Intensive studies on the biology of the spruce needle-miner, Pulicalvaria piceaella (Kft.), were carried out in the Province of Quebec between 1956 and 1959. The cycle is univoltine, larvae have five instars, and the insect overwinters in the larval stage. P. piceaella collected from the Gaspé Peninsula were significantly larger than those from southwestern Quebec, which in turn were larger than individuals from an incidental collection made near Syracuse, New York.

Young larvae were most often found in foliage damaged by associated defoliating insects. In these circumstances, they mined needles adjacent to the damaged sites or fed partly on the damaged material and partly by mining needles, and in some cases fed exclusively on the dead foliage. The majority of larvae entered dormancy about the third week of September in all localities and in all years, an apparent diapause reaction to a critical photoperiod of approximately 12 hours. Resumption of feeding activity the following spring was apparently governed by temperature. In the spring, larvae transferred to new feeding sites, either to the current year's buds or to the previous year's foliage. In the Gaspé Peninsula the larvae migrated to buds, whereas in southwestern Quebec reinitiation of larval activity preceded the opening of the buds by almost a month, and larvae transferred to new sites on the previous year's growth where they mined needles. Pupae were often found in silken cells within the various feeding sites but most larvae probably dropped to the soil to pupate.

Mating and oviposition habits of the moths are described. Mean fecundity was 22 as derived from dissections of gravid females, and mean number of eggs deposited per female averaged 11. Eggs were deposited singly and usually found in the same sites as young larvae.