Predicting activity patterns from resource exploitation in guilds of digger wasps’ natural enemies

Nests of central-place foraging Hymenoptera are attacked by a wide range of parasitoids, kleptoparasites and predators. Since the resource use differs among such functional groups (host larvae, provisions or adult hosts), the activity patterns could vary accordingly with the different “best-match” with the host resources. Alternatively, species within functional groups could segregate activity to avoid inter-specific competition. At a nest aggregation of the host digger wasp Bembix rostrata, nine species of natural enemies (three chrysidid wasps, two sarcophagid flies, one mutillid wasp, and three ants), spanning all these three functional groups, occur. Daily activity patterns varied among species. The three chrysidids and one sarcophagid (and, almost significantly, the other fly species) showed a positive quadratic distribution which roughly mirrored that of host provisioning activity, and agrees with the fact that these species are kleptoparasites attracted by host prey. Notably within chrysidids, however, such quadratic curves differed. On the other side, the mutillid wasp showed a clear negative quadratic distribution, and the ants did not show any recognizable trend. Being strict parasitoids (mutillids) or generalist predators/scavengers (ants), these species would not benefit from matching the host provisioning peak. We detected some positive correlations between natural enemies’ activity and host nest density, which, however, turned often negative on a per-nest bias. A Principal component analysis further showed that one species of ants and the mutillid wasp distributed in time and space much far from the host than the other natural enemies, as well as strict associations between the activity patterns of all kleptoparasites. Host resource use can be roughly used to predict activity patterns of digger wasps’ natural enemies, though finer differences between species within functional groups may suggest attempts to avoid inter-specific interference.