Number and volume of aquatic insects emerging from tributaries of the Miramichi River of northern New Brunswick, where forest‐covered watersheds had been sprayed from the air with 0.5 pounds of DDT per acre, are compared with insect emergence from unsprayed streams. Adult insects were captured as they emerged from the water in yard‐square cage‐traps. In the streams affected by DDT fewer kinds of insects, particularly of the larger species such as caddisflies, were found. The sprayed streams had, generally, larger numbers than the unsprayed but in all sprayed streams the volume represented was significantly lower because of the relative scarcity of the larger forms. The insect fauna of the sprayed streams was found to be deficient in the kinds of insects on which the salmon were mainly feeding in the unsprayed streams.