Effect of host plant on the potential of Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) for controlling the silverleaf whitefly, Bemisia argentifolii (Homoptera: Aleyrodidae) in greenhouses

We determined host plant effect on susceptibility of the silverleaf whitefly, Bemisia argentifolii, to the entomopathogenic fungus Paecilomyces fumosoroseus. Whiteflies were reared on three vegetable species (cucumber, cabbage, and tomato) and three cultivars of tomato (Heatwave, Better Boy, and Rutgers). Second instars were sprayed with 5 x 10(4) conidia/cm(2) of Pfr 97, a P. fumosoroseus strain, used as a microbial control agent of whiteflies. Trials were conducted in an experimental greenhouse, where temperature and relative humidity were adjusted to favor infection (22-33 degrees C, and 68-100% RH). Larval susceptibility to fungal infection was high and not significantly affected by the host plant. Mortality was > 70% 1 week after treatment and increased further during the second week. Percentages of cadavers with subsequent production of conidia observed in the greenhouse did not vary significantly either with the host vegetable species (85-93% 7 days after treatment and 99-100% 14 days after treatment), or with the cultivar of tomato (96-97% 7 days after treatment and 99-100% 14 days after treatment). After incubation under optimal laboratory conditions, the percentages based on the total number of sporulating cadavers (including in situ sporulating individuals and cadavers sporulating after in vitro incubation) were not significantly influenced either by host vegetable or cultivar of tomato. According to the conditions prevailing in the series of experiments with the three vegetable species or in the series of experiments with the three cultivars of tomatoes, the production of newly formed conidia varied from approximately 10,000 to 18,000 conidia/cadaver, However, in both series, there was no significant influence of the host vegetable species or cultivar. The survival of the newly formed conidia harvested 7 days following treatment reached more than 50% but was not affected by host plant. These results indicate that P. fumosoroseus shows potential as a microbial control agent for controlling B. argentifolii on greenhouse crops. (C) 1998 Academic Press.