A collaborative research programme led by Bioeconomy Science Institute with Lincoln University, Bioprotection Aotearoa, the University of Auckland, Te Pūnaha Matatini and the Department of Conservation, is seeking to identify and replicate the chemical signals female redback spiders use to attract males in a bid to pave the way for an effective local trapping system to help protect both people and critically endangered native species that share its habitats.
The venomous Australian redback spider poses a growing risk to human health and conservation in Aotearoa. Researchers say a major leap forward in managing the threat has come with the discovery of the female spider’s sex pheromones.
In a world-first, the team revealed in Scientific Reports the four compounds that make up the sex pheromones.
Researchers then trialled them at one of the two known redback locations in Aotearoa – Central Otago – where spiders are severely impacting the critically endangered Cromwell chafer beetle (Prodontria lewisii) and the Alexandra chafer beetle (Prodontria bicolorata). The Cromwell chafer beetle is the only beetle in the world to have its own nature reserve, signifying the effort being made to save this precious taonga.
Lincoln University Associate Professor Cor Vink is the team’s spider expert, bringing many years of knowledge of widow spiders (Latrodectus), of which the redback (Latrodectus hasseltii) is one.
“After discovering that the native katipō has been known to interbreed with the redback spider, I modelled 30 years of climate data to understand where they could establish in Aotearoa. What we found points to a potential risk to human health as redbacks can establish in areas where wine grapes can be grown commercially,” says Associate Professor Vink.
“As more regions become drier and hotter, once unsuitable regions then become suitable. Plus, longer, drier summers in areas where populations already exist will extend breeding seasons. As these spiders spread, the risk of human contact rises, and as these are venomous spiders, their bites can be harmful.”
Noting that virgin female spiders attract males using pheromones and that males only mate once as they commit suicide while mating, Associate Professor Vink had a lightbulb moment, thinking this may be a way to control them. He says the only current control method is pesticides—an option many would avoid—while biological control is unsuitable, as it could also harm the native katipō.
“So this research is vital as it offers the potential for a safe and effective way of managing the redback population.”
Dr Andrew Twidle, pheromone identification expert from Bioeconomy Science Institute, is the programme leader and has led the charge in identifying the pheromones by comparing the silk from mated and virgin female spiders. To do this, the team collected redback spiders and their egg sacs from the Alexandra, Cromwell and Bannockburn regions and housed them individually in the laboratory, including the spiderlings once they emerged from their egg sacs. This provided a rich population to study, enabling them to identify the key compounds.
“Interestingly, we found that virgin females release sex pheromones from their silk in abundance compared to mated females,” says Dr Twidle.
“Mated females can store sperm for some time, so there’s no need to attract further males.
“While redbacks use both short and long-range pheromones for mate attraction, we hoped the long-range pheromone would be sufficient to attract males. After testing, we found that the males walked towards the long-range lure, stopped close to it and then moved away. Once we added the short and long-range pheromones together, we were successful in bringing the males to the synthetic lure.”
The next step in the MBIE-funded Smart Idea, recently extended to four years, was to test the four identified compounds in traps located across vineyards in Central Otago, in areas known to have redback populations.
“Straight away, we captured males—the best possible outcome,” says Dr Twidle.
“Along with trialling in vineyards, we will test traps in the Cromwell Chafer Beetle Nature Reserve. This is significant because, following the breakthrough in identifying sex pheromones, designing a trap that does not harm other species is a must. As we complete more extensive field tests, we’ll refine our trapping system to see if we can reduce the redback population in the reserve.”
Associate Professor Vink explains how quickly this invasive pest can proliferate and become a major concern.
“A mated female can store sperm for several months and produce up to 20 egg sacs, each producing up to 200 spiderlings. Redbacks can also interbreed with siblings without adverse effects. So, it only takes one mated female arriving in a new location for a population to establish.”
The redback’s ease of spreading is why Associate Professor Vink believes this technology could have applications both here and internationally. During the 1990s, they were found in Osaka and have since been detected throughout most of Japan, highlighting their invasive nature in areas densely populated by humans. In contrast, their spread in more sparsely populated Aotearoa has been much slower.
Posing a quarantine threat for much of the world, redbacks are a constant threat. This innovative pheromone-based tool could offer an easy way to detect and manage them, the research teams says.
