Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/1997
Publication Date: N/A
Interpretive Summary: The diamondback moth is the most important pest, world-wide, of cabbage and other crucifer crops. The insect has quickly developed resistance to most insecticides used against it. Crucifer growers in the U.S. use seedlings produced in screenhouses in southern states for transplant and production in fields. Commercial seedlings can be contaminated with insecticide-resistant diamondback moths leading to later control problems in the field. As part of a program aimed at incorporating fungi as safe biological control agents in management schemes for this pest, we have tested three fungi as potential control agents when applied to cabbage seedlings. We infested seedlings with diamondback moths in a screenhouse, applied one of three fungi at weekly or twice-weekly intervals, and evaluated seedling damage and insect survival. We found that weekly or twice-weekly applications of the fungus Beauveria bassiana (applied as the commercial product Mycotrol) gave significant reductions in insect populations and in damage to seedlings. This treatment was as effective as a conventional insecticide. The fungus persisted on treated leaves for more than two weeks, providing continued coverage over time from a single application. The other two fungi did not provide adequate protection in one test; further testing is needed to verify their potential. These findings will help guide the next stage of research -- the use of fungi in larger-scale seedling production systems.
Technical Abstract: The diamondback moth, Plutella xylostella is a key pest of crucifers world-wide. 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 nbe contaminated with pesticide-resistant P. xylostella, leading to control problems in the field. We evaluated the efficacy of Beauveria bassiana applied as conidia in Mycotrol(Reg.) 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 applied as conidia in Bio-blast(Reg) & Paecilomyces fumosoroseus 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 Bacillus 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 two weeks, and mycosis of larvae reared on these leaves was greater than 50% 7 days 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 two weeks after treatment. Mycotrol can provide an option for control of P. xylostella larvae on seedlings.