Host egg characteristics, physiological host range, and parasitism following inundative releases of Trichogramma platneri (Hymenoptera: Trichogrammatidae) in walnut orchards

Abstract

Under controlled conditions we exposed eggs of 17 potential host taxa representing five orders and 14 families to females of Trichogramma platneri Nagarkatti, an egg parasitoid used as an inundative biological control agent against codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae). Trichogramma platneri successfully parasitized species from five lepidopteran families (Gelechiidae, Noctuidae, Pyralidae, Sphingidae, Tortricidae) and the green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae). Female wasps spent more time on heavier host eggs and the probability of successful parasitism was related to the structural integrity of the chorion of the host egg. We observed oviposition attempts on all other lepidopteran hosts offered and on eggs of Geocoris punctipes Say (Hemiptera: Lygaeidae) and Nezara viridula L. (Hemiptera: Pentatomidae). Dipteran and coleopteran eggs were not attacked. Sentinel eggs of the six physiologically acceptable hosts were exposed in a walnut orchard in California during inundative releases of T. platneri and all hosts were attacked equally. Parasitoids were also equally active at all heights from 1.5 to 6.5 m within the orchard canopy. Inundative releases of T. platneri may impact naturally occurring populations of green lacewings within walnut orchards, and have the potential to impact nontarget lepidopteran populations within the release area.