Ecological and chemical associations among late-season squash pests
1998
Moran, P.J. | Schultz, J.C.
Interactions can occur among insects and plant pathogens exploiting the 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 whether co-occurring insects and plant pathogens alter each other's exploitation 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 common disease symptoms on F2 individuals of domestic zucchini X wild gourd plants. We extracted bitter, toxic cucurbitacins and antipathogenic peroxidase enzymes from leaves and examined variation in chemistry based on the presence or absence of exploiters. We found that cucumber beetles were present in lower densities on plants with powdery mildew. No other interactions between insect occurrence and plant pathogen symptoms were found. Levels of insect infestation and plant pathogen symptom occurrence were not related to cucurbitacin content or peroxidase activity. Some exploiters do influence host use patterns by other pest insects and pathogens, but most insects and pathogens appear to interact idiosyncratically with the host plant late in the season in this system, perhaps because of low densities of exploiters and low induction of plant chemical resistance.
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