The end of an outbreak of a sawfly, Neodiprion excitans Rohwer, on Pinus taeda L. first was observed in north-central peninsular Florida during December 1962. To aid in dating oviposition, the position of egg pockets in 1962 summer-shoot pine needles was compared with growth of 1963 summer-shoot pine needles. By this method, peaks of adult emergence and oviposition were judged to have occurred during the last half of August and first half of October 1962.

Eggs hatched in the fall when laid in growing pine needles during October 1962. Larval development was protracted during unusually cold weather and cocoons were spun as late as mid-January 1963. Adult emergence from these cocoons began in late May 1963, two months later than had been previously recorded for Florida.

In contrast, eggs overwintered in the foliage when laid after needle growth had ceased in the fall of 1962. Larval eclosion was in late February and March 1963 and cocoons were spun by mid-May.

This combination of events suggested how a new species overwintering in the egg stage (Neodiprion hetricki Ross) might have evolved in temporal isolation from an ancestral species ordinarily overwintering only in the cocoon (N. excitans).