SUPPRESSION OF MAIZE WEEVIL, SITOPHILUS-ZEAMAIS (COLEOPTERA, CURCULIONIDAE), POPULATIONS IN DRUMS OF CORN BY SINGLE AND MULTIPLE RELEASES OF THE PARASITOID ANISOPTEROMALUS-CALANDRAE (HYMENOPTERA, PTEROMALIDAE)

Drums containing 45.36 kg (100 lbs) of shelled corn were used to test the ability of Anisopteromalus calandrae (Howard) to suppress populations of the maize weevil, Sitophilus zeamais Motschulsky. On July 15, 1992, 10 pairs of maize weevils were released into each drum. Three weeks later, A. calandrae were released in half the treatment drums (4 replicates) at rates of 5. 10, 20 or 40 pairs. No further A. calandrae were released in these drums. At the same time, releases of A. calandrae were begun in the other treatment drums at rates of 2, 5, 10 or 20 pairs and continued at these rates for 29 weeks. Insect populations were sampled four times during the experimental period: at 8, 14, 23 and 33 weeks. In control (untreated) drums and drums from single and multiple release treatments, maize weevil populations increased from 8 weeks to 33 weeks, however, populations in the controls increased much more rapidly than in either treatment. Both single release and multiple release treatments greatly suppressed maize weevil population growth. Final population counts showed that percentage suppression was over 90% in all release rates of both treatments. At high maize weevil population levels there was no significant difference between single and multiple release treatments in suppressing maize weevil populations in drums of corn.