none The leaf-mining flies Hydrellia sp. and H. pakistanae Deonier were observed attacking the aquatic weed Hydrilla verticillata (L.f.) L.C. (Hydrocharitaceae ) in south India. Their life histories were very similar. The duration of the immature stages of H. pakistanae was 25 to 29 days. The number of leaves of H. verticillata mined by a single larva varied from 8 to 12. In the laboratory, adults feeding on 50% aqueous solution of honey lived for 6 to 21 days and laid an average of 26 eggs. Several overlapping generations occurred in the field except during the period of drought. Both Hydrellia sp. and H. pakistanae were heavily parasitized by the braconids Ademon sp. nr. decrescens Nees and Chaenusa sp.