ECOLOGICAL AND CHEMICAL ASSOCIATIONS AMONG LATE-SEASON SQUASH PESTS

Interactions can occur among insects and plant pathogens exploiting th e same host plants, and induced changes in plant chemistry may mediate these interactions. Most studies have examined interactions from the perspective of individual insects or plant pathogens. We determined wh ether co-occurring insects and plant pathogens alter each other's expl oitation patterns in late-season surveys of mature cucurbits. We made field observations of the densities of 3 herbivore species, percentage of leaf damage and powdery mildew coverage, and occurrence of 2 commo n disease symptoms on F-2 individuals of domestic zucchini x wild gour d plants. We extracted bitter, toxic cucurbitacins and antipathogenic peroxidase enzymes from leaves and examined variation in chemistry bas ed on the presence or absence of exploiters. We found that cucumber be etles were present in lower densities on plants with powdery mildew. N o other interactions between insect occurrence and plant pathogen symp toms were found. Levels of insect infestation and plant pathogen sympt om occurrence were not related to cucurbitacin content or peroxidase a ctivity. Some exploiters do influence host use patterns by other pest insects and pathogens, but most insects and pathogens appear to intera ct idiosyncratically with the host plant late in the season in this sy stem, perhaps because of low densities of exploiters and low induction of plant chemical resistance.