Factors influencing insect visitation to apple and cherry flowers

Abstract

Animal mediated pollination is essential to the production of many plants that humans utilise for food. Managed pollination services rely heavily on the European honeybee (Apis mellifera), which has recently experienced population declines due to several threats. This has encouraged the investigation into alternate insects to use for their pollination services. To aid this process, this study investigates the potential pollinators of apple and cherry crops in Australia by examining the timing of floral resource release of both crops to see if it, as well as temperature variation, might influence the visitation patterns of insects. Stingless bees (Tetragonula carbonaria), honeybees (Apis mellifera) and ants (family Formicidae) were the main insect groups to visit apple and cherry flowers in this study. Stingless bees were the most abundant visitors to apple (1107 visits) and cherry (232 visits) crops in Bilpin New South Wales, Australia, whilst honeybees were responsible for all but three visits to apple (116 visits) flowers in Orange NSW Australia. Video recordings revealed that stingless bees only collected pollen from apple and cherry flowers. Conversely, honeybees foraged for both nectar and pollen, but showed a preference for pollen. It is unlikely that the ants present on apple and cherry crops in Bilpin played a significant role in the pollination of these crops. Repeat sampling of apple and cherry flowers using microcapillary tubes and a refractometer revealed that cherry flowers appear to release the majority of their nectar and pollen resources within the first day of opening. Nectar production increased as the day progressed, and almost all anthers had opened by the end of the first day. Comparatively, apple flowers released their resources more gradually; nectar and pollen release were limited on the first day, and nectar release was highest overall at 08:00 coinciding with low temperatures and high humidity. Finally, the patterns in abundance and foraging behaviour obtained using hourly observations and video recordings were compared to the timing of floral resource release and temperature fluctuations. This revealed that changes in stingless bee abundance best aligned with the changes in anther dehiscence of both crops, whilst changes to honeybee abundance best aligned with the changes in nectar sucrose concentration of both crops. The abundance of ants did not align with the changes seen in either factor. This study provides insight into the usefulness of stingless bees and ants as alternate pollinators and gives direction to future studies examining the pollination of apple and cherry crops.

Date of Award	2019
Original language	English