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This study focuses on the regulation of synchronization between the life cycle of the oligophagous whitefly, Trialeurodes lauri (Signoret), and its evergreen host tree Arbutus andrachne in Mediterranean chaparral. Whitefly infestations vary considerably among trees. The adults of the univoltine (one generation per year) whitefly emerge en masse during April and May and oviposit on the new spring foliage. Following approximately one month of development to the early fourth instar, the nymphs enter nine-month diapauses, terminating in February. This diapause is induced and maintained by the plant and can be experimentally avoided (in the case of developing young nymphs) or terminated (in the case of diapausing fourth instars), if whitefly-bearing branches are severed from the tree and placed in water under laboratory conditions. This study is the first report of a whitefly diapausing through both summer and winter seasons. The role of the host plant in the process is discussed. [ABSTRACT FROM PUBLISHER]

The potential of a new, previously unidentified Serangium species (Col., Coccinellidae) to control the high Bemisia tabaci (Gennadius) (Hom., Aleyrodidae) populations on cassava was evaluated. Field and laboratory studies were carried out to determine the abundance and feeding capacity of this Serangium species feeding on B. tabaci on cassava. Serangium nymphs and adults were most abundant in cassava fields late in the season, rising sharply from 5 months after planting (MAP) to a peak at 7–8 MAP. Pre-imaginal development averaged 21.2 days and was longest in eggs and shortest in the L1 instar. Mean total prey consumption of immature Serangium increased with the stage of development with the lowest consumption in the L1 instar and highest in the L4 instar. Mean daily consumption was lowest on the first day after hatching in the L1 instar and rose to a peak on the 13th day after hatching in the L4 instar. Each Serangium larva consumed a mean of over 1000 nymphs during its entire development. These results have demonstrated the potential of this Serangium species to control B. tabaci populations on cassava. [ABSTRACT FROM AUTHOR]

A study was set up to determine the sources and rates of mortality of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on field-grown cassava in Uganda. Using a cohort-based approach, daily direct observations were used to construct partial life tables for 12 generations of egg and nymph populations which were studied over a 1-year period. Mortality was categorized as dislodgement, predation, parasitism (for nymphs only), unknown death, and inviability (for eggs only). The highest mean rate of marginal mortality across all stages was attributed to parasitism, with dislodgement and predation following, respectively. Across all factors, the highest mean rate of marginal mortality was observed in the fourth instar followed by the eggs, first-, second-, and third-instars, respectively. Key factor analysis revealed that dislodgement was the major mortality factor contributing to generational mortality in eggs while for nymphs, parasitism in the fourth instar was the main driving force behind the observed generational mortality. Highest irreplaceable mortality in both the egg and nymph stages was attributed to dislodgement followed by parasitism and predation, and least was due to unknown death. Across stages, highest irreplaceable mortality rates were observed in the eggs and the fourth-instar nymphs. The other stages had relatively low rates of irreplaceable mortality. Rain-protection experiments revealed no significant differences in marginal mortality rates when compared to the open field situation. [ABSTRACT FROM AUTHOR]

Three field trials were conducted at Namulonge Agricultural and Animal Production Research Institute to investigate the population dynamics of Bemisia tabaci Gennadius and its associated aphelinid parasitoids in Uganda. Results showed that more whitefly occurred on the cassava mosaic disease-resistant variety, (Nase 4) compared to the susceptible variety, (Ebwanatereka). Two species of aphelinid parasitoids, Eretmocerus mundus Mercet and Encarsia sophia Girault and Dodd, were identified during the study. Overall percent parasitism did not differ significantly ( P >0.05) between varieties in all the trials, but significant differences occurred at 13, 15 and 21 weeks after planting during late season (2000), 18 weeks after planting during early season (2001), and 8 weeks after planting during late season (2001). The trends in the build up in numbers of both parasitoids species and apparent parasitism were similar, differed significantly on certain dates. It was, however, noted that percent parasitism decreased with nymph number. The significance of this phenomenon on the potential use of these aphelinid parasitoids as biocontrol agents of the cassava whitefly is discussed. [ABSTRACT FROM AUTHOR]

Wild and cultivated plants in the vicinity of Kibbutz Nahshon and a few additional locations in Israel were sampled for the presence of Bemisia tabaci Genna-dius (Homoptera: Aleyrodidae). The whiteflies, together with their parasites, Eretmocerus mundus and Encarsia lutea, were found to develop on numerous host species throughout the winter. Especially high levels were reached on Lan-tana camara, Abutilon grandifolium and Ipomoea batatas. During late winter and spring the population on these hosts declined. From April onwards the populations increased on potatoes and sunflowers. [ABSTRACT FROM AUTHOR]