Spatial Attack Patterns of Trichogramma pretiosum1 Around Release Sites Compared with a Random Diffusion Model 2

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Abstract
The spatial distribution of attack around release sites in cotton fields was measured for the parasite Trichogramma pretiosum Riley attacking eggs of the cabbage looper, Trichoplusia ni Hübner. The host eggs were presented 20/plant at equidistant “stations” in a cross pattern centered on the release site. Random diffusion theory predicts that the pattern should be a normal distribution in which the variance is a linearly increasing function of time. Out of 24 attack patterns, 14 were found to deviate significantly from a normal distribution. The deviations from normality tended toward a bimodal distribution. In addition, the time-trend of the variance showed a significant deviation from linearity. It is proposed that the deviations from normality may be due to time-varying drift and diffusion rates. In addition, saturation of the environment with parasites can cause a flattening of the attack pattern near the release site.

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