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

The biology of the univoltine, predatory sarcophagid fly Agria mamilla ta (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 i s oligophagus, attacking five Yponomeuta species in the Palaearctic. T he adult flies emerged in May. The presence of host odour was advantag eous to elicit mating. After a preoviposition period of 19 days, the o volarviparous females deposited eggs/first instar larvae on the cuticl e of late fifth instar prey larvae, or on cocoons of prey pupae. The p otential fecundity averaged 40 eggs per female. Field data indicated t hat females of the predator laid more eggs in tents with higher prey d ensity. Larval development lasted 11 days. Rain stimulates mature pred ator larvae to leave the tents of Y. evonymellus to pupate in the soil . Pupation was observed between early July and mid August. Predation r ates (= number of prey eaten per predator) were estimated from laborat ory food consumption tests and from the number of predator larvae and predated cocoons in prey tents in the field. It was shown that a singl e predator consumed an average of five Y. evonymellus individuals. Fie ld data indicated that predation rates cannot increase with higher num bers of prey available. It was shown that the number of prey eaten per predator decrease with higher predator densities per tent in the fiel d.