Dispersal Studies of Trichogramma semifumatum (Hymenoptera : Trichogrammatidae) Tagged with Radioactive Phosphorus12

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Abstract
About 2 million Trichogramma semifumatum (Perkins) were released in the first study, in the Imperial Valley, Calif., and about 1½ million in a second study near Shatter, Calif., in 1960. Females tended to disperse more rapidly than males, 1 ♀ being recovered 2000 ft from the release point 17 hours after release, while 2 ♂ were taken 400 ft from the release point after another 24 hours had elapsed. One individual (sex not determined) was recovered 3500 ft from the release point, 62 hours after release. Since the radioactive wasps were found to live at least 15 days after release, females could have dispersed up to 10 miles and males up to 1 mile if they dispersed unidirectionally from the area of release or emergence. Specimens were easily recovered within 200 ft of the release point, but the factor of area dilution is extremely important in connection with recovery of tagged specimens, whose number decreased markedly with increased distance. In the absence of rigorous weather conditions, the extent to which temperature and wind aided or hindered dispersal could not be determined. Tagging procedures and vacuum suction sampling methods are discussed.

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