Fall Armyworm Symposium--1984: Differential Growth Responses of Fall Armyworm Larvae on Developing Sorghum Seeds Incorporated Into a Meridic Diet

Abstract

Seed of developing sorghum, Sorghum bicolor (L.) Moench, mixed in a substandard meridic diet, was fed to larvae of fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). Larval weight differences were measured at 8-14 days after infestation. Differences between weights of FAW larvae fed NK `Savanna 5' and `Funk 5245' were found at the following stages of plant development: milk stage, soft dough stage, hard dough stage, high moisture dry seed, and low moisture dry seed. The larvae that were fed diets of NK `Savanna 5' were consistently smaller over all stages tested. Forty to 80 g of immature or mature seed per diet resulted in detectable differences between the 2 sorghum genotypes. An evaluation of 10 randomly selected sorghums mixed in the diets produced weights of larvae that showed significant differences among cultivar responses at the milk stage and dry seed stage. The FAW larvae that were fed diets of NK `Savanna 5' and `TAM 2566' were consistently smaller over several tests as compared with other sorghums evaluated. A nonsignificant relationship was found between FAW feeding responses on the fresh-milk stage cultivars mixed in diets and feeding responses on those diets made from frozen milk-stage seed. Indications were that the smaller larvae were produced on resistant sorghum cultivars and that this may have been due to a lack of adequate nutrients. No apparent relationship was found between tannin content of the dry seed and FAW growth responses.