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  • Writer's pictureMaggie James

Harnessing the Feeding Power of Pseudoscorpions

Following on from last month’s profile of Dr Ronald van Toor’s extensive work experiences, qualifications and contributions to apiculture in New Zealand, we explore the Canterbury scientist’s ongoing research into varroa devouring pseudoscorpions, and dive into his thoughts on New Zealand’s biosecurity programme. All while providing a “cathartic” experience for the esteemed scientist.

Beekeeping biosecurity and surveillance is a key area of interest for van Toor and since 2017 he has been a member of Apiculture New Zealand’s Biosecurity and Government Industry Agreement Focus Group. The committee aims to protect beekeepers from incursions, advising what actions can be taken by the industry with respect to organisms e.g. small hive beetle, and works closely with Government to help keep pests and disease out of New Zealand.

An adult pseudoscorpion eating a varroa mite next to an infested drone honey bee pupa. Photo: Robert Lamberts, PFR.

Of concern to van Toor is New Zealand does not have specific sentinel hives for honey bee surveillance programmes. Rather, under MPI mandate, hives are inspected and samples are collected from privately owned hives within high-risk zones to test for exotic diseases and pests (as detailed in Biosecurity Champions Helping to Protect our Bees).

Van Toor would like to see the surveillance programme extended to include the detection of early incursions of unwanted flowering species of plants. It could perhaps be put into a working system where beekeepers are paid to run hives, with pollen and bees sampled for DNA specific to weeds that are in flower.

“We are lacking government will to set up sentinel hives for early detection in hotspots around ports,” van Toor says.

“Within five kilometres of a beehive, this would be an economic and efficient way of using honey bees to do the job for us, instead of employing inspectors for flowering plant incursions.”

Molecular DNA techniques can be used to identify the organisms being brought into the hive, van Toor explains, noting that a microscope is not used and instead pollen has DNA removed.

Because honey bees will go to the most attractive flowering species for them, weed pest flowering species might have to be of a certain concentration before the system picks up their presence though. Despite that, van Toor would like to see the idea taken more seriously.

“There is potential for this system to work, but if Government are not prepared to fund, there’s no point in doing the support science,” he points out.

Confirmed ingestion of varroa destructor by pseudoscorpions

Among van Toor’s extensive work for the honey bee industry is research conducted between 2018-2021 into the ability of pseudoscorpions to consume varroa. Pseudoscorpions are related to spiders and New Zealand has 70 species, mainly native. The genus extensively researched by van Toor and found in various parts of the country is the Chelifer cancroides, probably introduced accidentally by European settlers in bee skeps, or farming equipment. The European chelifer has evolved with bees in New Zealand and at Plant and Food Research they investigated if they could control varroa in honey bee hives.

Chelifers first paralyse their prey with venom before eating them. A female chelifer lays one to three clusters of 30 eggs or less per year. At the 30°C temperature found in the brood chamber of hives, a female can produce 64 protonymphs (baby chelifers) per year. These young chelifers can eat varroa within a couple of days from hatching from an egg, but they only eat phoretic varroa and dead varroa are ignored, van Toor’s research found. This limits their ability to control the parasite, as they have access to varroa for only about four days of the varroa lifecycle, when the mites are roaming around the hive, before going into an uncapped brood cell. There is no evidence of chelifers harming bees.

Adult chelifers can live for four years. However, determining their varroa consumption rate is “tricky” van Toor says, as is a system that allows them to survive and thrive in a beehive.

The chelifers definitely consume varroa though. Van Toor developed DNA tests to undertake on the chelifer four weeks after their last feed, demonstrating varroa in their systems.

Dr Ronald van Toor, an advocate for specialised sentinel beehives for biosecurity purposes.

“We were happy our controls were valid and that the varroa DNA in the guts of the chelifers were derived from feeding on the varroa, and could have only come from the varroa mite,” he says.

This varroa DNA work had never been done before and he says he could not have undertaken it without his experience working with the Scottish Crop Research Institute in Scotland where he gained an understanding of the concept.

“We obtained three years funding from the Ministry of Business, Innovation and Employment to improve the killing potential of cancroides for controlling varroa by raising chelifers commercially in nest-bars. Now three years on, there will be no more research until there is additional funding from industry. However, we still maintain chelifer for research purposes,” van Toor says.

Because chelifers also could not remove phoretic varroa directly off bees, at the hive entrance, a device that removed varroa from bees to fall through a mesh bottom board to the chelifers residing below was added to the hive entrances. However, an effective varroa removal device would make the chelifers redundant. In one hive, van Toor observed a prototype device which could remove 20 varroa a day from the hive, with no apparent harm to the bee colony after 18 months. It would be a much cheaper form of control than using chelifers, but more research is required to improve the device’s efficacy before it can be commercialised and this would require additional investment, which is being sought.

The work is currently being written up for scientific publication, but more research which seeks to harness chelifer’s qualities is also underway, with van Toor and researchers from universities in Europe collaborating. They have extracted the venom from chelifers and identified a wide range of novel neurotoxic peptides that hold promise for use in organic pesticides. Some can also be used to control bacteria, and pathogens in humans, as there are antimicrobial peptides within the venom.

So, van Toor’s research continues and he could yet assist the apiculture industry more. For him, sitting back and discussing his work with this Apiarist’s Advocate interviewer over two articles has been rewarding.

“The process has been very cathartic and extremely reassuring for me,” he says, adding “I have always thought, until now, that I had not achieved much in life!”


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