Ecological Mechanism Of Buckwheat In Promoting Population Conservation Of Peristenus Spretus

In recent years,with the adjustment of crop cultivation structure and the reduced utilization of high-toxic pesticides,the mirid bug Apolygus lucorum（Meyer-Dür）（Hemiptera:Miridae）has become one of the important pests of cotton in China,especially in the Yangtze River Basin and Yellow River Basin.Peristenus spretus Chen et van Achterberg（Hymenoptera:Braconidae）is a dominant endoparasitoid of mirid bugs,with a great potential for preventing outbreaks of A.lucorum.Buckwheat Fagopyrum esculentum Moench is one of the most valuable nectary plants in China,which possesses a long flowering period,well-developed nectaries,and a high rate of nectar secretion,plays an important role in parasitoids’ growth and reproduction as an important food source.Previous studies found that buckwheat strips in cotton fields could improve the parasitism of P.spretus adults on A.lucorum nymphs.In this thesis,effects of buckwheat flowers on the survival and parasitism of P.spretus were studied in order to evaluate the role of buckwheat flowers in the population conservation of P,spretus.Besides,the behavioral selection and chemical recognition mechanisms,combined with chemical ecology methods,were studied to analyze the behavioral responses mechanism of P.spretus adults on buckwheat flowers.Finally,a multi-replicated plot experiment was carried out in the field to evaluate the effects of imidacloprid on the parasitic and pest control functions of P.spretus.The main results were as follows:（1）We compared the longevity of P.and their parasitism rate on A.lucorum by providing either moist cotton or fresh buckwheat flowers and moist cotton,and found that when feeding on buckwheat flowers,the lifespan of parasitic wasps increased by 1.7-to 3.1fold,and their daily parasitism rate increased by 10.3%,indicating that buckwheat flowers can significantly extend the longevity of P.spretus and enhance the parasitic performance on A.lucorum.（2）We collected buckwheat nectar and analyzed the composition and content of its soluble sugar,the results showed that the total soluble sugar in buckwheat nectar accounted for 6.3%of the nectar,mainly fructose,glucose,maltose,mannose,rafinose and sucrose.Previous research results showed that after feeding on fructose and glucose,the longevity of female P.spretus was 3.1-and 2.0-fold compared with that of CK,while the number of offspring was 3.3-and 1.8-fold compared with that of water,respectively,indicating that fructose and glucose played a key role in extending the lifespan and improving the fecundity of P.spretus.（3）The behavioral responses of P.spretus were determined by Y-tube insect olfactometer,and the results showed that both male and female P.spretus had a significant tendency toward buckwheat flowers.The combined analysis of SPME,GC-MS and EAG showed that there were mainly five active chemicals in buckwheat flower volatiles:cis-3-Hexenyl acetate,4Methylanisole,4-Oxoisophorone,p-methylphenol and 2-Ethylhexyl salicylate,and were the key substances of buckwheat flowers which caused antennal responses of P.spretus adults,and the antennal responses were the strongest at 10 mg/mL 4-Oxoisophorone.（4）Through a multi-replicated plot test,we found that under the amount of 240 g active.ingredient/hm2 of imidacloprid,the number of recaptured mirid bugs was reduced by 55.9%compared with that of water control.In contrast,the parasitic effects of imidacloprid at 240 g/hm2 on P.spretus was more negative,the density of parasitized A.lucorum nymphs was only 0.5 individuals/12 m2,which reduced by 77.2%,indicating that although imidacloprid at 240 g/hm2 reduced the density of A.lucorum nymphs,it also weakened the parasitism of P.spretus on A.lucorum in cotton fields.In summary,we studied the effects of buckwheat flowers on the survival,parasitism and behavioral selection mechanisms of P.spretus,as well as the effects of imidacloprid on the pest control function of P.spretus.It was found that buckwheat flowers could promote the population conservation of P.spretus,and the addition of buckwheat strips and reduced use of insecticides in cotton fields will promote the conservation biological control of P.spretus.