Genome-wide assessment and development of molecular diagnostic methods for imidacloprid-resistance in the brown planthopper, Nilaparvata lugens (Hemiptera; Delphacidae)

Cythochrome P450-mediated dinotefuran resistance in onion thrips, Thrips tabaci

Onion thrips, Thrips tabaci, have developed resistance to many insecticides, and over the last decade, resistant populations have spread widely across Japan. The cytochrome P450 (CYP) family, a widely conserved detoxification enzyme that metabolizes xenobiotics such as insecticides and phytochemicals, is believed to play important roles in the development of resistance in T. tabaci. However, CYPs involved in insecticide resistance in T. tabaci remain unclear. To comprehensively identify CYPs in T. tabaci, the genome sequences of the thelytokous T. tabaci (ANO strain) were constructed, and 18,965 genes (protein coding) were predicted. We identified 127 CYP genes in the predicted gene set by manual curation, and 38 of these CYP genes belonged to the CYP3 clan, including genes from the CYP6 family, which is one of the most important CYP families involved in resistance to neonicotinoids in many insect pests. To identify the CYPs involved in resistance to dinotefuran, which is one of the neonicotinoids used to control T. tabaci, RNA sequencing of dinotefuran-resistant and dinotefuran-susceptible strains was performed. Results revealed that, TtCYP3652A1, which belongs to the thrips-specific CYP3652A subfamily in the CYP3 clan, was significantly upregulated in the resistant strain. In vitro CYP metabolism assays using insect cells were conducted for TtCYP3652A1 and five highly expressed CYP6 genes. Only TtCYP3652A1 significantly metabolized dinotefuran, which is considered to contribute to detoxification of dinotefuran. As no amino acid mutations were identified in the known target-site genes of neonicotinoids, TtCYP3652A1 was considered to be the main factor involved in the resistance to dinotefuran.

Molecular Evolutionary Mechanisms of CYP6ER1vA-Type Variant Associated with Resistance to Neonicotinoid Insecticides in Field Populations of Nilaparvata lugens

The evolution of insecticide resistance has threatened the control of Nilaparvata lugens. Research on mechanisms behind neonicotinoid resistance in N. lugens remains incomplete. This study examined P450-mediated resistance to neonicotinoids in a resistant N. lugens strain (XA-2017-3G). The overexpression of CYP6ER1 in the XA-2017-3G strain plays a role in neonicotinoid resistance, as confirmed by RNA interference. Phenotypic analyses of CYP6ER1-mediated resistance in strains, including laboratory-susceptible, field-collected, and imidacloprid-laboratory further-selected strains, revealed that the vA-type/vL-type genotype exhibited greater resistance to neonicotinoids compared to the vA-type/vA-type genotype. The mRNA expression levels of CYP6ER1vA-type were closely correlated with the levels of neonicotinoid resistance in N. lugens strains, in which CYP6ER1vA-type overexpression is in part attributed to increased copy numbers of CYP6ER1. CYP6ER1vA-type-mediated neonicotinoid resistance was further confirmed by a CYP6ER1vA-type transgenic Drosophila melanogaster line. Taken together, our findings strongly suggest that the overexpression of CYP6ER1vA-type, which can be partially attributed to copy number variations, plays a crucial role in N. lugens resistance to neonicotinoids.

Transcriptomic modulation in response to an intoxication with deltamethrin in a population of Triatoma infestans with low resistance to pyrethroids

Background

Triatoma infestans is the main vector of Chagas disease in the Southern Cone. The resistance to pyrethroid insecticides developed by populations of this species impairs the effectiveness of vector control campaigns in wide regions of Argentina. The study of the global transcriptomic response to pyrethroid insecticides is important to deepen the knowledge about detoxification in triatomines.

Methodology and findings

We used RNA-Seq to explore the early transcriptomic response after intoxication with deltamethrin in a population of T. infestans which presents low resistance to pyrethroids. We were able to assemble a complete transcriptome of this vector and found evidence of differentially expressed genes belonging to diverse families such as chemosensory and odorant-binding proteins, ABC transporters and heat-shock proteins. Moreover, genes related to transcription and translation, energetic metabolism and cuticle rearrangements were also modulated. Finally, we characterized the repertoire of previously uncharacterized detoxification-related gene families in T. infestans and Rhodnius prolixus.

Conclusions and significance

Our work contributes to the understanding of the detoxification response in vectors of Chagas disease. Given the absence of an annotated genome from T. infestans, the analysis presented here constitutes a resource for molecular and physiological studies in this species. The results increase the knowledge on detoxification processes in vectors of Chagas disease, and provide relevant information to explore undescribed potential insecticide resistance mechanisms in populations of these insects.

A review of physiological resistance to insecticide stress in Nilaparvata lugens

Insecticides are widely used in agriculture as effective means to control pests. However, pests have not been completely mitigated with the increased use of insecticides. Instead, many side effects have arisen, especially the '3Rs' (resistance, resurgence, and residue). The brown planthopper, Nilaparvata lugens, is one of the most threatening rice pests. The main insecticides for controlling N. lugens belong to organochlorine, organophosphorus, carbamate, neonicotinoid and pyrethroid groups. However, metabolic enzymes, including cytochrome P450s, esterases, glutathione-S-transferases, and ATP-binding cassette transporters, effectively promote the detoxification of insecticides. Besides, mutations of neurological target sites, such as acetylcholinesterase, nicotinic acetylcholine, γ-aminobutyric acid receptor, and ryanodine receptor, result in insensitivity to insecticides. Here, we review the physiological metabolic resistance in N. lugens under insecticide stress to provide a theoretical basis for identifying and developing more effective and harmless insecticides.