Larval helpers and age polyethism in ambrosia beetles

Abstract

Division of labor among the workers of insect societies is a conspicuous feature of their biology. Social tasks are commonly shared among age groups but not between larvae and adults with completely different morphologies, as in bees, wasps, ants, and beetles (i.e., Holometabola). A unique yet hardly studied holometabolous group of insects is the ambrosia beetles. Along with one tribe of ants and one subfamily of termites, wood-dwelling ambrosia beetles are the only insect lineage culturing fungi, a trait predicted to favor cooperation and division of labor. Their sociality has not been fully demonstrated, because behavioral observations have been missing. Here we present behavioral data and experiments from within nests of an ambrosia beetle, Xyleborinus saxesenii. Larval and adult offspring of a single foundress cooperate in brood care, gallery maintenance, and fungus gardening, showing a clear division of labor between larval and adult colony members. Larvae enlarge the gallery and participate in brood care and gallery hygiene. The cooperative effort of adult females in the colony and the timing of their dispersal depend on the number of sibling recipients (larvae and pupae), on the presence of the mother, and on the number of adult workers. This suggests that altruistic help is triggered by demands of brood dependent on care. Thus, ambrosia beetles are not only highly social but also show a special form of division of labor that is unique among holometabolous insects.altruism | cooperative fungiculture | insect agriculture | larval workers | mutualism

Beyond promiscuity: mate-choice commitments in social breeding

“…Recent work on ambrosia beetles [128] has shown that inbred offspring help, both as larvae and adults, but (sib)mate and predominantly disperse to found new burrows, illustrating that high sibling relatedness combined with monogamy does not have to produce eusociality. Although some (dead wood) burrows of ambrosia beetles may last for two or three generations, most deteriorate sooner, precluding indirect fitness gains for later offspring that would fail to disperse after some variable period of helping-quite similar to wood-dwelling lower termites running out of food.…”

“…The aphids and thrips have nothing to gain from foraging unless they can gain access to a neighbouring gall, which would compromise genetic homogeneity and the inclusive fitness of residents and thus solicit vicious defence. They are also constrained in expanding their galls, so the number of broods remains low [148,150], similar to the ambrosia beetles nesting in dead wood [128]. Snapping shrimp obtain their food from the sponge tissues around their nests or passively via water flowing through [157].…”

Hidden burrow plugs and their function in the tiger beetle, Cosmodela batesi (Coleoptera, Cicindelidae)

“…C. batesi larvae also plug their burrows prior to pupation (personal observation). Other arthropods may perform plugging or blocking behavior for purposes other than water prevention, such as for shutting out natural enemies in Cephalotes ants (Powell 2008), and, in ambrosia beetles, for preventing larvae from accidentally crawling out (Biedermann and Taborsky 2011). Therefore, although water may be a primary factor that induces plugging behavior in C. batesi, the effect of other factors requires further investigation.…”

Farming of a defensive fungal mutualist by an attelabid weevil

“…In ant and termite farmers, agriculture tasks are partitioned between different castes, each specialized on one main task (Hart et al, 2002;Nobre et al, 2011). In ambrosia beetle (Xyleborinus saxesenii), division of labor is shown between larval and adult colony members (Biedermann and Taborsky, 2011).…”

“…The farming strategies of these insect farmers include evolved mechanisms for substrate preparation, inoculation with crop propagules, optimization of fungal growth through regular activities, protection of the crop against parasites or diseases and harvest and consumption of fungi (Schultz et al, 2004;Mueller et al, 2005). The insect farmers have developed taskpartitioned societies cooperating in their fungiculture biology (Biedermann and Taborsky, 2011;Nobre et al, 2011). In ant and termite farmers, agriculture tasks are partitioned between different castes, each specialized on one main task (Hart et al, 2002;Nobre et al, 2011).…”