Biology and behavior of Metaphycus angustifrons Compere (Hymenoptera: Encyrtidae), a newly discovered parasitoid of soft scale insects (Hemiptera: Coccidae) in California

Metaphycus angustifrons Compere has recently been found to be the most abundant parasitoid of brown soft scale, Coccus hesperidum L., in southern California. In laboratory experiments we examined several biological parameters of this species. M.angustifrons both oviposits and host feeds in brown soft scale and is a facultatively gregarious endoparasitoid of this soft scale insect. In contrast with other Metaphycus spp., M. angustifrons is a koinobiont parasitoid, allowing its host to grow up to 40% beyond its size at parasitism. Despite its high abundance on brown soft scale in the field, in the laboratory, high rates of parasitoid egg encapsulation are observed; about half of parasitized hosts failed to issue parasitoids. Furthermore, host scales that encapsulated parasitoids eggs showed significant reduction in development. Increased scale size at oviposition influences the size of emerging females but not the size of males. Female M. angustifrons are synovigenic. They emerge from their hosts without mature eggs and begin maturing eggs after they are provided a carbohydrate source. Carbohydrates prolong the life span of both female and male M. angustifrons. The size of female wasps influences egg load but not longevity. Finally, based on laboratory observations, M. angustifrons uses citricola scale almost exclusively for host feeding and not for oviposition. These results suggest that the role of this species in citricola scale’s decline in southern California in the 1950s–1960s was negligible.

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► Metaphycus angustifrons is a facultative gregarious parasitoid of brown soft scale, Coccus hesperidum.
► Metaphycus angustifrons is a synovigenic, koinobiont endoparasitoid of soft scale insects.
► Eggs of M. angustifrons are frequently encapsulated by brown soft scale in laboratory conditions despite the fact that it is the most abundant parasitoid of this host species in Southern California citrus.
► Citricola scale, Coccus pseudomagnoliarum, is not a suitable host for reproduction of M. angustifrons, which is used almost exclusively for host feeding. Thus the role of this parasitoid in citricola scale population decline in the 1950s–1960s was negligible.