Origin of corn earworm (Lepidoptera: Noctuidae) migrants as determined by Citrus pollen markers and synoptic weather systems

Pollen on corn earworm moths, Helicoverpa zea (Boddie), can provide an indication of their host plant visitations and migratory activities. Our study was conducted to determine the origin of Citrus sp. pollen-contaminated moths captured in Atoka County, Oklahoma, during 1990 and the host plant feeding range of moths present in Hidalgo County, Texas, and Atoka County. Captured moths were analyzed for pollen with scanning electron microscopy. H. zea moths captured in January 1989 in the Lower Rio Grande Valley of Texas when citrus was not blooming were not contaminated with Citrus spp. pollen. Sixty percent of those captured on 17 March 1989 during the citrus blooming period were contaminated with Citrus sp. pollen. None of the moths sampled in that area between 21 March and 2 April 1990 were contaminated with Citrus spp. after a major freeze in December 1989. Citrus blooming during 1990 was drastically reduced or eliminated in South Texas, northeastern Mexico, Louisiana, and central Florida. However, Citrus sp. pollen accounted for 3% of all pollen detected on migratory H. zea collected in Atoka County between 27 February and 24 April 1990. Lack of Citrus spp. pollen-contaminated H. zea in Hidalgo County, after the severe freeze suggests the H. zea contaminated with Citrus pollen was collected in Atoka County during April 1990 originated elsewhere. Evaluation of calculated trajectories, synoptic weather maps, and upper-air transport opportunities suggests southern Florida, the Bahamas, Cuba, Yucatan Peninsula, and northern Central America as potential source areas 1,515 km from the capture site. This would require the moths to be in flight over water for 72 h or have very limited diurnal resting periods on seaweed (Sargassum spp.), ships, oil platforms, or the sea surface.