Host influences on sex ratio, longevity, and egg load of two Metaphycus species parasitic on soft scales: implications for insectary rearing

Metaphycus flavus (Howard) and M. stanleyi Compere (Hymenoptera: Encyrtidae ) are currently being screened for use as augmentative biological control a gents of citrus-infesting soft scales (Homoptera: Coccidae). Two factors we re investigated, host quality-dependent sex allocation and local mate compe tition, which likely influence these parasitoid's sex allocation strategies and are therefore of interest for their mass-rearing. The results of these studies suggested that, under the mass-rearing protocol that is envisioned for these parasitoids, offspring sex ratios in both M. flavus and M. stanl eyi are dominated by host quality (= size) influences, but not by interacti ons with other females. These results indicated that host size strongly inf luences offspring sex ratios and brood sizes; larger hosts led to more fema le offspring and larger broods. In contrast, increasing the number of paren tal females did not lead to fewer female offspring as expected under local mate competition. Additionally, within-brood sex ratios did not vary with b rood size; this result is inconsistent with expected sex ratios due to loca l mate competition. Other results also indicated that host quality was a do minant influence on M. flavus' and M. stanleyi's sex ratios. Larger hosts l ed to a larger size in the emerging wasps, and larger wasps had greater egg loads and lived longer than smaller wasps. However, wasp longevity, and th e influence of wasp size on longevity were mediated by a wasp's diet. Metap hycus flavus females lived the longest when they had access to hosts, honey , and water, followed by honey and water, and shortest when they had access to water alone; M. stanleyi females lived longest with honey and water, fo llowed by hosts, honey, and water, and shortest with water alone. Greater w asp size led to greater longevity in females only when they had access to f ood (honey, or hosts and honey). Finally, other results suggested that both M. flavus and M. stanleyi are facultatively gregarious. Wasp size did not decrease with brood size as expected under superparasitism. Overall, the re sults of these studies suggested that holding newly emerged females of both M. flavus and M. stanleyi for several days in the presence of an appropria te food source before field release could enhance a female's performance as an augmentative biological control agent. It increases their initial life expectancy following release, and maximizes the females' egg load (both Met aphycus species) and resources for replacing oviposited eggs (M. flavus onl y).