Whether an insect will have a 'boy' or 'girl' offspring depends on the weather and temperature, according to a new study.
The research led by Joffrey Moiroux and Jacques Brodeur from the University of Montreal involved experimenting with a species of oophagous parasitoid (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 said.
"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 said.
"A pause means the egg will be fertilised. Conversely, the absence of a pause means the egg will not be fertilised," said Moiroux.
To know whether this particular behaviour is modified by climate, the researcher exposed female Trichogramma to three different temperatures: 34 degrees Celsius (high), 24 degrees Celsius (medium), and 14 degrees Celsius (low).
The study found that when it was hot, females deliberately produced more males than at medium temperature – at 34 degrees Celsius, the number of males produced increased by 80 degrees Celsius.
The ability of Trichogramma to "programme" 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," noted Moiroux.
"They intended to spawn as many females as during medium temperature, but the eggs were not fertilised after all. There were therefore more males produced at low temperature," said Moiroux.
In insects, fitness is positively correlated with the size of an individual, and this relationship is greater in females than in males.
"Larger females live longer and have higher fertility, whereas males are relatively less penalised than females when they are small," Moiroux said.
"It is therefore advantageous for mothers to have the largest female offspring possible and use hosts that will produce smaller offspring for males," said Moiroux.
However, in a hot environment, offspring are smaller. This is why females tend to use hosts found in hot areas to produce males and reserve hosts in colder areas (eg, in the shade of hedges) to produce females.
The study was published in the journal Animal Behaviour.