Oviposition Behavior ofColeomegilla maculata(Coleoptera: Coccinellidae): Diel Periodicity and Choice of Host Plants

Abstract

Previous research has shown that more Coleomegilla maculata (DeGeer) eggs occur on plants with glandular trichomes than on plants without such trichomes. Those studies also revealed that C. maculata eggs suffer greater predation (mostly cannibalism) on plants lacking glandular trichomes than on plants with glandular trichomes. Those results, however, left open the question of whether differences in observed egg densities on the two types of plants were caused by oviposition preference or differential removal of eggs by predators. Our primary objective was to determine whether C. maculata preferentially oviposit on plants with glandular trichomes. We also determined the diel periodicity of C. maculata oviposition; in addition to its intrinsic value in understanding the predator’s behavior, this knowledge facilitated our study of oviposition preference. Diel periodicity of oviposition was studied in the laboratory and in the field. In the laboratory, most oviposition occurred in the afternoon and early evening. In the field, the pattern was even more distinct, with all oviposition occurring between 1200 and 2000 hours and >80% occurring between 1400 and 1800 hours Eastern Daylight Time. To determine oviposition preference, we placed equal numbers of velvetleaf, Abutilon theophrasti (Medicus), and smooth pigweed, Amaranthus hybridus L., plants (with and without glandular trichomes, respectively) in the field and observed them continuously during the afternoon and early evening. Oviposition events by naturally occurring (i.e., wild, uncaged) C. maculata were recorded. The beetles clearly preferred to oviposit on plants with glandular trichomes, laying 51 of 52 egg clusters on velvetleaf, despite the fact that they visited smooth pigweed plants more often and spent more time per visit on those plants than on velvetleaf. We hypothesize that egg predation, especially cannibalism, has selected for this oviposition behavior.