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  • UC Riverside
  • College of Natural and Agricultural Sciences

Publications: Mark Chappell

M. Alleyne, M.A. Chappell, D.B. Gelman, N.E. Beckage (1997) Effects of Parasitism by the Braconid Wasp Cotesia congregata on Metabolic Rate in Host Larvae of the Tobacco Hornworm, Manduca sexta, Journal of Insect Physiology 43:143-154.


ABSTRACT -- We examined growth rates, gas exchange patterns, and energy metabolism of tobacco hornworm (Manduca sexta) larvae parasitized by the braconid wasp Cotesia congragata. Larvae parasitized at the beginning of the fourth instar had reduced growth compared to unparasitized larvae of the same age, but in parasitized larvae there was a positive correlation between parasitoid load and the final mass of the host-parasitoid complex. Short-term differences in metabolism (measured as rates of CO2 production, VCO2) were apparent almost immediately after wasp oviposition. However, over the growth period between parasitization and the last part of the fifth instar, there was no significant difference between parasitized and unparasitized hosts in the relationship between mass and VCO2. One or two days prior to parasitoid emergence, hosts stopped eating, ceased spontaneous locomotor activity, and showed a dramatic decline in metabolism. The 60% decline of VCO2 at this time is consistent with lack of specific dynamic action because the animals were not feeding. Gas exchange became highly cyclical on the day of parasitoid emergence, but the cause and significance of this phenomena (which disappeared by the third day following emergence) are not clear. Cycling was not induced by starvation or immobilization with tetrodotoxin. Ecdysteroids in host hemolymph increased on the day when parasitoids completed their L2-L3 molt and began emerging, but not during the wasps' earlier L1-L2 molt.