- Author: Ben Faber
Avocado is a neotropic tree which has been commercialized world-wide, yet it's native pollinators have been little studied. The most frequently studied pollinator has been the old-world insect, Apis mellifera. In commercial orchards it is common practice to introduce honey bee colonies, although it is not clear exactly what the extent of their effect is in California orchards in the presents of native bees and other pollinators. The purpose of this study is to evaluate the range of avocado flower visitors and to assess whether those numbers can be affected by the introduction of gardens that might promote their numbers in the orchards during the avocado bloom period.
Measuring pollinator performance is difficult because of weather impacts, alternate bearing habit and the high level of fruit shedding in avocado. In this study, pollination gardens have been established in three avocado orchards in coastal California near Santa Barbara, just north of Los Angeles. These gardens have been established since 2014 with a variety of perennials that can supply nectar and pollen over the year and especially during the prolonged flower season. The three orchards where the gardens are established each exceed 40 ha. Gardens have been established in just one portion of the orchards, so that flower visitation can be assessed near and far from the gardens. The individual visitation activity of flower visitors was evaluated per unit time and their abundance on avocado flowers near the gardens and away from the gardens. Visitation was also similarly assessed on the pollinator gardens. Pan traps were also used to assess the presence of native bees in the orchards.
The most abundant visitors in all years have been Syrphid spp. along with a variety of other flies and wasps. The most abundant native bee species have included Ceratina, Halictus, Agapostemon and several andrenid species. The highest diversity and abundance of visitors has occurred after the high rainfall year of 2016/17 after previous drought years.
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- Author: Ben Faber
Gordon Frankie a bee biologist at UC Berkeley and I are doing a study to ultimately identify what plants could grown in avocado orchards to attract more honeybees, as well as other pollinators and potential biocontrol agents. There are five orchards in Ventura and Santa Barbara where we have been monitoring flower visitation by different insects in order to get a baseline of what is there before introducing potential pollinator/biocontrol attractants. The numbers are finally in for last spring avocado bloom. Virtually no honeybees, but significant numbers of syrphid flies. They are also called flower flies or hover flies. They superficially resemble bees. They are predatory as larvae, primarily feeding on aphids. Then they become important pollinators as adults. They are not as efficient as honeybees because they lack all the hairs on their bodies where pollen gets stuck and carried to female flowers. The cause of the honeybee decline has many causes, but the most likely one is the drought in the avocado growing areas. There just aren't any plants in the foothill areas to provide pollen and nectar year round.
Images of egg, larvae (going after aphids) and adult syrphid flies