AGGRESSIVE AND EVASIVE BEHAVIORS IN POPILLIA-JAPONICA (COLEOPTERA, SCARABAEIDAE) LARVAE - DEFENSES AGAINST ENTOMOPATHOGENIC NEMATODE ATTACK

Larvae of the Japanese beetle, Popillia japonica, respond to attack by infective juveniles of the entomopathogenic nematode Heterorhabditis bacteriophora with aggressive and evasive behaviors. Brushing with the legs and rubbing with the abrasive raster were key aggressive behaviors associated with nematode attack in petri dish assays. Remarkably, contact with even a single live nematode triggered behavioral countermeasures directed at eliminating the attacker. Unrestrained P. japonica free to display aggressive behaviors removed more than 60% of attacking nematodes from their cuticle and experienced significantly less parasitism than larvae restrained from displaying defensive behaviors (13% or less of the nematodes removed). Unrestrained larvae were also capable of killing 20.6 +/- 4.7% of the attacking nematodes. Observations of aggressive behavior in soil assays supported our petri dish results. Moreover, larvae were observed to respond to the presence of nematodes with evasive behavior. These defense behaviors are so generalized it appears unlikely that they evolved as a specific scarab evolutionary response to selection pressure from entomopathogenic nematodes, but rather to any threat or irritant. (C) 1994 Academic Press, Inc.