Mycophagy as a factor limiting predation by aphids (Hemiptera: Aphididae) by staphylinid beetles (Coleoptera: Staphylinidae) in cereals.
Previous work demonstrated the potential of the staphylinids Tachyporus hypnorum (Fabricius), T. chrysomelinus (Linnaeus), T. obtusus (Linnaeus) and Philonthus cognatus (Stephens) to feed on the grain aphid, Sitobion avenae (Fabricius). However, gut dissection and observations of foraging behaviour showed that mycophagy could be a factor influencing the potential of Tachyporus spp. to control aphids. The main fungal material detected in the guts of Tachyporus spp. was spores (conidia) of Erysiphe spp. (powdery mildews). In the present study, numbers of conidia (pustules of mildew on leaf-sections) were offered with aphids in food-choice experiments to test how fungal food affected feeding on aphids by these staphylinids. An index of food preference was calculated for each species, sex and for two age classes of larvae, based on the number of conidia and aphids remaining after feeding. Results showed a preference for mildew conidia by T. hypnorum, no preference by T. chrysomelinus and Tachyporus spp. larvae and a preference for aphids by T. obtusus and P. cognatus (adults and larvae). Food-preferences compared well with dietary composition in recent studies of field collected staphylinids. Furthermore, a functional response was detected to increasing numbers of mildew conidia presented (in mildew only consumption-rate experiments) and to the increase in total food density in food-choice experiments. Mycophagy limited aphid predation and explained the numerical response of staphylinid beetles to areas of cereals with high aphid densities, whilst, in other studies, the proportion of aphids eaten by those beetles did not increase.