The Influence of Host Plants on Parasitism of Eggs of the Tobacco Hornworm12

Abstract

Eggs of Manduca sexta (Johannson) were parasitized by Tetenomus sphingis (Ashmead), Trichogramma minutum Riley, and Anastatus sp. on solanaceous hosts other than tobacco in North Carolina. Although low and variable during midsummer, parasitism rose to 48% of naturally occurring eggs in September on Jimson-weed, Datura stramonium L. At this time 75% of the parasitized eggs yielded Telenomus sphingis and 25% Trichogramma minutum. Comparable samples of eggs from tobacco were not parasitized. In the laboratory, T. minutum failed to parasitize eggs on fresh tobacco foliage but readily attacked eggs on other substrates. The tiny parasites became stuck to the tobacco leaf in the gummy exudate of the trichomes. Telenomus sphingis, being larger than Trichogramma minutum, was able to cope with the sticky substrate to some extent, but Its movements on tobacco were inhibited and it parasitized significantly fewer eggs on tobacco than on any other substrate.