| Bemisia tabaci is a major agricultural pest in the world.In recent years,it has invaded and spread in China.On the one hand,it can cause plant coal pollution by feeding on plant sap and secreting honeydew in plants,on the other hand,it can also spread plant viruses and cause huge damage to plant production.Because B.tabaci is prone to pesticide resistance,it is urgent to develop biological control technology for B.tabaci.Encarsia formosa is one of the parasitic wasps commonly used to control B.tabaci.Field application shows that only when the E.formosa is released at the initial stage of B.tabaci invasion can the B.tabaci be effectively prevented and controlled.Once the population of B.tabaci reaches a certain number,the two populations will always be in a balanced state.Therefore,how to improve the parasitic efficiency of E.formosa in the early stage of B.tabaci invasion is the key to prevent and control B.tabaci.After being attacked by pests,plants can quickly release some specific volatiles and then attract parasitic wasps or predators to achieve the purpose of preventing and controlling pests.Previous studies have shown that E.formosa can also use specific volatiles induced by B.tabaci adults as clues to host location.However,it is not clear whether the volatiles induced by B.tabaci nymph and adult host(such as tomato)are the same,whether the artificial release of specific volatiles induced by B.tabaci can improve the biocontrol efficiency of E.formosa in the field.Besides,considering that B.tabaci often transmits geminiviruses to host plants,it is also worth paying attention to whether the virus-carrying status of plants and B.tabaci will affect the host search efficiency of E.formosa.In this paper,B.tabaci-tomato-E.formosa was used as the research system,and four tomato varieties(Moneymaker,Castlemart,Zhefen 302,Zheza 809)were selected as the test plants.Firstly,the effects of tomato volatiles induced by B.tabaci nymph or adult on the host selection behavior of E.formosa and the selective response of E.formosa to leaves damaged by B.tabaci nymph or adult were compared.Secondly,the chemical fingerprint spectrum of tomato volatiles induced by B.tabaci nymph or adult was extracted and compared.Then,the effects of different volatile components induced by B.tabaci on host selection and parasitic efficiency were determined,the active components of tomato volatiles induced by B.tabaci that attracted E.formosa were screened out.Finally,the effects of tomato plants and B.tabaci adults infected with tomato yellow leaf curl virus on the host selection and the parasitism efficiency of E.formosa were compared.The specific research results are as follows:1.The host selection of E.formosa on tomato volatiles and insect leaves induced by B.tabaci.In this experiment,the selective response of E.formosa to B.tabaci(nymph or adult)infected tomato and healthy tomato was measured by Y-olfactometer.The results showed that,compared with healthy tomato odor sources,E.formosa prefers to choose tomato odor sources damaged by adults(except Castlemart).On the contrary,E.formosa has no obvious preference for the odor sources of healthy tomatoes and nymph-damaged tomatoes.This indicated that the E.formosa mainly used tomato volatiles induced by B.tabaci adults to locate its host a long distance.Secondly,the selective response of E.formosa to tomato leaves damaged by nymph or adult of B.tabaci was detected in a Petri dish.The results showed that no matter what kind of tomato,there was no significant difference in residence time between nymph-damaged leaves and adult-damaged leaves.However,when the nymph remained on the leaves,the retention time of E.formosa on the leaves damaged by the nymph increased significantly.The above results show that when the E.formosa is far away from the host(B.tabaci nymph),the host location mainly depends on the tomato volatiles induced by B.tabaci adults.When E.formosa is close to the host,it depends on the visual or tactile cues brought by B.tabaci nymph to locate the host.2.Confirming the synthetic compounds of tomato volatiles induced by .tabaci to attract E.formosa.The volatiles of healthy,nymph-damaged and adult-damaged tomato plants were collected by dynamic headspace method,and analyzed by GC-MS.The results showed that compared with healthy tomato volatiles,no matter what kind of tomato,there was no significant change in the composition and release of tomato volatiles after nymph damage.However,after the adults harmed Moneymaker,Zhefen 302 and Zheza 809,the release of volatiles β-myrcene and β-caryophyllene increased significantly.Also,the release of linalool increased significantly after the adults damaged Zheza 809.Then,we measured the effects of artificial addition ofβ-myrcene,β-caryophyllene and linalool on olfactory selection and parasitism efficiency of E.formosa.The results showed that: compared with healthy tomato odor sources,E.formosa preferred to choose the odor sources of tomato plants supplemented with β-myrcene and β-caryophyllene.However,there was no preference for tomato odor sources supplemented with linalool.Similarly,artificial supplementation of β-myrcene and β-caryophyllene can significantly improve the parasitism rate of E.formosa to B.tabaci,but linalool supplementation does not improve the parasitism rate of E.formosa to B.tabaci.These results indicated thatβ-myrcene and β-caryophyllene,the volatiles from tomato induced by B.tabaci adults,were the active ingredients to attract E.formosa and the artificial release of this two volatiles could improve the biocontrol efficiency of E.formosa against B.tabaci.3.The effect of geminivirus infection on host selection behavior of E. formosa.In this experiment,the density and length of leaf trichomes of healthy tomatoes,infected with tomato yellow leaf curl virus by artificiality and virus transmitted by B.tabaci were measured.The results showed that,compared with healthy tomatoes,the density of tomato leaf trichomes in the artificially infected and insect-transmitted tomatoes increased significantly.Then,the effect of the host plant and whitefly nymph carrying virus or not on the parasitic rate of E.formosa were studied.The results showed that,when tomato infected with the virus,the parasitic rate of E.formosa on the B.tabaci nymph was significantly reduced.And when E.formosa chooses between nonviruliferous B.tabaci and viruliferous B.tabaci nymph,the E.formosa prefers to parasitize the nonviruliferous B.tabaci nymphs.However,in the condition of no selection,there was no significant difference in parasitic and fatality rate of E.formosa on the nonviruliferous B.tabaci and viruliferous B.tabaci nymphs.In summary,we guess that the decrease in the parasitism rate of E.formosa on viruliferous tomato plants may be caused by the increase in leaf trichomes density of the viruliferous plants,which reduces the efficiency of its host search.Besides,the parasitism preference for the nonviruliferous B.tabaci nymphs,which maybe because the viruliferous B.tabaci nymphs will harm the development of the offspring of E.formosa. |
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