National / Science & Health

Cockroach longevity linked to female cohabitation

by Mie Sakamoto

Staff Writer

Female cockroaches living in groups with other females are more likely to have their unfertilized eggs hatch, a research team at Hokkaido University has found, providing a possible explanation for the reason the insect has managed to survive for hundreds of millions of years.

When three female American cockroaches — a species widely found throughout the world — were placed together in a study, ootheca, or the egg case of the cockroaches, formed more quickly than when a single female was observed, the team said.

“It explains well the fact that several female cockroaches will be able to maintain a colony in a more stable manner than a single female cockroach,” which can be regarded as a sign of cooperative behavior that is optimized for reproduction seen in other insects like white ants, the research team said in a news release Monday.

A group of more than 15 female cockroaches was able to maintain a colony for more than three years, indicating that ootheca form faster the more cockroaches there are, it said.

“We found that ootheca formation is facilitated when a female cockroach recognizes another female by touching it with their antennae, which are also used for smelling and tasting,” said Ko Kato, a graduate student who took part in the study.

Backing the findings, ootheca formation in a group of female cockroaches with severed antennae was slower than those with the sensory appendages, the team said.

In a case in which a female cockroach and a male cockroach incapable of copulating were placed together, the formation of ootheca took longer than the female-only group, the team said.

To exterminate cockroaches, “It will be essential to prevent the spread of the females, as there are cockroaches that can expand their habitat range through parthenogenesis,” or asexual reproduction, the team said.

The findings will be published on the zoology journal website Zoological Letters.

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