Harari, A.R., Department of Entomology, The Hebrew University, Faculty of Agriculture, POB 12, Rehovol, 76100, Israel
Ben-Yakir, D., Department of Entomology, The Volcani Center, POB 6, Bet Dagan, 50250, Israel
Rosen, D., Department of Entomology, The Hebrew University, Faculty of Agriculture, POB 12, Rehovol, 76100, Israel

Adult Maladera matrida Argaman (Coleoptera: Scarabaeidae: Melolonthinae) males emerge from soil for an active period at dusk, a few minutes before the females. Adults are found during most of the active hours on the foliage in aggregations composed of an equal sex ratio. The mechanism of aggregation behavior of M. matrida beetles was studied in a Y-shaped olfactometer. No evidence was found for the existence of an aggregation pheromone released either by males or by females, but behavior tests indicate that adult M. matrida beetles, males as well as females, are attracted to volatiles of an injured host plant. The following scenario is suggested: Males emerge daily from soil at dusk, a few minutes before the females, and immediately start feeding. Additional males are attracted to the injured host's volatiles and form aggregations. When females emerge from soil, the attractant volatiles are concentrated in spots, and the females join the aggregations, forming an equal sex ratio. © 1994 Plenum Publishing Corporation.