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Polyphagous aphids often have host-specialized lineages, and the mechanisms remain to be elucidated. The aphid Aphis gossypii has several host-specialized lineages including one specialized on Cucurbitaceae and one on Malvaceae. We found that the performance of Malvaceae lineage was poor on cucumbers, but significantly improved on cucumbers that were previously infested by Cucurbit lineage for 14 d. Following two-generation feeding experience on pre-infested cucumbers, Malvaceae lineage acquired the ability to use uninfested cucumbers. The pre-infestation largely decreased insect-negative metabolites such as cucurbitacins and phenols and increased insect-positive metabolites such as soluble sugars. The pre-infestation decreased the salicylic acid by 25.9% but increased the jasmonic acid by 1337% in cucumbers, which corresponded to expression of marker genes in phytohormone signaling pathways. Exogenous salicylic acid significantly decreased the performance improvement of Malvaceae lineage on pre-infested cucumbers, but exogenous jasmonic acid did not. Those results indicate that infestation by Cucurbit lineage altered the metabolism of cucumbers and interrupted the defense-associated phytohormones, from which we conclude that the disability in overcoming cucumber's defenses caused the incompatibility of Malvaceae lineage to cucumbers. The acclimation to cucumbers of Malvaceae lineage aphids may result from activation of some effector genes targeting cucumbers. Our findings provide new insights into the mechanisms of aphid host-specialization and new clues for preventing A. gossypii switching from Malvaceae hosts to cucurbits. [ABSTRACT FROM AUTHOR]

Simple Summary: Aphids are generally dietary specialists, colonizing a specific plant or a group of closely related plants, but a few species are generalists, colonizing hundreds of hosts across multiple plant families. In these generalist aphids, host-specialized lineages or host-specialized biotypes are often observed in nature. This is the case for the cotton-melon aphid, Aphis gossypii Glover. When introduced to alternative hosts, the host-specialized biotypes show poor fitness and may even die within a few days. The underlying mechanisms of aphid host specialization remain unknown until now. We hypothesized that host-specialized biotypes express biotype-specific salivary effectors or elicitors that determine the compatibility of aphid-plant interactions. In this research, we described three strategies to identify biotype-specific effectors in two host-specialized biotypes of A. gossypii, a biotype specialized in Malvaceae and another in Cucurbitaceae. The strategy of combining transcriptome and proteome has the highest efficiency, obtaining less than one dozen effector candidates, and we strongly recommend this strategy to identify biotype-specific effectors in aphids and other sap-sucking insects. Polyphagous aphids often consist of host-specialized biotypes that perform poorly in non-native hosts. The underlying mechanisms remain unknown. Host-specialized biotypes may express biotype-specific salivary effectors or elicitors that determine aphid hosts. Here, we tried three strategies to identify possible effectors in Malvaceae- (MA) and Cucurbitaceae-specialized (CU) biotypes of the cotton-melon aphid Aphis gossypii Glover. The whole-aphid RNA-seq identified 765 differentially expressed genes (DEGs), and 139 of them were possible effectors; aphid-head RNA-seq identified 523 DEGs were identified, and 98 of them were possible effectors. The homologous genes of published aphid effectors were not differentially expressed between CU and MA. Next, quantitative proteomic analyses of saliva identified 177 possible proteins, and 44 of them were different proteins. However, none of the genes of the 44 proteins were differentially expressed, reflecting the discrepancy between transcriptome and proteome data. Finally, we searched for DEGs of the 177 salivary proteins in the aphid-head transcriptomes, and the salivary proteins with expression differences were regarded as effector candidates. Through this strategy, 11 effector candidates were identified, and their expression differences were all confirmed by RT-qPCR. The combinatorial analysis has great potential to identify biotype-specific effector candidates in aphids and other sap-sucking insects. [ABSTRACT FROM AUTHOR]

Simple Summary: The cotton-melon aphid, Aphis gossypii Glover, is a polyphagous insect pest with many host-specialized biotypes. The mechanism of host specificity remains unknown in this aphid. In this study, we investigated whether bacterial symbionts control the host specificity of A. gossypii, as reported in some aphids. The two typical host-specialized biotypes used in this study produced significantly fewer nymphs on non-native hosts than on a native host, indicating a high host specificity of the two biotypes. We found that the winged morph of both biotypes had a significantly lower host specificity than its corresponding wingless morph. Bacterial analysis indicated that the composition of the bacterial symbionts was not different between the two biotypes, but within each biotype, the Buchnera abundance in the winged morph was only about 10% of that in the wingless morph. We suspected that a low Buchnera abundance was associated with a low host specificity. We compared the reproduction of A. gossypii with different Buchnera abundances, and did not find that a low Buchnera abundance resulted in a low host specificity. We then concluded that the host specificity of A. gossypii is not controlled by specific bacterial symbionts or Buchnera abundance. The cotton-melon aphid, Aphis gossypii Glover, is a polyphagous insect pest with many host-specialized biotypes, such as the Cucurbitaceae- and Malvaceae-specialized (CU and MA) biotypes. Bacterial symbionts were reported to determine the host range in some aphids. Whether this is the case in A. gossypii remains unknown. Here, we tested the host specificity of the CU and MA biotypes, compared the host specificity between the wingless and winged morph within the same biotype, and analyzed the composition of the bacterial symbionts. The reproduction of the CU and MA biotypes reduced by 66.67% and 82.79%, respectively, on non-native hosts, compared with on native hosts. The composition of bacterial symbionts was not significantly different between the CU and MA biotypes, with a Buchnera abundance >95% in both biotypes. Meanwhile, the winged morph produced significantly more nymphs than the wingless morph on non-native hosts, and the Buchnera abundance in the winged morph was only about 10% of that in the wingless morph. There seemed to be a relationship between the Buchnera abundance and host specificity. We regulated the Buchnera abundance by temperature and antibiotics, but did not find that a low Buchnera abundance resulted in the high reproduction on non-native hosts. We conclude that the host specificity of A. gossypii is not controlled by specific bacterial symbionts or by Buchnera abundance. [ABSTRACT FROM AUTHOR]

Polyphagous aphids often consist of host‐specialized lineages, which have greater fitness on their native hosts than on others. The underlying causes are important for understanding of the evolution of diet breadth and host shift of aphids. The cotton‐melon aphid Aphis gossypii Glover is extremely polyphagous with many strict host‐specialized lineages. Whether and how the lineage specialized on the primary host hibiscus shifts to the secondary host cucumber remains elusive. We found that the hibiscus‐specialized lineage suffered high mortality and gave birth to very few nymphs developing into yellow dwarfs on fresh cucumber leaves, and did not inflict any damage symptoms on cucumber plants. The poor performance did not improve with prolonged exposure to cucumber; however, it did significantly improve when the cucumber leaves were pre‐infected with a biotrophic phytopathogen Pseudoperonospora cubensis. More importantly, the hibiscus‐specialized lineage with two‐generation feeding experience on pre‐infected cucumber leaves performed as well as the cucumber‐specialized lineage did on fresh cucumber leaves, and inflicted typical damage symptoms on intact cucumber plants. Electrical penetration graph (EPG) indicated that the hibiscus‐specialized lineage did not ingest phloem sap from fresh cucumber leaves but succeeded in ingesting phloem sap from pre‐infected cucumber leaves, which explained the performance improvement of the hibiscus‐specialized lineage on pre‐infected cucumber leaves. This study revealed a new pathway for the hibiscus‐specialized lineage to quickly acclimate to cucumber under the assistance of the phytopathogen. We considered that the short feeding experience on pre‐infected cucumber may activate expression of effector genes that are related to specific host utilization. We suggest to identify host‐specific effectors by comparing proteomes or/and transcriptomes of the hibiscus‐specialized lineage before and after acclimating to cucumber. [ABSTRACT FROM AUTHOR]

Introduction: Brown planthoppers (Nilaparvata lugens) are the most serious insect pests of rice, one of the world's most important staple crops. They reproduce year‐round in the tropical parts of their distribution, but cannot overwinter in the temperate areas where they occur, and invade seasonally from elsewhere. Decades of research have not revealed their source unambiguously. Methods and Results: We sequenced the genomes of brown planthopper populations from across temperate and tropical parts of their distribution and show that the Indochinese peninsula is the major source of migration into temperate China. The Philippines, once considered a key source, is not significant, with little evidence for their migration into China. We find support for immigration from the west of China contributing to these regional dynamics. Discussion: The lack of connectivity between the Philippine population and the mainland Chinese populations explains the different evolution of Imidacloprid resistance in these populations. This study highlights the promise of whole‐genome sequence data to understand migration when gene flow is high—a situation that has been difficult to resolve using traditional genetic markers. [ABSTRACT FROM AUTHOR]

BACKGROUND: The rice stem borer, Chilo suppressalis, is a serious pest of rice, but also damages an aquatic vegetable, water oats (Zizania latifolia Turcz.). The time at which mating occurs is different between populations of rice stem borer associated with rice and those associated with water‐oats, which suggests that undetected cryptic species may be associated with these plant hosts. If true, this would have significant management implications. This study is the first empirical test of this idea, using population genetic tools from two sampling cohorts. We genotyped 320 rice stem borer individuals from 2014, collected from rice and water‐oats across five locations (where they exist in sympatry), using seven microsatellite loci. RESULTS: We found no genetic structuring associated with host plant species. On water oats, some rice stem borers were found that had a similar mating time to the rice population, so in 2016, a second cohort of samples was screened by their timing of mating to get 'pure rice feeders' and 'pure water oats feeders'. These samples were genotyped with microsatellites, mitochondrial DNA (mtDNA) (COI and COII), and a nuclear gene (EF1‐α). Our mtDNA data suggest a relatively low amount of population subdivision associated with plant host, but the microsatellite data revealed no such genetic structure, and we were only able to identify one haplotype of EF1‐α. CONCLUSIONS: Our results indicate gene flow between rice and water oats populations of rice stem borer, indicating that water oats will likely provide a refuge for resistance management of Bt rice. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Female multiple mating (polyandry) is widespread across Insecta, even if mating can be costly to females. To explain the evolution and maintenance of polyandry, several hypotheses, mainly focusing on the material (direct) and/or the genetic (indirect) benefits, have been proposed and empirically tested in many species. Considering only the direct benefits, repeatedly‐mated females are expected to exhibit the same fitness as multiply‐mated females under the same mating frequency. In the present study, we compare the fitness of females received monandrous repeated mating (MM) and polyandrous multiple mating (PM) in a polyandrous leaf beetle Galerucella birmanica and assess female mate preference with regard to polyandry or monandry. Our data indicate that the longevity and the egg‐laying duration of MM females are significantly longer than that of PM females. MM females produce significantly more hatched eggs than PM females over their lifetime under the same mating frequency, which results from the high hatching rate of eggs produced by MM females. PM females mated with novel virgin males in the second mating suffer decreased longevity and lifetime fecundity compared with PM females mated with novel mated males in the second mating. Once‐mated females are more likely to re‐mate with familiar males than novel males. By contrast to expectations, the results of the present study suggest that repeated mating provides females with more direct benefits than multiple mating in G. birmanica, and females prefer to re‐mate with familiar males. The possible causes of this finding are discussed. [ABSTRACT FROM AUTHOR]

The striped stem borer, Chilo suppressalis Walker, is a widespread insect pest in China, which feeds both on rice ( Oryza sativa L.) and water-oats ( Zizania latifolia Griseb.). The populations collected from rice (rice population, CSR) and water-oats (water-oats population, CSW) were observed for mating behavior. Results showed that the mating rhythm of CSR in scotophase was unimodal distribution, while that of CSW was bimodal distribution. The first mating peak of CSW occurred about 3.5 h after the onset of scotophase, which overlapped well with the single mating peak of CSR. The second mating peak of CSW occurred about 5.5 h after the onset of scotophase. The descendant populations from those three mating peaks were also observed for mating behavior, and the temporal patterns were found to be hereditable. In the second generation, mating rate was abnormally low in crossings between females of the first mating peak and males of the second mating peak. Pupae weight differed significantly between CSR and CSW in the first generation but did not in the second generation reared with the same food in laboratory. Our results indicated population collected from water-oats is mixed population, containing indigenous water-oats feeders and temporary residences from rice field. It was discussed that water-oats acts as a refuge crop to delay the resistance development to pesticides and Bt ( Bacillus thuringiensis) rice. [ABSTRACT FROM AUTHOR]

Areawide management has a long history of achieving solutions that target pests, however, there has been little focus on the areawide management of arthropod natural enemies. Landscape ecology studies that show a positive relationship between natural enemy abundance and habitat diversity demonstrate landscape-dependent pest suppression, but have not yet clearly linked their findings to pest management or to the suite of pests associated with crops that require control. Instead the focus has often been on model systems of single pest species and their natural enemies. We suggest that management actions to capture pest control from natural enemies may be forth coming if: (i) the suite of response and predictor variables focus on pest complexes and specific management actions; (ii) the contribution of 'the landscape' is identified by assessing the timing and numbers of natural enemies immigrating and emigrating to and from the target crop, as well as pests; and (iii) pest control thresholds aligned with crop development stages are the benchmark to measure impact of natural enemies on pests, in turn allowing for comparison between study regions, and generalizations. To achieve pest control we will need to incorporate what has been learned from an ecological understanding of model pest and natural enemy systems and integrate areawide landscape management with in-field pest management. [ABSTRACT FROM AUTHOR]

Multiple mating is common in insects and may bring direct and/or indirect benefits to females. Galerucella birmanica Jacoby feeds monophagously on water caltrop Trapa natans L. and is a serious pest in Asia where water caltrop is grown as an aquatic vegetable. It is also used as an effective biological control agent in North America, where water caltrop is a major invasive plant species. In this study, we tested the direct benefits of multiple mating when females were continuously exposed to males and had restricted exposure to males. Under restricted exposure conditions, where females were exposed to males only when mating, multiple mating significantly reduced female longevity but promoted female daily and lifetime reproductive output (LRO) significantly. The average LRO increased from 404 to 674 eggs per female when mating number increased from one to five. Multiple mating also boosted the hatch rate of eggs, especially those produced in the late oviposition stage. Under continuous exposure conditions, females housed with four males died significantly younger than females housed with two or one male, and they also died younger than females subjected to multiple mating but with restricted exposure to males. The LRO decreased significantly with the increase of the number of males that the female was exposed to and was significantly lower for females continuously exposed to males than those with restricted exposure to males. Continuous exposure to males had no significant effect on egg hatch rate throughout the ovipositing period. These results demonstrated that multiple mating is important for female G. birmanica to achieve optimal reproductive output, but male harassment on females caused by exposure to males outweighs this benefit. [ABSTRACT FROM AUTHOR]

Rice lines genetically modified with the crystal toxin genes from Bacillus thuringiensis (Bt) have experienced rapid development, with biosafety certificates for two Bt rice lines issued in 2009. There has still been no commercial release of these lines yet due to public concerns about human health and environmental risks. Some studies confirmed that Bt rice was as safe as conventional rice to non-target organisms when pesticides were not applied, however, pesticides are still required in Bt rice to control non-lepidopteran pests. In this study, we assessed the environmental effects of two Bt rice lines expressing either the cry1Ab/1Ac or cry2A genes, respectively, by using zooplanktons as indicator species under normal field management practices using pesticides when required. In the whole rice growing season, non-Bt rice was sprayed 5 times while Bt rice was sprayed 2 times, which ensured both rice achieved a normal yield. Field investigations showed that rice type (Bt and non-Bt) significantly influenced zooplankton abundance and diversity, which were up to 95% and 80% lower in non-Bt rice fields than Bt rice fields. Laboratory rearing showed that water from non-Bt rice fields was significantly less suitable for the survival and reproduction of Daphnia magna and Paramecium caudatum in comparison with water from Bt rice fields. Higher pesticide residues were detected in the water from non-Bt than Bt rice fields, accounting for the bad performance of zooplankton in non-Bt field water. Our results demonstrate that Bt rice is safer to aquatic ecosystems than non-Bt rice, and its commercialization will be beneficial for biodiversity restoration in rice-based ecosystems. [ABSTRACT FROM AUTHOR]

The rice leafroller Cnaphalocrocis medinalis (Guenée) is a serious insect pest of rice with migratory ability. In this work, we studied the effects of age, temperature and reproductive status on the wing beat frequency (WBF). The longevity of this moth reached 30.6 days at 16 °C, which was significantly longer than that at 26 and 32 °C (10.7 and 8.8 days, respectively). The WBF of the 1-day-old moths did not differ significantly among the three temperature treatments. However, the WBF of the 2- to 7-day-old moths differed significantly among those temperatures, with the highest WBF at 26 °C and the lowest WBF at 32 °C. Both age and temperature significantly affected the WBF. No significant differences in WBF were detected either between mated and unmated or between parous and nulliparous female moths. There were no significant differences on WBF among field-collected females on different stages of ovary development. Significant correlations were found between the WBF and the tethered flight duration in field-collected moths as well as in laboratory-reared moths. These results indicated that the WBF was intensively influenced by age and temperature, and it may be a potential index to evaluate the flight ability of this species. [ABSTRACT FROM AUTHOR]