Influence of Entomopathogenic Fungi on Serangium parcesetosum (Coleoptera: Coccinellidae), an Important Predator of Whiteflies (Homoptera: Aleyrodidae)

Abstract

The lethal and sublethal effects of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces fumosoroseus (Wize) Brown & Smith against the coccinellid predator Serangium parcesetosum Sicard were studied in the laboratory. We also tested if the ingestion of whiteflies contaminated with B. bassiana affected predator survivorship in 3 tests: (1) S. parcesetosum larvae were fed contaminated whiteflies for a 10-d period; (2) larvae were fed 1 time-only prey contaminated 24-, 48-, 72-, or 96-h previously; and (3) larvae were fed prey after the conidia were washed off the leaves and prey cuticles. The predator had significantly lower survivorship when sprayed with B. bassiana than with P. fumosoroseus. However, survivorship was not affected by the dosage rates for each pathogen. Survivorship curves for P. fumosoroseus treatments also did not differ significantly from blank and carrier controls. Mean larval duration was longest (≈22.5 d) in S. parcesetosum sprayed at the medium and high dosages of B bassiana, intermediate (≈20d) for the low dosage of B bassiana, and lowest (≈18d) for the blank and carrier controls and the P. fumosoroseus treatments. The pupal stages averaged 6.6-8.0d. Mean adult body weights ranged from 0.97 mg (B. bassiana low dosage) to 1.54 mg (P. fumosoroseus medium dosage), but were not significantly different. Analysis of cumulative predation showed that predators sprayed with P. fumosoroseus consumed prey at a rate similar to that of the controls (≈130 prey daily per predator), which was significantly higher than that of predators sprayed with B. bassiana (≈60 prey daily per predator). Again, dosage was not a significant factor. Feeding on B. bassiana-contaminated prey caused ≈86% mortality in S. parcesetosum immatures, compared with ≈13% in the controls. Prey contaminated 24-, 48-, 72-, and 96-h previously induced mortalities of 92.5, 71.4, 71.4, and 44.4%, respectively. Washing conidia off the leaves and the cuticle of whiteflies did not result in lowered mortality of the predator relative to the other treatments.