BUSINESS new pollination agents
Three fly species were tested on Hass avocados in 2023: Eristalis tenax (left), Calliphora dubia (center), and Calliphora vicina (right).
Fly enclosures around Hass avocado trees at Capel during the 2023 flowering period.
Fly success in avocado orchards
In November 2023, the final avocado pollination field trial for the national project Managing Flies for Crop Pollination concluded after the flowering season.
Words David Cook, Research Scientist, Department of Primary Industries and Regional Development
FUNDED by Hort Innovations and avocado levy contributions, this study explored innovative pollination solutions to address the reliance on honey bees for pollination needs and to future-proof food production by having a range of managed pollination agents.
Three fly proof enclosures were built around 29 avocado trees in Capel, Western Australia. The enclosures contained 26 Hass trees and three polliniser trees (Edranol and Ettinger). One of three fly species was released into each enclosure, these included two blowfly species (Calliphora vicina and Calliphora dubia) and the hover fly Eristalis tenax.
In total, 15,000 blowflies (C. vicina and C. dubia) and 5,000 E. tenax were released per enclosure. Simultaneously, managed honey bee hives were introduced into the open orchard which were free foraging, to gauge comparative pollination success. The flies remained in the enclosures until the end of flowering, after which the netting was removed. Fruitlet formation, visually assessed two weeks later, was compared between enclosed trees and those open-pollinated by honey bees and other insects. Notably, insect presence in the orchard was low during flowering, highlighting the decline in wild pollinators aiding avocado production.
Results are promising, the increased density of 15,000 flies of both C. vicina and C. dubia significantly improved pollination, with C. vicina performing as effectively as honey bees and C. dubia outperforming them. E. tenax enclosures showed higher fruitlet formation than open orchard trees pollinated by honey bees. Observations confirm the need for supplemental pollinators like flies to enhance avocado pollination success in areas with declining wild insect activity.
A more detailed assessment in February 2024 revealed that fruitlet formation in trees enclosed with flies was comparable or superior to those in open orchard conditions.
Among the three fly species, E. tenax produced nearly double the fruitlets of honeybee-pollinated trees, and C. dubia increased fruit count by 30% (see Figure 1).
A hot, dry spring in 2023 limited C. vicina’s activity, as this blowfly favours cooler weather. Additionally, the noticeable lack of insects in the orchard reaffirms the ongoing global decline of pollinating insects, underscoring the importance of managed fly pollination alongside honeybees.
FIGURE 1: Visual ranking and fruitlet count for trees enclosed with Eristalis tenax, Calliphora dubia, or Calliphora vicina, as well as honeybee-pollinated trees in the open orchard
FIGURE 2: Mature fruit count (a) and yield (b) per tree for trees under fly enclosures with Eristalis tenax, Calliphora dubia, or Calliphora vicina, compared to honeybee-pollinated open orchard trees
By August 2024, mature fruit counts indicated that trees pollinated by E. tenax yielded the highest number of mature fruits and total yield per tree, followed by those pollinated by C. dubia. Both outperformed the trees pollinated by honeybees alone (see Figure 2).
With these successful results, further work on fly pollination is set to continue in 2025, supported by the avocado industry and commercial initiatives. E. tenax will be the initial focus for scaling up as a managed pollination agent.