Effects Of Low Concentration Imidacloprid On The Olfactory Behavior,Antennal And Brain Transcriptome Of The Hippodamia Variegata(Goeze)

Hippodamia variegate（Goeze）is one of the important predatory natural enemies of the cotton aphid Aphis gossypii Glover in cotton fields in Xinjiang and has an essential ecological role in the integrated management of cotton aphids.The residues of imidacloprid,a commonly used insecticide for the chemical control of cotton aphids,hurt Hippodamia variegate after spraying in cotton fields.In this study,adult ladybird beetles were fed cotton aphids sprayed with 3.93 mg a.i./L(This concentration is the LC₂₀ concentration obtained from the cotton aphid toxicity assay,referred to as"LC₂₀ concentration")and 13.62 mg a.i./L(This concentration is the LC₅₀ concentration obtained from the cotton aphid toxicity assay,referred to as"LC₅₀ concentration".)of imidacloprid,and the effects of low concentration of imidacloprid on the olfactory sensation of ladybird beetles was analyzed by a Y olfactometer.The effects of imidacloprid on the antennas and brain tissue of the aphid was also analyzed by transcriptome analysis.The results of the study are as follows:（1）The LC₂₀ and LC₅₀ concentrations of imidacloprid weakened the olfactory selection behaviour of Hippodamia variegate on cotton aphid-infested cotton plants.Using a Y olfactometer,study the effects of two concentration of imidacloprid on the olfactory selective behaviour of the Hippodamia variegate.The results showed that the control ladybird had a significant positive tendency towards cotton aphid-infested cotton plants.In contrast,the ladybird in both imidacloprid treatment groups had no significant tendency towards clean air,healthy cotton plants,and cotton aphid-infested cotton plants,and there was no significant difference between the two imidacloprid treatment groups;the selection rate of the ladybird in both imidacloprid treatment groups towards cotton aphid-infested cotton plants was significantly lower than that of the ladybird in the control group;indicating that the LC₂₀ and LC₅₀ concentrations of imidacloprid reduced the ability of the ladybird to search for prey.（2）A total of eight different volatiles were identified between healthy cotton plants and those infested by cotton aphids.Using solid phase microextraction（SPME）,volatiles from cotton aphid-infested and healthy cotton plants were collected and separated by gas chromatography-mass spectrometry（GC-MS）to identify a total of eight different volatiles between them,namely:lauricene,limonene,1-decyne,3-carene,（3E）-4,8-Dimethyl-1,3,7-nonatriene（DMNT）,β-gabdalene,α-Humulene,（3E,7E）-4,8,12-trimethyltrideca-1,3,7,11-tetraene（TMTT）,of which TMTT was a new volatile produced by healthy cotton plants after being infested by cotton aphids,and DMNT increased the most after infestation by cotton aphids,55.97 times more than healthy cotton plants.（3）The LC₂₀ and LC₅₀ concentrations of imidacloprid impair the olfactory recognition of differential volatiles by Hippodamia variegate.The results showed that only TMTT had a significant attraction effects on the control ladybird among the eight volatiles,while the ladybird in both imidacloprid treatment groups showed no significant positive tendency to the eight volatiles and no significant difference between them;the ladybird in both imidacloprid treatment groups showed a significantly lower selection rate for TMTT than the control ladybird,while the non-selection rate was significantly higher than the control;the results indicated that the LC₂₀ and LC₅₀ concentrations of imidacloprid reduced the ladybird’s ability to recognize the differential volatiles.（4）The LC₂₀ and LC₅₀ concentrations of imidacloprid affected the transcriptome of antennas and brain tissue of the ladybird beetle,Hippodamia variegate.In the transcriptome analysis of antennas and brain tissue,the results of differentially expressed genes in GO and KEGG annotation showed that differential genes were mainly enriched in metabolic processes,enzyme activities,biosynthesis,ribosomes,RNA transport and neural signaling pathways;some genes related to olfaction were abnormally expressed in antennas and brain tissues of the two imidacloprid treatment groups of Hippodamia variegate,Such as OBP 2,6,OR 160,35,etc.;indicating that low concentration of imidacloprid caused abnormal olfactory recognition and neural signaling in Hippodamia variegate,reducing its olfactory sensitivity and thus weakening its olfactory recognition ability.This experiment confirmed that low concentration of imidacloprid could weaken the ladybird beetle’s olfactory behavior and odor recognition ability and initially revealed the molecular mechanism causing this phenomenon.The study results are beneficial to the conservation and use of the Hippodamia variegate in cotton fields,providing a scientific basis for its greater pest control role in cotton field ecosystems and a scientific reference for the coordination between chemical and biological control of cotton aphids.