Evaluation of the entomopathogenic fungi Beauveria bassiana and Paecilomyces fumosoroseus for microbial control of the silverleaf whitefly, Bemisia argentifolii

Collaborative research was conducted at the USDA-ARS Subtropical Agricultur al Research Center in southern Texas to assess the microbial control potent ial of Beauveria bassiana and Paecilomyces fumosoroseus against Bemisia whi teflies. Laboratory assays demonstrated the capacity of both pathogens to i nfect Bemisia argentifolii nymphs on excised hibiscus leaves incubated at r elative humidities as low as 25% at 23 +/- 2 degrees C (ca. 35% infection b y B. bassiana and P. fumosoroseus resulted from applications of 0.6-1.4 x 1 0(3) conidia/mm(2) of leaf surface). In small-scale field trials using port able air-assist sprayers, applications at a high rate of 5 x 10(13) conidia in 180 liters water/ha produced conidial densities of ca. 1-2.5 x 10(3) co nidia/mm(2) on the lower surfaces of cucurbit leaves. Multiple applications of one isolate of P. fumosoroseus and four isolates of B. bassiana made at this rate at 4- to 5-day intervals provided >90% control of large (third- and fourth-instar) nymphs on cucumbers and cantaloupe melons. The same rate applied at 7-day intervals also provided >90% control in zucchini squash, and a one-fourth rate (1.25 x 10(13) conidia/ha) applied at 4- to 5-day int ervals reduced numbers of large nymphs by >85% in cantaloupe melons. In con trast to the high efficacy of the fungal applications against nymphs, effec ts against adult whiteflies were minimal. The results indicated that both B . bassiana and P. fumosoroseus have strong potential for microbial control of nymphal whiteflies infesting cucurbit crops. (C) 2000 Academic Press.