Results from a no-choice field study indicate a negative interaction between non-blooming nectariless cotton and the Heliothis egg parasite, Trichogramma pretiosum. Following a single release of parasites in each test plot, the percentage of H. zea eggs parasitized by T. pretiosum declined 3.5 x over a two day period on the nectariless cotton (from 72.3% on day 0 to 22.0% on day 2) while the decline was only 1.5 x on the nectaried phenotype (from 74.7% on day 0 to 48.3% on day 2). Extrafloral nectar may serve as an alternative or essential source of food and/or moisture for Trichogramma adults inhabiting cotton.