An outbreak of needle miner on lodgepole pine occurred in the late 1940's, decreased to low levels in the 1950's. but increased aeain recently. In both outbreaks, populations were highest in a band along the middle of the slopes of the valleys.

The moths are crepuscular with most of the flight, feeding, and laying activities taking place at sundown. Temperatures and wind at this time are critical for these activities. Low temperatures and wind which are more common at higher elevations probably reduce oviposition rates. Some downward drift of the moths also probably takes place making the rate of increase through the adult and egg stages much higher at valley bottom than further up the slope.