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The benefits of living in groups drive the evolution of sociality, and these benefits could vary across a life-cycle. However, there may be experimental problems in linking group size at one time in a life-cycle to benefits that only become apparent later on when group size has changed, leading to what we call "temporal dissonance". In the only known social colletid bee, Amphylaeus morosus , parasite pressures arise at various times throughout the life-cycle from different parasitoid species. Amphylaeus morosus is impacted by eight different parasitoid species operating at different host-colony phenology phases, including five species of Gasteruption wasps, a bombyliid fly and two mutillid wasp species. We found that, as the reproductive season progressed, the number of host adults in a nest declined, often to zero, but the presence of even one adult host female during late brood-rearing stages appeared to offer substantial brood protection against mutillids. We propose that the apparent benefits of colony size at one point in time may not reflect the benefits that become apparent at a later point in the season, leading to a temporal dissonance between group size and its later fitness benefits. We also show that A. morosus is strongly protogynous, with variation in parasitoid pressure across the reproductive phenology distorting operational sex ratios away from initial investment ratios. Combined, our data suggest that seasonal variation in parasitoid pressure may have major consequences for understanding social evolution, but these kinds of consequences are largely unexplored in current studies of insect social evolution. [ABSTRACT FROM AUTHOR]

Gasteruption is an easily recognized genus of wasps whose larvae are predator-inquilines in the nests of cavity-nesting solitary bees (Apidae, Colletidae, Halictidae and Megachilidae), with some records for solitary wasps as hosts (Crabronidae, Vespidae and Sphecidae). There is conflicting information about the biology and host associations for the genus because of a lack of information from the majority of biogeographical regions in the world. Here we concatenate all available literature records pertaining to the biology of adults, host associations and larval development. We conclude that bee hosts are more readily used compared to wasp hosts (71 bee, 13 wasp species), with the majority of wasp observations without sufficient data to be confident of the host association. The majority of known records are for hosts nesting in cavity nests (76 species) rather than ground nests (eight species), with most species recorded from a single host association. From available data, the approximate rates of host nests with parasitized broods are low: 4–7%. We also provide suggestions for improving the quality of future observations in the group. [ABSTRACT FROM AUTHOR]

Among some of the most unusual traits of the gasteruptiid wasps is their unique hovering flight and the expansion of their hind tibiae. Tibial expansions in female parasitoid hymenopterans often involve an enlarged sensory structure for vibration detection, the subgenual organ, thus enabling refined substrate-borne detection of concealed hosts. In the present paper, we utilize a combination of microscopy, chemical analysis, gene expression, and behavior to explore the function of the expanded hind tibia of gasteruptiid wasps. We find that the expanded hind tibia of gasteruptiids is filled largely with fat body, a cell cluster thought not typically to occur in insect legs. Based on its position relative to flexible tibial structures and the subgenual organ, the gasteruptiid tibial fat body may function to amplify vibrational signals. We show the tibial fat body to be filled with both trophocytes and, depending on gasteruptiid lineage, oenocytes. Transcriptomics reveals enrichment for fat-related genes more than expected in an insect leg and raises several additional possibilities for functions of fat in the leg including detoxification. Finally, our flight observations support the hypothesis that this structure may also function in balance and maneuvering in the unusual leg-dangling flight behavior of this wasp. [ABSTRACT FROM AUTHOR]