Study on Avocado Pollinators in Western Australia

Miyuki  Taniguchi

doi:10.60867/00000159

Avocado (Persea americana) production in Western Australia (WA) relies heavily on the European honeybee (Apis mellifera) for pollination support. However, avocado flowers are not consistently attractive to A. mellifera, and reliance on a single managed pollinator species may increase vulnerability, particularly as honeybees are affected by pests and diseases, including the ectoparasitic mite Varroa destructor. To support more resilient avocado production systems, this study investigated native and non-Apis flower-visiting insects as candidate alternative or complementary pollination-relevant taxa in Western Australian avocado orchards. Fieldwork was conducted in avocado orchards in Carabooda and Pemberton during the 2019, 2020, and 2021 flowering seasons. Visual observations, passive trapping, morphological identification, and DNA barcoding were used to document avocado-associated insect assemblages. Several native bee and syrphid fly taxa were identified as focal putative avocado pollinators based on direct observation on avocado flowers and contact with floral reproductive structures. These included Lasioglossum bees, particularly L. lanarium, L. castor, and L. erythrurum, and syrphid flies, including Simosyrphus grandicornis, Melangyna viridiceps, and Eristalis tenax. Habitat analyses showed that the distribution and richness of focal insect taxa varied among orchards, blocks, and years and were associated with canopy cover, ground cover, and flowering plant species richness. To further investigate behavioural responses to avocado floral cues, avocado flower extracts were obtained using accelerated solvent extraction (ASE) and analysed using gas chromatography–mass spectrometry (GC–MS). Y-tube olfactometer assays showed that L. lanarium and S. grandicornis responded to avocado flower extracts in a flower-phase- and concentration-dependent manner. GC–MS analysis identified candidate volatile and semi-volatile compounds that may contribute to insect responses to avocado floral cues. Field trials provided preliminary evidence that selected compounds may influence captures of flower-visiting insects, although responses varied among taxa and compounds. This research provides a taxonomic, ecological, and chemical-ecological foundation for understanding insect taxa associated with avocado flowering in Western Australia. The findings identify focal putative avocado pollinators and associated flower-visiting taxa that warrant further investigation, but do not directly demonstrate pollination effectiveness or fruit-set contribution. Future studies should test pollen deposition, pollen tube growth, single-visit effectiveness, and fruit set to determine the contribution of these taxa to avocado pollination. Overall, this thesis contributes to the development of more resilient avocado pollination research and management strategies by identifying candidate insects, habitat factors, and floral chemical cues relevant to avocado flower visitation.

Study on Avocado Pollinators in Western Australia

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