Visual Orientation of Nondiapausing and Prediapausing AdultLeptinotarsa decemlineata(Say) (Coleoptera: Chrysomelidae) in Free Flight

Abstract

The effect of black stripes on the flight path of nondiapausing adult Colorado potato beetles, Leptinotarsa decemlineata (Say), was studied in a white flight chamber. Flights generally ended in even frequencies throughout the length of the chamber except for peaks of abundance immediately ahead of the release cone and immediately ahead of the white end wall. The peak of flight frequency immediately ahead of the white end wall disappeared when the end wall was covered in black. Colorado potato beetles flew toward alternating white and black vertical stripes each 3.8 cm in width but changed paths to avoid a wall of alternating white and black stripes each 11.6 cm in width. These results indicate that Colorado potato beetles in free flight, like walking beetles, have the visual ability to detect and discriminate stripes of at least 2° (11.6 cm) in width. Single vertical black stripes 5–60 cm in width were not avoided. Colorado potato beetles in flight given access to an adjacent unlit area of light intensity 53% lower than that of the lit test chamber did not enter it. The unlit area was avoided by Colorado potato beetles in flight as much as a black wall. These results indicate that the flight behavior of the Colorado potato beetle as it approaches artificial or landscape structures is affected not only by their size (visual width) but could be affected also by the change in light intensity in their neighborhood. The avoidance behavior of large black stripes and objects by nondiapausing Colorado potato beetles was also seen in beetles preparing for diapause. Contrary to walking Colorado potato beetles, flying beetles, regardless of their prediapausing status, avoided rather than moved toward wide stripes. The results are discussed within the context of Colorado potato beetle fall dispersal. The previously proposed hypothesis that the occurrence of long migratory flights oriented toward silhouetted forest edges to overwinter is in response to the exposure to diapause-inducing conditions is not supported by the experimental data.