Blow flies (Diptera: Calliphoridae) ability to pollinate Hass avocado trees within paired tree enclosures

Abstract

AbstractAvocado pollination remains a major focus for producers as fruit‐set is typically very low (less than 1%). Most avocado producers in Australia utilize honey bees (Apis mellifera) to improve yield; however, there are risks with reliance on one species for future pollination security. Flies regularly visit flowers including avocado flowers. However, their pollination ability is poorly understood. To address this, visual observations of flies foraging in avocado orchards along with releases of two species of blow fly (within replicate enclosures of paired avocado trees; Hass and Type B cultivars) were conducted at a commercial orchard in south‐western Western Australia. Visual observations during flowering identified that most non‐bee flower visits were by hover flies (Melangyna viridiceps and Sphaerophoria macrogaster) and blow flies (Calliphora vicina and C. albifrontalis). Hover flies mostly foraged on flowers in the morning while blow flies were generally more active in the afternoon. Pollination as measured by harvestable fruit was higher by C. dubia (45.6 ± 10.0) than by C. albifrontalis. (26.3 ± 6.6). Compared with open trees pollinated by bees and other insects present, trees pollinated by C. dubia produced nearly two‐thirds the number of fruit. When presented with equal numbers of avocado flowers, C. dubia fed three times more often than C. albifrontalis, which may explain their higher pollination rate. Both C. dubia and C. albifrontalis transferred on average one pollen grain/flower visit. Blow flies improved avocado yield above no insect pollinators (3 fruit/tree) by an average of 31 fruit/tree (across both fly species), but considerably less than trees in the open pollinated by honey bees (128 fruit/tree). Future trials with multi‐tree enclosures will assess avocado pollination by different fly species. This study demonstrated that at least one species of blow fly could pollinate avocado and provide potential as a managed pollinator in Australian horticulture.