PLANT-MEDIATED INTERACTIONS BETWEEN INSECTS AND A FUNGAL PLANT PATHOGEN AND THE ROLE OF PLANT-CHEMICAL RESPONSES TO INFECTION

Diverse organisms simultaneously exploit plants in nature, but most st udies do not examine multiple types of exploiters like phytophagous in sects and fungal, bacterial, and viral plant pathogens. This study exa mined patterns of induction of antipathogenic peroxidase enzymes and p henolics after infection by the cucurbit scab fungus, Cladosporium cuc umerinum, and then determined if induction mediated ecological effects on Colletotrichum orbiculare, another fungal pathogen, and two insect herbivores, spotted cucumber beetles, and melon aphids. Peroxidase in duction occurred in inoculated, 'local,' symptom-bearing leaves 3 days after inoculation, and in 'systemic,' symptom-free leaves on the same plants 1 day later. Phenolics were elevated in systemic but not in lo cal leaves 3 days after inoculation. Detached systemic leaves from pla nts inoculated with C. cucumerinum developed significantly fewer and s maller lesions after challenge with C. orbiculare. Spotted cucumber be etles did not show consistently significant preferences for infected v ersus control leaf disks in comparisons using local or systemic leaves , but trends differed significantly between leaf positions. In no-choi ce tests, beetles removed more leaf area from local but not from syste mic infected leaves compared to control leaves, and melon aphid reprod uction was enhanced on local infected leaves. In the field, cucumber b eetle and melon aphid densities did not differ between infected and co ntrol plants. Antipathogenic plant chemical responses did not predict reduced herbivory by insects. Other changes in metabolism may explain the positive direction and spatially dependent nature of plant-mediate d interactions between pathogens and insects in this system.