Soil organic amendment impacts on corn resistance to Helicoverpa zea: Constitutive or induced?

Earthworm produced compost or vermicompost has been shown to improve plant growth and productivity. Vermicompost amendment to the soil also results in plant resistance to arthropod pests. In the present study we used corn, Zea mays L., and the corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae) to investigate the effects of two vermicompost sources Oregon (OSC) and Raleigh (Ral) and previous feeding by H. zea larvae on the response and preference of immature and adult stages of the insect to corn plants. Results from our study show that Ral and OSC vermicompost were both effective in inducing corn antixenosis (non preference) and antibiosis (lower performance) resistance to H. zea that is effective against adult (decreased oviposition) and immature insect stages (lower immature weight gain and survival), respectively. We also found that previous conspecific induction appears to have a phagostimulatory effect on larval vermicompost leaf tissue consumption, especially for the Ral treatment. Conspecific induction also buffered the resistance effects of the vermicompost resulting in a stimulatory effect on oviposition by adults. The potential factors leading to the insect responses observed are discussed within the context of previous studies evaluating vermicompost-mediated resistance to pests.