| Foraging and reproductive behaviour of Dendrocerus carpenteri (Hymenoptera: Megaspilidae), a solitary hyperparasitoid of aphids, was studied in the laboratory using as hosts the pea aphid (Acyrthosiphon pisum) and three primary hymenopterous parasitoids (Aphidius ervi, Ephedrus californicus, and Praon pequodorum). Examination and oviposition times by females of D. carpenteri varied with the species and the developmental stages of the primary parasitoids within mummified aphids; host choice was influenced more by the developmental stage than by the species of primary parasitoid.; Females of D. carpenteri located single or clumped mummies on plants with equal success, but the structure of the plant canopy influenced searching behaviour and efficiency. When the density of mummies on a leaf was increased, females responded by increasing patch time and brood size in a density-dependent manner. Giving-up time increased with host density and the decision to leave a patch was apparently influenced by re-encounters with self-marked hosts, but not by prior foraging experience. Brood sex ratio did not vary with host density.; Females of D. carpenteri produced non-binomial sex ratios of offspring by adjusting the sequence of male and female eggs laid during a single oviposition bout. Both the order and type of sequentially encountered hosts influenced the allocation of offspring sexes. The production schedule of sons and daughters was reset after a period during which no hosts were encountered. Re-encounters with self-marked hosts affected the ratio of male to female eggs laid in broods. Females appear to use simple decision rules to ensure that daughters will find mates regardless of variations in host quality and patch size.; Pea aphids containing larvae of A. ervi, A. pisivorus, Monoctonus paulensis, and P. pequodorum remained at their feeding sites. In contrast, those containing immature E. californicus generally dispersed from their colonies prior to mummification; dispersal increased with density but was inhibited in the absence of light. The foraging and reproductive patterns of D. carpenteri may have evolved as a result of the physiological and behavioural interactions among its host complex. |
