A study to ultimately protect bees against a deadly parasite has tested more than 400 samples. Photo: John Roberts.
Canberra researchers have revealed a non-invasive way to detect a deadly pest.
CSIRO and University of Canberra researchers, as well as other collaborators, have developed a species-specific PCR test (polymerase chain reaction) capable of detecting varroa mites.
Lead author Dr John Roberts has spent 15 years studying the mites, a parasite that attacks honey bees. Dr Roberts now leads the CSIRO’s bee pathology research area.
“Australia has been the last country to get varroa mites [detected in June 2022],” he told Region.
“That’s where we’ve been able to look at it from a different perspective.”
The mites do not pose a risk to human health or food safety but attack the bees, eventually killing them. The parasite also leaves the bees more susceptible to other pests and diseases.
The study is the first to directly compare environmental DNA (eDNA) detection with traditional methods used to detect varroa mites.
Researchers use the PCR test to identify the presence of varroa mites in sample hives through its eDNA, the DNA shed or left behind by an organism in its environment.
“The PCR test is essentially the same as PCR tests you would do for COVID,” Dr Roberts said.
“We’ve just designed it in a way that is very specific – it’s not going to give false positives from bee DNA … it can detect very low amounts of varroa eDNA.”
Samples were taken from honey stores, the hive entrance and brood frames within beehives from New Zealand and Australia, plus the Chatham Islands which are free from the mites.
Researchers found each site had benefits. For example, samples from brood chambers showed greater sensitivity at low mite parasite loads, but it was a more invasive method.
The study paper also proposes using swabs taken from a hive’s surface as a non-invasive option during winter, particularly in routine testing around its spread.
“[We] reliably detected varroa eDNA from hive surface swabs,” the study paper reads.
eDNA makes Australian biosecurity programs more sophisticated. Photo: John Roberts.
Dr Roberts said the work showed eDNA as an alternative way to detect varroa mites, especially in early infestation stages.
The test’s detection sensitivity is comparable to an alcohol wash – a method that kills the sampled bees.
“Bee colonies can handle that, it’s unlikely to be a big impact on them in a modest level of monitoring,” Dr Roberts said.
“It still puts a bit of pressure on that hive and can also be a factor in the frequency of monitoring for some beekeepers as well.”
He said while the simple PCR test could be carried out in any molecular diagnostics lab, it needed specialised equipment and would be problematic for beekeepers to do it themselves.
“It still requires a lab,” he said.
“For now, it’s something we could be using as part of our biosecurity programs.”
He said keeping tabs on the parasite’s presence would be a priority, especially in Tasmania and Western Australia where it hadn’t been detected.
The next frontier for researchers will be refining the test.
“When you have very low mite levels, the reliability of the test reduces … much less varroa eDNA or varroa DNA in the hive, so there’s a lot more chance that comes into it,” Dr Roberts said.
“[It can] affect whether your sample has picked up enough varroa DNA for detection.
“We think we can probably do that by increasing the number of samples we take. The more sampling we take, the better chance we have of picking up those low concentrations of varroa DNA.”
The paper, Environmental DNA Methods for Detection of Varroa destructor in Honey Bee (Apis mellifera) Hives, is available online.
