Influence of Sweet Corn Growth Stages on European Corn Borer (Lepidoptera: Crambidae) Oviposition

Oviposition rates of the European corn borer, Ostrinia nubilalis (Hubner), were examined on corn plants from the S-leaf through postharvest growth stages during 1994-1996. Per-plant rates in the field during vegetative stages showed a gradual increase as new leaves appeared, and a sharp increase when reproductive plant parts emerged. Laboratory studies indicated a similar relationship between oviposition rate and plant growth stage: significantly greater rates occurred on reproductive plants. Laboratory experiments showed that when only 4-leaf to early green tassel (preanthesis) plants were present (simulating conditions during early-season European corn borer activity), per-plant oviposition was significantly greater on the oldest (11-leaf to green tassel) plants. When the oviposition rate was based on leaf area rather than on a per-plant basis, however, statistical differences between vegetative stages were lost. When European corn borer females were given only reproductive plant stages (simulating conditions during late-season European corn borer oviposition), plants in the green tassel, anthesis, green silk, and brown silk stages had generally equal oviposition rates, and these were significantly greater than on postharvest plants. This European corn borer oviposition simulation, when based on leaf area, showed the same pattern as the per-plant oviposition. Thus, leaf area appears to influence oviposition during the vegetative stages, when leaf area is rapidly expanding, but is of little influence after tassels emerge and leaf area is expanding at a slower rate or declining. Moth alighting in the laboratory indicate a behavioral difference between sexes. Females alighted on plants identical to those favored for oviposition. In contrast, males showed no preference for any growth stage of corn.