ECOLOGICAL CONSTRAINTS ON INDEPENDENT NESTING IN FACULTATIVELY EUSOCIAL HOVER WASPS

Recent field experiments suggest that cooperative breeding in vertebra tes can be driven by a shortage of breeding territories. We did analog ous experiments on facultatively eusocial hover wasps (Stenogastrinae: Liostenogaster flavolineata). We provided nesting opportunities by re moving residents from 39 nests within a large aggregation (1995), and by glueing 20 nests obtained from a distant site into a second aggrega tion (1996). We prevented nest-less floaters from competing for these opportunities in 1995 but not in 1996. In both years, helpers in unman ipulated groups were given opportunities to nest independently without having to incur nest-building costs and with a reduced wait before po tential helpers emerged. Helpers visited the nests we provided, but ad opted only a small proportion (5% of 111 vacancies created in 1995!. O thers were adopted by floaters, but a significant proportion of nests were never adopted (9 out of 20 in 1995, 7 out of 20 in 1996). Helpers that visited nests did not originate from particular kinds of social group. Nests containing older broods were more likely to be adopted, a nd adopting females rarely destroyed older brood. A general feature of social insect, but not vertebrate life histories, namely the long per iod of offspring dependency relative to the short life expectancy of a dult carers, may be a key factor constraining independent nesting.