Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2001
Publication Date: N/A
Interpretive Summary: The Colorado potato beetle is the principal insect pest of potato and other solanaceous vegetables in the U.S. Beetle populations readily develop resistance to chemical insecticides, and safe, effective alternatives are needed for effective pest management. The fungus Beauveria bassiana is a naturally-occurring pathogen of the beetle. Fungal spores serve as the active ingredient in a microbial insecticide formulated for use against this and other insects. In order to use the fungus effectively in the field, a basic understanding of factors influencing fungal infection of beetles must be developed. In this laboratory study we evaluated different ways to inoculate beetle larvae with fungal spores. Spores sprayed directly on beetles germinated most quickly but the resulting mortality was lower than other inoculation methods. In contrast, spores sprayed on foliage upon which larvae later crawled germinated more slowly. However, beetles acquired more spores by crawling on leaf surfaces and experienced higher levels of infection. The findings indicate that improving the persistence of viable spores sprayed on leaf surfaces in the field will play a key role in optimizing the effectiveness of this microbial control agent.
The effect of mode of exposure of second instar Colorado potato beetles to Beauveria bassiana on conidial acquisition and mortality were investigated in laboratory studies. Larvae sprayed directly with B. bassiana conidial suspensions, exposed to treated foliage, or inoculated by both methods experienced mortality of 40, 65 and 73%, respectively. The total number of fconidia and the percentage germination varied significantly on various bod parts depending upon the mode of inoculation. Larvae exposed to fungus-treated potato foliage increased their inoculum load, and the proportion of conidia germinating, over time. Conidia germinated significantly faster on larvae inoculated by spraying. Variation in deposition and germination rates may be due to enhanced conidial lodging on sprayed insects and inhibition of conidial germination by phytochemicals.