Contribution of Insect Pollination to Macadamia integrifolia Production in Hawaii

Abstract

The honeybee, Apis mellifera, is commonly accepted to be an important pollinator in many agricultural crop systems in Hawaii. However, specific details on the importance of A. mellifera, along with other insect visitors have not been determined for macadamia nut orchards in Hawaii. Reductions in feral honeybee populations in Hawaii attributable to invasions by varroa mites (Varroa destruc- tor) and small hive beetle (Aethina tumida) have resulted in growers becoming dependent on managed bees, requiring increased understanding of the role they play as pollinators. Several parameters determining the contributions of insect pollinators in macadamia nuts were measured: (1) species richness and abun- dance of insects visiting macadamia flowers, (2) the effects of insect pollination in regards to fruit set, fruit retention, fruit size, and weight, and (3) insect pollen removal efficacy based on the mean number of pollen grains an individual insect removed from the stigma while foraging on a macadamia flower. The results from data collected in the study orchard showed that while the order Diptera ranked highest in species richness (9 species), A. mellifera was the most abundant species visiting the macadamia inflorescences (62.7% in abundance, with an average of 17 honeybees seen per 15 minutes compared to 8 flies per 15 minutes). Inflores- cences that were accessible to insects for pollination produced higher fruit sets and yield compared to inflorescences from which insect visitation was excluded. Abundance, foraging behavior and stigma contact, suggested that honeybees are the greatest contributors to macadamia nut pollination over other insects observed in the orchard. The hoverflies (Syrphidae) observed in the orchard may have con- tributed to pollination, but likely to a lesser extent than the honeybees due to the low abundance of the flies.