Aphid predation by Harpalus rufipes (Degeer) (Coleoptera: Carabidae) in the laboratory and field.
The ability of Harpalus rufipes (Deg.) to feed on aphids was studied in the laboratory in the UK and compared with evidence of predation on aphids in small outdoor plots of cereals and other crops. In the laboratory, adult carabids consumed up to 130 examples of Myzus persicae (Sulz.) per day. There was no apparent preference for any instar, but more apterous than alate individuals were consumed. Functional response curves were derived, using both the disc equation and the random predator equation. A typical type II curve was obtained for H. rufipes. The time taken to consume 1 aphid was a little more than 1 min and represented about half the total handling time (1.63-2.04 min). Feeding time increased when the beetle had already fed on many aphids. In the laboratory, H. rufipes was active on oat plants infested with Rhopalosiphum padi (L.). This activity increased with aphid density, and males were not seen on plants at densities below 50 aphids/plant. Activity also increased with temperature; the lower threshold was below 10 deg C. Up to 35% of the examples of H. rufipes taken weekly in dry pitfall traps had fed on aphids, but the mean percentage was only 1.24%. The percentage that had fed on aphids increased with increasing aphid density; 34% of H. rufipes caught in a formalin-filled time-sorting trap had fed on aphids. The beetle was swept from cereal plants at night above a threshold of about 6 deg C; 35% of the swept examples had fed on aphids. It is concluded that this carabid has a potential as an aphid predator, but that the aphid and temperature thresholds limit its usefulness at the time of year when predation would be of most benefit.