Evidence for the Participation of Chemosensory Proteins in Response to Insecticide Challenge in Conopomorpha sinensis

New and emerging mechanisms of insecticide resistance

The continuous use of insecticides over the last eight decades has led to the development of resistance to these insecticides. Research in the last few decades showed that the mechanisms underlying resistance are diverse but can generally be classified under several modes of resistance such as target-site resistance, metabolic resistance, and penetration resistance. In this review, we highlight new discoveries in insecticide resistance research made over the past few years, including an emerging new mode of resistance, sequestration resistance, where the overexpression of olfactory proteins binds and sequesters insecticides in resistant strains, as well as recent research on how posttranscriptional regulation can impact resistance. Future research will determine the generality of these emerging mechanisms across insect species.

Identification and characterization of circadian clock genes in the head transcriptome of Conopomorpha sinensis Bradley

Conopomorpha sinensis Bradley is the most detrimental pest to litchi and longan in China. Adult eclosion, locomotion, mating and oviposition of C. sinensis usually occur at night, regulated by a circadian rhythm. Nevertheless, our understanding of the linkages between adult circadian rhythms and clock genes remains inadequate. To address this gap, transcriptomic analysis was conducted on female and male heads (including antennae) of C. sinensis using the Illumina HiSeq 6000 platform to identify major circadian clock-related genes. The annotated sequences were analyzed by BLASTx, and candidate clock genes were classified based on conservation, predicted domain architectures, and phylogenetic analysis. The analysis revealed a higher conservation of these genes among the compared moths. Further, the expression profile analysis showed a significant spatiotemporal and circadian rhythmic accumulation of some clock genes during development. The candidate clock genes were predominantly expressed in the head, highlighting their crucial function in circadian rhythm regulation. Moreover, CsinPer, CsinTim1, and CsinCry1 displayed similar dynamic expressions with a peak expression level in the 4th age adults, suggesting their involvement in regulation of courtship and mating behaviors. The CsinPer and CsinTim1 mRNA oscillated strongly with a similar phase, containing a peak expression just before the female mating peak. This work will greatly contribute to understanding the circadian clock system of C. sinensis and provide valuable information for further studies of the molecular mechanisms involved in rhythmicity in fruit-boring pests.

Three chemosensory proteins enriched in antennae and tarsi of Rhaphuma horsfieldi differentially contribute to the binding of insecticides

Antennae and legs (primarily the tarsal segments) of insects are the foremost sensory organs that contact a diverse range of toxic chemicals including insecticides. Binding proteins expressed in the two tissues are potential molecular candidates serving as the binding and sequestering of insecticides, like chemosensory proteins (CSPs). Insect CSPs endowed with multiple roles have been suggested to participate in insecticide resistance, focusing mainly on moths, aphids and mosquitos. Yet, the molecular underpinnings underlying the interactions of cerambycid CSPs and insecticides remain unexplored. Here, we present binding properties of three antenna- and tarsus-enriched RhorCSPs (RhorCSP1, CSP2 and CSP3) in Rhaphuma horsfieldi to eight insecticide classes totaling 15 chemicals. From the transcriptome of this beetle, totally 16 CSP-coding genes were found, with seven full-length sequences. In phylogeny, these RhorCSPs were distributed dispersedly in different clades. Expression profiles revealed the abundant expression of RhorCSP1, CSP2 and CSP3 in antennae and tarsi, thus as representatives for studying the protein-insecticide interactions. Binding assays showed that the three RhorCSPs were tuned differentially to insecticides but exhibited the highest affinities with hexaflumuron, chlorpyrifos and rotenone (dissociation constants <13 μM). In particular, RhorCSP3 could interact strongly with 10 of tested insecticides, of which four residues (Tyr25, Phe42, Val65 and Phe68) contributed significantly to the binding of six, four, three and four ligands, respectively. Of these, the binding of four mutated RhorCSP3s to a botanical insecticide rotenone was significantly weakened compared to the wildtype protein. Furthermore, we also evidenced that RhorCSP3 was a broadly-tuned carrier protein in response to a wide variety of plant odorants outside insecticides. Altogether, our findings shed light on different binding mechanisms and odorant-tuning profiles of three RhorCSPs in R. horsfieldi and identify key residues of the RhorCSP3-insecticide interactions.

Functional characterization of four antenna-biased chemosensory proteins in Dioryctria abietella reveals a broadly tuned olfactory DabiCSP1 and its key residues in ligand-binding

The orientation of the oligophagous cone-feeding moth Dioryctria abietella (Lepidoptera: Pyralidae) to host plants primarily relies on olfactory-related proteins, particularly those candidates highly expressed in antennae. Here, through a combination of expression profile, ligand-binding assay, molecular docking and site-directed mutagenesis strategies, we characterized the chemosensory protein (CSP) gene family in D. abietella. Quantitative real-time PCR (qPCR) analyses revealed the detectable expression of all 22 DabiCSPs in the antennae, of which seven genes were significantly enriched in this tissue. In addition, the majority of the genes (19/22 relatives) had the expression in at least one reproductive tissue. In the interactions of four antenna-dominant DabiCSPs and different chemical classes, DabiCSP1 was broadly tuned to 27 plant-derived odors, three man-made insecticides and one herbicide with high affinities (Ki < 6.60 μM). By contrast, three other DabiCSPs (DabiCSP4, CSP6 and CSP17) exhibited a narrow odor binding spectrum, in response to six compounds for each protein. Our mutation analyses combined with molecular docking simulations and binding assays further identified four key residues (Tyr25, Thr26, Ile65 and Val69) in the interactions of DabiCSP1 and ligands, of which binding abilities of this protein to 12, 15, 16 and three compounds were significantly decreased compared to the wildtype protein, respectively. Our study reveals different odor binding spectra of four DabiCSPs enriched in antennae and identifies key residues responsible for the binding of DabiCSP1 and potentially active compounds for the control of this pest.

Safety Evaluation of Chlorantraniliprole in Lychee Based on Residue and Dietary Risk Assessment

This report presents the development of a highly effective method employing high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to investigate chlorantraniliprole's dissipation, risk assessment, and residue distribution in whole lychee fruit and its pulp. Mean recoveries of the samples ranged from 80 to 105%, exhibiting a relative standard deviation (RSD) of below 8%. The limits of quantification (LOQ) for lychee and pulp were determined as 0.001 mg/kg, and half-lives (t1/2) ranged from 8.0 to 12.2 days. Terminal residue concentrations in whole litchi and pulp were determined as 0.008-0.45 mg/kg and ≤0.001 mg/kg. These residues were treated twice and thrice at two different dosage levels with pre-harvest intervals (PHIs) of 7, 14, and 21 days. The potential chronic risk posed by chlorantraniliprole to humans was non-negligible, as indicated by the risk quotient (RQ) value not exceeding 1. Therefore, this study provides significant fresh data about the safe application of chlorantraniliprole in the production of lychee, which will help China develop maximum residual limits (MRLs).

Candidate odorant-binding protein and chemosensory protein genes in the turnip aphid Lipaphis erysimi

The turnip aphid, Lipaphis erysimi Kaltenbach, inflicts heavy damage on cruciferous crops worldwide. In these insects, olfactory perception is crucial for mating, host location, and oviposition. Both odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are responsible for the delivery of host odorants and pheromones during initial molecular interactions. In this study, antennal and body transcriptomes of L. erysimi were generated through the deep sequencing of RNA libraries. A dataset of 11 LeryOBP and four LeryCSP transcripts was identified among assembled unigenes and subjected to sequence analysis. Phylogenetic analysis found a one-to-one orthologous relationship between LeryOBP/LeryCSP and its corresponding homologs from other aphid species. Further quantitative real-time PCR analyses across developmental stages and tissues showed that five LeryOBP genes (i.e., LeryGOBP, LeryOBP6, LeryOBP7, LeryOBP9, and LeryOBP13) and LeryCSP10 were specifically or significantly elevated in the antennae compared with other tissues. Moreover, two transcripts (i.e., LeryGOBP and LeryOBP6) exhibited remarkably higher expression levels in alate aphids, implying their potentially functional role in the perception of new host plant locations. These results present the identification and expression of OBP/CSP genes in L. erysimi, providing valuable insights into their putative role in olfactory signal transduction.