Effects of sugar spray and aphid honeydew on field populations of the parasitoid Bathyplectes curculionis (Hymenoptera : Ichneumonidae)

Sugar spray applied to crop foliage may serve as a surrogate for homopteran honeydew in meeting the nutritional needs for self-maintenance in adult pa rasitoids of crop pests. We tested the importance of tinting of application of sugar spray and the interaction between sugar spray and naturally occur ring aphid honeydew in influencing the local abundance of the alfalfa weevi l parasitoid Bathyplectas curculionis (Thomson). Plots of hay alfalfa in no rthern Utah were sprayed with sucrose dissolved in water (sugar plots) or w ith water only (control plots) early, midway, or late during the prefloweri ng period in the 5th yr of production. When sampled 2 d later, numbers of a dult parasitoids were consistently higher in sugar plots than in control pl ots. Increased wasp density in response to local pea aphid density also occ urred, but only in plots that did not receive sugar spray. Weevil parasitis m was elevated in sugar plots compared with control plots only when sprays were applied late in the 1st crop. Lack of enhanced rates of wasp ovipositi on in sugar plots early and midway during the 1st crop may have resulted fr om poor weather, mutual interference among the wasps, or wasp feeding. Our study was conducted in a field harboring relatively low numbers of aphids. In general, sugar sprays may be redundant for adult parasitoids in a crop w hen naturally occurring homopteran honeydew is abundant. But the positive r esponses of B. curculionis to sugar sprays recorded in this study suggest a pplication of this material may be beneficial to the wasp throughout the Is t crop of alfalfa if aphid densities (and associated availability of natura l honeydew) remain low.