MECHANISM OF SOUTHWARD MIGRATION OF A NOCTUID MOTH [AGROTIS-IPSILON (HUFNAGEL)] - A COMPLETE MIGRANT

To determine whether an economically important moth species emigrates from the western Com Belt (Iowa and Missouri) to the gulf coastal area s of Louisiana and Texas each autumn, adult populations of Agrotis ips ilon (Hufnagel) males were monitored with traps baited with female sex pheromone, 16 July to 31 October 1986-1987. Concurrently, to estimate the potential for southward displacement of A. ipsilon, moths marked with a vital dye, Calco Red N-1700, were released at dusk 28 September and 2 October 1986, and 10 and 17 September 1987, from Ankeny, Iowa. Increased nightly moth-capture in Texas was positively related to numb ers of nights with near-surface (100-300 m) northerly airflow (southwa rd displacement of air) and decreased moth-capture in the western Corn Belt. Capture in Louisiana was also negatively correlated with captur e of moths in the western Com Belt. The recapture in autumn 1986 of tw o moths in Missouri, 397 km and 460 km south of the release site, resp ectively, was possible because of nightly near-surface northerly airfl ow. Near-surface northerly airflow the night of and subsequent to 17 S eptember 1987 was responsible for a marked moth being recaptured near Neota, Illinois, and another being recaptured near Brownsville, Texas, 276 km southeast and 1900 km southwest of the release site, respectiv ely. We conclude that during late summer and autumn, A., ipsilon, and probably other insect species, respond to deteriorating environmental conditions by using certain weather systems with northerly (southward displacement) near-surface airflow to complete midcontinental migratio ns to more favorable areas.