Pheromone chemical could control redback spider spread

Monday 22 October 2018

Bryan SA, Vink CJ, Barratt BIP, Seddon PJ, & van Heezik Y. 2017. Investigation of two new putative pheromone components of the invasive Australian redback spider, Latrodectus hasseltii, with potential applications for control. New Zealand Journal of Zoology.

Redback spider

Australian redback spiders need to be controlled because they prey on endemic New Zealand species. Image: Bryce McQuillan. All Rights Reserved

The invasive Australian redback spider (Latrodectus hasseltii) needs to be controlled in New Zealand because it preys on at least 10 endemic species, including the endangered Cromwell chafer beetle.

Redback spiders were first found near Wanaka in 1981 and have expanded their range to other parts of Central Otago and New Plymouth. Climate and habitat simulations have shown that they could spread to other parts of New Zealand, including Auckland and Christchurch.

Unmated female redback spiders produce a special combination of chemicals, called a pheromone, on their silk. The pheromone is carried in the air to attract nearby males to mate. Male redbacks typically only mate once, because during copulation they offer themselves to the female to be eaten. 

This study, conducted by scientists from Canterbury Museum, the University of Otago and AgResearch, aimed to determine which of the chemicals in the airborne pheromone attracted male redbacks. It analysed the response of male redback spiders to two chemicals found on the silk of virgin but not mated females: butyric acid and isolvaleric acid.

The researchers compared the responses of male redbacks to paired combinations of a control, virgin silk, butyric acid and isovaleric acid. Their experiments found male redbacks were equally attracted to butyric acid and virgin silk.

This led to the conclusion that butyric acid – also the chemical that gives vomit and parmesan cheese their distinctive smell – is the pheromone component that attracts male redbacks.

Butyric acid could be used to control the redback population by luring male redbacks into traps. However, further research is needed to identify the ratio of chemicals needed to make effective pheromone traps for male redbacks.

Trapping male redbacks would likely be a particularly effective way to control the population; because males only mate once, other males can't fill the gaps left by trapped males by mating with multiple females.

The University of Otago, Otago Museum and the Whakatane Historical Society Scholarship Trust provided funding and support for this research.

See our media release here

See the paper here

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