During an outbreak of N, sertifer in Brentonico (on Monte Baldo, Trentino, North Italy), in altitudes of 1,400-1,600 m, surveys were made in 1996 and 1997 on the voltinism of these short-day-Diprionide, wherely over 2,000 cocoons were reared (fig. 1; tab. 1-4). Therefore L4-5 larvae of N. sertifer from different altitudes were transferred to Denno (430 m) and to Brixen (550 m) and were reared there under outdoor conditions. These surveys were completed with further observations of populations from South Tyrol, of St. Ulrich Val Gardena (1,200 m) and italian provenances from Riolo Terme (150 m) in Brixen (fig. 2). These comparative studies revealed a correlative connection between the time of cocoonspinning and adult emergence. They showed the following principle: the later the cocoonspinning, the earlier the adult emergence. Early spinners (e. g., May/June) emerge only late in October, while late spinners (e. g., early August) emerge as soon at the end of August. In the case of late cocoon spinning the obligatory summer cocoon diapause is so reducted, eventually - at the start of the short-day phase (with only 15 hours brightness), in early August - leading to a subitan development. These different cocoon spinning periods cause varying fly-waves, W1-W4, of N. sertifer, similarly to other Diprionidae; this seems evident also by pheromon-trap catches (fig. 2: 3). The possible variable combinations of these fly-waves are discussed. It is shown that voltinism and diapause behaviour of N. sertifer are essentially conditioned by the photoperiod and correlated climatic factors. The determined low diapause rate, of just 1-2%, is connected with the southern and warmer location of the outbreak area of Brentonico (45 degrees 49' N). The exceptional longevity of adults, which can amount to several weeks, also plays an important role.
