Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/1998
Publication Date: N/A
Interpretive Summary: The diamondback moth is the most important pest world-wide of cabbage and other crucifer crops. The estimated annual cost for control exceeds $1 billion. The insect has been especially problematic for crucifer growers because populations in several parts of the world have developed resistance to most commercial insecticides. Because of this, it is important to search hfor biological insectides as safe, reliable alternatives. The objectives o this study were to test the effectiveness of the sprays of the fungus Beauveria bassiana against larvae of the diamondback moth on whole plants. We compared effectiveness of applications in the greenhouse and field plots using varying rates and formulations of fungus spores. We found that a single application of fungus spores reduced larval populations in all but one test. Two applications, and applications done at the higher of two concentrations, consistently reduced the numbers of both younger and older larvae. Both wettable powder and emulsifiable suspension formulations of fungal spores gave good results. Fungal spores persisted on cabbage leaves for up to one week although concentrations dropped by 50 percent in three days. These trials indicate the potential for including the fungus Beauveria bassiana in management programs for the diamondback moth.
Technical Abstract: Evaluations of the efficacy and persistence of Beauvaria bassiana for control of the diamondback moth, Plutella xylostella were done in growth chambers, the greenhouse and the field. In growth chamber studies done at 21 or 26 degrees C and 60% or 90% RH neither temperature nor humidity affected the survival of larvae, but treatment with the fungus always provided significant mortality. In two greenhouse trials B. bassuana significantly reduced larval populations. Both treatment and insect stage at treatment significantly affected larval survival in field trials. Fungus treatments with a wettable powder at the higher of two rates and with an emulsifiable suspension at a high rate provided significant reductions in larval counts. Two applications of the wettable powder at the higher rate resulted in lower larval counts than did a single application. Two applications (but not one) of wettable powder at the lower rate resulted in nsignificantly lower larval counts for younger but not older larvae. Both treatment and time affected both the persistence of viable B. bassiana spores on leaves and the retention of efficacy of treated leaves for larvae These trials indicate the potential for including B. bassiana in an overall management program for P. xylostella.