Floral biology of Macadamia integrifolia (Macadamia nut) – Final Report

Final report on the project

Dr Elizabeth M. Exley, Department of Entomology, The University of Queensland
23 March 1988

Experiments carried out with travel and salaries monies provided by the A.F.F. are listed below.

Experiments were performed only in orchards due to the inaccessibility of racemes of trees in natural locations. Furthermore, since the refugia of wild macadamia trees are small, they no longer represent “natural” situations.

l. Pollinating insect diversity and abundance in 11 macadamia orchards in Queensland and NSW.
The eleven orchard sites surveyed for diversity and abundance of pollinating insects are shown on Fig 1.

A mean of greater than 90% of macadamia flower visitors belonged to two species of social bees, honey bees (Apis mellifera) or Trigona bees (Trigona carbonaria). The abundance of insects other than honey bees was correlated with the extent of surrounding vegetation.

2. Pollinating insect diversity, abundance and behaviour at one site (Closeburn) for the full duration of the flowering season.
Honey bees and Trigona bees were present through the entire flowering season of macadamia. Other insects were rare at the beginning of the flowering season (July) but common later in the flowering season (October).

Results show that whereas honey bees forage for nectar, Trigona bees visit the flowers mainly for pollen. This results in Trigona bees coming into contact with the stigma of the macadamia flower more often than honey bees, suggesting they are more efficient pollinators.

3. Foraging preferences of the two major pollinating insects (viz honey bees and Trigona bees) to determine which bee species visit racemes in sunny and/or shady positions and on both heavily and lightly flowering trees.
No statistical analysis is yet completed but it appears that both honey bees and Trigona bees forage equally actively in open sunny positions and shady positions.

4. Relative pollinator efficiency of the two major insect visitors by covering racemes with a wire mesh that allows only the smaller Trigona bees to forage and assessing the resulting initial nut set and final nut set.
Macadamia racemes visited only by Trigona bees showed high initial nut set suggesting these bees are efficient pollinators. Data for final nut set is not yet available.

5. Determining the relationship between the number of bee visits and the initial and final nut set by bagging racemes and removing the bags for varying periods each day for the full duration of raceme life.
Treatments that resulted in higher levels of insect visitation also had higher initial nut set. Data for final nut set is not yet available.