Heterogeneous microcosm mazes affect reproduction and survival in a wingless hyperparasitoid wasp

In nature, resources necessary for reproduction and survival are often spatially distributed or scarce. Parasitoid wasps are insects that develop as larvae in or on a single invertebrate resource (often another insect), while the adults are free-living and rely on carbohydrates, for example, floral nectar, for maintenance. Finding these different types of resources may affect fitness-related traits such as fecundity and survival. We compared reproduction and longevity in a hyperparasitoid wasp, Gelis agilis, using cocoons of the primary parasitoid Cotesia glomerata as hosts in microcosm arenas consisting of a single Petri dish or two dishes connected by a tube. The number of compartments in each dish was varied, and the provisioning of food and hosts was either temporally separated at 48 h intervals (single-dish microcosms) or spatially separated (two-dish microcosms). In the two experimental designs, batches of host cocoons were offered to G. agilis females, and cocoon fate (emergence of an adult primary or hyperparasitoid or precocious death) was recorded. In the single-dish arenas where the provisioning of cocoons and food was alternated every 48 h, there were no consistent effects of the number of compartments in the dishes on hyperparasitoid longevity and fecundity or host survival. However, when food and host access were spatially separated in two petri dishes connected by a plastic tube, the longevity and fecundity of G. agilis traits were reduced. Conversely, the survival of C. glomerata increased, particularly when the number of compartments was increased. Additional experiments further showed that finding food is a major factor limiting longevity and, concomitantly, the fecundity of hyperparasitoids in more complex environments. Habitat heterogeneity and complexity, even at small scales, play a crucial role not only in influencing the dynamics of host-parasitoid interactions but also in determining the risk of overexploitation or underexploitation of resources by consumers.