A Rotorua scientist has been recognised for her work in helping to discover a biological control for an exotic pest that was destroying a “critical source” of pollen and nectar for honey bees.
Scion forest entomologist Stephanie Sopow was awarded the Peter Molan trophy for exceptional contribution to apiculture science at Apiculture New Zealand’s annual conference, which hosted 700 delegates from the apiculture industry at the Rotorua Energy Events Centre in June.
The arrival of the giant willow aphid to New Zealand in 2013 has caused a broad range of impacts not only on host trees but also on bees and beekeepers, as a result of bees and wasps harvesting the aphid honeydew.
Sopow has been leading work on the biological control of giant willow aphid with a parasitoid as part of the Ministry for Primary Industries’ Sustainable Farming Fund project “Management of Giant Willow Aphid”.
Sopow said it was “lovely” to have received the award.
“The apiculture community has been very supportive throughout the duration of the project.”
Sopow said the aphids suck the life out of willows, depleting them of liquids and weakening the trees, which were widely used in New Zealand for slope stabilisation, flood protection and as vital pollen and nectar resources for honeybees in the early springtime.
Feeding aphids secrete a sticky honeydew that pest wasps were also drawn to, which created a twofold problem for the beekeeping industry, she said.
“The honeydew leads to an increase in pest wasps that kill honeybees and rob honey. Beekeepers also lose productivity because honey produced from this honeydew is granular and can’t be extracted.”
Pesticides were not an option because the aphids would transfer them into the honeydew, putting honeybees and birds at risk, she said.
Sopow and her team’s discovery of a parasitoid wasp from California that preys on giant willow aphids sparked three years of containment and host specificity testing, showing the imported wasp only attacked the giant willow aphid.
The parasitoid wasp was released in the autumn of 2020 and 2021, resulting in widespread coverage across New Zealand. After monitoring the early impact of the wasp on giant willow aphid populations, Sopow said the proportion of aphid-free trees increased and aphid numbers dropped.
As a biological control, the wasp was continuing to be found in new areas and the giant willow aphid was becoming more difficult to locate, she said.
“Normally it takes years. I am really pleased with how it has gone. I count myself lucky that I ended up with a good system that is doing so well.
“It is important in a multitude of ways.”
Sopow said the biological control programme had officially wrapped up but they had been monitoring to determine the spread of the biological control agent - particularly in the South Island, where there were “fewer eyes on the ground”.
They were able to do some surveys through May and June this year to determine if it had spread in the South Island and the impact so far did not seem as strong as it was in the North Island, she said.
An Apiculture New Zealand spokeswoman said willow species were a critical source of pollen and nectar for honey bees early in the honey season when other sources could be scarce.
“The large populations of giant willow aphids that have been found in New Zealand since 2013 have depleted willow trees of the nutrients and moisture they need to survive, resulting in sick and dying populations.
“In addition to this, the aphids secrete honeydew as they feed. Vespid wasps that feed on the sugary honeydew secreted by the aphids thrive as a result and become a hazard to bee colonies in these areas.”
The spokeswoman said although biological controls usually took many years to show their full benefits, the early results from Sopow’s work were “already exceeding expectations”.
“If this trend continues it will make a great difference to the health of bee colonies in affected areas.
“Bee health is a priority for Apiculture New Zealand and the amazing work that is done by researchers such as Stephanie Sopow is invaluable to our sector. This award was one way the apiculture sector could show its appreciation for Stephanie’s contribution to the health of our bees.”