Proo. of Second World Avocado Congress 1992 p. 268

The Resistance by Encapsulation of the Pyriform Scale Protopulvinaria pyriformis (Cockerell) to Successful Parasitization by the Encrytid Parasitoid Metaphycus Stanleyi Compere

Daniel Blumberg

Department of Entomology, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

Abstract. Since the early 1980's, the pyriform scale, Protopulvinaria pyriformis (Cockerell) (Homoptera: Coccidae), has been an important pest of avocado in the Coastal Plain of Israel. Encapsulation of eggs of the introduced parasitoid, Metaphycus stanleyi Compere (Hymenoptera: Encyrdidae, by the scale under both greenhouse and field conditions occurred almost the year round (1986-1988). Encapsulation rates varied considerably during the year and were correlated with the ambient temperatures. The rates of efficient encapsulation (percentage scales wherein encapsulation completely prevented parasitoid development): (i) in scales infesting Hedera helix and Schefflera arboricola under greenhouse conditions, were lowest during December to May (6-17%) and highest during July to September (78-100%); (ii) in scales infesting avocado in a Bet Dagan orchard, were lowest during October to May (0-11%) and highest during June to August (54-57%). Under greenhouse conditions, encapsulation rates did not differ in scales grown on H. helix and S. arboricola, but were significantly lower in scales grown on avocado. The increased resistance by encapsulation of P. pyriformis to successful parasitization of M. Stanleyi during summer may account for the inability of the parasitoid to prevent the autumn and winter outbreaks of the pest.