BIONOMICS AND THE DEVELOPMENT OF DENDROCTONUS MICANS KUG IN THE MASSIF-CENTRAL

The bionomics and development of Dendroctonus micans Kug (Col Scolytidae) on Picea excelsa Link were observed by laboratory rearing attempts using an artificial (meridic) diet and a natural medium (spruce trunks, table I). Observations were also made between 1976 and 1983 in the French Massif Central in a stand at an elevation of about 1 400 m. With the artificial diet it was impossible to obtain the entire development from egg to adult. However, development from the 4th or 5th larval instar to adults was possible. This gives virgin females for rearing attempts on natural medium. Virgin females are unable to bore a normal gallery system Observations of natural conditions were made on the day of the attacks by periodic marking or bore, and by monthly observations on the demographic composition of the insect populations. Fertilization occurs in the native gallery. The emergence of the adults may occur at variable periods in the year. For example, the first attacks were observed at end of April in 1978, mid-June in 1976, and mid-September in 1980 (fig 1b). Females alone could bore a new system without contribution of the males. Emergence was also greatly spaced out (95 d in laboratory conditions and about 4-5 months in natural renditions, table II). This results in a spacing out of the oviposition, and a considerable variability of the development duration: about 13-22.23 months in natural conditions. This is because the insects issued from late-layed eggs are subject to 2 hibernating periods. This also results in the fact that many stages of the insects are present in a same stand all year round, without homology between years, as indicated by observations on the demographic composition of the population (fig 1).