The Heat Is Online

Climate found to determine gender of insects

Study: Climate Affects Gender of Parasitic Insect Offspring

The Latin Post, May 23, 2014

Temperature, that is to say, the weather, can affect the determination of sex in insect offspring, says new research out of the University of Montreal in Canada.

According to a study led by Joffrey Moiroux and Jacques Brodeur of the school's Department of Biological Sciences, and published in the May issue of the journal Animal Behaviour, an insect will either have a male or female offspring depending on how hot or cold the climate happens to be.

The research focused on a species of oophagous parasitoid known as Trichogramma euproctidis, an insect that lays its eggs inside a host insect, which will then be consumed by the future larvae.

 "We know that climate affects the reproductive behavior of insects. But we never clearly demonstrated the effects of climate change on sex allocation in parasitoids," Moiroux said in a news release.

As with bees, wasps and ants, the gender determination of Trichogramma parasitoids is called "haplodiploid," which means fertilized eggs produce female offspring while unfertilized eggs produce male offspring, Moiroux explained.

"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 fertilized. Conversely, the absence of a pause means the egg will not be fertilized."

In order to determine if that particular fertilization behavior is modified by climatic changes, the research team exposed female Trichogramma to three different temperature ranges: 34 degrees Celcius (93.2 degrees Fahrenheit ), which was considered high; 24 degrees Celsius (75.2 degrees Fahrenheit ), medium; and 14 degrees Celsius (57.2 degrees Fahrenheit ), which was considered low.

The experiments revealed when the temperature was hot, the female insects deliberately produced more males than at medium temperature - at 34 degrees Celcius, or 93.2 degrees Fahrenheit, the number of males produced rose by 80 percent.

Conversely, the Trichogramma's ability to "program" the sex of its offspring appeared compromised, when the temperature was cold, said Moiroux. "There was a physiological stress that was not related to the females' choice...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."

In insects, fitness has been shown to affect the size of individuals, particularly with females more than males.
"Larger females live longer and have higher fertility, whereas males are relatively less penalized 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."

But, it was found that insect offspring tend to be smaller when the weather is hotter - which is why, said Moiroux, females tend to use hosts found in hot areas to produce males and hosts found in colder areas to produce females.