Resistance to cycloxaprid in Laodelphax striatellus is associated with altered expression of nicotinic acetylcholine receptor subunits

Overexpression of an Integument Esterase Gene LbEST-inte4 Infers the Malathion Detoxification in Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Liposcelis bostrychophila, commonly known as booklouse, is an important stored-product pest worldwide. Studies have demonstrated that booklices have developed resistance to several insecticides. In this study, an integument esterase gene, LbEST-inte4, with upregulated expression, was characterized in L. bostrychophila. Knockdown of LbEST-inte4 resulted in a substantial increase in the booklice susceptibility to malathion. Overexpression of LbEST-inte4 in Drosophila melanogaster significantly enhanced its malathion tolerance. Molecular modeling and docking analysis suggested potential interactions between LbEST-inte4 and malathion. When overexpressed LbEST-inte4 in Sf9 cells, a notable elevation in esterase activity and malathion tolerance was observed. HPLC analysis indicated that the LbEST-inte4 enzyme could effectively degrade malathion. Taken together, the upregulated LbEST-inte4 appears to contribute to malathion tolerance in L. bostrychophila by facilitating the depletion of malathion. This study elucidates the molecular mechanism underlying malathion detoxification and provides the foundations for the development of effective prevention and control measures against psocids.

The Molecular Resistance Mechanisms of European Earwigs from Apple Orchards Subjected to Different Management Strategies

To date, apple orchards are among the most treated crops in Europe with up to 35 chemical treatments per year. Combining control methods that reduce the number of pesticide treatments is essential for agriculture and more respectful of the environment, and the use of predatory insects such as earwigs may be valuable to achieve this goal. European earwigs, Forficula auricularia (Dermaptera: Forficulidae) are considered beneficial insects in apple orchards where they can feed on many pests like aphids. The aim of this study was to investigate the potential impact of orchards' insecticide treatments on resistance-associated molecular processes in natural populations of earwigs. Because very few molecular data are presently available on earwigs, our first goal was to identify earwig resistance-associated genes and potential mutations. Using earwigs from organic, integrated pest management or conventional orchards, we identified mutations in acetylcholinesterase 2, α1 and β2 nicotinic acetylcholine receptors. In addition, the expression level of these targets and of some essential detoxification genes were monitored using RT-qPCR. Unexpectedly, earwigs collected in organic orchards showed the highest expression for acetylcholinesterase 2. Four cytochromes P450, one esterase and one glutathione S-transferases were over-expressed in earwigs exposed to various management strategies in orchards. This first study on resistance-associated genes in Forficula auricularia paves the way for future experimental studies aimed at better understanding the potential competition between natural enemies in apple orchards in order to optimize the efficiency of biocontrol.

A rice plant expressing viral glycoprotein NSvc2-NS reduces the transmission of rice stripe virus by the small brown planthopper

BACKGROUND

Plant viruses transmitted by arthropod vectors threaten crop health worldwide. Rice stripe virus (RSV) is one of the most important rice viruses in East Asia and is transmitted by the small brown planthopper (SBPH). Previously, it was demonstrated that the viral glycoprotein NSvs2-N could mediate RSV infection of the vector midgut. Therefore, NSvc2-N protein could potentially be used to reduce RSV transmission by competitively blocking midgut receptors.

RESULTS

Here, we report that transgenic rice plants expressing viral glycoprotein can interfere with RSV acquisition and transmission by SBPH. The soluble fraction (30-268 amino acids, designated NSvs2-N_S ) of NSvs2-N was transformed into rice calli, which produced plants harboring the exogenous gene. When SBPH was fed on transgenic plants prior to RSV-infected rice (sequential feeding) and when insects were fed on RSV-infected transgenic plants (concomitant feeding), virus acquisition by the insect vector was inhibited, and subsequent viral titers were reduced. Immunofluorescence labeling also indicated that viral infection of the insect midgut was inhibited after SBPH was fed on transgenic plants. The system by which RSV infected insect cells in vitro was used to corroborate the role of NSvc2-N_S in reducing viral infection. After the cells were incubated with transgenic rice sap, the virus infection rate of the cells decreased significantly, and viral accumulation in the cells was lower than that in the control group.

CONCLUSION

These results demonstrated the negative effect of NSvs2-N_S transgenic plants on RSV transmission by insect vectors, which provides a novel and effective way to control plant viral diseases. © 2022 Society of Chemical Industry.

Knockdown of a Nicotinic Acetylcholine Receptor Subunit Gene Bdorβ1 Decreases Susceptibility to Oxa-Bridged trans- instead of cis-Nitromethylene Neonicotinoid Insecticides in Bactrocera dorsalis

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate the fast action of acetylcholine in synaptic cholinergic transmissions. Insect nAChRs are the target of several classes of insecticides. Here, the full-length cDNA encoding a nAChR beta1 subunit (Bdorβ1) was identified and characterized from a destructive pest, Bactrocera dorsalis. The amino acid sequence of Bdorβ1 shows high identities to other insect nAChRs β1 subunits. Double injection of dsBdorβ1 reduced the expression of Bdorβ1 and in turn significantly decreased susceptibility to oxa-bridged trans- instead of cis-nitromethylene neonicotinoids. Our results support the involvement of Bdorβ1 in the susceptibility of B. dorsalis to oxa-bridged trans- instead of cis-nitromethylene neonicotinoids and imply that these two classes of neonicotinoids might be acting at different nAChR subtypes.

Cross-Resistance and Fitness Costs of the cis-Nitromethylene Neonicotinoid Cycloxaprid Resistance in Melon Aphid, Aphis gossypii (Hemiptera: Aphididae)

The melon aphid, Aphis gossypii Glover, is an important pest on various vegetables around the world and has developed resistance to neonicotinoids in fields. Cycloxaprid is a novel cis-nitromethylene configuration neonicotinoid insecticide that is different from trans-configuration neonicotinoids like imidacloprid and thiamethoxam. Herein, the cross-resistance to the other seven insecticides and fitness costs were investigated in the cycloxaprid-resistant A. gossypii strain (Cpd-R), which has developed 69.5-fold resistance to cycloxaprid. The results showed that the Cpd-R strain had very low levels of cross-resistance to imidacloprid (4.3-fold), acetamiprid (2.9-fold), thiamethoxam (3.7-fold), nitenpyram (6.1-fold), flupyradifurone (2.2-fold), and sulfoxaflor (4.5-fold), while it exhibited a cross-resistance to dinotefuran (10.6-fold). The fitness of the Cpd-R strain by life table analysis was only 0.799 compared to the susceptible strain (Cpd-S). This Cpd-R strain exhibited significantly reduction in fecundity, oviposition days, and developmental time of nymph stage compared to the Cpd-S strain. Moreover, the expression levels of some genes related to the development and reproduction, including EcR, USP, JHAMT, and JHEH were significantly up-regulated, while Vg was down-regulated in the Cpd-R strain. This study indicates that the Cpd-R strain possessed a certain fitness cost. The above research results are useful for rational application of cycloxaprid and implementing the appropriate resistance management strategy for A. gossypii.

The actions of neonicotinoid insecticides on nicotinic acetylcholine subunits Ldα1 and Ldα8 of Leptinotarsa decemlineata and assembled receptors

The insect nicotinic acetylcholine receptor (nAChR) is a pentameric channel protein and also a target for neonicotinoids. There are few reported studies on the molecular interactions of Leptinotarsa decemlineata nAChRs with neonicotinoids. In this study, we analyzed the response of acetylcholine and neonicotinoids (thiamethoxam [TMX], imidacloprid [IMI], and clothianidin [CLO]) on hybrid receptors constructed by nAChR α1 and α8 subunits of L. decemlineata (Ldα1 and Ldα8) co-expressed with rat β2 subunit (rβ2) at different capped RNA (cRNA) ratios in Xenopus oocytes. In addition, we evaluated the expression changes of Ldα1 and Ldα8 after median lethal dose of TMX treatment for 72 h by quantitative polymerase chain reaction (qPCR). The resulting functional nAChRs Ldα1/rβ2 and Ldα1/Ldα8/rβ2 showed different pharmacological characteristics. The neonicotinoids tested showed lower agonist affinity on Ldα1/Ldα8/rβ2 compared to Ldα1/rβ2 at same ratios of subunit cRNAs. The sensitivities of neonicotinoids tested for Ldα1/rβ2 and Ldα1/Ldα8/rβ2 at cRNA ratios of 5:1, 1:1 and 5:5:1, 1:1:1, respectively, were lower than those for nAChRs at ratios of 1:5 and 1:1:5, respectively, whereas the values of maximum response (I_max ) varied. For Ldα1/Ldα8/rβ2, a reduction of Lda8 cRNA resulted in increased sensitivity to IMI and decreased sensitivity to TMX. The expression of Ldα1 and Ldα8 significantly decreased in adults by 82.12% and 47.02%, respectively, while Ldα8 was significantly upregulated by 2.44 times in 4th instar larvae after exposure to TMX. We infer that Ldα1 and Ldα8 together play an important role in the sensitivity of L. decemlineata to neonicotinoids.

Known Target and Nontarget Effects of the Novel Neonicotinoid Cycloxaprid to Arthropods: A Systematic Review

Neonicotinoids are the most widely used insecticide class worldwide, and unfortunately, the widely used neonicotinoid imidacloprid is problematic for pollinators and other nontarget organisms. These nontarget impacts and the development of resistance prompt the ongoing development and testing of new neonicotinoids. The novel neonicotinoid cycloxaprid was described in 2011 and registered in China in 2015. Studies investigating its use and effect on target and nontarget species are recent and ongoing, and empirical evidence has not yet been collectively considered. Therefore, a systematic review was performed to identify and summarize data associated with target and nontarget, lethal and sublethal impacts of cycloxaprid for its use as a new insecticide. We performed keyword literature searches in Web of Science, PubMed, Academic Search Complete, and Google Scholar and explored citations used in identified articles. The search strategy yielded 66 citations; 25 citations fulfilled eligibility criteria and were included in the review. Under experimental conditions, cycloxaprid reduced populations of plant-feeding insect pests, suppressed populations of sucking and biting insect pests, and affected reproduction, development time, longevity, growth, gene regulation and expression, and phloem-feeding behavior of various life stages of certain insects. Studies focus on pest control efficacy and comparison with imidacloprid. Five nontarget organisms have been evaluated: Apis mellifera, Chrysoperla sinica, Harmonia axyridis, Daphnia magna, and Eisenia fetida. Variation in study design, to date, precludes a metaanalysis. However, these results provide valuable insight into possible effects to target and nontarget arthropods. Because cycloxaprid is a new insecticide, additional research is needed to clarify the mechanism of action of cycloxaprid and its metabolites, and to determine if it harms natural enemies or other nontarget organisms, if resistance develops, and if it exhibits cross-resistance with other insecticides. Although research on target arthropods will inform some effects on nontarget organisms, studies focusing explicitly on impacts to nontarget organisms are needed. Integr Environ Assess Manag 2020;16:831-840. © 2020 SETAC.

Molecular Insights into the Insensitivity of Lepidopteran Pests to Cycloxaprid

Cycloxaprid (CYC) is effective in the control of hemipteran pests, but its bioactivity against lepidopteran pests is still unclear. Here, the bioactivity of CYC against lepidopteran pests was found to be much worse than that against hemipteran insects. To reveal the mechanism, the transcriptomes of CYC-treated and untreated Ostrinia furnacalis larvae were compared. Among the top 20 differentially expressed genes, 11 encode proteins involved in cuticle formation, while only one encodes a detoxifying enzyme. Thus, the cuticle appears to be important for the insensitivity of O. furnacalis to CYC. A pretreatment of O. furnacalis larvae with methoprene enhanced the bioactivity of CYC by 1.12-fold. Moreover, mixtures of CYC with graphene oxide increased the bioactivity of CYC by 1.88-fold. Because lepidopteran and hemipteran insects often harm crops at the same time, the work can help make full use of CYC and reduce the environmental impacts of using multiple pesticides.

Characterization of nitenpyram resistance in Nilaparvata lugens (Stål)

Nitenpyram is very effective in controlling Nilaparvata lugens (brown planthopper, BPH), and its resistance has been reported in field populations; however, the resistance mechanism remains unclear. In the present study, cross-resistance and resistance mechanisms in nitenpyram-resistant BPH were investigated. A resistant strain (NR) with a high resistance level (164.18-fold) to nitenpyram was evolved through successive selection for 42 generations from a laboratory susceptible strain (NS). The bioassay results showed that the NR exhibited cross-resistance to imidacloprid (37.46-fold), thiamethoxam (71.66-fold), clothianidin (149.17-fold), dinotefuran (98.13-fold), sulfoxaflor (47.24-fold), cycloxaprid (9.33-fold), etofenprox (10.51-fold) and isoprocarb (9.97-fold) but not to triflumezopyrim, chlorpyrifos and buprofezin. The NR showed a 3.21-fold increase in cytochrome P450 monooxygenase (P450) activity compared to that in the NS, while resistance was also synergized (4.03-fold) with the inhibitor piperonyl butoxide (PBO), suggesting a role of P450. Furthermore, the mRNA expression levels of cytochrome P450 (CYP) genes by quantitative real-time PCR results indicated that twelve P450 genes were significantly overexpressed in the NR strain, especially CYP6ER1 (203.22-fold). RNA interference (RNAi) suppression of CYP6ER1 through injection of dsCYP6ER1 led to significant susceptibility in the NR strain. The current study expands our understanding of the nitenpyram resistance mechanism in N. lugens, provides an important reference for integrated pest management (IPM), and enriches the theoretical system of insect toxicology.