Relationship of individual worker mass and population decline in a Formosan subterranean termite colony (Isoptera: Rhinotermitidae)

Current knowledge of the developmental cycle of subterranean termite (Isoptera Rhinotermitidae) colonies is primarily based on observations of colonies maintained in laboratory containers. Because-laboratory-reared colonies never attain the population size of field colonies. Little is known of the mature or declining phases of colony growth. In a unique long-term study we report 16 yr of observations on the estimated population size and wet mass of individual termites collected from a Coptotermes formosanus Shiraki field colony in Hawaii. During this period, the mean wet body mass of individual foraging workers more than doubled, from 6 mg, while the estimated colony foraging population declined exponentially. The size of the colony foraging population (y) was negatively related to individual worker body mass (x) by a power equation of the form y = 37.136x-2.109. These data support the conclusion that older or less vigorous C. formosanus colonies contain workers that are larger in body mass than younger colonies, although other genetic and environmental variables also may influence observed variation in individual mass among termite colonies. Given a baseline estimate of colony foraging population, the subsequent proportional decrease in the population of this C. formosanus colony (y) could be predicted from the proportional increase in individual wet mass (x), as expressed by y = 36.402x0.169.