Dispersal behaviour of Trichogramma brassicae in maize fields

摘要

Glue-sprayed maize plants were used to study dispersal behaviour of the egg parasitoid Trichogramma brassicae Bezdenko (Hy-menoptera Trichogrammatidae) in maize fields. To estimate the distance covered during an initial flight, T brassicae were studiedin a field cage with 73 glue-sprayed plants. Most of the parasitoids were found close to the release point, but several reachedplants at distances up to 180 cm showing that walking and jumping are not the only mechanisms involved in initial dispersal.Mean distance of recapture from the release point was 60 cm. In a second experiment, glue-sprayed plants were placed in a maizefield in a cross-pattern with 1.5 m distance between plants. On plants neighbouring the glue-sprayed plants, egg masses were fixedto measure parasitism. Only 0.7 to 3% of the released parasitoids were recaptured in the field. During the first day there was asharp gradient with distance in the numbers of parasitoids recaptured, but during the second and third day there was no longer asignificant gradient. The numbers captured on the second and third day were much lower than those captured on the first day.There was little correlation between the number of wasps landing on a plant and parasitism. In the field, apparently 75% of thewasps had left the area within 7.5 meter of the release point at the end of the first day, and 95% had left this area at the end of thesecond day. It is concluded that T. brassicae disperses in maize fields mainly by short flights.