A tractor mounted machine, termed the 'biosprayer', was evaluated for the application of Trichogramma wasps to cotton for bollworm control. Passage of Trichogramma host eggs through the biosprayer reduced wasp emergence by 22%. Additional mortality resulted from predation, primarily fire ants. In the absence of predators, rain and dew, 88% of the applied host eggs were retained on cotton leaves for three days. Most (79%) of the host eggs retained by the cotton canopy were deposited in the plant terminal. Application of 100,000-200,000 Trichogramma pupae per acre twice a week did not consistently increase parasitism of bollworm eggs in field plots.