The parasitoids in the genera of Encarsia and Eretmocerus （Hymenoptera： Aphelinidae） are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong ...The parasitoids in the genera of Encarsia and Eretmocerus （Hymenoptera： Aphelinidae） are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host-feeding capacity. Two whitefly parasitoid species, Encarsia sophia and Eretmocerus melanoscutus were examined to determine if mating and host density affected their host feeding and parasitism. The whitefly host, Bemisia tabaci, was presented to these two wasp species in densities of 10, 20, 30, 40, 50 and 60 third-instar nymphs per clip cage. Mated whitefly parasitoid females fed on more hosts than unmated females under a range of host densities （under all six host densities for En. sophia; under the densities of 40 nymphs or more for Er. melanoscutus）. Meanwhile, mated females parasitized more whitefly nymphs than unmated females under all host densities for both species. With increase of host density, mated or unmated Er. melanoscutus females killed more hosts by host feeding and parasitism. Mated En. sophia females killed more hosts by host feeding with increase of host density, whereas unmated females did not parasitze whitefly nymphs at all. Our results suggest that only mated female parasitoids with host-feeding behavior should be released in crop systems to increase their bio-control efficiency.展开更多
The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich ＆ Rose and Encarsia sophia Girault ＆ Dodd, of whitefly Bemisia tabaci Gennadius Middle East-Asia Minor 1 were studied under laboratory cond...The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich ＆ Rose and Encarsia sophia Girault ＆ Dodd, of whitefly Bemisia tabaci Gennadius Middle East-Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars （first and second instar）, whereas no advantage was found on old host instars （third and fourth instar）. The biological control effect ofEr hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.展开更多
基金We appreciate the assistance of Y.-M. Zhang and Texas AgriLife Research, Texas A＆M University Sys- tem during this study. The research was financially supported by the National Natural Science Foundation of China （30930062）, the National Basic Research and Development Program of China （2006CB102005-3 and 2009CB 119200） and the Fund for Modem Agro-industry Technology Research System （nycytx-004）.
文摘The parasitoids in the genera of Encarsia and Eretmocerus （Hymenoptera： Aphelinidae） are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host-feeding capacity. Two whitefly parasitoid species, Encarsia sophia and Eretmocerus melanoscutus were examined to determine if mating and host density affected their host feeding and parasitism. The whitefly host, Bemisia tabaci, was presented to these two wasp species in densities of 10, 20, 30, 40, 50 and 60 third-instar nymphs per clip cage. Mated whitefly parasitoid females fed on more hosts than unmated females under a range of host densities （under all six host densities for En. sophia; under the densities of 40 nymphs or more for Er. melanoscutus）. Meanwhile, mated females parasitized more whitefly nymphs than unmated females under all host densities for both species. With increase of host density, mated or unmated Er. melanoscutus females killed more hosts by host feeding and parasitism. Mated En. sophia females killed more hosts by host feeding with increase of host density, whereas unmated females did not parasitze whitefly nymphs at all. Our results suggest that only mated female parasitoids with host-feeding behavior should be released in crop systems to increase their bio-control efficiency.
基金Acknowledgments This research was financially supported by the Na- tional Natural Science Foundation of China （30930062, 31301726） and the National Basic Research Program of China （2013CBl27605）. The authors thank Steven A. Juliano （Illinois State University） and Xiang-Hong Yu （Graduate School of Chinese Academy of Agricultural Sciences） for statistical assistance.
文摘The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich ＆ Rose and Encarsia sophia Girault ＆ Dodd, of whitefly Bemisia tabaci Gennadius Middle East-Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars （first and second instar）, whereas no advantage was found on old host instars （third and fourth instar）. The biological control effect ofEr hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.
