Population Fluctuations and Causes of Mortality for the Forest Tent Caterpillar, Malacosoma disstria (Lepidoptera: Lasiocampidae), on Three Different Sites in Southern Louisiana

Abstract

Population fluctuations of forest tent caterpillar, Malacosoma disstria Hubner, were investigated at two permanently flooded plots and one plot that was dry during summers of 1980–83 in southern Louisiana. Tupelo gum, Nyssa aquatica L., and swamp tupelo, Nyssa sylvatica var. biflora (Walt.) Sarg., made up 63% of the dry plot forest stand and 93.8 and 87% of the two wet plots. Egg parasitism ranged from 8.8 to 29.7%, and egg infertility varied from 1.2 to 6.7%. An analysis of egg mortality factors demonstrated no density-dependent relationships or significant plot differences. Pupal parasitism by Sarcophaga houghi Aldrich varied from 18 to 78% during 1981–82. Lower rates of parasitism were found on wet plots due, presumably, to drowning of parasite puparia. Populations of forest tent caterpillar at the dry plot were reduced by apparent density-dependent parasitism by S. houghi . We found that a generation survival rate of 0.1% resulted in population decline and that survival ≥0.7% resulted in a population increase the following season. Starvation may have been a major factor in population fluctuation at wet plots.