They’ve been around for the past 300 million years, outlasting the dinosaurs and teaming up with evolution to outsmart our attempts to get rid of them. Now, Japanese researchers at Hokkaido University have revealed yet another reason why we have been unable to put a dent in their populations: female solidarity.
Cockroaches, along with termites, snakes and sharks, have long been known to be capable of “virgin birth” or parthenogenesis, a form of asexual reproduction that occurs without fertilization. What is less known are the factors that trigger this process. Is the absence of male cockroaches the only condition necessary for asexual reproduction to take place or does the social environment play a part too? Given that cockroaches are social creatures that live in groups, the Hokkaido University researchers believed that there had to be factors other than male-absent conditions.
To test their hypothesis, the researchers conducted 11 sets of experiments with different groups of American cockroaches, a common pest. The control group comprised a male and female that were allowed to mate. Others comprised virgin females that were kept in isolation; in groups of up to five; and with castrated males. In addition, the researchers also added female sex pheromones – which are secreted in greater quantities by virgin females than those that have already mated – to containers housing single roaches to see if they would regard it as a male-absent signal and produce more eggs as a result.