BIOLOGY AND PREDATION RATE OF THE SARCOPHAGID FLY, AGRIA-MAMILLATA, A PREDATOR OF EUROPEAN SMALL ERMINE MOTHS

The biology of the univoltine, predatory sarcophagid fly Agria mamillata (Pandelle) was studied in a population of Yponomeuta evonymellus(L.) (Yponomeutidae) attacking Prunus padus L. in the Valais, Switzerland. Clarification of the literature records suggests that A. mamillata is oligophagus, attacking five Yponomeuta species in the Palaearctic. The adult flies emerged in May. The presence of host odour was advantageous to elicit mating. After a preoviposition period of 19 days, the ovolarviparous females deposited eggs/first instar larvae on the cuticle of late fifth instar prey larvae, or on cocoons of prey pupae. The potential fecundity averaged 40 eggs per female. Field data indicated that females of the predator laid more eggs in tents with higher prey density. Larval development lasted 11 days. Rain stimulates mature predator larvae to leave the tents of Y. evonymellus to pupate in the soil. Pupation was observed between early July and mid August. Predation rates (= number of prey eaten per predator) were estimated from laboratory food consumption tests and from the number of predator larvae and predated cocoons in prey tents in the field. It was shown that a single predator consumed an average of five Y. evonymellus individuals. Field data indicated that predation rates cannot increase with higher numbers of prey available. It was shown that the number of prey eaten per predator decrease with higher predator densities per tent in the field.