Evaluation of Suitable Host Plant, as Banker Plant for Eretmocerus mundus, Whiteflies Parasitoid

Whiteflies (Homoptera; Aleyrodidae) are the key pests of agricultural crops worldwide. Two species, which seriously damage crops, are the Silver leaf whitefly “Bemisia tabaci (Gennadius)” and the Greenhouse whitefly “Trialeorodes vaporariorum (Westwood)”. These pests are active on the underside of the leaves where they are relatively protected from insecticide. Moreover, emergence of resistant biotypes of whitelies impose much more costs on its chemical control. Therefore, during falling the past population, several researches have been carried out to find and use efficient biocontrol methods. One of the biocontrol agents to control B. tabaci is “Eretmocerus mundus” (Hy., Aphelinidae). The parasitoid should be introduced to control pest in the greenhouses. One of the methods, which is used in introducing of biological control agents, is ‘Banker Plant System’. In this system, the host plant has a population of reproducing natural enemy used as a reservoir. Therefore, as soon as the pest infection occurs, the parasitoids can find them and control the damage. İn a banker plant system, several aspects should be considered. Some of the behavioral and biological aspects are important. For example characteristics of leaf surface influence on the host finding time of the parasitoid. The biochemical characteristics of the host plants affect the parasitoid fitness. Therefore, we tried to compare these aspects of E. mundus in two host plants (eggplant and cotton) from banker plant point of view, to control B. tabaci in the greenhouses.
The two host plants (eggplant and cotton), were planted in the greenhouse and a culture of B. tabaci was reared on the plants. After two weeks, some of the infested plants were put in separate cages, and the parasitoid, E. mundus, that was collected from the egg plant and cotton fields of the Varamin region were released on the plants. Then, the biological characteristics of the parasitoid were evaluated on the two different host plants. The sex ratio was recorded in two different ways; 1) 100 pupae developed on each plants were put in vials, and 2) the wasps that emerged daily from collected leaves. In the next experiment, a leaflet of each host plant (2.5  3 cm), that was infested with the second and third stages of B. tabaci), was fixed upside down on a piece of wet cotton in a Petri dish. Then, a female parasitoid was release on each to record the host finding time for one minute. Finally, the four female parasitoids were released on an infested host plant for 48 hours, then the wasps were removed and the plants were kept in a climate room. Two weeks later, the leaves were collected and put up side down on cotton pieces in Petri dishes and the duration of the larval stages, the mortality and the number of females and males that come out from them were recorded for the two hosts.
In total, 438 wasps form the eggplant leaves and 297 from cotton leaves were collected, while 14 and 17 dead pupa were recorded on them, respectively. The data analysis did not show significant differences between them. In host finding experiment, 9 of 15 parasitoids could find the host during one minute on the eggplants leave, whereas, all female parasitoids could find the host on cottons leave, which was significantly different (P value of Fisher's exact test= 0.01689). In the biology parameter experiments on leaves, 192 parasitoid wasps form cotton and 158 from eggplant leaf were collected that were not significantly different (F=5.6; p=0.026). In contrast, on whole plant experiment, 156 wasps (76 females and 80males) from cotton plants and 134 wasps (66 females and 68 males) from eggplants were collected that were not significantly different (f=1.2; P= 0.32).
The results showed that the number of parasitoid and the sex ratio were not significantly different between two host plants, whereas the movement and searching activity of the parasitoid were better on cotton than eggplant. Base on the results and all of the factors that were considered in this work, eggplant could be a good host in a banker plant system for Bemisia tabaci and its parasitoid Eretmocerus mundus.