Study On The Repellent Protection And Potential Effect Of Azadirachtin On Harmonia Axyridis Pallas

Azadirachtin is recognized as the best bio-pesticide in the world.It has many characteristics such as high efficiency,low toxicity,easy degradation and no residue.It has biological activity against more than 400 agricultural,forestry,grain storage and sanitation pests of more than 10 orders,such as Lepidoptera,Coleoptera,Hymenoptera,and Diptera.The control spectrum is very wide.The action modes of azadirachtin on pests mainly include antifeeding,inhibition of growth and development,stomach toxicity,contact killing,avoidance,and avoidance of egg laying.Natural enemy insects are susceptible to the adverse effects of chemical pesticides in nature,so this article hopes to find a new way,that is,to use the repellent effect of azadirachtin to achieve the purpose of controlling pests and protecting natural enemies,and strengthening the joint control of pests by green pesticides and natural enemies mechanism.According to the above objectives,this article studied the repellent and protective effects of azadirachtin on Harmonia axyridis under selective conditions,and studied the potential effects of azadirachtin on H.axyridis under mandatory conditions.The research content is as follows:1.The myxoaphids method was used to study the selective antifeedant effect of azadirachtin on Harmonia axyridis under selective conditions.Under selective conditions,azadirachtin showed selective antifeeding effect on both larvae and adults.With the increase of azadirachtin concentration,selective antifeeding phenomenon was obvious.With the extension of treatment time,the antifeedant rate decreased:azadirachtin concentration was 10 mg/kg,the predation of the 4th instar larvae of H.axyridis at each time point was significantly different from the control group（P<0.01）.The predation of 4th instar larvae on CK and 10 mg/kg aphids was 12,24,and 48 hours were 8,3,18,12.33 and 29.67,25.33,and the antifeedant rates were 45.45,18.68 and7.88%.The antifeedant effect of azadirachtin on the adult H.axyridis is stronger than that of the larva.Studies have shown that azadirachtin has a repellent and protective effect on H.axyridis.2.The effect of azadirachtin on the eggs of H.axyridis was determined by directly impregnating the eggs of H.axyridis and measuring its hatching rate.The results showed that the hatching rate of H.axyridis eggs decreased with the increase of azadirachtin concentration,but the hatching rates were all above 94%,and there was no significant difference compared with the control.The effects of azadirachtin on the body weight of H.axyridis larvae and adults were studied by direct dipping and feeding with poisonous aphid.The effect of azadirachtin on the body weight of adults was reduced,but the difference was not significant;The effect of body weight of larvae is more obvious,which is reduced with the increase of the treatment concentration and increased with the extension of the treatment time,and is related to the treatment method.The aphid feeding method has a greater impact on body weight than direct immersion method.After 48 hours of direct immersion treatment,the average weight of larvae in the azadirachtin treatment group（50 mg/kg）was 4.50±0.75 mg,which was significantly lower than the average weight of larvae in the control group（8.62±0.51 mg）.After 48 hours of treatment with poisonous aphid feeding,the average body weight of larvae in the 50 mg/kg treatment groups was 2.39±0.13 mg,which was significantly lower than the average body weight of larvae in the control group（8.97±0.20 mg）.3.Under compulsory conditions,the predation of azadirachtin toxic aphid feeding on H.axyridis larvae and adults,compared with the control,all three concentrations of azadirachtin caused a reduction in the predation of H.axyridis.4.The effect of three concentrations of azadirachtin on the functional response of H.axyridis larvae and adult prey to Acyrthosiphon pisum was studied by poison aphid feeding method.The results showed that:after azadirachtin treatment,the H.axyridis predator function response model has not changed,and it is still the typical Holling typeⅡ,but the parameters of the model have changed,specifically manifested as a reduction in instantaneous attack rate and maximum daily predation,and an increase in processing time.This indicates that azadirachtin adversely affects the predation function of H.axyridis.The search effect results showed that the search effect of H.axyridis on A.pisum treated with azadirachtin was lower than that of the control.At the same time,the predation behavior of H.axyridis was observed,and it was found that the aphid treated with azadirachtin changed the predation behavior of H.axyridis,and the number of trials increased.Adult of H.axyridis is also accompanied by long and intense cleaning of the antennae,mandible,and forefoot.5.Azadirachtin affects the activity of three protective enzymes（SOD,CAT,POD）in H.axyridis 4^th instar larvae and adults,and the enzyme activity may be inhibited or activated,indicating that azadirachtin has a heterochromatic scoop insects have an adverse effect.6.Scanning electron microscopy was used to observe the sensory changes of the antennae,mandible and forefoot of H.axyridis.The results showed that after treatment with azadirachtin,the adult antennal stalk node,forefoot leg segment,tibia segment,appendix segment,and hairy sensor on the mandible had different degrees of damage or shedding.H.axyridis’special sensor（ear spoon shape）on the attachment of the forefoot is also damaged.At the same time,azadirachtin causes more impurities on the surface of the axillary mandible.7.Illumina RNA-seq sequencing was used to analyze the effect of azadirachtin on H.axyridis at the molecular level.The results showed that after 10 and 50 mg/kg azadirachtin were treated,the number of genes that were significantly differentially expressed in H.axyridis larvae there were 1240 and 1274,respectively,and 179 and372 adults.The results of GO enrichment indicated that azadirachtin treatment had a significant effect on the metabolic process of H.axyridis.Enrichment analysis of KEGG metabolic pathways by differential genes showed that the azadirachtin metabolic pathway with the greatest impact on H.axyridis larvae was the drug metabolism-enzyme pathway,and the metabolic pathway with the greatest impact on H.axyridis adults was the ribosomal pathway.Under selective conditions,azadirachtin will exhibit selective antifeedant effect on H.axyridis,and play a role in repelling and protecting H.axyridis;under mandatory conditions,azadirachtin treatment reduces the body weight of H.axyridis larvae,reduces the predation of H.axyridis larvae and adults,and changes the activity of three protective enzymes in the ladybird.Azadirachtin treatment did not significantly reduce the hatching rate of eggs,and did not change the type of predatory function response of H.axyridis,but changed the specific parameters.Scanning electron microscopy results showed that azadirachtin caused damage to the trichomes of ladybug antennae and other parts,which also partially explained the changes in the predation behavior of H.axyridis.H.axyridis has a molecular impact.The above results show that azadirachtin is not absolutely safe to Harmonia axyridis and will have adverse effects.