Effects of heat shock and ambient temperature on female soldier production in a polyembryonic parasitic wasp

Abstract

AbstractLarval castes are well known in both sexes of polyembryonic parasitic wasps, in which sterile soldier larvae are clonally produced from a single egg and thousands of reproductive larvae develop into adults. The proportion of soldier larvae in Copidosoma floridanum is first determined genetically in both sexes but subsequently increases in females as a result of environmental disturbances, such as the presence of competitive parasitoids. Because temperature is the most influential environmental factor affecting ectotherms, we hypothesize that an increase in ambient temperature also affects the production of female soldier larvae. Conversely, we hypothesize that there would be no effect of temperature on the production of male soldier larvae. In the present study, we show that heat stress experienced by C. floridanum at an early stage in host development increases the number of female soldier larvae produced during the last instar stage of the host. We also show that rearing at extreme (high and low) temperatures induces an increase in the number of female soldiers produced. The effect of heat stress and ambient temperature on soldier production is found only in females, as is the response to heterospecific competitors. By contrast, no responses are detected in males for either heat stress or ambient temperature. The adaptive effect of these phenomena is not known, although the results of the present study imply the existence of a common physiological cascade that causes an increase in the number of soldier larvae in females.