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Female-only cockroach reproduction boosted in groups of 3 or more: research

SAPPORO -- The ability of female American cockroaches (Periplaneta americana) to reproduce without males is boosted in groups of three or more females, experiments conducted by a team at Hokkaido University indicate.

    The research announced by the team on March 13 suggests that other types of cockroaches known to be parthenogenetic, being able to reproduce without males, may possess the same qualities as the American cockroach, which is found all over Japan.

    Some types of pest control involve attracting the males with pheromones and killing them, hindering the insects' ability to reproduce. The latest findings, however, suggest that such methods may have little effect in controlling the American cockroach without also targeting the females.

    The researchers created 11 patterns of cockroach groups, from a male and female pair, to a female alone, to between two and five females, and raised at least 14 of each group in containers. They examined how long it took for the groups to form oothecae, or egg cases, two times.

    They found that in groups of three or more females, it took around 10 days on average to form the first ootheca, around three days faster than a sole cockroach. The second time around it was around nine days faster. When starting with at least 15 cockroaches, a colony could be maintained for three years or more with females alone. When the antennae of cockroaches, which perceive smell and objects, are removed, the formation of oothecae is delayed. This fact led researchers to conclude that the antennae are needed to confirm the existence of other females.

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