The use of protective covers for crops can lead to a decline in honey bee (Apis mellifera) foraging and colony strength, according to a recent study funded by Zespri and the Ministry for Primary Industries Sustainable Farming Fund and conducted by Plant & Food Research.
Horticultural industries worldwide are increasingly relying on protected cropping for food and fibre production. Understanding the effects of protective covers on honey bees is essential for developing new management options for beekeepers and orchard managers.
Plant & Food Research scientists studied honey bee foraging dynamics, colony health and pollination services in Bay of Plenty kiwifruit orchards that were either covered with hail netting or uncovered. They found that colonies in the covered orchards lost adult bees at a faster rate than the colonies in uncovered orchards.
“The study illustrates the need for strategies to improve the effectiveness and sustainability of honey bee pollination in these environments,” says Dr Lisa Evans, who led the research.
Global food production relies on managed and unmanaged animal pollinators. Protective covers (greenhouses, poly-tunnels, and hail netting) have increasingly been used to enhance crop quality and yield by safeguarding against factors such as weather, plant pests and pathogens. But these covers can restrict the movement of pollinators, with negative consequences for hive health and pollination.
In this study the covered orchards showed an acute loss of foragers – with more than 40% of marked bees under cover failing to return to the colony after their first flight. This is three times as many bees as those lost from hives not under cover.
There were also changes in the behaviour of successful foragers – under cover they foraged for shorter time periods and completed fewer foraging trips. During direct observation of bees in the covered orchard, very few bees were seen returning with pollen, suggesting that few were foraging successfully.
The loss of foraging bees and behavioural changes could be explained by several factors, including orientation failure or ‘light traps’ within the foraging environment. Covers may also restrict bee access to additional resources that they need for healthy development.
Plant & Food Research is now working on several projects in both New Zealand and Australia to further understand pollination in protected cropping environments, and to directly test methods for improving honey bee performance under nets. The team has also been working to develop strategies for managing other pollinators, such as bumble bees and flies, which seem to be less negatively affected by covers.
Source: Plant & Food Research