Loss of horticultural pollination services from wild insects following bushfires (PH20002)

What was it all about?

This project estimated the impact of the loss of pollination services by conducting a case study of an extreme event (major bushfire) on wild pollinator communities and the pollination services they provide to a focal horticultural crop (apple).

Challenge

Extreme weather events, such as bushfires and floods, are important features of the Australian environment and are predicted to increase in frequency with climate change. However, little is known about how this may impact crop pollination.

In general, extreme events can cause major losses of both pollinating insects and floral resources, but these losses could be either short or long-term so research was needed to measure the extent and nature of losses and how quickly they can recover. To address these issues rigorously, it is important to measure pollination services before an event occurs in order to quantify changes and potentially attribute them to the extreme event.

Response

A unique opportunity to investigate how bushfires disrupt pollination presented itself after a three-year study of apple pollination in Bilpin NSW through Hort Frontiers project Healthy bee populations for sustainable pollination in horticulture (PH15001) was followed by a major bushfire event in 2019/20. Under PH15001 the contribution of wild honeybees to orchard pollination was estimated, therefore these learnings will be combined with post-fire pollination surveys to provide a case study.

The research team aimed to survey landscape floral resources every 6-8 weeks throughout the year and conduct on-crop pollinator surveys and honeybee marking each crop flowering season (2020-2022). However, due to COVID travel restrictions (2021) and hive movement restrictions (2022), they were only able to conduct marking in 2020, and on-crop surveys in 2020 and 2022. In contrast, landscape floral resources surveys were only minimally impacted.

Benefit

This research delivered new knowledge on the impacts of bushfires on floral resources, wild pollinators, and pollination services to apples crops, as well as an assessment of how extreme events may impact wild honeybee populations and the services they provide.

Overall, the research found substantial changes in the plant species providing floral resources to pollinators in the burnt landscape around the farms, but little change in the non-crop (mostly weedy species) plants on farms. The research team saw a decrease in the number of flower visits by honey and stingless bees (some measures) and an increase in visits by flies (all measures). However, the total crop visitation by the two main pollinators (honey and stingless bees), which account for almost 90 per cent of all visits, was within the range of what was observed across seasons before the fire event. A dramatic result in 2022 was an almost complete absence of stingless bees from apple flowers, but this is well explained by the unusually cool, wet weather under La Nina conditions.

In the marking experiment, about 50 per cent of honeybees visiting the crop were not from hives on the farm, so either from wild colonies or distant managed hives. Interestingly, the research team also recorded marked bees from one farm visiting the same crop on other farms up to 1.5 km away. This case study provides a fairly simple way to quantify the contribution of managed on-farm hives versus wild honeybees and has potential use in other cropping scenarios. It also suggests that if varroa substantially reduces wild honeybee colonies, as now expected, orchards may suffer considerable loss of important “free” pollination services from wild honeybees. Other regions and crops that rely significantly on pollination by wild honeybees will also face this challenge.