Effects Of Rearing Host Species On The Host-Feeding Capacity And Parasitism Of The Whitefly Parasitoids

Parasitoids of the Encarsia genus (Hymenoptera:Aphelinidae) are important biological control agents against whiteflies, and some of the species in this genus not only parasitise their hosts, but also kill them through host-feeding. In this study, Bemisia tabaci’Q’(Gennadius) and Trialeurodes vaporariorum (Westwood) were used as rearing host species, the whitefly parasitoids, Encarsia formosa Gahan, E. sophia and Eretmocerus hayati Zolnerowich and Rose were examined to determine whether the rearing host species affected their subsequent host-feeding capacity and parasitism.1. En. formosa reared on T. vaporariorum were significantly larger in body size than those reared on B. tabaci, but these wasps killed a similar number of whitefly nymphs by host feeding when they attacked the same host species on which they were reared. The results indicated that a similar number of B. tabaci nymphs were killed by parasitism and host feeding regardless of the rearing host species. Currently coexistence of B. tabaci and T. vaporariorum on vegetable crops usually occur in some areas, our results may provide helpful information on mass-reared parasitoids against mixed whitefly infestations in biological control programs.2. In this study, En. sophia females and males were reared on primary hosts, T. vaporariorum and B. tabaci’Q’, and the host-feeding and parasitism of wasps on both whitefly species were determined in all different mating combinations:(i) En. sophia female reared on B. tabaci (ESF-BT) mated with En. sophia male from B. tabaci (ESM-BT),(ii) En. sophia female reared on T. vaporariorum (ESF-TV) mated with En. sophia male from T. vaporariorum (ESM-TV),(iii) ESF-BT mated with ESM-TV,(iv) ESF-TV mated with ESM-BT. ESF-TV mated with ESM-TV killed most whitefly nymphs of B. tabaci and T. vaporariorum through host feeding. The larger ESF-TV in body size mated with larger ESM-TV killed more whitefly nymphs through host feeding than those mated with smaller ESM-BT. Whether B. tabaci or T. vaporariorum were used as hosts, ESF-TV mated with ESM-TV and ESM-BT, and ESF-BT mated with ESM-TV significantly parasitized more whitefly nymphs than ESF-BT mated with ESM-TV. In general, the mating combination of female and male originated from T. vaporariorum caused largest mortality of whitefly through parasitism and host feeding on both whitefly species, but the combination of ESF-BT mated with ESM-TV killed fewest whiteflies. These results indicated that the performance of autoparasitoids on insect pests was not only dependent on females, but also affected by mating males from different primary host species.3. The results indicated Er. hayati could parasitize and host-feed on various stage whitefly nymphs of B. tabaci. E. hayati exhibited a tendency to feed on more B. tabaci nymphs with increase of host stage. There was significant difference in number of nymphs parasitized by Er. hayati on different stage hosts. Generally, female wasp parasitized more second and third instars, followed by first and fourth instars. When T. vaporariorum was offered for host attacked, Er. hayati could host-feed on various stage whitefly nymphs. However, this parasitoid could not parasitize T. vaporariorum. These results indicated Er. hayati exhibited the potential as bio-control agent to control the invasive whitefly, B. tabaci "Q" through host feeding and parasitism. However, it could not be released for controlling the indigenous whitefly, T. vaparariorum.