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 Corn Belt (Iowa and Missouri) to the gulf coastal areas of Louisiana and Texas each autumn, adult populations of Agrotis ipsilon (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 numbers of nights with near—surface (100—300 m) northerly airflow (southward displacement of air) and decreased moth—capture in the western Corn Belt. Capture in Louisiana was also negatively correlated with capture of moths in the western Corn Belt. The recapture in autumn 1986 of two moths in Missouri, 397 km and 460 km south of the release site, respectively, was possible because of nightly near—surface northerly airflow. Near—surface northerly airflow the night of and subsequent to 17 September 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, respectively. 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 migrations to more favorable areas.