Effects of insect opportunists on a four-level trophobiotic system involving nectar-producing galls of the cynipid wasp Disholcaspis quercusmamma (Hymenoptera: Cynipidae)

The induction of plant galls is considered an adaptive life history trait found in many insect groups. Order Hymenoptera has many gall-making species belonging to the gall wasp family Cynipidae. As an extended phenotype of the gall makers, some galls exhibit very sophisticated adaptive mechanisms involving multilevel species interactions. The oak galls of the Cynipid species Disholcaspis quercusmamma produce a nectar-like secretion that attracts other insects. It is hypothesized that these visiting insects discourage potential parasitoids and inquilines questing for oviposition sites within the galls. Several studies on the species interactions involved in this four-level trophobiosis have examined the role of visiting ant species. However, the roles of other visiting insect species on this system have not yet been studied. This study aimed to examine the effects of all visiting insects on the success of the gall-makers. Statistical analyses of field data found no effect of exclusion treatment on gall wasp success, parasitism, or inquilinism. However, additional tests showed a positive correlation between gall wasp success and inquilinism rate compared to gall cluster size. Gall diameter correlated positively with gall maker success and negatively with inquilinism rate. This suggests an underlying complexity to this uniquely adapted relationship.