Hedgerow Gardens Provide Floral Resources for Diverse Insect Visitors to Avocado Fowers in Southern California

In 2010, we initiated research on pollinator habitat gardens (hedgerows) in 8 stone fruit orchards in Brentwood, in northern California. One goal was to install native and non-native plant species in linear gardens to attract native bee species, which we used successfully statewide (Frankie et al., 2005, 2009, 2014). Our 2010-2018 Brentwood research demonstrated that planned hedgerows attracted diverse native bee taxa (144 species), and that many species (23) also visited a variety of crop flowers (Frankie et al., 2018). In our current study, we applied these past experiences to avocado orchards in southern California to examine avocado flower visitors in installed habitat gardens, or hedgerows. Gardens were installed in 3 avocado orchards in Santa Barbara and Ventura Counties to evaluate native bee diversity and abundance between hedgerows (treatment sites) and surrounding orchards and wildlands (control sites). Native bees and Western honey bees (Apis mellifera) were monitored at each orchard over 6 years from 2014-2019, with supplemental collections done in 2020-2021. Hedgerow sites had greater bee species diversity, and slightly greater bee abundance. At the 3 orchards, 105 bee taxa were recorded from standardized monitoring periods during avocado flowering season (March-May). Honey bees were found to visit many hedgerow plants, and avocado growers indicated the importance of having floral resources year-round for the bees. 'Lisbon' lemons are often grown in close proximity to avocado trees, and control of Citrus pests, especially the Asian citrus psyllid, was factored into variables impacting avocado visitors. At least 60 insect taxa were recorded visiting avocado flowers. Half of these were native bee taxa, and the rest were flies (especially syrphids), wasps, and beetles. Factors impacting long-term bee monitoring results included unusual weather conditions, wildfires, and possible pesticide drift. Frequent communication with growers was critical for sharing findings, collaborating in plant installations, and addressing questions.