Pathogenicity of Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) Against Bemisia argentifolii (Homoptera: Aleyrodidae) with a Description of a Bioassay Method

Abstract

We examined the infectivity of 30 isolates of Paecilomyces fumosoroseus (Wize) Brown & Smith originating from various insect hosts [Bemisia tabaci (Gennadius) and Bemisia argentifolii Bellows & Perring principally, and some species of Lepidoptera] from the southern United States, Europe, Pakistan, Nepal, and India against B. argentifolii under laboratory conditions. Bioassays were conducted on leaf disks of ornamental sweetpotato that were infested with 2nd instars of B. argentifolii and transferred to petri dishes containing sterile KNOP medium. Using a Potter tower, insects were treated with 3.8 X 10 4 conidia per square centimeter of each of the 30 fungal isolates. Four replicate tests, each undertaken on a separate date, were conducted for each isolate. A 2nd series of bioassays was conducted on 5 selected isolates using 5 dosages ranging from 38 to 3.8 x 105 conidia per square centimeter. In all bioassays, after 24 h at 100% RH and 24°C, the dishes were ventilated and maintained at 60% RH and a photoperiod of 16:8 (L:D) h. After 10 d, mortality and nymphal instar at time of death were recorded. Of the 30 isolates, only 1 produced total mortality (i.e., occuring in all instars combined) that was not significantly different from the controls. For the 29 isolates causing highly significant mortality, total mortality ranged from 68 to 94% with no significant difference between isolates. LD 50 s of the selected isolates varied from 619 to 1,269 conidia per square centimeter, without significant intraspecific difference. Nymphs that were exposed to conidia in the 2nd instar died principally during the 4th instar. There was a significant difference between isolates depending on the nymphal instar at time of death in nymphs killed by P. fumosoroseus. The laboratory results are promising and confirmed the potential of P. fumosoroseus as a microbial control agent against B. argentifolii.