Natural enemy diversity reduces temporal variability in wasp but not bee parasitism

Biodiversity may enhance and stabilise ecosystem functioning, but little evidence exists for diversity–function relationships involving multitrophic interactions in real landscapes. In multitrophic communities diversity may vary at different trophic levels, with either synergistic or antagonistic effects on ecosystem functioning. Intensification of land-use systems is often found to reduce diversity, which in turn may lead to reduced associated ecological functions in natural food webs, such as host-parasite interactions. In this study we investigated the relationship between the number of natural enemy and host species and the mean rate and temporal variability of parasitism (inverse of stability), along an intensification gradient of coffee agroforests in Ecuador. We used standardised trap nests for bees and wasps and their natural enemies in 14 agroforests, and evaluated these monthly over a period of 17 months. We found that parasitism rates of wasps and bees increased with increasing number of enemy species and decreased with increasing number of host species. Temporal variability in parasitism rates decreased with increasing number of enemy species and increased with temporal variability in enemy species richness; however, these effects were restricted to wasp hosts. Intensification of agroforests did not significantly affect species richness of hosts or enemies or their relation to parasitism and its temporal variability. We conclude that high enemy diversity may enhance parasitism rates and that high host diversity may provide resistance against consumption. Furthermore, we show that a diverse and stable enemy community may also have a stabilizing effect on parasitism rates. However, these effects may be host-guild specific, as these relations were restricted to wasps.