Improving our Understanding of Helicoverpa zea Migration in the Midwest: Assessment of Source Populations

Abstract

Corn earworm (Helicoverpa zea) (CEW) generally are not able to overwinter annually in the Upper Midwest, thus they must migrate northward to affect the primary vegetable-growing locations in this area. Migration of CEW is highly dependent on the weather. Provided a source region in the southern United States, migration of CEW from south to north appeared to occur when a high-pressure system was located in the eastern United States and a low-pressure system and attendant frontal boundary was observed to the east of the Rocky Mountains and/or northern plains states. Southerly wind flow located west of the high and east of the low forms an “insect pump.” Convection cells allowed CEW to lift and advance from their source region northward in the low-level insect pump. When CEW encountered an area of downward motion during their northward flight, such as a frontal boundary or a light precipitation area, they had a tendency to “drop out” of the sky into fields below, an area referred to as the “Drop Zone.” Favorable weather patterns for CEW migration and subsequent infestation of fields in north-central Illinois were confirmed by high CEW trap counts at Rochelle over the last four decades.Accepted for publication 5 September 2006. Published 19 July 2007.