Encapsulation rates of three encyrtid parasitoids by three mealybug species (Homoptera: Pseudococcidae) found commonly as pests in commercial greenhouses

Encapsulation rates of the parasitoids Leptomastix dactylopii Howard, Leptomastix epona (Walker), and Anagyrus fusciventris (Girault) (Hymenoptera: Encyrtidae) by the mealybugs Planococcus citri Risso, Pseudococcus viburni (Signoret), and Pseudococcus longispinus (Targioni-Tozzeti) (Homoptera: Pseudococcidae) were studied under controlled laboratory conditions. At 23 degreesC, of the nine host-parasitoid combinations studied, encapsulation was absent only in the combination of L. dactylopii with P. citri. Complete encapsulation (100% of all parasitoid eggs) occurred with L. dactylopii on P. viburni and L. epona on P. citri. In all other combinations studied (six at 23 degreesC and three at 28 degreesC), various degrees of encapsulation were observed. At 23 degreesC, rates of effective encapsulation (the percentage mealybugs in which encapsulation of all parasitoid eggs occurred) were 53.4% (L. dactylopii in P. longispinus), 33.4% (L. epona in P. viburni), 11.2% (L. epona in P. longispinus), 86.4% (A. fusciventris in P. citri), 69.6% (A. fusciventris in P. viburni), and 3.3% (A. fusciventris in P. longispinus). At 28 degreesC, encapsulation of L. dactylopii in P. longispinus was significantly higher than that at 23 degreesC (68.4% vs 53.8%, respectively). However, in A fusciventris, encapsulation in P. viburni at 28 degreesC was significantly lower than that at 23 degreesC (36.5% vs 69.6%, respectively). Encapsulation rates of A fusciventris in P. longispinus were not affected by the rearing temperature. Numbers of parasitoid eggs laid per host were similar for all host-parasitoid combinations (1.0-2.2); only L. epona in P. citri was significantly higher (2.2) than the other host-parasitoid combinations (1.0-1.5). Percentage parasitism of hosts was lowest for A fusciventris in P. citri (16.3% vs 51.7-66.4%, for all other host-parasitoid combinations). Parasitoid larvae that emerged from encapsulated egg capsules were detected in some host-parasitoid combinations at 23 and 28 degreesC. Such larval escape from encapsulation significantly increased mealybug mortality only for A. fusciventris on P. viburni (up 14.8%) as compared to all other combinations studied (0.7 to 2.6%). Differences in levels of encapsulation observed in these host-parasitoid combinations have practical implications for choice of appropriate parasitoids for biological control. (C) 2001 Academic Press.