Study On The Mechanism Of Azadirachtin Influencing The Feeding Behavior Of Plutella Xylostella(Linnaeus)

The feeding behavior of insects refers to a series of activities that occur when insects ingest food.In general,the feeding behavior of individual insects can not only show the similarity of the population but also show the unique fixed pattern to the population.The learning behavior of insects refers to the reversible or recurring phenomenon caused by the experience of individual insects.It is mainly divided into five types:habituation,sensitization,induction of preference,associative learning and aversion learning.In our previous study,we founded that azadirachtin can induce learning and memory behavior of Spodoptera litura（Fabricius）.On this basis,the larvae of Plutella xylostella were used to study the differences in feeding habits of Spodoptera litura larvae to different hosts and the mechanism of azadirachtin feeding behavior on Spodoptera litura.The research contents are as follows.1.The priority order of Plutella xylostella larvae to different host hobbies is:pak-choi（shanghaiqing）>flowering cabbage>pea.Under the condition of no choice,the larvae of Plutella xylostella had a habitual learning response to the young leaves of the peas,which were not normally fed under natural conditions.0-12 h,the feeding area of Plutella xylostella larvae to pak-choi（shanghaiqing）and pea seedlings was182.29±7.60 mm²、76.71±5.77mm²,respectively（P<0.05）,and the difference was significant.36-48 h,the feeding area was 332.29±5.74 mm²、312.29±8.34 mm²,and there was no significant difference between the two.2.Under the mandatory conditions,the larvae of Plutella xylostella had a habitual learning response to azadirachtin,and they fed on artificial diet containing azadirachtin had less food intake during the initial period than with the normal diet group.With the extension of time,Plutella xylostella increased the feed intake of azadirachtin-containing feed.0-24 h,the quality of Plutella xylostella larvae feeding normal feed and drug-containing feed(concentration:1,10,20 mg·kg^-1)were 2.35±0.17 g、1.98±0.11 g、1.46±0.24 g、0.86±0.08 g,respectively.It can be seen that the feed intake is negatively correlated with the azadirachtin treatment concentration.72-96 h,the quality of feed taken was 4.43±0.23 g、4.39±0.29 g、4.09±0.15 g、3.60±0.25 g.At the time of weighing at 96h,the body weight of individual larvae fed on normal feed and medicated feed(concentration:1,10,20 mg·kg^-1)were 4.23±0.18 mg、3.47±0.09 mg、3.10±0.07 mg、2.10±0.08 mg,respectively,and the differences between the groups were significant（P<0.05）.It can be seen that with the prolongation of time,the larvae of Plutella xylostella obviously have a habitual learning response to the azadirachtin-containing feed.Under the same concentration treatment,the feed intake increases the body weight of Plutella xylostella larvae.3.For further study,the morphological changes of Plutella xylostella in the habitual response to the artificial feed containing azadirachtin were studied by scanning electron microscope（SEM）,paraffin section and fluorescent Tunel technique.SEM was used to observe the changes of chemoreceptors related to feeding on the head surface of Plutella xylostella larvae.It was observed that after feeding on azadirachtin,the head receptors were damaged to varying degrees,which were mainly manifested as wear and fracture of sensilla basiconica and sensilla styloconica,and in severe cases,spinneret fracture.4.In order to reveal the learning mechanism of the habituation of azadirachtin in Plutella xylostella larvae under mandatory conditions,transcriptome sequencing technology was used to detect the expression level of Plutella xylostella larvae treated with azadirachtin.At 24 h,compared with normal diet,there were 86 significantly different genes in Plutella xylostella larvae feeding on medicated diet under mandatory conditions,among which 51 genes were up-regulated and 35 genes were down-regulated.At 48 h,compared with the normal diet,380 significantly different genes were found in the diet of Plutella xylostella,297 genes were up-regulated and 83 genes were decreased.The effect of azadirachtin on the metabolic process of diamondback moth was analyzed by GO analysis and KEGG analysis.After GO analysis,the main effect was on the metabolic process.After 24 h,there were 5 genes affecting the metabolic process,among which 2 genes were up-regulated and 3 genes were down-regulated.At 48 h,the metabolic process was regulated by 12 genes,among which 10 genes were up-regulated and 2 genes were down-regulated.After KEGG analysis,it mainly affected related metabolic pathways.On this basis,5 genes related to learning and memory CREB were screened as CREBL2,CREB3L3,CREBA,CREB and CREBBP.Rt-qpcr showed that the expressions of creb-related genes were up-regulated at 24 h and 48 h,which was consistent with the transcriptome results,indicating that azadirachtin regulated the feeding behavior of Plutella xylostella larvae by up-regulating the CREB gene.