Trichogramma pretiosum (Hymenoptera: Trichogrammatidae): Effects of Augmented Densities and Distributions of Heliothis zea (Lepidoptera: Noctuidae) Host Eggs and Kairomones on Field Performance 1

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Abstract
Responses of laboratory-reared Trichogramma pretiosum Riley to selected densities and distributions of augmented numbers of Heliothis zea (Boddie) eggs were measured in cotton. In studies conducted near Tifton, Ga., rates of parasitization increased progressively from 24.4 to 31.0 to 36.0 to 43.7%, respectively, when 1, 3, 15, and 75 eggs were applied per 0.9 row m. The percentage of parasitization was also conditionally increased by the application of a hexane extract of H. zea moth scales (kairomones) at a dosage of 1 ml/0.3 m. The increase was apparently dependent on low levels of naturally occurring kairomone. Rates of parasitization also increased progressively beyond that of the control when 60 supplemental H. zea eggs were applied per m of row, on rows two and six of eight-row plots, on alternate rows, and on all eight plot rows. In studies near Kerman, Calif., rates of parasitization on H. zea eggs spaced 1/0.9 row m on kairomone-treated leaves increased from 24.3 to 53.6% when 60 supplemental H. zea eggs were applied per 0.9 rowm. Data suggest that higher host densities intercept and retain proportionally more T. pretiosum, which in turn yield higher rates of parasitization.

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