Discovery And Biological Characteristics Of A Fruit Fly Pupal Parasitoid,with Preliminary Study On Its Biological Control Potential

With various kinds of species,parasitoids are of great importance in the ecological system and biological control.Drosophila melanogaster has been the model insect for a long period and manifested to be good material for studying parasitoids.Different parasitoids on fruit fly employ different parasitic strategies aiming to increase the survival rate of wasp offsprings.Parasitoids cause humoral immnune response and cellular immune response of the host and expressional level of genes in immune related pathway changes after the host are attacked by parasitoids.Virulent factors differ among various parasitoids and play a key role in the successful parasitization.As agricultural pests,fruit flies damage gardening development greatly.Traditional chemical control methods are of low efficiency and harmful to public health.Therefore local parasitoids are needed badly.In this study,we trapped a pupal parasitoid on fruit fly by a fruit trap and identified it by morphological and molecular biological methods.Some biological data of the new pupal parasitoid has been primarily studied.We also primarily explored its parasitic strategy and discussed its potential on biological control.The main results are shown as follows:1 Identification and development of the parasitoidThe parasitoids are morphologically and molecularly identified as Trichopria sp.Under the condition of 2011 ? and 50%RH,the developmental durarion of the wasp is about 18d,the female wasps emerge about ld later than the male wasps.The wasp develops entirely in the fly pupa before emergence.The eggs hatch after 24h and the larva could be sorted into 4 instars according to the morphological data and features.The larvae undergo great morphological changes from egg to larva and from larva to adult.2 Preliminary study on the parasitic strategy of Trichopria sp.The female reproduction system of Trichopria sp.includes 1 pair of ovary,4 oviducts,1 pair of Doufour's gland and the venom apparatus.VL(?)s have been observed in the ovary and gential lumen.Mature VLPs are round in shape and membrane-bound,with a diameter of 0.1-0.15?m.Many radial appendages are found on the surface of mature VLPs.It can be speculated that the virulent factors of Trichopria sp.are venom and VLPs.In general,Trichopria sp.triggers JAK/STAT,Toll,Imd and PO pathways after attacking fly pupae,in which the host immune system is considered harmful to the successful parasitization of parasitoids.However,we find that the melanization of the pupa are postponed to some extent after Trichopria sp.attack.Therefore we can suggest that with the help of venom and VLPs,Trichopria sp.employs an inactive approach where the immune-related pathways are activated but Trichopria sp.is able to escape from the host immunity and survive,and then utilize host nutrition to reachasuccessfuleclosion.3 Discussion on the biological control potential of Trichopria sp.As a biological control agent,Trichopria sp.is of strong fecundity(each female adult could produce 73±1.6 eggs),long longevity(the adults could survive more than 60 days under the temperature of 18? with food)and high stress resistance(under the temperature of 4? and 37?,Trichopria sp.adults could survive at least 15 days;Trichopria sp.adults could survive 8 days with starvation).A high parasitic rate of Trichopria sp.could also be observed under lab conditions,which ranged from 85%to 96.7%according to different host pupal stages.