Interactions between host attributes and wasp size: a laboratory evaluation of Trichogramma platneri as an augmentative biological control agent for two avocado pests

We compared egg parasitization of two sporadic pests of avocado, Persea americana Miller, by Trichogramma platneri Nagarkatti reared on Sitotroga cerealella (Oliver) (=smaller parasitoids) with those reared on Trichoplusia ni (Hübner) (= larger parasitoids) in the laboratory. Large T. platneri females invested less time than smaller parasitoids in obtaining offspring from eggs of either Amorbia cuneana Walsingham or Sabulodes aegrotata (Gueneé). Furthermore, large T. platneri invested substantially more time (ca. 3-fold) in obtaining offspring from S. aegrotata than A. cuneana eggs. These investment times positively correlated with percentage egg-load retained by a female after it had ceased exploiting a host species. This occurred even though the offspring produced by a parasitoid from either host species manifested the same size and fecundity (= quality). Host species utilization in the laboratory mirrored that observed in the avocado groves of southern California following augmentative release of commercially produced T. platneri (Oatman & Platner, 1985). Explanations for these differences in host utilization are discussed along with their implications for augmentative biological control.