| Encarsia formosa Gahan is an effective parasitoid of Bemisia tabacci (Gennadius) & Trialeurodes vaporariorum (Westwood) which are two noxious agricultural pests. In the past 10 years, B. tabacci B-type has resulted in big losses in agricultural production, and developing better management becomes high request, especially by using E. formosa as an effective control agent.This research dealt with the following questions. Firstly, what are the roles of the volatile phytochemicals of whitefly host plants to attract E. formosa for host finding? The second, how learning experience of E. formosa help its host-finding efficacy? The experiments based on above two questions were designed for understanding and answering. The results were as follows.1 Olfactive response of Encarsia formosa to plant volatile phytochemicalsBy 2-2 combined testing that E. formosa works on cucumber plant, results show volatile communication chemical prouduced by plants that are healthy or with mechanical damage, inbreak of B. tabaci type B or T. vaporariorum all attract E. formosa. Attract action appear tensity as: cucumber damaged by 3-4 instar B. tabaci＞cucumber damaged by 3-4 instar T. vaporariorum＞cucumber damaged mechanically＞undamaged cucumber. Also, in the combination of damaged by insect pest and healthy cucumber plant, the selectivity & otherness of E. showed as grade obvious or extremely obvious. This shows that volatile communication chemical produced by abducting insect pest has stronger attraction to parasitical wasp.The volatile produced by same treatment but of different scales on certain host plant will also effect the response of E. formosa. They are all inclined to take volatile produced by cucumber plant that is seriously harmed or damaged. And with the accretion of difference damage in different test combinations, the selectivity difference of E. formosa will also increase.2 Identification and compare on volatiles chemicalsGC-MS study on volatiles chemicals of host plant, which is got by continuous air extraction on complete plant, shows that 30 volatile phytochemical communication compounds are received from cucumber plants of different treatment, and host plants have different chemical illustrative plates when they are differently treated or treated with different tensities. Healthy plants only produce a few volatile while mechanical damage and inducement by insect pest will all make host plants produce volatiles of more categories and contents, and plants infringed by B. tabaci and T. vaporariorum will have more categories on volatiles than they are caused by mechanical damages. The content of volatile that is caused by B. tabaci and T. vaporariorum will increase with the enhanced treatment.3 Olfaction selectivity action of Encarsia formosa effected by normative sample of volatile of host plantsSelect normative samples of volatile from 5 different host plants and confect them into 4 different concentration grads. Testing for E. formosa on this different concentration grads shows that this different normative samples of proper concentration all have abduction to E. formosa, and different normative chemical samples have different initial abduction concentration. Cis-3-Hexenyl Acetate, 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate, 2,6-Di-tert-butyl-4-methyl phenol at 10-3, Iinalool at 10-4 Naphthalene at 10-5. When consistency is lower than other 10-5, normative samples all lose their efficiency of abduction except for Naphthalene. When consistency is higher than 10-2, except for Cis-3-Hexenyl Acetate which can still effect inducement on E. formosa, other 4 normative samples all lose their efficiency of inducement and even avoiding effect happens (2,2,4-Trimethyl-1,3-pentanediol diisobutyrate and Naphthalene). This shows that solution of proper concentration, which is from volatile caused by inducement of insect pest, can be used to induce and gather autoecious wasp. In this way, consistency of wasp will be enhanced in objective farm to improve effect of prevention and cure.4 Olfaction selectivity action of Encarsia formosa effected by learning experienceE. formosa gets different experience from environment during its larva and pupae period. This experience will effect its behavior during its adult period. Compared with E. formosa that doesn't experience environment change, experienced E. formosa generally choose outside host plant while does not take host plant where it will take it for its eclosion. Experience of pupae period also have better efficiency than it of larva period.Domestication over E. formosa during its adult period can make it obtain experience. However, this experience of short period does not have obvious effect on its coming behaviour. E. formosa still choose host plant that it had when growing up as larva. With domestication time extending, E. formosa acquires experience of taking food & autoeciousness. This sets up a certain relationship, consequently have favorite inducement over its coming behaviour, to make E. formosa to choose host plant where had been for its domestication. This shows that E. formosa's learning in its adult period is the combination of affiliation learning and favorite learning.E. formosa has learning ability on the smell of normative sample of volatile from its host plant when it's in its larva & pupae period, but using normative sample has less effect on its action response than host plant works while it's just opposite in adult period. Therefore, during the period of manual propagation or affranchising E. formosa, it can be put to experience and learn the smell of host plant in objective farm to enhance effect of controlling pests.
|
PDF Full Text Request