Behavioural aspects of staphylinid beetles that limit their aphid feeding potential in cereal crops.

Abstract

The activity of staphylinid beetles on the ground and on plants was studied to determine their ability to climb cereal plants to positions where aphid species feed. The efficiency of the beetles in finding and feeding on aphids was measured by watching beetles in laboratory arenas and small field cages that contained stems of wheat on which there were different prey types. Philonthus cognatus is a diurnal hunter on the ground, but wheat plants were climbed only prior to dispersal flights. Tachyporus species adults had similar daytime, predominantly crepuscular activity periods but larvae of these species were mainly nocturnal. Lower positions on plants were searched by the species than would provide regular contact with aphid colonies. The predominant food on the lower leaves were infections of the fungal pathogens, Septoria and Erisiphe species. Furthermore, many adult Tachyporus spp. were observed resting overnight on leaves of wheat on which mycophagy was observed. Mycophagy was resumed in the following activity period. The foraging behaviour of the different staphylinid species corresponded to the food preferences shown when offered aphids and mycoflora in laboratory experiments. Search on lower leaves by T. hypnorum resulted mainly in mycophagy. However, Tachyporus spp. larvae and the less abundant T. obtusus, climbed higher on wheat plants and fed on aphids. When the other species climbed to higher positions on plants it was for the purpose of take-off for dispersal flights. From 75 climbs observed of these staphylinids, 9.5% of the total aphid population was eaten and 35% was displaced to the ground where risk of predation was greater from the numerically important Carabidae.