Comparison of the Response of Heliothis virescens to Parasitism by Euplectrus comstockii and Euplectrus plathypenae

Abstract

Two major similarities were observed in larvae of Heliothis virescens parasitized by either Euplectrus comstockii or Euplectrus plathypenae. Parasitism by either parasitoid arrested larval-larval ecdysis and caused comparable alterations in the titer of storage proteins found in the host hemolymph. However, each larval stadium responded differently to parasitism. Parasitized 3rd-instar larvae increased in weight to ca. twice that of control larvae while parasitized 4th- and 5th-instar larvae increased in weight to ca. 1.3 times the maximum observed in control larvae for that stadium. The titer of storage proteins present in the hemolymph increased in parasitized 3rd- and 4th-instar larvae but decreased in parasitized 5th-instar larvae, by comparison to the titers found in control 3rd-, 4th- and 5th-instar larvae, respectively. Feeding by the parasitoids did not cause further alteration in the composition of the hemolymph proteins of the host. A plausible explanation for the increase in weight and/or increase in the storage protein titer in the younger host larvae is to provide a sufficient nutritional source to extend the viability of the host while it remains in that stadium and is fed upon by the developing parasitoids.