none A complex of insects, developing in Phragmites australis, one of the most resistant and wide-spread weeds on the territory of Tajikistan has been studied. The data on the biology of phytophagous Arenostola unicolor Warr., Hydraecia sp. (Lepidoptera, Noctuidae), Lipara lucens Mg. (Diptera, Chloropidae), Acmenychus inermis Zubk. (Coleptera, Chrysomildae) are given. The influence of these insects on the host plant is appreciated. The biology of attendant species has been studied, among them - endoparasite Polemochartus liparae (Hymenoptera, Braconidae), developing in the larvae of L. lucens Mg. and saprophage Anacamptoneurum obliquum Beck. (Diptera, Chloropidae), following the caterpillars Hydraecia sp. in stems.