Farm-, field-, and plant-scale effects on European corn borer oviposition
New technologies and strategies in commodity agriculture result in higher yields and quality harvests. Corn, one of the most economically important crops in the United States, is a crucial source of food, fuel, and consumer products. The European corn borer (Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae)) threatens producers in the U.S. and Canada with more than $1 billion in annual crop damage. Many studies have investigated various aspects of European corn borer biology; however, little is known about female corn borer movement, which directly impacts where larval damage will occur. Temporal and spatial aspects of dispersal also affect pesticide resistance management and population gene flow. The development of current knowledge also requires more insight into female corn borer oviposition (egg-laying) decision-making.
This dissertation research uses results from a range of experimental scales to synthesize the description of factors that influence female European corn borer oviposition behavior. Previous research has shown that female corn borers prefer taller, more mature plants when laying eggs. Individual plant-based experiments suggested that plant leaf area is a major plant maturity factor influencing female oviposition choice. However, no solid evidence indicated that females respond to plant height when laying eggs.
First-generation European corn borers tended to oviposit on the earliest-planted corn, while second-generation females preferred later plantings. During the second-generation peak, these late plantings were in late vegetative or early reproductive stages; earlier plantings were less succulent and near physiological maturity. Although female European corn borers exhibit general plant maturity preferences, egg infestation predictions based on comparisons among available planting dates are not accurate. Infestation predictions may only be feasible with exhaustive sampling, which is impractical.
Field- and farm-scale dispersal studies showed that many newly-emerged females flew out of the immediate area before laying egg masses. These results suggested that many females fly over 500 meters, though some mate and lay eggs less than 50 meters from their emergence point. Oviposition decay by distance, a function of dispersal, is apparent within 1 acre of a mass emergence site. Beyond this local scale, however, dispersal patterns are less evident.
Analysis of larval survival among various plant growth stages suggested European corn borer oviposition preference follows optimal oviposition theory. Offspring success generally corresponded with oviposition preference. Larval survival was highest on plants infested at early reproductive stages; these were found to be most attractive to ovipositing females in the other experiments. Survival rates and larval weights were lowest in the youngest vegetative plantings. Within-plant egg mass position also affected larval success; larvae were significantly more likely to survive on plants infested at the ear zone than those placed on higher leaves.