that would explain why winter flooding adversely affects L. oryzophilus immatures remains unclear.

The jasmonic acid cascade plays a pivotal role in induced plant resistance to herbivores. There have been a number of investigations into the potential uses of derivatives of this hormone for pest management. Understanding the phenotypic plasticity of plant defense traits interactions in agricultural systems may facilitate the development of novel and improved management practices, which is desirable as management of insects in most agricultural systems is currently heavily reliant on insecticides. The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel, is a pest of rice, Oryza sativa, in the southern U.S. and globally. The effects of the jasmonic acid derivative, methyl jasmonate (MJ), on induced defenses to RWW in rice, and the potential costs of MJ-induced resistance to plant growth and fitness, were tested in a series of field and greenhouse trials. It was hypothesized that seed treatments with MJ would reduce densities of larval RWW. A second hypothesis was that MJ seed treatments would alter emergence, biomass accumulation, and yield of rice. The final hypothesis was that induction of plant resistance to the RWW would diminish as the time from seed treatment increased. In order to investigate these hypotheses, RWW densities were determined in greenhouse and field trials. Plant growth was measured in the field by assessing plant emergence, root and shoot biomass, time of heading, and yield (grain mass). Results indicated that MJ seed treatments induced resistance to RWW, although this effect decayed over time. Additionally, there were costs to plant growth and fitness; emergence and heading were delayed and biomass was reduced. Importantly, however, yields on a per-plant were not significantly reduced by MJ treatment. Overall, these results are promising and show the potential for the use of jasmonate elicitors as part of a pest management program in rice.

Current pest management practices for the rice water weevil (Lissorhoptrus oryzophilus Kuschel) and the Mexican rice borer (Eoreuma loftini Dyar) in U.S. rice rely heavily on a small number of insecticides. Thus, additional products are needed to delay resistance development and replace products no longer available to farmers. Evaluation of novel and widely used insecticidal seed treatments was conducted in eight small plot field trials from 2015 to 2019 in Louisiana and Texas. Treatments evaluated included the insecticides cyantraniliprole, chlorantraniliprole, thiamethoxam, and clothianidin. Seed treated with chlorantraniliprole and seed treated with both cyantraniliprole and thiamethoxam together provided the best control of L. oryzophilus across trials. Thiamethoxam and clothianidin seed treatments did not provide satisfactory control of L. oryzophilus. Only chlorantraniliprole seed treatment controlled E. loftini. Improved yield was recorded from plots treated with chlorantraniliprole or cyantraniliprole + thiamethoxam across trials from 2017 to 2019 over fungicide only controls. Yield differences among treatments were not detected in 2015–2016 trials. Registration of cyantraniliprole seed treatment for use in U.S. rice provides a new tool for diversification of pest management practices and insecticide resistance management.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the U.S. This insect poses a global threat to rice production, having invaded rice-producing regions of Asia and Europe. Tolerance is a type of plant resistance that allows crop plants to maintain yield in spite of injury by herbivores. This study was conducted to test the hypothesis that tolerance to L. oryzophilus infestations differs between hybrid and inbred rice cultivars. Field experiments were conducted in Louisiana in 2016–2017 and in multiple locations (Texas, Mississippi, and Louisiana) in 2018. Plant tolerance was assessed by evaluating L. oryzophilus infestations and yields from insecticide-protected and unprotected plots of hybrid and inbred rice cultivars. Infestations of L. oryzophilus negatively affected rice yields, with losses across cultivars ranging from 16.4 to 48.0% in 2016 and 4.2–29.2% in 2017. In the multiple location experiment in 2018, yield losses ranged from 4.1 to 29.7, 7.7–17.2, and 4.5–12.2% in Louisiana, Texas, and Mississippi, respectively. Comparisons of yields between insecticide-protected and unprotected plots indicated that hybrid cultivars exhibited higher tolerance to L. oryzophilus infestations than inbred cultivars in 2016 and 2017. Moreover, in the multiple location experiment in 2018, yield losses were lower in hybrid compared to inbred cultivars in Texas, but no differences in yield losses across cultivars were observed in Louisiana and Mississippi. Rice cultivars expressing tolerance to L. oryzophilus could be used to reduce pest damage in situations where use of insecticides is not practical, too expensive, or only partially effective.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important insect pest of rice in the United States. Management of L. oryzophilus mainly depends upon the use of insecticides due to the lack of effective alternative management tactics. A 3-yr field study was conducted to determine if difference exists among rice genotypes and cultivars of inbred tropical japonica subspecies commercially grown in the southern United States [Cocodrie (PI 606331), CL171, and CL151 (PI 654463)] and the germplasm lines of indica subspecies adapted to tropical climates of Asia [WC 4644 (PI 312777), TNI (PI 495830), Rondo (PI 615022), 4612 (PI 615039), TeQing (PI 536047), and 4593 (PI 615031)] for resistance to L. oryzophilus . Experiments were established as a split-plot design with cultivars as main plots and insecticide treatment as subplots. No significant differences were observed in number of L. oryzophilus larvae recovered across cultivars and genotypes, indicating no significant variation in their preference to L. oryzophilus oviposition. Insecticide treatment had a significant impact on L. oryzophilus larval density. However, grain yield did not vary significantly between treated and untreated plots for any of the cultivars and genotypes. The amount of yield loss in response to L. oryzophilus infestation did not vary significantly across genotypes and cultivars, indicating no variation among these genotypes for resistance to L. oryzophilus.

Pantoea agglomerans is an important bacterial symbiont of insects. Despite its frequent discovery in various insects, little is known of its strain diversity and quantitative dynamics. In this study, we investigated these aspects of the bacterium in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), a serious pest of rice in North America and East Asia. Based on the cloning and sequencing of a bacterial 16S rRNA gene, we identified three novel P. agglomerans strains from different weevil populations, with each population harboring only one strain. In female adults, gut was the dominant tissue harboring P. agglomerans. This bacterium was also present in the ovary, but its density was very low there. The bacterium was maintained at a low density across all immature stages (from egg to pupa); however, the density increased substantially as adults emerged. Its density was low in the overwintering stage, but increased stepwise after the overwintered adults were allowed to feed on host plants, i.e., when they developed from early to actively reproducing stages. The infection density returned to a low level in the adults at a late reproductive stage. In conclusion, each of the L. oryzophilus populations we investigated was probably infected by a single P. agglomerans strain, and the gut of adults is the major tissue/developmental stage to harbor this bacterium, with actively reproducing adults attaining a high level of infection.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most widely distributed and destructive insect pest of rice, Oryza sativa L., in the United States. The objective of this study was to determine overall damage levels of rice water weevils in Florida rice fields. Fifty rice fields were sampled over 2 yr for adult foliar damage. These damage data were used as the criteria for determining when control measures are justified. Although the weevils were widespread in Florida rice fields, damage levels at which control is required occurred in only 2% of fields sampled. An increase in adult feeding damage was observed as the rice season progressed. And, there was a significant correlation of feeding damage among fields within a paddy. These data suggest that Florida rice growers may not have to sample all fields in a paddy to estimate weevil damage in the paddy.

Nardonella (gamma-proteobacteria) are a group of ancient endosymbiotic bacteria that occur only in weevils (superfamily Curculionoidea). Despite the extensive surveys of their existence and phylogeny done in a number of weevil subfamilies, little is known about their strain diversity, quantitative dynamics, and biological roles in the ontogeny of hosts. Here, based on the cloning and analyses of bacterial 16S RNA gene sequences from nine geographic populations of rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), we identified two distinct Nardonella lineages. One lineage was widespread, occurring in each of the L. oryzophilus populations investigated, whereas the other was much geographically limited and found in only one population. These bacteria had a low density in both larval and pupal stages of the weevil; however, they increased substantially as adults emerged. In female adults, they were harbored dominantly in ovary; guts were also infected, but the density was very low. By treating adult females with various antibiotics (rifampicin, tetracycline, and gentamycin) and observing their fecundity, egg viability, as well as the density of Nardonella and the other two bacteria ( Wolbachia and Rickettsia ) present in the ovary, we found females did not produce viable eggs despite the presence of abundant Nardonella. This suggests that Nardonella might be not playing critical roles in the reproduction of L. oryzophilus. The results are expected to extend our knowledge of the biology of Nardonella and their associations with weevils’ reproduction.

This is the first report of the invasive rice pest, rice water weevil (Lissorhoptrus oryzophilus Kuschel) in the Balkans. Adult specimens were collected in the rice field region of Central Macedonia, Greece during July–August, 2016. Morphological identification was verified by DNA barcoding, and the first COI sequence of L. oryzophilus from Greece was deposited in the GenBank database. This semi-aquatic insect is considered one of the most important rice pests globally, and its presence in the region may result in important yield and economic losses in rice production. Considering the highly invasive nature of this species, it is possible that it has spread to neighboring rice wetlands of the Southern Balkans, and additional field investigations are essential to accurately determine its geographic distribution and to help contain its spread.

Densities of insect pests in agricultural communities may be affected by herbicides commonly used for weed management via several routes. First, herbicides may cause direct mortality to insects present both during and immediately following application. Second, herbicides may induce plant defenses that increase resistance to insect herbivores. Third, herbicides may alter the quantity and composition of weed populations, which in turn may change the structure of insect communities found subsequently in the crop. This study was designed to investigate the effects of an array of herbicides on the densities of several major pests found in rice in the southern United States. These pests included the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), the rice stinkbug, Oebalus pugnax (Fabricius) (Hemiptera: Pentatomidae), and a stemborer complex comprised of three lepidopteran species (Lepidoptera: Crambidae). Insects directly exposed to herbicides experienced high mortality; while those fed leaf material that had been exposed to herbicides did not. Herbicide application did not significantly increase resistance in rice to subsequent herbivore infestation. Results provided modest support for the third hypothesis represented by positive correlations between weed densities and insect pest densities.

Plants face numerous challenges from both aboveground and belowground stressors, and defend themselves against harmful insects and microorganisms in many ways. Because plant responses to biotic stresses are not only local but also systemic, belowground interactions can influence aboveground interactions in both natural and agricultural ecosystems. Arbuscular mycorrhizal fungi (AMF) are soilborne organisms that form symbiotic associations with many plant roots and are thought to play a central role in plant nutrition, growth, and fitness. In the present study, we focused on the influence of AMF on rice defense against pests. We inoculated rice plants with AMF in several field and greenhouse experiments to test whether the interaction of AMF with rice roots changes the resistance of rice against two chewing insects, the rice water weevil (Lissorhoptrus oryzophilus Kuschel, RWW) and the fall armyworm (Spodoptera frugiperda, FAW), and against infection by sheath blight (Rhizoctonia solani, ShB). Both in field and greenhouse experiments, the performance of insects and the pathogen on rice was enhanced when plants were inoculated with AMF. In the field, inoculating rice plants with AMF resulted in higher numbers of RWW larvae on rice roots. In the greenhouse, more RWW first instars emerged from AMF-colonized rice plants than from non-colonized control plants. Weight gains of FAW larvae were higher on rice plants treated with AMF inoculum. Lesion lengths and susceptibility to ShB infection were higher in rice plants colonized by AMF. Although AMF inoculation enhanced the growth of rice plants, the nutritional analyses of root and shoot tissues indicated no major increases in the concentrations of nutrients in rice plants colonized by AMF. The large effects on rice susceptibility to pests in the absence of large effects on plant nutrition suggest that AMF colonization influences other mechanisms of susceptibility (e.g., defense signaling processes). This study represents the first study conducted in the U.S. in rice showing AMF-induced plant susceptibility to several antagonists that specialize on different plant tissues. Given the widespread occurrence of AMF, our findings will help to provide a different perspective into the causal basis of rice systemic resistance/susceptibility to insects and pathogens.

The resistance of commercial rice (Oryza sativa L.) varieties widely grown in Louisiana was assessed against the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), the major insect pest of rice in the United States, in a 5-yr field study that included conventional inbred, herbicide-tolerant, and hybrid varieties. Resistance was evaluated by comparing densities of immature rice water weevils (larvae and pupae) in root-soil core samples taken at two time points after flooding. Randomized block experiments were conducted in two different locations to enable identification of potentially resistant varieties over diverse environments. There were small but significant differences in the resistance of commercial varieties over the 5-yr field study. The variety 'Jefferson' was found to support larval densities 6-70% lower than other varieties, while 'Jupiter' often supported higher larval densities. Greenhouse experiments evaluated adult preference for oviposition and survivorship of larvae on different varieties. Females exhibited limited ovipositional preference for varieties: numbers of weevil eggs per plant differed significantly among varieties in choice tests but not in no-choice tests, while first instar densities in both choice and no-choice tests showed no significant differences among varieties. Analysis of data from both choice and no-choice tests showed that numbers of late instars and pupae differed significantly among varieties, suggesting presence of antibiosis in some cultivars. Our results suggest that none of the varieties tested possess high levels of resistance to rice water weevil infestation, although 'Jupiter' appears to be more susceptible than other varieties and 'Jefferson' appears to be somewhat more resistant.

Hybrid rice and insecticide seed treatments targeting rice water weevil, Lissorhoptrus oryzophilus Kuschel, have altered the landscape of rice production. The effect of reduced seeding rates on seed treatment efficacy in hybrid rice has not been studied. During 2011 and 2012, an experiment was conducted at seven locations to determine the relationship between low seeding rates used in hybrid rice and efficacy of selected insecticidal seed treatments as measured by rice water weevil densities and yield. Labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin were compared with higher rates of these products to determine if labeled rates provide an acceptable level of control of the rice water weevil. Study locations were divided into low, moderate, and high groups based on rice water weevil larval densities. All seed treatments and seed treatment rates reduced rice water weevil densities. However, there was no observed yield or economic benefit from the use of an insecticidal seed treatment in areas of low pressure. Differences in yield were observed among seed treatments and seed treatment rates in moderate and high pressure locations, and all seed treatments yielded better than the untreated plots, but these differences were not always economical. All seed treatments showed an economic advantage in areas of high weevil pressure, and there were no differences among seed treatment products or rates, suggesting that currently labeled seed treatment rates in hybrid rice are effective for rice water weevil management.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important pest of rice (Oryza sativa L.) grown in Florida. Reports on the effect of flood depth on rice water weevil populations have been inconsistent. Our objective was to determine if flood depth has any significant effect on rice water weevil populations and other arthropods in rice grown in Florida. Sampling was conducted using adult foliar damage scars, core samples for larvae, and sweep nets for arthropods above the water. Results showed that shallow flooding reduced rice water weevil populations in Florida. Sweep net data showed that flood depth had little, if any, effect on populations of damselflies (Odonata), leafhoppers (Cicadellidae), spiders (Arachnida), or stink bugs (Oebalus spp.).

Two experiments were conducted at the Delta Research and Extension Center in Stoneville, MS, during 2011 and 2012 to determine the impact of water management practices on the efficacy of insecticidal seed treatments targeting rice water weevil, Lissorhoptrus oryzophilus Kuschel. Larval densities and yield were compared for plots treated with labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin and an untreated control. In the first experiment, plots were subjected to flood initiated at 6 and 8 wk after planting. Seed treatments significantly reduced larval densities with the 8-wk flood timing, but not the 6-wk flood timing. Overall, the treated plots yielded higher than the control plots. In the second experiment, the impact of multiple flushes on the efficacy of insecticidal seed treatments was evaluated. Plots were subjected to zero, one, or two flushes with water. All seed treatments reduced larval densities compared with the untreated control. Significantly fewer larvae were observed in plots that received one or two flushes compared with plots that did not receive a flush. All seed treatments resulted in higher yields compared to the untreated control in the zero and one flush treatments. When two flushes were applied, yield from the thiamethoxam and clothianidin treated plots was not significantly different from those of the control plots, while the chlorantraniliprole treated plots yielded significantly higher than the control. These data suggest that time from planting to flood did not impact the efficacy of seed treatments, but multiple flushes reduced the efficacy of thiamethoxam and clothianidin.

The rice water weevil Lissorhoptrus oryzophilus (Coleoptera: Curculionidae: Brachycerinae) was detected in Northern Italy in 2004. As Italy is the major European rice producer, and the rice water weevil is considered to be one of the major pests of rice in the world, a multiyear study was carried out to determine the spread of the pest in Northern Italy, to evaluate its establishment potential and to improve the knowledge on its biology in this new habitat. The survey allowed the distribution of the insect in Italian rice areas to be evaluated and confirmed that L. oryzophilus behaves as a monovoltine parthenogenetic species in Northern Italy. Information about the phenology of the insect and its management are also provided. Situation actuelle du charancon aquatique du riz Lissorhoptrus oryzophilus en Italie, apres onze ans d'invasion Le charancon aquatique du riz Lissorhoptrus oryzophilus a ete detecte dans le nord de l'Italie en 2004. L'Italie est le principal producteur de riz en Europe, et ce charancon est considere comme l'un des principaux organismes nuisibles du riz dans le monde. Une etude pluriannuelle a ete realisee pour determiner sa dissemination dans le nord de l'Italie, evaluer son potentiel d'etablissement et ameliorer les connaissances sur sa biologie dans ce nouvel habitat. La prospection a permis de determiner la repartition de L. oryzophilus dans les zones de production de riz en Italie et a confirme qu'il se comporte comme une espece univoltine parthenogenetique dans le nord de l'Italie. Des informations sont egalement fournies sur la phenologie de l'insecte et sa gestion. Teкyщий cтaтyc pиcoвoгo вoдянoгo дoлгoнocикa Lissorhoptrus oryzophilus в Итaлии: oдиннaдцaтилeтняя инвaзия Pиcoвый вoдянoй дoлгoнocик Lissorhoptrus oryzophilus был выявлeн в ceвepнoй чacти Итaлии в 2004 г. B cвязи c тeм, чтo Итaлия являeтcя глaвным eвpoпeйcким пpoизвoдитeлeм pиca, a pиcoвый вoдянoй дoлгoнocик cчитaeтcя oдним из глaвныx вpeдитeлeй pиca вo вceм миpe, былo пpoвeдeнo мнoгoлeтнee иccлeдoвaниe c тeм, чтoбы oпpeдeлить pacпpocтpaнeниe этoгo вpeдитeля в Ceвepнoй Итaлии, oцeнить пoтeнциaл eгo aкклимaтизaции и yлyчшить знaниe eгo биoлoгии в нoвoм мecтe oбитaния. Oбcлeдoвaниe пoзвoлилo oпpeдeлить pacпpocтpaнeннocть этoгo нaceкoмoгo в итaльянcкиx зoнax пpoизвoдcтвa pиca и пoдтвepдилo, чтo в Ceвepнoй чacти Итaлии L.oryzophilus вeдeт ceбя кaк мoнoвoльтинный пaтoгeничecкий вид. B cтaтьe пpeдcтaвлeнa тaкжe инфopмaция пo фeнoлoгии этoгo нaceкoмoгo и yпpaвлeнию им.

Reproductive plasticity is a key determinant of species invasiveness. However, there are a limited number of studies addressing this issue in exotic insects. The rice water weevil Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), which is native to North America, is one of the most invasive insect pests in east Asia. In this study, we investigated the reproductive status of first-generation females (progeny of overwintered weevils) from five geographic regions in southern and northern China in the field, and reproductive status and ovipositional features of females provided with suitable host plants in the laboratory after collection. Under field conditions, a proportion of females oviposited, while the rest remained in diapause from all three southern regions investigated, but reproductive development did not take place in females from the two northern regions, where the weevil produces only one generation per year. However, when fed host plants in the laboratory, females from all regions laid eggs. They typically had a very short ovipositional period (3-6 d on average on rice at a temperature of 27°C), laid a low number of eggs, and did not die soon after oviposition; this was different from common reproductive females. We concluded that first-generation L. oryzophilus females, which largely enter diapause after emergence, are highly plastic in their reproductive performance and are ready to reproduce under favorable conditions. Our results indicate the significance of their reproductive plasticity for geographic spread and population development.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), native to North America, is one of the most destructive insect pests of rice in the US and eastern Asia. It was introduced into China in the 1980s and so far has spread widely throughout the country. Much work has been done with respect to its ecology and control methods. Here, we review the invasion history, mechanisms underlying its invasions and rapid spread, and major control methods in China. We also discuss factors responsible for its wide spread in China. In addition, we report on options employed to control this weevil. Finally, we propose future directions for research, particularly on the ecology and the development of a more comprehensive control strategy for this weevil in China.

The rice water weevil ( Lissorhoptrus oryzophilus Kuschel) is a native curculionid pest of rice in the southern and eastern United States. It was first identified as Lissorhoptrus simplex Say in the first report of damage from southern Georgia in 1881. In 1951 Chilean systematist Giullermo Kuschel reclassified it as L. oryzophilus following a reevaluation of New World genera within Curculionidae. Management of the weevil has changed throughout the years, as environmental issues, regulatory actions, and pesticide resistance have required researchers, pest management practitioners, and growers to adapt. In the 2010s, management of the rice water weevil has expanded with the use of anthralic diamides and neonicotinoids as the latest conventional options, generally delivered as seed treatments in southern U.S. rice production, and the possible emergence of Bacillus thuringiensis as a viable alternative to chemical controls. Delayed flooding and planting are common cultural controls used in southern U.S. rice production while levee weed control and winter flooding are used in California production. The history of this insect pest including management, life history, and invasion biology in rice production regions of the temperate world will be discussed with an emphasis on the United States.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most injurious insect pest in US rice production. Yield losses in excess of 25% can occur from severe infestations. Management demonstrations were conducted in the 2008, 2009, 2010, and 2011 growing seasons to evaluate the use of commercially available insecticides to control L. oryzophilus in commercial rice fields. The demonstration tests, conducted on farms throughout Louisiana, compared the efficacies of recently registered seed treatment insecticides to untreated controls and to foliar applications of pyrethroids. Efficacy was assessed by collecting root/soil core samples three to four weeks after application of permanent flood and counting numbers of larvae and pupae in core samples. Tests were replicated across locations in multiple rice-producing Louisiana parishes. Densities of larvae and pupae in core samples exceeded the larval threshold (three larvae or pupae per core sample) in over 80% of untreated plots/cuts, confirming the ubiquity and severity of this insect as a pest of rice. Use of chlorantraniliprole (Dermacor® X-100, DuPont™ Crop Protection, Wilmington, DE), thiamethoxam (CruiserMaxx® Rice, Syngenta® Crop Protection, Greensboro, NC), and clothianidin (NipsIt Inside®, Valent® USA Corporation, Walnut Creek, CA) seed treatments significantly reduced L. oryzophilus infestation compared to untreated checks. Fewer larvae and pupae were observed in rice treated with chlorantraniliprole than in rice treated with other insecticides.

Four transgenic rice lines harboring insect-resistant gene cry3A showed ideal field performances characterized by high considerable resistance to rice water weevil ( Lis-sorhoptrus oryzophilus Kuschel). In this study, we estimated the insertion number of foreign genes, and analyzed the flanking sequences of T-DNAs in rice genome. As a result, T-DNA of BT12R1 line was inserted in exon region of rice chromosome 10. Two copies of T-DNAs were inserted in line BT12R2. BT12R3 line was analyzed at only left border flanking sequence. BT12R4 line was confirmed one copy of foreign gene insertion at the position 24,516,607 ~ 24,516,636 of rice chromosome 5, accompanied by a deletion of 30 bp known genomic sequences. This intergenic position was confirmed none of expressed gene and any deletion/addition of T-DNA sequence. In conclusion, these molecular data of rice water weevil resistant Bt rice would be used to conduct the biosafety and environment risk assessment for GM crop commercialization.

For poikilothermic groups such as insects, the capacity to adapt to different temperature regimes is particularly important for survival. To investigate the possible role of heat shock proteins (Hsps) in the invasive pest, the rice water weevil (Lissorhoptrus oryzophilus Kuschel, Coleoptera: Curculionidae), we first analyzed the composition and expression profile of Hsp families under sub-lethal temperatures of 0 °C and 43 °C, using the quantitative realtime polymerase chain reaction. Eight genes coding Hsp90, Hsp70, and small Hsps were upregulated under heat stress, while only 1 Hsp70 gene and 1 Hsp90 gene were up-regulated under cold stress. Results indicate that Hsps from all families except Hsp60 are responsible for the capacity of L. oryzophilus to tolerate temperature stress, although more genes were up-regulated, and more rapidly, under heat stress than under cold stress. Secondly Hsp expression patterns in diapausing and non-diapausing female adults were investigated. The results showed t...

Gut bacteria play important roles in the biology of insects. In this study, gut bacterial communities were investigated in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), which is a serious pest in rice growing-areas of the United States and some Asian countries. Overwintered female adults were collected from rice plants in five geographic locations: Beaumont, TX; Colt, AR; and Biggs, CA; in the United States, and Tanghai of Hebei and Yueqing of Zhejiang in China. Using polymerase chain reaction, bacterial 16S rRNA clone libraries were constructed. From the libraries, we identified 19 bacterial phylotypes (operational taxonomic units, OTUs). Of them, only 3–5 OTUs were identified in each population, except in the Beaumont weevils, which had 10 OTUs. The OTUs were affiliated with the bacteria in six classes of four phyla: α-, β-, γ-proteobacteria, Bacilli, Sphingobacteria, and Actinobacteria, with the γ-proteobacteria being the richest. Bacteria of the genera Pantoea and Wolbachia were detected in all weevil populations examined. There were also some bacteria that were specifically detected in certain locations but had a high relative abundance, such as the ones matched to Enterobacter oryzae, Lactococcus lactis, and Rickettsia felis. Geographic variations were found among bacterial communities in their richness, diversity, and evenness. This was the first study depicting a detailed profile of bacterial communities in L. oryzophilus, and the results provide important information for future studies on the bacterial functions, mutual interactions, and use for developing a biocontrol technique against this weevil.

The rice water weevil (RWW), Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Curculionidae), is the most destructive insect pest of rice in the United States. Water-seeded rice, which is flooded at an earlier stage of crop development than drill-seeded rice, is at heightened risk of loss from root-feeding RWW larvae. Pyrethroids, the most widely used group of foliar insecticides for RWW control, have inherent limitations such as limited residual activity, narrow window of activity and extreme toxicity to non-target aquatic organisms. An array of field, lab and greenhouse experiments was conducted to compare the activity of two neonicotinoids with that of λ-cyhalothrin, a widely used pyrethroid, against the RWW. Small-plot efficacy trials were conducted during 2009, 2010 and 2011. Foliar clothianidin (Belay 2.13 SC) and a granular formulation (3%) of dinotefuran applied to plots were as effective as, and showed greater residual activity than, foliar applications of λ-cyhalothrin. Topical bioassays on adult weevils revealed that clothianidin possessed lower contact toxicity than λ-cyhalothrin. Residual assays using weevils placed on foliage of sprayed plots revealed that the toxic and sublethal behavioral effects of clothianidian on adult weevils were more persistent for clothianidin than for λ-cyhalothrin. Granular dinotefuran applied to greenhouse-grown plants previously infested with weevil larvae showed excellent larvicidal activity. Overall, these studies showed that neonicotinoids have potential as pyrethroid replacements against the RWW in water-seeded rice culture.

Adult male and female rice water weevils from fields of rice, Oryza sativa L., in the Mexican state of Morelos were collected for taxonomic identification. Based on morphological characteristics of male and female individuals, the species of rice water weevil in the State of Morelos was Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) according to taxonomic keys. The male had a tridentate mucro in the posterior tibiae; two outward-facing bifurcated apical teeth, one moderately large apical tooth, acute, facing inward, with two distinct curved submedian setae. Females had a deeply emarginated, VII tergite with a deep indentation or notch in the middle apical part.

In the southern US, rice, Oryza sativa L., is frequently attacked simultaneously by rice water weevil, Lissorhoptrus oryzophilus Kuschel, and sheath blight pathogen, Rhizoctonia solani J.G. Kuhn. Field studies were used to determine the impact of L. oryzophilus infestation on development of sheath blight and combined effects of both L. oryzophilus and R. solani on yield of rice cultivars, ‘Cocodrie’ and ‘Jefferson’. Infestation by L. oryzophilus had no influence on severity of sheath blight in either Cocodrie or Jefferson. Grain yield of both cultivars was significantly less in response to infestation by L. oryzophilus. Infection by R. solani alone significantly reduced yield only in the susceptible cultivar Cocodrie. Percent yield losses in Cococdrie in response to exposure to L. oryzophilus and R. solani alone and in combination were 5.6, 23.9, and 20.0%, respectively. Similarly, percent yield losses in Jefferson in response to exposure to L. oryzophilus and R. solani alone and in combination were 7.3, 10.6, and 5.4%, respectively. Combined impact of infestation by L. oryzophilus and infection by R. solani on yield did not differ significantly from the impact of pathogen infection alone in Cocodrie. The combined impact of R. solani and L. oryzophilus on yield in Jefferson did not vary significantly from the impact of either alone. Results suggested that L. oryzophilus did not affect severity of sheath blight in rice, and the combined impact of L. oryzophilus and R. solani on rice yield was less than additive. Understanding the interaction between L. oryzophilus and R. solani, important pests of rice in the southern US, will help manage these pests more effectively.

The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel, is the most widely distributed and destructive early season insect pest of rice, Oryza sativa L. worldwide. The rice plants were transformed with cryIIIA insecticidal gene as well as with the bar gene coding phosphinothricin acetyltransferase. CryIIIA gene under the control of a modified RCg2 promoter drives the insect-toxic gene expression in roots and/or leaves. The cryIIIA gene was transferred into O. sativa L. cv. Nakdong by Agrobacterium-mediated transformation. Stable integration of the transgene was confirmed in putative transformed rice by Southern blot analysis. The expression of the cryIIIA toxin gene in the roots of transgenic rice plants was verified by RT-PCR and immunoblot analysis. Transgenic rice plants were also evaluated for resistance to natural infestations of the RWW under field conditions between 2007 and 2011. The transgenic Btt8R and Btt12R lines reduced the growth rate of RWW larvae and pupae populations compared with non-transgenic control plants by approximately 52 and 58 %, respectively. To further examine the efficacy of the RWW bioassay, we used pots and performed experiments in trays and under field conditions in 2012. The Btt12R line reduced the total populations of RWW larvae and pupae in trays and under field conditions by 56 and 45 %, respectively. The bioassay experiments conducted over 6 years, showed a significant reduction rate of RWW larvae and pupae populations demonstrating that the cryIIIA gene in transgenic rice confers resistance to RWW.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most widely distributed and destructive insect pest of rice, Oryza sativa L., in the United States. The objective of this research was to determine the distribution of rice water weevil adult damage in Florida rice fields. Adult leaf scars were used to determine if rice water weevil adult damage was more dense on field edges than farther into fields. Samples were taken from a road midpoint of each field and 10, 50, 100, and 150 m from the road on a transect toward the field center. Leaf scar samples also were taken along 2 transects running parallel to a levee in each field. One transect was 10 m from the levee and the other transect 50 m from the levee. Transect and levee data were remarkably consistent in showing that rice water weevil leaf scars had a uniform distribution into Florida rice fields. Our data suggest that rice water weevil damage may be overlooked by Florida rice growers because it is uni...

Gut bacteria are known to play important and often essential roles in the biology of insects. Theoretically, they can be genetically manipulated, then reintroduced into insects to negatively modify specific biological features. The weevil superfamily Curculionoidea is one of the most species-rich and successful animal groups on earth, but currently the overall knowledge of the bacterial communities in weevils and their associations with hosts is still limited. In this study, we isolated and characterized the bacteria in the midgut of an invasive weevil, Lissorhoptrus oryzophilus Kuschel, by culturing methods. Female adults of this weevil were collected from four different geographic regions of the United States and mainland China. Sequencing of the bacterial 16S rRNA amplicons demonstrated that the major culturable gut bacteria of rice water weevil are γ-proteobacteria and Bacilli. The gut bacterial composition differs among regions, with many of the bacteria isolated from only a single region while several were detected from more than one region. Overall, the diversity of gut bacteria in rice water weevil is relatively low. The possible origins of certain bacteria are discussed in relation to the weevil, rice plant, and bacteria.

BACKGROUND The systemic insecticides chlorantraniliprole (CAP) and thiamethoxam (TMX), applied to rice as seed treatments, may affect multiple life stages of the rice water weevil, Lissorhoptrus oryzophilus. Effects of CAP and TMX on adult survival, egg-laying and first- and late-instar survivals were determined by infesting plants treated as seeds with different rates of insecticides. The biological activity was related to insecticidal concentrations in leaves, shoots and roots. RESULTS CAP did not affect adult survival but decreased egg numbers and reduced the survival of the first and late instars. The greatest reduction in weevil population occurred in late instars feeding on roots. In contrast, TMX reduced adult survival and egg and larval numbers. The high biological activity of CAP on root-feeding stages was consistent with the accumulation of CAP in roots, whereas in TMX-treated plants the high activity on adults correlated with high concentrations of TMX in leaves and stems. CONCLUSIONS The differential activity of insecticides on adults suggests poor inherent potency of CAP as an adulticide and/or its limited systemicity in foliage. The distribution of insecticide in specific plant parts can be attributed to the different physicochemical properties of CAP and TMX. The field implications of this research on management of L. oryzophilus are discussed. © 2013 Society of Chemical Industry

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is an important insect pest of rice, Oryza sativa L., in the United States and Asian countries. Previous reports indicated that most first-generation adults (summer weevils) entered reproductive diapause with only a few of the population reproducing to form a second generation. However, the environmental factors responsible for diapause induction have not been thoroughly studied. Southern cutgrass, Leersia hexandra Swartz, is a widely distributed perennial grass in the rice ecosystem of regions where rice water weevil occurs. After feeding on cutgrass for 30 days, summer weevils initiated oviposition rapidly after being transferred to young rice plants, and the percentage of ovipositing weevils was 80–100% after 2 weeks. Summer weevils feeding on southern cutgrass did not enter diapause but developed into a reproductive state, suggesting the grass might allow rice water weevils to avoid summer diapause. Such “d...