Entomologia Experimentalis et Applicata 83: 21–30, 1997. 21 c 1997 Kluwer Academic Publishers. Printed in Belgium. Foraging success of parasitoid wasps on flowers: interplay of insect morphology, floral architecture and searching behavior Joseph M. Patt, George C. Hamilton & James H. Lashomb Department of Entomology, Rutgers University, New Brunswick, NJ 08903, USA Accepted: November 19, 1996 Key words: searching behavior, biocontrol, parasitoids, Edovum puttleri, Pediobius foveolatus, intercropping, floral architecture, Anethum graveolens, Foeniculum vulgare, Coriandrum sativa Abstract Intercropping with flowering herbaceous plants increases parasitoid survivorship, fecundity and retention and pest suppression in agroecosystems. Few studies, however, have examined the compatibility of parasitoid morphology and foraging ability with floral architecture. This study shows that floral architecture influences the selection of floral host resources used to provide nutrients to parasitoids in cropping systems. Parasitoid foraging performance was evaluated using real and artificial flowers which varied in degree of nectar accessibility for two eulophid parasitoids, Edovum puttleri Grissell and Pediobius foveolatus Crawford. Comparisons were made of searching performance on artificial flowers with nectars that were either scented (made from 1:1 honey-water solution) or scentless (made from 1 m sucrose solution) and differences in head widths were compared with corolla apertures. Our results showed a disparity in the ability of E. puttleri and P. foveolatus to gain access to nectar from particular types of floral architectures. E. puttleri fed efficiently only from flowers with exposed nectaries while P. foveolatus foraged efficiently from flowers having either exposed nectaries or nectaries partially obstructed by petals and stamens. Neither wasp species could forage on flowers with cup- or tube-shaped corollas because their heads are wider than the floral apertures. E. puttleri’s foraging performance decreased as nectar inaccessibility increased in the artificial flowers, while P. foveolatus’ foraging performance was uniform among the different artificial flowers. This indicates that E. puttleri has less propensity to search small openings for nectar than does P. foveolatus. The foraging success of both E. puttleri and P. foveolatus on artificial flowers was lower when 1 M sucrose solution was used as an artificial nectar rather than honey-water solution, indicating that the wasps were stimulated and attracted by the nectar odor. Our systematic evaluation of floral architecture with respect to parasitoid foraging ability has enabled us to predict which types of flowers would serve as suitable floral host plants for parasitoids in the field. That is, only flowers with nectaries that are completely exposed would function as suitable floral host plants for E. puttleri, while P. foveolatus could forage on flowers with either exposed or partially exposed nectaries. Examples of potentially suitable floral hosts suggested from our study include dill (Anethum graveolens L.) and fennel (Foeniculum vulgare L.) for both E. puttleri and P. foveolatus and coriander (Coriandrum sativa L.) for P. foveolatus. Introduction Since critical nutrients for adult parasitoids are often scarce in large monocultures, provisioning of food resources via the interplanting of flowering herbaceous plants within the cropping system may be required for biological control programs to succeed (Wolcott, 1942; Clausen, 1956; Leius, 1967; Syme, 1975; Zandstra & Mootka, 1978; Altieri & Whitcomb, 1979; Altieri & Letourneau, 1982; van Emden, 1989; Andow, 1991; King & Olkowski, 1991; Grossman & Quarles, 1993). For example, parasitism of green pea aphids (Myzus persicae Sulzer) by the wasp Diaeretiella rapae McIn- tosh is enhanced when sweet alyssum (Lobularia mari- tima L.) is interplanted within the lettuce fields (W. Chaney pers. comm., Grossman & Quarles, 1993);