The gall-midge Psectrosema tamaricum (Kieffer 1912) (Diptera: Cecidomyiidae) forms small ovoid or fusiform swelling galls on the leaf branches and flowering shoots of Tamarix nilotica (Ehrenb.) (Family: Tamaricaceae). The present work studies the interaction of P. tamaricum with T. nilotica. It is an attempt to predict the potential current distribution of P. tamaricum and the host plant T. nilotica in Egypt using ecological-niche modeling.; in addition to the effect of altitude and vegetation cover on its distribution. Within the study areas, the number of galls per plant and plant cover had a significant positive correlation. There was no statistically significant relationship between the number of galls per plant and elevation. Temperature, elevation, and relative humidity were the strongest determinants of P. tamaricum potential distribution. Precipitation, soil types, and temperature were the most significant predictors for the potential distribution of T. nilotica. The present study suggests that gall-forming insects prefer larger plants to small plants. The present study reported that the highly suitable habitat for P. tamaricum is lower than for T. nilotica by 93.4% of the total highly suitable area.
