Predicting oviposition of corn earworm (Helicoverpa zea (Boddie)) in sweet corn with pheromone traps
Abstract
Pest managers currently apply insecticides to sweet corn for control of Helicoverpa zea (Boddie) when fresh silks are present and 10 or more moths are caught in a pheromone trap. This study has three major objectives. First, determine the relationship between catches of male H.zea moths in pheromone traps with oviposition and subsequent larval damage to ears of sweet corn. Secondly, determine how environmental conditions such as temperature, wind speed, relative humidity, and rainfall affect pheromone trap catches and oviposition on sweet corn ears. Finally, determine how the stage of development of field corn grown in the immediate vicinity affects the level of oviposition in sweet corn. Each location in Indiana had 9–10 planting dates of two hybrids of sweet corn with maturity dates differing by 7 days. Planting was initiated in mid-March and the final harvest completed in late September. Within each planting date and hybrid, 500 ears were covered with paper bags at the initiation of silking to prevent oviposition. On each of 10 nights during the silking period, 50 bags were removed to allow moths to oviposit on the exposed silks. Half of the 50 exposed ears had the silks clipped and eggs counted and half were harvested at maturity and examined for earworm damage. Egg numbers and damage for each night's exposure to oviposition were correlated with the daily pheromone trap catches and weather variables. No direct relationship was found between male trap catch and female oviposition. However, environmental factors affecting corn earworm trap catch and oviposition were identified. After running one-way ANOVAs, relative humidity and phase of the moon both showed significant impacts of trap catches. Relative humidity, phase of the moon, and the stage of surrounding field corn were all shown to have a significant impact on oviposition. With this new information it is now possible to reevaluate the current nominal threshold currently in use to control corn earworm damage in sweet corn.
Degree
M.S.
Advisors
Foster, Purdue University.
Subject Area
Entomology
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