Nov. 4 (UPI) -- Inside ambrosia beetle colonies, mothers and daughters work and reproduce alongside one another, according to a new study published Wednesday in the Frontiers in Ecology and Evolution.
In most ant and termite colonies, the division of labor is distributed among male workers. Inside the colonies of Xyleborus affinis beetles, however, the new research showed brood and fungus care is undertaken by fertile "helper" females.
"Beetles are the most diverse insect order, but social beetles are relatively rare," said Peter H. Biedermann, sole author of the new study.
"Our successful development of laboratory rearing of X. affinis allows us to design experiments to determine why some beetle helpers refrain from reproduction, yielding important insights into the early evolutionary stages of insect sociality," said Biedermann, a professor at the Albert-Ludwigs University in Freiburg, Germany.
Scolytid ambrosia beetles, or sugarcane shot-hole borers, nest in moist, fallen logs in forests across the Americas.
The beetles cultivate fungi inside their nests to feed their offspring. When females start new nests and found new colonies, they use a special pouch in their mouths to carry spores from their natal nests to establish new fungal gardens.
For the new study, Biedermann collected a couple dozen mated female X. affinis beetles, or foundresses. He then placed them in sterile glass tubes filled with sawdust and watched as the beetles created new colonies.
After roughly two months, Biedermann analyzed the abundance and distribution of males and females inside.
Biedermann also determined the reproductive status of each colony's females by dissecting their ovaries. Additionally, the researcher analyzed the varieties of fungus growing in each garden.
His findings showed females grow ovaries in response to garden growth and the opportunity to breed -- when there's more food, more offspring can be supported.
The research also showed both non-fertile and fertile females assist their mother to keep the nest clean, tend the fungal garden and care for the brood.
Fertile females sometimes leave to start their own colonies, but many stay near the brood and compete with their mothers for mating opportunities.
Unlike in most ant and termite colonies, male ambrosia beetles don't work; they simply wait to mate.
"Here I showed that X. affinis has convergently evolved a facultative eusocial system very similar to wasps and bees that lack castes," Biedermann said.
"In ambrosia beetles, egg-laying females work more than their non-fertile sisters, whereas females in distinctive sterile castes do all the work in in ants and termites. Also, farming has evolved convergently in ambrosia beetles, ants, and termites, in that a single asexual fungus seems to be the main domesticated food source in all these insect farmers," he said.