The cedar web-spinning sawfly, Cephalcia tannourinensis (Hymenoptera: Pamphiliidae) is considered a major defoliator of the cedar forests in Lebanon. In the early 1990’s, a severe damage of the Tannourine Hadath El-Jebbeh cedar forest was caused by the sudden outbreak of this insect. The insect has a complex life cycle with two types of diapause: annual diapause and multiple years diapause. The present study aimed at studying soil characteristics and their influence on the survival and diapausing cycles of C. tannourinensis prepupae. Different soil samples collected from three different cedars forests in Lebanon were incubated with prepupae of C. tannourinensis under laboratory conditions. The effect of soil origins and properties on prepupal mortality, annual diapause and multiple years diapause cycles were analyzed. The influence of soil moisture and soil temperature on prepupal development was studied separately through two constant temperatures and three constant soil moisture levels. Prepupal mortality was found to be highly correlated with soil properties and types. Prepupae survived well in soil coming from Tannourine and Bcharry followed by Chouf. However mortality was almost 100% in the two reference soils sand and peat. Diapause cycle was strongly correlated with temperature while the effect of moisture was mainly on the prepupal survival.
Key words: Cephalcia tannourinensis, soil moisture, soil temperature, annual diapause, multiple years diapauses.