Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 1999
Publication Date: N/A
Interpretive Summary: Whiteflies are among the most destructive of the world's insect pests. The silverleaf whitefly, which invaded the United States and spread rapidly across the South in the 1980s, has caused more than $1 billion in losses to U. S. agriculture. Worldwide explorations have revealed that fungi are among the most important natural enemies of whiteflies, and their development into effective biological control agents is being pursued. One of the most successful of these efforts has involved a collaboration between Mycotech Corporation, a private biotechnology company located in Butte, Montana, and the USDA Agricultural Research Service. This paper reports results of laboratory and field experiments conducted during the early stages of the Mycotech-USDA collaboration. Small-scale field trials are described in which weekly applications of fungus reduced larval whitefly populations by more than 90% in cucumbers, cantaloupe melons, and zucchini squash. These positive results provided the initial incentive for an extensive development effort between 1993 and 1995 that culminated in the U. S. EPA registration of a new biological insecticide, Mycotrol. This product, containing spores of the fungus Beauveria bassiana, is now being mass produced in a new Mycotech factory in Montana and is commercially available for control of whiteflies and other insect pests infesting diverse field and greenhouse crops. The results presented will contribute to the continuing scientific and commercial development of this and other mycoinsecticide products.
Collaborative research was conducted at the USDA-ARS Subtropical Agricultural Research Center in southern Texas to assess the microbial control potential of Beauveria bassiana and Paecilomyces fumosoroseus against Bemisia whiteflies. Laboratory assays demonstrated the capacity of both pathogens to infect Bemisia argentifolii nymphs on excised hibiscus leaves incubated at relative humidities (RH) as low as 25% at 25 C (approx. 35% infection by B. bassiana and P. fumosoroseus resulted form applications of 600 and 1,400 conidia/mm2, respectively). In small- scale field trials using back-pack and hand-held air-assist sprayers, applications at rates of 5 x 1013 conidia in 180 l water/ha produced densities of approx. 1k-2k conidia/mm2 on the lower surfaces of cucurbit leaves. Multiple applications of one isolate of P. fumosoroseus and three isolates of B. bassiana applied at this rate at 4-5-day intervals provided >90% control of large (third- and fourth instar) nymphs on cucumbers and cantaloupe melons. Applications at this high rate at 7-day intervals also provided >90% control in zucchini squash, and a one-fourth rate (1.25 x 1013 conidia/ha) applied at 4-5 d intervals reduced numbers of large nymphs by >85% in cantaloupe melons. The high efficacy observed in all trials was attributed to the high doses of spores achieved using the hand-held sprayers and the favorable weather conditions that prevailed during the trials (mean of 20-26 C and 75-85% RH in most trials). In contrast to the high susceptibility of nymphs, adult whiteflies were resistant to infection. The reported results contributed to the selection of B. bassiana strain GHA for continued development and ultimately to the registration of this fungus for whitefly control.