Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 1998
Publication Date: N/A
Interpretive Summary: The diamondback moth is the most important pest, world-wide, of cabbage and related crucifer crops. This insect has developed resistance to most chemical insecticides used against it. As a first step in a research program aimed at incorporating fungi as a safe biological component within diamondback moth management schemes in the U.S., we have developed a laboratory assay protocol to test the effectiveness of the fungus Beauveri bassiana. The objectives of this study were to compare two strains of this fungus for their effectiveness against diamondback moth. We found the two strains did not differ significantly in the average number of spores required to kill a diamondback moth larva. One strain was more sensitive to changes in dose and killed larvae more quickly. Both strains were equally effective against the three larval stages tested and both worked well at a wide range of temperatures, although the fungi were less effective at both the lowest and highest temperatures tested. These findings are important to further efforts to incorporate this fungus into field management of the diamondback moth.
Technical Abstract: Two isolates of the fungus Beauveria bassiana were used in bioassays against larvae of the diamondback moth, Plutella xylostella. One isolate, ARSEF 4543, originated from an infected diamondback moth larva collected in New York and the other, Mycotech GHA, was obtained from MycotrolTM, a B. bassiana product registered for control certain grasshoppers and homopterans. Dose-response assays of suspended spores sprayed on larvae resulted in similar LC50s (518 and 614 spores per square centimeter for ARSEF 4543 and Mycotech GHA, respectively) but different slopes for the probit regression lines 0.64 and 0.89). Survival times for larvae inoculated at a range of doses were variable for ARSEF 4543 but decreased with increasing dose for Mycotech GHA. Third- and fourth-instar larvae were more susceptible than second-instar larvae, although survival times varied between the two isolates for larvae of different stages. The isolates did not differ significantly in their activities over a range of temperatures. Highest mortality & lowest survival times were observed at 25 C; mortality decreased and survival time increased at temperatures both above and below 25 C. Further studies will be aimed at determining other factors that influence the insect's susceptibility to infection, and at incorporating this fungus into field management of the diamondback moth.