Abstract. This study investigates the feeding of the parasitoid Cotesia glomerata on the floral nectar of Anethum graveolens and Origanum vulgare and evaluates the nutritional value of these food sources for increasing flight capacity. A significantly higher proportion of females are observed feeding on A. graveolens immediately after being released onto the floral nectar plants compared with those of the group released onto O. vulgare, although female wasps from both groups spent a similar period of time feeding on both nectar sources and there is no significant difference in their body weight increase. Laboratory tests on computer-linked flight mills demonstrate that adult feeding significantly influences flight capacity, as defined by the number of flights, the longest single flight and the total distance flown during a given period of time, in female wasps but not in males, albeit the extent of influence varying with the type of food sources. After ad libitum feeding on the floral nectar of A. graveolens, female wasps perform flight activity as well as those feeding on honey, which is superior to those feeding on sucrose, in all the measured parameters. Feeding on the floral nectar of O. vulgare has a similar effect to feeding on the extrafloral nectar of Vicia faba and significantly increases the total distance flown but not the number of flights or the longest single flight. Feeding on sucrose does not increase flight capacity in the parasitoids beyond those having access to water only. The findings of this study suggest that judicious selection of floral nectar plants and habitat manipulation might play a key role in the biological control of pest insects.Key words. Adult feeding, flight capacity, floral nectar, parasitoid. IntroductionAdult feeding is necessary to meet nutritional requirements for successful reproduction in many parasitoids, especially in those synovigenic species (Godfray, 1994). Some species are known to feed on their hosts (Schmale et al., 2005); many others are exclusively reliant on nonhost food, such as, floral and extrafloral nectar or honeydew (Wa¨ckers, 1999). However, even those host-feeding species need to occasionally use saccharides as the main source of energy at adult stage (Jervis & Kidd, 1986;Jervis et al., 1996;Heimpel et al., 1997). In the field, adult parasitoids are observed visiting flowering plants to feed on floral or extrafloral nectar (Jervis et al., 1993;Idris & Grafius, 1995), and crops with nearby flowering vegetation have higher parasitism rates (Landis & Hass, 1992;Zhao et al., 1992;Stephens et al., 1998), although the finding of a recent field study suggests that vegetative characteristics of floral resource plants rather than flowers might influence the abundance of natural enemies (Rebek et al., 2005). In the laboratory, plant nectar shows a higher nutritional value compared with honeydew for sustaining longevity and fecundity in hymenopteran parasitoids (McDougall & Mills, 1997;Wa¨ckers, 2002;Lee et al., 2004).Previous laboratory studies show that adult...

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Summary1. Dispersal and host-foraging activity are important behavioural characteristics for parasitoid species used as biological control agents. Appropriate marking techniques are often needed for field investigations into these behaviours because of the small size of parasitoids. This study developed a novel technique using the rare stable calcium isotope 44 Ca to mark parasitoids. 2. As demonstrated with a tri-trophic model system consisting of cabbage plant Brassica oleracea , caterpillar Pieris brassicae and gregarious parasitoid Cotesia glomerata , marking parasitoids with the isotope 44 Ca is systemic and non-disruptive. Significant uptake and translocation of 44 Ca occurred in cabbage plants after being drenched with 50 mMol aqueous isotope solution, and the isotope was transferred to wasps emerging from the parasitized host caterpillars that fed on the isotope-enriched plant. The isotope enrichment did not adversely influence the survivorship of hosts or the development of parasitoids. The 44Ca-enriched female wasps could pass the isotope marker further via oviposition into the parasitized host caterpillars, hence allowing the marker to be transferred across parasitoid generations. Greenhouse release experiments validated the transferability of 44 Ca from the enriched wasps to hosts through parasitism. The 95% upper confidence limit for the mean 44 Ca/ 40 Ca isotope ratio in the hosts without 44 Ca enrichment (control) could be used as a statistical marking criterion to identify reliably the individual parasitized hosts within the first 3 days of parasitism. 4. Synthesis and applications . We have, for the first time, documented the efficient transfer of a stable isotope marker from enriched parasitoids to host insects through parasitism. This isotope technique enables the study of dispersal and host-foraging activity of parasitoids in the field without having to recapture marked individual parasitoids. Information on the dispersal pattern and host-foraging activity of the parasitoid species concerned is obtained from the spatial distribution of the parasitized marked host insects. Furthermore, this isotope technique can be used to quantify the efficacy of parasitism by the parasitoids released in the field.

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