Aggregation in Hemiptera: A life history approach

Many species of Hemiptera are gregarious, displaying a tendency to aggregate into discrete groups independent of environmental microstructure. The proximal cues mediating this behavior are well-documented in the literature; these include chemical, tactile, and visual stimuli, in addition to moderating factors, such as stage of development, feeding and drinking activity, molting, external temperature, humidity, and time of day. However, less is known about the ultimate benefits gained by aggregated individuals and whether these benefits differ among the life history stages of a species.;Aggregation behavior is loosely associated with aposematic coloration. The theoretical literature focusing on the evolution and/or maintenance of aposematic coloration often assumes than kin are spatially associated. We demonstrate that, in the aposematically colored large milkweed bug, Oncoveltus fasciatus, both recent hatchlings and second instars siblings reared together form aggregations randomly with respect to relatedness. Any potential kin-biased spatial distribution of O. fasciatus must therefore be explained through dispersal patterns rather than through kin-biased aggregation.;The effect of density on fitness depends both on the species and instar studied. In six species of Hemiptera studied in the laboratory, nymphs reared alone showed a trend to have lower survivorship than those reared at densities of two per cage. Survivorship increased with increasing density in the two Lygaeid species, O. fasciatus and Lygaeus kalmii , which both feed on milkweed (Asclepius) seeds, but decreased with higher densities in the other four non-Lygaeid species. The highest levels of mortality occurred during the first instar.;The increased mortality seen in solitary O. fasciatus first instar nymphs appears to be, at least in part, due to an inability to feed efficiently on dry, mature Asclepias seeds. Previous studies have shown that groups of O. fasciatus often feed on the same seed. Provisioning first instars with green seed pods or unhatched conspecific eggs increases survivorship, as does rearing them with second instars, which may have an increased ability to pierce the outside hull of mature seeds.;Caged field experiments verify that O. fasciatus nymphs have highest survivorship rates at intermediate densities.