Evidence is mounting that pollinators of crop and wildland plants are declining worldwide. Our research group at UC Berkeley and UC Davis conducted a 3-year survey of bee pollinators in seven cities from Northern California to Southern California. Results indicate that many types of urban residential gardens provide floral and nesting resources for the reproduction and survival of bees, especially a diversity of native bees. Habitat gardening for bees, using targeted ornamental plants, can predictably increase bee diversity and abundance, and provide clear pollination benefits.
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.
In 2009 the USDA-NRCS asked the Urban Bee Lab at the University of California, Berkeley if urban bee-flower knowledge could be used to attract native bees to farms in Brentwood, Contra Costa Co. in Northern California. The overarching question was, could native bees play a role in supplementing honey bees by providing pollination services for crop flowers? If so, how many native bee species were visiting farms and how frequently did they occur?Eight small farms (4-60 ha) were selected to investigate this question; four were control and four were treatment farms where bee habitat gardens were constructed. Habitat gardens were stocked with native and non-native ornamental plants known to attract native bees (and honey bees).Bees were monitored yearly in spring at each farm from 2010-2016 to evaluate species richness and abundance, which yielded several findings:I. Farms near urban areas and a creek were consistently more attractive to diverse and abundant bee speciesII. Inconsistent bee garden maintenance and major changes in farm operations in other farms resulted in consistently lower measurements of bee richness and abundanceIII. Over the seven-year monitoring period, 144 bee species were recorded among all farmsIV. Nearby urban areas had most of the same species as the agricultural areas, suggesting a relationship of bees moving between two areasV. A total of 23 diverse native bee species were recorded from apple, berry, and cherry flowers, and many of them in substantial numbers, indicating that native bees were providing pollination servicesFinally, maintaining frequent professional contact with growers was considered crucial in conducting research over the long term. These contacts were also critical in designing outreach packages to growers who expressed interest in applying our native bee findings to their farming operations.
ISHS XXX International Horticultural Congress IHC2018: VII International Symposium on Tropical and Subtropical Fruits, Avocado, II International Symposium on Jackfruit and Other Moraceae and II International Symposium on Date Palm Native pollinators of avocado as affected by constructed pollinator habitat gardens in southern California
