Submitted to: XI Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: 11/20/2003
Publication Date: 7/20/2004
Citation: Proceedings of the XI International Symposium on Biological Control of Weeds (eds Cullen, J.M., Briese, D.T., Kriticos, D.J., Lonsdale, W.M., Morin, L. and Scott, J.K.) pp. 117-120. CSIRO Entomology, Canberra, Australia
Interpretive Summary: After the identification of four new species of Thrypticus (Diptera, Dolichopodidae) rearing in Water hyacinth, biological and ecological research was carried out on two of them. T. truncatus and T. sagittatus Bickel & Hernandez were prioritized for further investigations due to their abundance and wide geographic distribution. Preliminary host range testing showed that none of the following plants were attacked: Eichhornia azurea, Pontederia cordata var. cordata and var. lancifolia, P. rotundifolia, Echinodorus grandiflorus, Canna glauca, Myriophyllum aquaticum, Heteranthera reniformis, H. callifolia and Monochoria africana. These results indicate that these candidates are qualified to be biological control agents once the complementary studies have been completed.
Technical Abstract: For about thirty years Thrypticus spp. (Diptera, Dolichopodidae) were considered as possible candidates for biocontrol of water hyacinth (Eichhornia crassipes) in its adventive range. Initially it was thought that there was only one species attacking plants within the Pontederiaceae. However, four new species of Thrypticus have been identified from water hyacinth. Due to their abundance and wide geographic distribution, T. truncatus and T. sagittatus Bickel & Hernandez were prioritized for further investigation. Both species have similar behavior and appear to share the same similar ecological niche. The larvae bore a horizontal mine in the petiole making a small incision in the vascular bundles. The larvae then feed mainly on the exuded sap. In the southern hemisphere the flies reproduce from spring through to the end of summer. During autumn and winter no oviposition was recorded, suggesting that both Thrypticus species spend the winter months as larvae in the petioles. One generation in summer requires about 7 weeks. Preliminary host range testing, conducted in the laboratory and in the field by interspersing test plants among infested water hyacinth plants, showed that none of the following plants were attacked: Eichhornia azurea, Pontederia cordata var. cordata and var. lancifolia, P. rotundifolia, Echinodorus grandiflorus, Canna glauca, Myriophyllum aquaticum, Heteranthera reniformis, H. callifolia and Monochoria africana. During field surveys, both species of flies were only reared from E. crassipes. These results indicate that both species warrant further studies on their biology and specificity.