Mating behaviour of Bactrocera cacuminata (Hering) (Diptera: Tephritidae: Dacinae) on its larval host plant Solanum mauritianum Scopoli in southeast Queensland

Abstract

The concept of the larval host plant as the centre of activity for dacine fruit flies, which is supported by a wealth of information on the Queensland fruit fly Bactrocera tryoni (Froggatt), has been refuted by two recently published studies. Conclusions in the first study are based solely on a failure to observe mating by Bactrocera cacuminata (Hering) on its major larval host plant Solanum mauritianum Scopoli in Queensland, and the second on a field cage experiment that concluded that B. cacuminata flies respond strongly to methyl eugenol at dusk, primarily to mate. We thus undertook a detailed study of the mating behaviour of Bactrocera cacuminata (Hering) both in the laboratory and in nature, and we also analysed a variety of plant tissues from S. mauritianum for methyl eugenol. Contrary to current understanding, female B. cacuminata are not monandrous but mate up to 3 times over their life span in the laboratory. In the field, over a 15 month period, we made 44,171 observations of adult B. cacuminata individuals and observed 1,109 mating pairs on its major larval host plant Solanum mauritianum Scopoli in a single plant at each of two study sites in southeast Queensland. We also consistently observed and filmed calling behaviour by male flies on the underside of leaves of S. mauritianum, and female flies responding to such groups of 10 -15 calling males at dusk. Female flies that arrived into these groups of calling males were mated and remained coupled until dawn. We detected no methyl eugenol from the analysis of a variety of tissues from S. mauritianum. Thus B. cacuminata does not need to aggregate at sites where methyl eugenol is present and the hypothesis that this chemical plays a role in the selection of mating sites by B cacuminata is not supported by our studies. We conclude that the concept of the larval host plant as the centre of activity for dacine fruit flies remains robust and is also important in the development of strategies for the management of pest fruit flies as well as in our understanding of the speciation processes in the Tephritidae.