A study by the Tasmanian Institute of Agriculture (TIA) has highlighted the impact Varroa mite will have on crop pollination in Tasmania if the parasitic mite becomes established in the state.
The study was prompted by the spread of Varroa on mainland Australia which is wreaking havoc on European honey bee colonies. Managed honey bee colonies can be monitored and treated for Varroa by beekeepers, but feral honey bee colonies are unmanaged and likely to be at greater risk if Varroa becomes prevalent in Tasmania.
TIA entomologist Dr Jonathan Finch said many agricultural crops in Tasmania rely on feral honey bee colonies for pollination.
“International experience suggests that Varroa can reduce feral honey bee populations by more than 90 per cent within several years of establishment. A major decline in feral honey bees could reduce pollination services currently supporting Tasmanian crops, including fruit, berry and seed crops,” Dr Finch said.
“Apple production, particularly in the Huon Valley, showed the strongest evidence of reliance on background pollination services, including feral honey bees.
“If feral honey bee populations decline due to Varroa, apple growers who currently use few or no managed hives may need to review their pollination plans.”
The study found that vegetable seed production is highly dependent on managed hives.
“If Varroa increases the cost and complexity of maintaining strong hives, that could have implications for seed growers as well as fruit and berry growers,” Dr Finch said.
Tasmania is currently Varroa-free but if it were to enter the state the impacts to agricultural industries would be significant.
The project investigated how Tasmanian fruit, berry and vegetable seed crops are currently pollinated.
The study examined extensive grower and industry survey data. Growers also provided valuable information about how many managed honey bee hives they place in crops during flowering.
Dr Finch said the project provided a practical way to identify crops and regions where background pollination plays an important role.
“Managed and feral honey bees cannot be distinguished by eye in the field, so directly measuring the contribution of feral bees is difficult,” he said.
“By comparing grower-reported hive use with published benchmark rates, we can identify crops where managed hive use appears lower than expected. That does not prove all the remaining pollination is coming from feral honey bees, but it does indicate where background pollination services may be important.”
Researchers are urging Tasmanian growers who rely on managed hives to talk with their beekeepers about Varroa preparedness, including hive monitoring, treatment plans, hive strength, future availability and potential changes in pollination costs.
“The message is that growers should understand how much they currently rely on managed hives versus background pollination, and plan ahead for a future in which feral honey bees may be less abundant and managed hives may become more expensive or harder to source,” Dr Finch said.
