Biology and host range of gall fly, Cecidochares connexa (Macquart) (Diptera: Tephritidae) as a biological control agent of siam weed

Abstract

Gall fly, Cecidochares connexa (Macquart) (Diptera: Tephritidae) is an important natural enemy of siam weed Chromolaena odorata (L.) King & Robinson (Asteraceae), that was introduced to Indonesia from Colombia in 1993. After being release in 1995, the biological aspects of the fly have not been evaluated yet. This research was conducted to study: 1) the biology of C. connexa in the field, 2) the development and number of larval instars, and 3) the host range of the gall fly. Biological parameters observed were larval development, life cycle, longevity of adults and fecundity of the females. Larval instars were determined by observing morphological characters of mandible, sclerite hypopharyng and larval size (volume). The fly host range was evaluated by observing fly infestation and oviposition, larval development and survival, as well as gall formation on three different plant species that were closely related to siam weed (Asteraceae). Results of the study indicated that the eggs were laid in clusters in tissue of terminal or axillary bud. After hatching, larvae bored deeper into the bud and lived inside the gall that was formed on the infested bud until pupation. Gall were visible about two week after oviposition. One gall contained 1 to 13 larvae. There was no correlation between the gall size and number of larvae living in the gall. The gall fly pupate inside the gall. The adults emerged from the pupae and leaved the gall through out gall windows that were prepared and made by the last instar larvae before pupation. The life cycle of the gall fly was completed in 56-77 days. In the study was found that the highest mortality occurred when the fly was in the larval stage, and the natural enemies, especially predators, were the most important mortality factors. Longevity of the fly was about 8-17 days and 7-11 days for female and male, respectively. The fecundity of the fly was 140-329 eggs/female. Based on the size of the mandible and sclerite hypopharyng, there was indication that C. connexa larva had four instars to complete its development. The characters of mandible and hypopharyng were good indicators to determine larval development stage of C. connexa, but not the larval volume. Mandible character was found to be the best indicator to determine the development stage of C. connexa. The shape and size of mandible was different among different instars of C. connexa larvae. Form the host range test, it was known that C. connexa laid eggs on all species of tested plants. However, larvae could survive on the tested plants for no longer than two weeks. On babadotan, the fly infestations were able to stimulate gall formation but the larvae were fail to complete their development. It can be concluded that C. connexa is a host specific species that can develop and complete its life cycle only on siam weed.