Jack W. Debolt

Parasitism of Lygus hesperus (Miridae) by Anaphes iole (Mymaridae) and Leiophron uniformis (Braconidae) in California strawberry

Abstract Augmentative releases of two parasitoids, Anaphes iole Girault and Leiophron uniformis (Gahan), were evaluated for control of Lygus hesperus Knight populations on strawberry. Small cages were used to evaluate a range of parasitoid release rates on known densities of L. hesperus eggs or nymphs. In addition, the number of ovipositions per female L. uniformis and the distribution of ovipositions per nymph were determined for two densities of L. hesperus nymphs. Parasitism levels reached 80% for A. iole and nearly 100% for L. uniformis , indicating that these parasitoids will search for and parasitize Lygus in strawberry. A. iole was successfully reared from Lygus eggs within strawberry plants. Thus this host plant does not appear to be a barrier to the development of augmentative biological control. The distribution of L. uniformis ovipositions per host did not vary consistently from random in response to either host or parasitoid density. Ovipositions per parasitoid did not change in response to parasitoid release rate if high numbers of nymphs (300 per cage) were present. When half this number of nymphs were exposed to the same parasitoid release rates, the number of ovipositions per parasitoid declined as parasitoid densities increased. This indicates that for L. uniformis the level of mutual interference is influenced by both host and parasitoid density, not parasitoid density alone.

Encapsulation of Leiophron uniformis by Lygus lineolaris and its relationship to host acceptance behavior

In no‐choice tests Leiophron uniformis (Gahan) from the Southwestern United States readily attacked their reported hosts, Lygus hesperus Knight, L. lineolaris (Palisot de Beauvois), L. elisus Van Duzee, and a previously unreported host, L. desertinus Knight. Only 6.7% of the L. lineolaris attacked were successfully parasitized compared to 84–87% parasitization of the other species. Such low parasitism of L. lineolaris was obtained with both laboratory‐reared and field‐collected parasitoids. Two factors caused the low rate of parasitism of L. lineolaris. (1) This host successfully encapsulates most of the L. uniformis eggs oviposited in them. This is the first time such an immune response to a parasitoid has been demonstrated in the Heteroptera. (2) Female L. uniformis oviposit less frequently into L. lineolaris than into other hosts.