Abstract
Communal nesting, rare in the crabronid wasps, has been recorded for various species in the Spilomenina clade of the Pemphredoninae. A new communally nesting species, Spilomena socialis, is described from peninsular Malaysia where it nested on buildings at Bukit Fraser. The nest consists of a group of closely spaced clusters of vertically oriented cells attached to walls, and is constructed of tiny pieces of vegetal and mineral origin, parts of insects, and fungal hyphae bound together by silk secreted from each female wasp’s abdominal gland. Nests contained up to 39 cells (average 10.4 cells, N = 35). Nest entrances were at the upper end of the cells and were protected on one side by a “roof”. Cells constructed side-by-side have their roofs connected to form a tube that allowed access to all the cells. Nests were inhabited by 1–13 females (average 4.3 females per nest, N = 21) and 0–4 males, the overall sex ratio being 0.22. Ovarian development among the females in a nest varied. In 8 of 20 nests with 3 or more females only one female had developed ovaries, but female size (measured as head width) did not correlate with ovarian development. Cells are apparently progressively provisioned with thrips, and are often re-used. Adult females cooperatively defend the nests against intruders.
Highlights
In the superfamily Apoidea, which includes the apoid wasps of the family Crabronidae, nesting habits vary from strictly solitary to eusocial
The maximum number of females (11) is similar to that reported for other species (13 in Microstigmus comes (Matthews 1991), 6 for M. nigrophtalmus (Melo 2000, Lucas et al 2011), 26 for M. sp. (West-Eberhard 1977), in Arpactophilus mimi (Matthews and Naumann 1989), Spilomena subterranea (McCorquodale and Naumann 1988), and a Costa Rican Spilomena sp. (West-Eberhard 1977))
It was not possible to demonstrate a reproductive division of labor between the various females in a nest, as occurs in M. comes, because other females in the colonies display at least some ovarian development
Summary
In the superfamily Apoidea, which includes the apoid wasps of the family Crabronidae, nesting habits vary from strictly solitary to eusocial. The majority of the more than 8000 described crabronid species are characterized by solitary nesting habits but some members of one clade in the subfamily Pemphredoninae, the Spilomenina, consisting of the genera Arpactophilus, Microstigmus, Spilomena, and Xysma, have evolved relatively complex social behavior (Matthews 1991). Reproductive division of labor has so far only been ascertained in the Neotropical Microstigmus comes Krombein, where nests are usually founded by solitary females and relatedness between female colony members varies from 0.6 to 0.7 indicating the presence of mother-daughter associations with single-mated foundresses (Matthews 1968, Ross and Matthews 1989a and b). In the Australian Arpactophilus mimi Matthews and Naumann, an average of three females occupied and progressively provisioned the nest, but displayed no differences in ovarian development (Matthews and Naumann 1989)
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