A native bug's life: avoid sex, live longer

The University of Auckland's Morgane Merien has been working with the Clitarchus hookeri - possibly our most common stick insect, and one of our strangest species. Photo / Supplied

If you have abstain from sex, you live longer.

At least that's if you're one of New Zealand's weirdest native species.

The University of Auckland's Morgane Merien has been working with Clitarchus hookeri - possibly our most common stick insect, and known for hitching rides to the countries on the other side of the world.

Biologists also regard the so-called smooth or ti-tree stick insect for another strange ability - females of the species are facultative parthenogenetic, or have the ability to either mate with males or reproduce asexually.

Merien collected 80 males and 60 females and split the females into three groups: one group was given a single mate, another multiple mates, and the third, no mates.

Her research showed a direct correlation between lifespan and the number of mates a female had, with multiple-partner females having the shortest lives, monogamous females living slightly longer and asexually reproductive females out-living everyone else.

"We know there are a number of biological reasons why sex may be costly for female insects including physical harm during mating, increased energy expenditure and a higher risk of predation," Merien said.

"But it's great to have some clear evidence on the link between sexual reproduction and lifespan."

The study also found that asexual reproduction, where offspring develop from unfertilised eggs, resulted in a higher number of eggs laid than either monogamous or polyandrous females.

There was, however, one piece of good news for promiscuous females: they were more likely to produce viable offspring than monogamous females.

One factor could be the biological imperative of "trading up" - females exposed to multiple partners have the opportunity to mate with a higher-quality male if the first one doesn't quite make the grade.

The stick insects are also found in the Isles of Scilly, a small archipelago off the southern coast of England, and are thought to have got there after hatching from soils shipped with New Zealand plant material more than half a century ago.

Soon after they arrived, they evolved to reproduce without the need for male sperm, effectively becoming just like the asexual New Zealand prickly stick insect, which reached the islands around the same time.

Scientists recently brought some back to New Zealand to learn whether naturalised females could still reproduce their old way - or were over men for good.

Merien, graduating this week with a Bachelor of Science with Honours, recently enrolled in a PhD to continue studying the insects.

The New Caledonian-born researcher is following in the steps of her mother, who graduated from the university with a PhD in biology in 2016.

"I loved working with them in the lab, although it was time-consuming and busy every day, the research went really well and if I possibly can, I'd like to have a career in entomology."

A bug's life

• Possibly our most common stick insect, Clitarchus hookeri is green but sometimes also brown and red in colour, and typically measures about 90mm.

• More than half a century ago, the species arrived in Britain in the form of eggs buried in shipped New Zealand plant material.

• Turning up amid the colourful and diverse plant life of the Isles of Scilly, female Clitarchus hookeri managed to achieve parthenogenesis - asexual reproduction without the need for its male counterparts back home.