CHANGES IN THE FECUNDITY OF TENT CATERPILLARS - A CORRELATED CHARACTER OF DISEASE RESISTANCE OR SUBLETHAL EFFECT OF DISEASE

Over the fluctuation in population density of tent caterpillars, Malac osoma californicum pluviale and M. disstria, fecundity changes from be ing high at peak density to low for several years during the decline. During the increase phase, fecundity rapidly returns to moderately hig h levels with a further increase occurring toward the end of the incre ase phase. Two hypotheses which might explain these shifts are that (1 ) mortality from Viral disease which is common during population decli nes selects for resistant individuals with low fecundity as an associa ted characteristic, and (2) sublethal viral disease reduces fecundity of moths during population decline. In this study we observed rapid sh ifts in the frequencies of large and small egg masses and in the mean fecundity between different phases of the population fluctuation. Vira l disease was more common in caterpillars from small egg masses of the forest tent caterpillar. These observations are consistent with the h ypothesis that sublethal effects of virus reduce the fecundity of moth s during the population decline, but high fecundity is quickly restore d when disease is rare during the population increase.