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°C, 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°C and three at 28°C), various degrees of encapsulation were observed. At 23°C, 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°C, encapsulation of L. dactylopii in P. longispinus was significantly higher than that at 23°C (68.4% vs 53.8%, respectively). However, in A. fusciventris, encapsulation in P. viburni at 28°C was significantly lower than that at 23°C (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°C. 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.