Susceptibility of secondary screwworm (Diptera: Calliphoridae) to the larval parasitoid Tachinaephagus zealandicus (Hymenoptera: Encyrtidae).

Abstract

The reinfestation of New World screwworm (Cochliomyia hominivorax [Coquerel]) (Diptera: Calliphoridae) in North America has prompted a broad effort to identify new management tools. In this study, the larval parasitoid Tachinaephagus zealandicus (Ashmead) (Hymenoptera: Encyrtidae) was evaluated as a potential biocontrol using the congeneric secondary screwworm Cochliomyia macellaria (Fab.) (Diptera: Calliphoridae) as a proxy host. When host:parasitoid ratios were varied from 5:1 to 40:1, female parasitoids killed up to 18 hosts (at 40:1) and produced 66 adult wasp progeny per female over 24 h. Parasitized pupae produced from 5.6 to 11.7 adult parasitoids per pupa at host:parasitoid ratios of 40:1 and 5:1, respectively. Parasitoids showed no preference for larvae of C. macellaria or Sarcophaga bullata Parker (Diptera: Sarcophagidae). Kill rates and successful parasitism was twice as high in moist (15% moisture) as in dry sandy loam soil. Addition of a layer of leaf litter to the soil surface had no effect on the ability of parasitoids to locate hosts. Parasitism in moist clay soil was similar to that in moist sandy soil, but higher parasitism was observed in dry clay than on dry sandy soil. Placing faux rocks as potential larval refuge on the pupation substrate surface provided larvae with some protection from parasitism in dry substrates. When larvae were given a 2-h head start before adding parasitoids, there was no effect on host mortality or parasitism in dry soil. Results are encouraging for possible use of T. zealandicus as a supplemental management tool for calliphorid pests.