Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 1997
Publication Date: N/A
Interpretive Summary: Several environmental factors limit the survival of insect fungal pathogens in the field, among these low moisture, high temperatures and ultraviolet light. We studied the role that some chemicals present in plants and possibly in insects, might play in the survival of fungal insect pathogens when sprayed for insect pest control. Some of the compounds inhibited germination of fungal spores, while others only delayed it. We have shown that some plant chemicals can present an additional constraint to the survival and effective use of formulations of fungal biological control agents.
Technical Abstract: Seven secondary plant compounds (catechol, chlorogenic acid, gallic acid, salicylic acid, saponin, sinigrin and tannic acid) mixed with potato dextrose agar (PDA) or Noble agar (NA) at three concentrations (100, 500, and 1000 ppm) were tested for their effects on blastospore germination of the fungal entomopathogen Paecilomyces fumosoroseus. When using PDA, with the exception of catechol at 1000 ppm, there were no significant differences in colony forming units between treatments and the control (PDA alone). With allelochemical concentration at 100 ppm in NA, there were no significant differences in blastospore germination percentages 24 hours after spraying, although there were differences 4 and 8 hours after spraying, indicating that germination is delayed. In contrast, at 500 ppm, catechol, salicylic acid, and tannic acid significantly reduced blastospore germination at all time periods examined. Other chemicals also reduced blastospore germination, but these differences were not significant 24 hours after spraying. At 1000 ppm, results were similar to those found at 500 ppm. Results indicate that the presence of allelochemicals on a substrate (e.g., insect cuticle or leaf) could present an additional constraint to the survival of entomopathogenic fungi. Possible roles for allelochemicals in the infection process in insects are discussed.