G. it. Ent., 5 (27): 219-238
April 30, 1991
Insect pollination of Acacia bidwillii Benth. (Mimosaceae)
at Townsville, northern Queensland, Australia
by
TREVOR J. HAWKESWOOD
Abstract - Forty-seven (47) species of insects, belonging to four Orders (Lepidoptera, Hymenoptera, Coleoptera and Hemiptera) were collected from open flowers of Acacia bidwillii Benth. (Mimosaceae) growing in open woodland on the James Cook University grounds, Townsville, during the flowering season from 12 to 26 November 1981. Samples of all insect species were examined for their pollen loads and the places of pollen deposition recorded. Incidental and other foliage-feeding insects were also identified an examined for the presence of pollen. Observations on feeding and flight behaviour of the most common insect species as well as certain less common ones were undertaken. Observations on the 11 species of Lepidoptera (butterflies) collected from the flowers have been presented in a previous paper. Results of the present study on the remaining 36 insect species, suggests that bees and wasps (Hymenoptera) and beetles (Coleoptera) are the most important self-pollinators of A. bidwillii at Townsville, while bees and wasps are the most important cross-pollinators. The study also revealed many more species of insect visitors to an Acacia species than previously recorded in any other study on mimosoids. Comparisons of the A. bidwillii vector array are also made with contemporary studies in Victoria, Africa and North America on mimosoid pollination vectors. The pollination system of A. bidwillii differs markedly overall from that of other mimosoids. This is probably due to a combination of different flowering times, floral attractants and a different insect fauna in the Townsville area. Most of the insects recorded here have not been recorded previously from Acacia flowers and are the first records of them as pollinators. Thyreus (Anthophoridae) are generally regarded as nest parasites in the burrows of other anthophorid bees, so the record of T. lamprosomus (Boisduval) from A. bidwillii flowers appears to be unique and unusual. It is apparent that the simple flowers of Acacia are an adaptation for attracting a wide range of potential insect pollen vectors. In tropical Australia, where climatic conditions are often erratic and variable and insect populations often fluctuate each season in terms of abundance and composition, the strategy adopted by A. bidwillii in order to secure successful pollination is to produce strong-scented flowers and to blossom at a time of the year when there is a high probability of attracting at least a minimum of insect species.
