Blumberg, D. 1990a [Encapsulation of eggs of the parasitoid Metaphycus stanleyi by the pyriform scale, Protopulvinaria pyriformis, and its effect on parasitoid efficacy.]. Hassadeh 70: 1313-1316.

Notes: Seasonal encapsulation rates in scales infesting Hedera helix and Schefflera arboricola under greenhouse and field conditions; increased resistance, by encapsulation, of P. pyriformis to successful parasitization by M. stanleyi during the summer, may account for the inability of the parasitoid to prevent autumn and winter outbreaks of this pest.