Search

BACKGROUND: Odorant‐binding proteins (OBPs) in insects contribute to the sensitivity of the olfactory system and connect external odorants to olfactory receptor neurons. Determination of the chemosensory functions in Diaphorina citri, a vector of the citrus Huanglongbing pathogen, may help in developing a potential target for pest management. RESULTS: Diaphorina citri showed dose‐dependent electroantennogram recording (EAG) responses to 12 host plant volatiles. A two‐choice behavioral trap experiment showed that four compounds (methyl salicylate, linalool, citral and R‐(+)‐limonene) that elicited high EAG responses also had significant attraction to adults. The expression profiles induced by these compounds were detected in nine OBP genes, DcitOBP1–9. DcitOBP3, DcitOBP6 and DcitOBP7 commonly showed significant upregulation or downregulation compared with the control. Microscale thermophoresis (MST) showed that the recombinant protein DcitOBP7 had high in vitro binding affinities (Kd < 10 μm) to methyl salicylate, linalool and R‐(+)‐limonene, and moderate binding affinity to citral with a Kd value of 15.95 μm. Furthermore, RNA interference (RNAi)‐suppressed messenger RNA (mRNA) expression of DcitOBP7 resulted in a significant reduction in EAG activity and in adult D. citri behavioral responses to tested volatiles and the preferred host, Murraya paniculata. The hydrophilic residue Arg107 of DcitOBP7 may have a key role in binding odorants via formation of hydrogen bonds. CONCLUSION: These results show that DcitOBP7 plays an important role in the olfactory response. This finding may provide new insight into the functions of OBP families in D. citri and aid in the development of safe strategies for managing D. citri populations. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND The oriental fruit fly, Bactrocera dorsalis (Hendel), is a widespread agricultural pest that has evolved resistance to many commonly used insecticides including malathion. Glutathione S‐transferases (GSTs) are multifunctional enzymes that metabolize insecticides directly or indirectly. The specific mechanism used by GSTs to confer malathion resistance in B. dorsalis is unclear. RESULTS: BdGSTd9 was identified from B. dorsalis and was expressed at twice the level in a malathion‐resistant strain (MR) than in a susceptible strain (MS). By using RNAi of BdGSTd9, the toxicity of malathion against MR was increased. Protein modelling and docking of BdGSTd9 with malathion and malaoxon indicated key amino acid residues for direct binding in the active site. In vitro assays with engineered Sf9 cells overexpressing BdGSTd9 demonstrated lower cytotoxicity of malathion. High performance liquid chromatography (HPLC) analysis indicated that malathion could be broken down significantly by BdGSTd9, and it also could deplete the malathion metabolite malaoxon, which possesses a higher toxicity to B. dorsalis. Taken together, the BdGSTd9 of B. dorsalis could not only deplete malathion, but also react with malaoxon and therefore enhance malathion resistance. CONCLUSION: BdGSTd9 is a component of malathion resistance in B. dorsalis. It acts by depleting both malathion and malaoxon. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: The oriental fruit fly Bactrocera dorsalis (Hendel), a widespread agricultural pest, has evolved resistance to many insecticides, including organophosphorus compounds. Glutathione S‐transferases (GSTs) are involved in xenobiotic detoxification and insecticide resistance in many insects. However, the role of delta class GSTs in detoxifying malathion in B. dorsalis is unknown. Here, we evaluated the roles of two delta class GSTs in malathion detoxification in this species. RESULTS: Two delta class GSTs genes, BdGSTd1 and BdGSTd10, were characterized in B. dorsalis. They were highly expressed in 5‐day‐old adults, as well as in midgut and Malpighian tubules. Upon malathion exposure, the two genes were upregulated by 2.63‐ and 2.85‐fold, respectively. Injection of double‐stranded RNA targeting BdGSTd1 or BdGSTd10 significantly reduced their mRNA levels in adults and also significantly increased adult susceptibility to malathion. The expression of these two GSTs in Escherichia coli helped the host to endure malathion stress at a concentration of 10 µg mL−1 according to a Cell Counting Kit‐8 assay. High‐performance liquid chromatography analyses indicated that malathion could be significantly depleted by the two delta GSTs. The role of BdGSTd10 in malathion sequestration was also discussed. CONCLUSION: BdGSTd1 and BdGSTd10 play important roles in the detoxification of malathion in B. dorsalis. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Extensive use of insecticides in many orchards has prompted resistance development in the oriental fruit fly, Bactrocera dorsalis (Hendel). In this study, a laboratory selected strain of B. dorsalis (MR) with a 21-fold higher resistance to malathion was used to examine the resistance mechanisms to this organophosphate insecticide. Carboxylesterase (CarE) was found to be involved in malathion resistance in B. dorsalis from the synergism bioassay by CarE-specific inhibitor triphenylphosphate (TPP). Molecular studies further identified a previously uncharacterized α-esterase gene, BdCarE2 , that may function in the development of malathion resistance in B. dorsalis via gene upregulation. This gene is predominantly expressed in the Malpighian tubules, a key insect tissue for detoxification. The transcript levels of BdCarE2 were also compared between the MR and a malathion-susceptible (MS) strain of B. dorsalis , and it was significantly more abundant in the MR strain. No sequence mutation or gene copy changes were detected between the two strains. Functional studies using RNA interference (RNAi)-mediated knockdown of BdCarE2 significantly increased the malathion susceptibility in the adult files. Furthermore, heterologous expression of BdCarE2 combined with cytotoxicity assay in Sf9 cells demonstrated that BdCarE2 could probably detoxify malathion. Taken together, the current study bring new molecular evidence supporting the involvement of CarE-mediated metabolism in resistance development against malathion in B. dorsalis and also provide bases on functional analysis of insect α-esterase associated with insecticide resistance. [ABSTRACT FROM AUTHOR]

There are many evidences that insect carboxylesterase possess important physiological roles in xenobiotic metabolism and are implicated in the detoxification of organophosphate (OP) insecticides. Despite the ongoing resistance development in the oriental fruit fly, Bactrocera dorsalis (Hendel), the molecular basis of carboxylesterase and its ability to confer OP resistance remain largely obscure. This study was initiated to provide a better understanding of carboxylesterase-mediated resistance mechanism in a tephritid pest fly. Here, we narrow this research gap by demonstrating a well-conserved esterase B1 gene, BdB1 , mediates malathion resistance development via gene upregulation with the use of a laboratory selected malathion-resistant strain (MR) of B. dorsalis . No sequence mutation of BdB1 was detected between MR and the susceptible strain (MS) of B. dorsalis . BdB1 is predominantly expressed in the midgut, a key insect tissue for detoxification. As compared with transcripts in MS, BdB1 was significantly more abundant in multiple tissues in the MR. RNA interference (RNAi)-mediated knockdown of BdB1 significantly increased malathion susceptibility. Furthermore, heterologous expression along with cytotoxicity assay revealed BdB1 could probably have the function of malathion detoxification. [ABSTRACT FROM AUTHOR]