Nectar Availability and Parasitoid Sugar Feeding

Habitat diversification can potentially benefit natural enemies by providing alternative prey, a suitable microclimate, or nectar and pollen (Landis et al., 2000). Laboratory and field cage studies demonstrate that parasitoids with access to sugar have greater longevity, fecundity, and more femalebiased sex ratios than starved parasitoids (Idris and Grafius, 1995; Dyer and Landis, 1996; Berndt et al., 2002). Many parasitoids have been observed to feed on floral nectar in fields (Jervis et al., 1993), and crops with nearby flowering vegetation have higher parasitism rates (Landis and Haas, 1992; Zhao et al., 1992; Stephens et al., 1998). These studies have led to the hypothesis that diversifying fields with nectar-producing floral vegetation would improve parasitism rates; however, the proportion of parasitoids that utilize floral nectar in these diversified fields is largely unknown. Parasitoids may not feed on nectar in the field as readily as in laboratory and field cage experiments where they are given ample nectar supplies and have no other competitors removing the nectar. Also, the higher parasitism rates in diversified versus simplified habitats may be related to differences in microclimates or in host densities (Baggen and Gurr, 1998) rather than to sugar feeding. In order for floral nectar sources to benefit parasitoids, the nectar supply should be readily available when parasitoids are active and parasitoids must feed from the source. The objectives of this study were (1) to determine the availability of nectar from buckwheat plantings to parasitoids throughout the day and (2) to quantify the proportion of parasitoids feeding from this sugar source.