WINTER INCREASE OF DENDROCTONUS FRONTALIS ZIMMERMANN (COL, SCOLYTIDAE) - A PRECURSOR FOR OUTBREAKS

In Louisiana successful attacks, egg densities, brood adult emergence, and survival of southern pine beetle (SPB), Dendroctonus frontalis, from an epidemic period (1984-1986) were compared with endemic period (1960-1971) data from east Texas, Louisiana, and southwest Mississippi. Endemic SPB emergence counts are low and exhibit a right-skewed distribution. Before the start of the Louisiana SPB epidemic in 1985 on the Catahoula Ranger District, Kisatchie National Forest, there was a significant increase in the median counts of emerging adult beetles from July to December 1984. Also emergence counts shifted from a right-skewed distribution to a symmetric distribution. An increase in egg densities was measured from winter 1984 through spring 1985, and higher brood survival was observed during the last 3 months of 1984. Although many infestations were detected in the spring of 1985, the low emergence counts for brood adults showed that reproduction had returned to endemic levels. This phenomenon had not been observed previously because research has concentrated on infestation during summers. Seasonal surveys of population densities may be useful for anticipating SPB activity and timing management plans.