Whether an insect will have a male or female offspring depends on the weather, according to a study led by Joffrey Moiroux and Jacques Brodeur of the University of Montreal's Department of Biological Sciences. The research involved experimenting with a species of oophagous（食卵的） parasitoid（拟寄生的） (Trichogramma euproctidis), an insect that lays its eggs inside a host insect that will be consumed by the future larvae. "We know that climate affects the reproductive behaviour of insects. But we never clearly demonstrated the effects of climate change on sex allocation in parasitoids," Moiroux explained. The study was carried out in collaboration with Guy Boivin of the Horticulture Research and Development Centre of Agriculture and Agri-Food Canada, and published in the May issue of the journal Animal Behaviour.

Cold impairs gender selection

As in bees, wasps, and ants, the gender determination of Trichogramma parasitoids is called "haplodiploid," that is, fertilized eggs produce female offspring, while unfertilized eggs produce male offspring, summarizes Moiroux. "It is possible to predict whether the parasitoid will lay a son or daughter by observing the presence or absence of a pause in its abdominal contractions at the time of spawning," he says. "A pause means the egg will be fertilized. Conversely, the absence of a pause means the egg will not be fertilized."

To know whether this particular behaviour is modified by climate, the researcher exposed female Trichogramma to three different temperatures: 34°C (high), 24°C (medium), and 14°C (low). The study found that when it was hot, females deliberately produced more males than at medium temperature -- at 34°C, the number of males produced increased by 80%.

The ability of Trichogramma to "program" the sex of their offspring is compromised, however, when the temperature is cold. "There was a physiological stress that was not related to the females' choice," notes Moiroux. "They intended to spawn as many females as during medium temperature, but the eggs were not fertilized after all. There were therefore more males produced at low temperature."