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This contribution aimed to uncover the unique host plant-finding and spatial ecology of reproductive and diapausing Argentine stem weevil, Listronotus bonariensis , and its adaptive implications in Aotearoa-New Zealand pasture. Still-air two-armed olfactometers revealed the reproductive and diapausing L. bonariensis preferences for plant and weevil-derived volatiles. Winter-collected diapausing weevils were strongly attracted to host plant feeding damage by conspecifics and their frass. Such attraction disappeared when 20 stem weevils were added to the damaged ryegrass. This suggests that L. bonariensis on a damaged host plant above a certain density causes repellency probably avoiding over-exploitation of the host plant. Neither the weevils' sex nor related physiological condition were found to impart any significant effects. Volatile organic compound (VOC) analysis showed that phenylacetaldehyde was the only de novo synthesised herbivore-induced volatile compound found resulting from diapausing L. bonariensis feeding damage. This study therefore found that the seasonal behaviour of L. bonariensis was very closely related to that of the rice water weevil Lissorhoptrus oryzophilus and its very similar responses to phenylacetaldehyde. In both cases the compound attracts spring populations (emerging from diapause) to their host plants and conspecifics. Thereafter, as with L. oryzophilus , L. bonariensis similarly on becoming reproductive, its sensitivity to phenylacetaldehyde ceases. Such close connection between L. bonariensis and L. oryzophilus seasonal responses to phenylacetaldehyde therefore greatly reenforces the concept of evolved L. bonariensis behaviour in its native range as being relict behaviour in New Zealand's grassland ecosystem. [ABSTRACT FROM AUTHOR]

In the southern US rice is often managed for production of a second, or "ratoon" crop, with minimal input costs. The impact of rice insect pests including the rice water weevil, Lissorhoptrus oryzophilus , and a complex of Lepidopteran stem borers during the main or ratoon crop on ratoon crop yields is unknown. A series of field trials was conducted from 2021 to 2023 to evaluate the influence of insecticidal protection on pest infestations and yields in both the main and ratoon crops. Insecticidal seed treatments reduced infestations of L. oryzophilus in the main crop by 20% (thiamethoxam-treated) and 65% (chlorantraniliprole-treated) relative to non-treated controls. Chlorantraniliprole seed treatments reduced stem borer injury by 80% relative to thiamethoxam-treated and non-treated plots. Main crop yields were 9.7% greater in plots protected with insecticides relative to non-treated plots. Neither insecticidal seed treatments nor foliar insecticides applied in the ratoon crop affect pest densities in the ratoon crop. Densities of L. oryzophilus across treatments were 2–5-fold greater in the main crop than ratoon crop. No benefits of insecticidal seed treatments or foliar insecticides were observed in ratoon rice yields. Collectively, results suggest management of insect pests in the ratoon crop is of reduced economic importance relative to the main crop. Protection from root and stem injury during the main crop has little to no benefit on ratoon crop production. Benefits of controlling insect pests in the ratoon crop remain unknown. • Insecticidal seed treatments reduced L. oryzophilus densities in the main crop. • Chlorantraniliprole seed treatments reduced densities of Lepidopteran stem borers in the main crop. • Insecticidal seed treatments improved main crop yield, but did not impact ratoon yield. • Neither foliar- or seed-applied insecticides affected insect pest desnities in the ratoon crop. • Management of insect pests in the ratoon crop is of minimal economic importance relative to the main crop. [ABSTRACT FROM AUTHOR]

As an agricultural pest, the rice water weevil (RWW), Lissorhoptrus oryzophilus, poses a severe threat to agriculture in China. This study aimed to predict the suitable distribution of the RWW in China under current and future climatic conditions based on MaxEnt model with tuning parameters. The results showed that the dominant environmental variables that influenced the geographic distribution of RWW were temperature seasonality (Bio4), mean temperature of the coldest quarter (Bio11), precipitation seasonality (Bio15), and precipitation of the warmest quarter (Bio18). Under the current climatic conditions, the total suitable area of RWW in China was 391.0698 million hm2, accounting for 40.77% of China. These suitable areas were mainly located in eastern China, central China and southern China. There was considerable overlap between the suitable areas of RWW and rice cropping regions in China. Under future scenarios, the highly suitable areas for RWW would increase significantly. The centroid migration in the suitable areas of RWW showed a trend of moving eastward and northward. The results of this study can provide theory and data support for the monitoring, early warning and control of RWW. [ABSTRACT FROM AUTHOR]

Simple Summary: The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is indigenous to the United States and has become a significant invasive agricultural pest in China. In this study, we identified and cloned one trehalase gene (LoTRE1) encoding a soluble protein in L. oryzophilus and compared the relative expression levels of LoTRE1 in different tissues. The purified LoTRE1 protein was obtained using a prokaryotic expression system, and its enzymatic properties were explored. Amino acid sequence homology modeling of LoTRE1 and molecular docking between the LoTRE1 protein and substrate trehalose were simulated, which further provided a theoretical basis for revealing the role of LoTRE1 in the degradation mechanism of trehalose. In addition, the LoTRE1 double-stranded RNA (dsRNA) was synthesized in vitro, and its RNAi effect in L. oryzophilus was detected via feeding. The results suggested that LoTRE1 played a vital role in L. oryzophilus development, which could be useful for providing information for insect pest control in the future. Trehalase is the only enzyme known for the irreversible splitting of trehalose and plays a major role in insect growth and development. In this report, we describe a basic study of the trehalase gene fragment encoding a soluble trehalase from Lissorhoptrus oryzophilus (LoTRE1). Sequence alignment and phylogenetic analysis suggested that LoTRE1 was similar to some known insect trehalases and belongs to the Coleoptera trehalase group. Additionally, LoTRE1 was expressed mainly in the fat body. Purified protein was obtained using heterologous expression of LoTRE1 in Escherichia coli, and the recombinant protein exhibited the ability to decompose trehalose. Enzyme–substrate docking indicated the potential involvement of other residues in the catalytic activity, in addition to Asp 333. Moreover, feeding of adults on LoTRE1 dsRNA silenced the transcription of LoTRE1 and thereby reduced the activity of trehalase and increased the trehalose content; it also led to a 12% death rate. This study reveals essential molecular features of trehalase and offers insights into the structural aspects of this enzyme, which might be related to its function. Taken together, the findings demonstrate that LoTRE1 is indispensable for adults of this pest and provide a new target for the control of L. oryzophilus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

Plants possess defense‐related traits that both reduce injury from herbivores (resistance) and the amount of yield loss per unit injury (tolerance). Plant resistance and tolerance can be utilized in pest management programs. The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most destructive early‐season pest of rice (Oryza sativa L., Poaceae) in the USA. Additionally, lepidopteran stemborers, particularly the invasive Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), are increasing in economic importance as pests of rice in Louisiana, USA. This study was conducted to evaluate both the resistance and tolerance of commonly grown inbred rice cultivars in Louisiana to combined infestations of rice water weevils and stemborers. Field experiments were established at the Rice Research Station in Crowley, LA, USA from 2017 to 2019. Eight commonly grown inbred cultivars were selected and pest infestation levels were manipulated using insecticidal seed treatments. The rice cultivar 'Jupiter' supported the highest numbers of immature rice water weevils, whereas weevil densities on other cultivars were intermediate. Low levels of stemborer injury were observed in 'Cheniere' and 'Jazzman‐2', which suggests that these cultivars express some resistance to stemborers, whereas high stemborer injury was observed in 'Cocodrie, 'CL151', and 'Mermentau'. Together, rice water weevil and stemborer infestations negatively affected rice yields, with losses up to 18%. However, differences among cultivars in overall yield losses were minimal. Comparisons of slopes of yield × weevil density relationships among cultivars revealed a greater decline, that is, yield loss per weevil, for Cheniere relative to Cocodrie. Our data suggest that plant resistance can serve as a valuable component of an integrated pest management program, particularly for stemborers. [ABSTRACT FROM AUTHOR]

Trehalase is the only enzyme known for the irreversible splitting of trehalose and plays a major role in insect growth and development. In this report, we describe a basic study of the trehalase gene fragment encoding a soluble trehalase from Lissorhoptrus oryzophilus (LoTRE1). Sequence alignment and phylogenetic analysis suggested that LoTRE1 was similar to some known insect trehalases and belongs to the Coleoptera trehalase group. Additionally, LoTRE1 was expressed mainly in the fat body. Purified protein was obtained using heterologous expression of LoTRE1 in Escherichia coli, and the recombinant protein exhibited the ability to decompose trehalose. Enzyme–substrate docking indicated the potential involvement of other residues in the catalytic activity, in addition to Asp 333. Moreover, feeding of adults on LoTRE1 dsRNA silenced the transcription of LoTRE1 and thereby reduced the activity of trehalase and increased the trehalose content; it also led to a 12% death rate. This study reveals essential molecular features of trehalase and offers insights into the structural aspects of this enzyme, which might be related to its function. Taken together, the findings demonstrate that LoTRE1 is indispensable for adults of this pest and provide a new target for the control of L. oryzophilus.

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. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

1. Interactions among herbivores mediated by plant responses to herbivore injury may have large impacts on herbivore population densities. Responses may persist for weeks after injury and may affect not only the initial (inducing) herbivore, but also herbivores that are spatially or temporally separated from the initial attacker. 2. In many plant–insect interactions, multiple life stages of the insect may be associated with the same plant, and these various stages may interact indirectly with one another via induced responses. The rice water weevil (RWW), Lissorhoptrus oryzophilus, a serious global pest of rice, is one such insect. A series of experiments were performed with root‐feeding larvae and leaf‐feeding adults of the RWW using three conventional rice varieties. 3. The first objective of this study was to test whether RWW adult feeding on rice leaves resulted in altered oviposition by subsequent adults. The hypothesis for the first objective was that RWW adult feeding would decrease plant suitability, resulting in reduced oviposition by subsequent adults. 4. The second objective was to test whether injury by RWW larvae to rice roots resulted in altered oviposition by subsequent adults. The hypothesis for the second objective was that below‐ground RWW larval feeding would decrease plant suitability of rice to above‐ground RWW adults, resulting in decreased oviposition. 5. Results provided inconsistent support for the first hypothesis, indicating that responses differed among combinations of variety and injury level. Conversely, consistent support for the second hypothesis was found, indicating that larval feeding on roots decreased suitability of rice plants for oviposition. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image [ABSTRACT FROM AUTHOR]

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 < 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.

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. [ABSTRACT FROM AUTHOR]

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is one of the most serious pests of rice in the United States and East Asia. Several symbiotic bacteria have been isolated from the gut of this weevil, but none of them have been evaluated for the potential to be paratransgenesis candidates for biological control. We transformed three bacterial strains, Enterococcus faecalis, Bacillus cereus, and Enterobacter sp. isolated from the weevil, with a DsRed-labeled plasmid. We then investigated their fate in the host gut. To assess their biological impacts on the host, we measured adult consumption, survival, egg production, and hatch rate after weevils were inoculated with the transformed bacteria. Our results showed that each of the three bacteria could be successfully transformed. The intestinal bacterial densities were low 2 d after inoculation. However, their populations increased dramatically the following day, regardless whether the adults were fed or starved, and reached their peak abundance 4 d after inoculation. Each strain colonized the adult gut for at least 9-15 d, accumulating mostly in the hindgut. No apparent effects by the transformed strains were observed on weevil performance. In conclusion, due to the ability to colonize the host gut and to ease of culturing, these bacteria might be promising paratransgenesis candidates. They can be engineered and re-introduced into the gut of adult rice water weevils potentially producing effector molecules capable of impairing weevil development and survival. [ABSTRACT FROM AUTHOR]

The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is a destructive rice pest that threatens the rice industry worldwide. Odorant receptors (ORs) and odorant receptor coreceptors (Orcos) play an important role in the process of insects' whole life activities; however, there are no related functional studies on RWW. On this basis, a heterologous study of LoryOR20/LoryOrco in Xenopus laevis oocytes was performed to detect the effects of certain natural compounds on RWWs and four active compounds were found. Electroantennogram (EAG) recordings and a behavior test showed that RWWs exhibited a significant response to phenylacetaldehyde (PAA) and an EAG measurement of dsRNA-LoryOR20-treated RWWs revealed a significant decrease in response to PAA. Our results revealed an olfactory molecular mechanism for the recognition of PAA by RWWs, thus providing a potential genetic target at the peripheral olfactory sensing level, contributing to the development of novel control strategies for pest management.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rice water weevil (Lissorhoptrus oryzophilus Kuschel) is a common pest of rice production in the United States whose larvae cause yield loss by feeding on the roots. We conducted studies from 2011–2013 on M-202 and M-206, two commonly grown California medium grain rice varieties, to determine if M-206 demonstrated tolerance to rice water weevil damage. Observations from field studies suggested the possibility of a level of tolerance in M-206 that was more prevalent at high seeding rates. We did this study using two different experimental units, open and ring plots. In both units, we quantified grain yields across four levels, 56, 112, 168, and 224 kg/ha, of seeding rates to detect potential yield recovery by M-206. In the open plots, we used naturally occurring weevil populations compared with controls that reduced the populations with insecticides. In the ring plots, we tested three levels of weevil infestation, none, low, and high, to look at the weevil density effects on yield and scarred plants. Our studies showed that M-206 and M-202 had generally similar densities of immature weevils and yield. Compensation for yield loss did not occur at higher seeding rates. These results suggest that M-206 does not have the ability to tolerate rice water weevil damage better than M-202. There was weak evidence that the number of scarred plants increased as plant density was reduced. The results are discussed in relation to the utility of this study to grower choices of varieties for long-term rice water weevil management. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 sig-nificantly 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. [ABSTRACT FROM AUTHOR]

Rice water weevil (Lissorhoptrus oryzophilus Kushel) is the most damaging insect pest of rice in the United States. Larval feeding on the roots stunt growth and reduce yield. Current pest management against the weevil in California relies heavily on pyrethroids that can be damaging to aquatic food webs. Examination of an environmentally friendly alternative biopesticide based on Bacillus thuringiensis spp. galleriae chemistry against rice water weevil larvae showed moderate levels of activity in pilot studies. We further examined the performance of different formulations of Bt.galleriae against the leading insecticide used in California rice, λ-cyhalothrin. The granular formulation performed as well as the λ-cyhalothrin in use in California in some of our greenhouse and field studies. This is the first reported use of B. thuringiensis spp. galleriae against rice water weevil. [ABSTRACT FROM PUBLISHER]

The use of multiple insecticidal seed treatments in combination to control a greater spectrum of pests has been increasing in rice production in the U.S. Mid-South. The economic benefits of individual seed treatments in rice are well documented, but returns on investment (ROI) on combinations are unknown. Efficacy and economic returns of insecticidal seed treatments alone and in combination were evaluated through a series of five field trials conducted in Louisiana from 2018 to 2020. In all trials, treatments containing chlorantraniliprole or cyantraniliprole provided the best control of rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), and control was not significantly improved by the addition of a second insecticide. Insecticidal control of L. oryzophilus by all seed treatments was reduced in late-planted rice fields relative to rice planted within the recommended planting window. Control of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), did not improve rice yields. Fungicidal seed treatments generally protected rice yields over treatments without fungicides despite having no effect on early-season plant populations. All seed treatments provided returns on investment which ranged from $94.30 (fungicide only 2018) to $519.75/ha (chlorantraniliprole + thiamethoxam + fungicides in 2019–2020). Increased yields resulting from the use of multiple insecticides in combination appears to justify the added expense. Collectively, results demonstrate the immense value of insecticidal seed treatments to rice production in Louisiana and throughout the U.S. Mid-South. Future research efforts should aim to assess returns on seed treatments across a range of rice production conditions and to quantify the impacts of sporadic pests on rice yields. • The use of insecticidal and fungicidal seed treatments is economically justified in rice production in the southern U.S. • Economic returns on seed treatments result primarily from control of the rice water weevil, Lissorhoptrus oryzophilus. • The use of multiple seed treatments in combination may improve economic returns over the use of single treatments alone. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 -y-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. [ABSTRACT FROM AUTHOR]

Plant age- and plant stage-related changes in the resistance of rice, O ryza sativa, to its most important insect pest in the US, the rice water weevil ( L issorhoptrus oryzophilus), were investigated in a series of field and greenhouse choice and no-choice studies. Rice plants were susceptible to infestation by rice water weevils over a broad range of plant ontogenetic stages, from at least the early vegetative stage to well into the reproductive stage. There was, however, a clear preference expressed by rice water weevils in both choice and no-choice experiments for plants in (or nearly in) the tillering stage of development, with pre-tillering and reproductive stage plants less preferred. The relationship between rice plant age and susceptibility to weevils is thus nonlinear. This study constitutes one of the most thorough studies to date of the relationship in a grass species between plant age and susceptibility to herbivores. The results provide a biological explanation for observed patterns of weevil infestations and a rationale for the cultural practice of delayed flooding. [ABSTRACT FROM AUTHOR]

Wolbachia spp. are obligate intracellular bacteria present in reproductive tissues of many arthropod species. Wolbachia infection status and roles in host reproduction were studied in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae), an introduced species in China. We examined Wolbachia infection status in five populations in China where it reproduces parthenogenetically, and one native population in Southeast Texas, where it reproduces bisexually. All populations were infected by Wolbachia, and all specimens in each population were infected by Wolbachia of a single strain. Phylogenetic analyses based on multilocus sequence typing system indicated that Wolbachia in non-native L. oryzophilus weevils diverges evidently from those in native weevils. After treatments with tetracycline, parthenogenetic weevils reduced the fecundity significantly and eggs were not viable. Our results suggest that Wolbachia are necessary for oocyte production in L oryzophilus. [ABSTRACT FROM AUTHOR]

Feeding by herbivores can change plants in ways that make them more resistant to subsequent herbivory. Such induced responses are better-studied in a number of model dicots than in rice and other cereals. In a series of greenhouse and field experiments, we assessed the effects of prior herbivory by the fall armyworm, Spodoptera frugiperda (J.E. Smith) and of exogenous applications of jasmonic acid (JA) on the resistance of rice plants to the rice water weevil, Lissorhoptrus oryzophilus (Kuschel), the major pest of rice in the United States. Prior feeding by S. frugiperda and treatment of plants with exogenous JA resulted in increases in the resistance of plants to the weevil. Increases in resistance were manifested as reduced numbers of eggs and first-instars associated with armyworm-injured or JA-treated plants relative to control plants. In field experiments, there was a transient but significant reduction in the number of immature L. oryzophilus on JA-treated plants relative to untreated plants. To our knowledge, this is the first example of direct induced resistance in rice demonstrated in small-plot field experiments. We discuss the potential for the use of elicitor induced resistance in rice. [ABSTRACT FROM AUTHOR]

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most widely distributed and destructive early season insect pest of rice, Oryza sativa L., in the United States. Economic losses result primarily from feeding by the larval stage of this insect on the roots of flooded rice plants. Prior studies suggest that infestations of rice water weevil larvae are more severe at low plant densities. Moreover, because feeding by the rice water weevil reduces rice plant tillering, a process particularly important to yield at low seeding rates, infestations by weevil larvae may have a greater impact on rice yields when rice is seeded at low rates. In total, six experiments were conducted over a 3-yr period in Louisiana and Missouri to investigate the impacts of rice seeding rate on levels of infestations by, and yield losses from, the rice water weevil. An inverse relationship between seeding rate and densities of rice water weevil larvae and pupae on a per area basis was found in two of the six experiments. Furthermore, in two of the three experiments conducted with 'Bengal' (a susceptible cultivar) in Louisiana, percentages of yield loss were significantly higher at lower seeding rates than at higher seeding rates. Overall, these results indicate that rice sown at low rates is more vulnerable to infestation by rice water weevils and more susceptible to yield losses from weevil injury. The significance of these findings in light of recent trends toward the use of lower seeding rates in drill-seeded rice is discussed. [ABSTRACT FROM AUTHOR]

Results of planting date and insecticide efficacy experiments targeting Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) on rice, Oryza sativa L., in southeastern Texas between 2002 and 2007 were used to determine density-yield relationships as a function of planting date. Soil core samples were collected on two dates during main crop development to estimate immature L. oryzophilus populations followed by main and ratoon crop harvests. Analysis of covariance (ANCOVA) revealed that planting date did not affect the density-main crop yield relationship during most years and that these relationships varied substantially among years. For ratoon crop yield, an effect of main crop L. oryzophilus immature infestation was detected during some years, but the real effect of these populations on ratoon crop yield remains unclear. Using estimates of yield reduction per L. oryzophilus immature, economic injury levels were calculated. Main crop yields from treated plots and first soil core sample L. oryzophilus immature populations from untreated plots were significantly higher in plots planted at recommended dates than in plots planted earlier or later. This suggests that the presence of high populations of reproductive L. oryzophilus coincides with the period when rice fields planted at optimum dates are flooded. Results from this study reinforce the importance of managing L. oryzophilus populations when planting rice at recommended dates in southeastern Texas. [ABSTRACT FROM AUTHOR]