BEHAVIORAL-ASPECTS OF STAPHYLINID BEETLES THAT LIMIT THEIR APHID FEEDING POTENTIAL IN CEREAL CROPS

The activity of staphylinid beetles on the ground and on plants was st udied to determine their ability to climb cereal plants to positions w here aphid species feed. The efficiency of the beetles in finding and feeding on aphids was measured by watching beetles in laboratory arena s and small field cages that contained stems of wheat on which there w ere different prey types. Philonthus cognatus is a diurnal hunter on t he ground, but wheat plants were climbed only prior to dispersal night s. Tachyporus species adults had similar daytime, predominantly crepus cular activity periods but larvae of these species were mainly nocturn al. Lower positions on plants were searched by the species than would provide regular contact with aphid colonies. The predominant food on t he lower leaves were infections of the fungal pathogens, Septoria and Erisiphe species. Furthermore, many adult Tachyporus spp. were observe d 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 fo od preferences shown when offered aphids and mycoflora in laboratory e xperiments. Search on lower leaves by Tachyporus resulted mainly in my cophagy. However, Tachyporus spp. larvae and the less abundant T. obtu sus, climbed higher on wheat plants and fed on aphids. When the other species climbed to higher positions on plants it was for the purpose o f take-off for dispersal flights. From 75 climbs observed of these sta phylinids, 9.5% of the total aphid population was eaten and 35% was di splaced to the ground where risk of predation was greater from the num erically important Carabidae.