SUPPRESSION OF OVIPOSITION IN ORYZAEPHILUS-SURINAMENSIS (L) (COLEOPTERA, CUCUJIDAE) FOLLOWING PROLONGED RETENTION IN HIGH-DENSITY CULTURES OR SHORT-TERM EXPOSURE TO LARVAL VOLATILES

After 20 days in a high-density culture containing many larvae, female sawtoothed grain beetles, Oryzaephilus surinamensis (L.), laid half as many eggs in a 24-hr oviposition bioassay as females held for six days in the same culture, or for six or 20 days in a low-density culture. Oviposition by females held for six days in a high-density culture was reduced to a similar extent when they were exposed in the oviposition bioassay to an oat flake treated with an extract of Porapak Q-captured larval volatiles (equivalent to 5000 larval hours). A retained suppression of oviposition rate after prolonged exposure to larvae or an induced reduction caused by short-term exposure to larval volatiles both could be of adaptive advantage in reducing the risk of oviposition in an already densely populated habitat. © 1990 Plenum Publishing Corporation.