Efficacy and persistence of Beauveria bassiana and other fungi for control of diamondback moth (Lepidoptera: Plutellidae) on cabbage seedlings

The diamondback moth, Plutella xylostella (L.), is a key pest of crucifers worldwide. Resistance by diamondback moths to chemical insecticides and Bacillus thuringiensis Berliner toxins highlights the need for alternative controls. Crucifer growers often depend on seedlings produced in screenhouses and later transplanted to the field. Commercial seedlings can be contaminated with pesticide-resistant P. xylostella, leading to control problems in the field. We evaluated the efficacy of Beauveria bassiana (Balsamo) Vuillemin applied as conidia in Mycotrol(R) WP in three experiments by evaluating insect control, damage reduction, and fungus persistence on treated leaves of cabbage seedlings. In one experiment, we also evaluated Metarhizium anisopliae Metschnikoff (Sorokin) applied as conidia in Bio-blast(R) and Paecilomyces fumosoroseus (Wize) Brown & Smith applied as freshly-cultivated unformulated blastospores. We observed significant reductions, compared to controls, in insect populations and damage ratings when Mycotrol was applied once-or twice-weekly. Mycotrol treatments were as effective as a B. thuringiensis product in preventing damage when three spray nozzles were used to insure adequate pesticide coverage. Mycotrol persisted on treated leaves in screenhouses for more than 2 wks, and mycosis of larvae reared on these leaves was >50% 7 d after a single application of fungus. Treatment with either M. anisopliae or P. fumosoroseus resulted in no significant reduction in insect numbers or damage, but each fungus persisted on leaves and caused mycosis in lab-reared larvae more than 2 wks after treatment. Mycotrol can provide an option for control of P. xylostella larvae on seedlings, and may be especially useful in a resistance management program.