Malacosoma

Abstract: The different types of individuals among the progeny of the western tent caterpillar, Malacosoma pluviale (Dyar), are concentrated in different parts of the egg mass. The most agile progeny come from some of the first eggs laid, and the least viable are among the last deposited. There is evidence that this serial arrangement stems from unequal partitioning of the maternal food reserves during egg production: a relationship similar to that recently demonstrated in the spruce budworm by I. M. Campbell. In M . pluviale , however, there also is evidence that the differences in feeding rate and food capacity displayed by the different types of females during their own larval stage affect the proportions of the various types of progeny per egg mass as well as the viability of consecutive groups of eggs within the mass. Although these maternal influences are not heritable in the usual genetic sense, they are clearly transmissible between generations. And field studies have shown that their more adverse consequences for local populations are cumulative and ultimately lethal.

Abstract: Temperature and food quality can both influence growth rates, consumption rates, utilization efficiencies and developmental time of herbivorous insects. Gravimetric analyses were conducted during two consecutive years to assess the effects of temperature and food quality on fourth instar larvae of the forest tent caterpillar Malacosoma disstria Hubner. Larvae were reared in the laboratory at three different temperatures (18, 24 and 30 degrees C) and on two types of diet; leaves of sugar maple trees Acer saccharum Marsh. located at the forest edge (sun-exposed leaves) or within the forest interior (shade-exposed leaves). In general, larvae reared at 18 degrees C had lower growth rates and lower consumption rates than larvae reared at the warmer temperatures (24 and 30 degrees C). Moreover, the duration of the instar decreased significantly with increasing temperatures. Type of diet also affected the growth rates and amount of food ingested by larvae but did not affect the duration of the instar. Larvae fed sun-exposed leaves consumed more food and gained higher biomasses. Values of approximate digestibility and efficiency of conversion of ingested food were also higher when larvae were fed sun-exposed leaves. Higher growth rates with increasing temperatures were primarily the result of the shorter stadium duration. The higher growth rates of larvae fed sun-exposed leaves were possibly the result of stimulatory feeding and consequently greater food intake and also a more efficient use of food ingested. This study suggests that the performance of M. disstria caterpillars could be enhanced by warmer temperatures and higher leaf quality.