Knockdown, mortality, and progeny production of lesser grain borers (Coleoptera: Bostrichidae) and rice weevils (Coleoptera: Curculionidae) exposed for short intervals on wheat treated with cyfluthrin

Abstract

Adult lesser grain borers, Rhyzopertha dominica (F.), and adult rice weevils, Sitophilus oryzae (L.), were exposed at bimonthly intervals for 2, 4, 8, and 24 h on wheat treated with 0, 1, 2, and 4 ppm cyfluthrin EC, then removed and held for 2 wk on untreated wheat. The percentage of lesser grain borers that were knocked down after they were exposed increased as exposure interval and concentration increased, and was usually >90% at intervals >4 h for 8 mo after the wheat was treated. Mortality after 2 wk on untreated wheat generally decreased as residues aged, with no difference in mortality among exposure intervals. F1 production of lesser grain borers was low in untreated controls, so effect of exposure could not be determined. The percentage of rice weevils that were knocked down after exposure also increased as exposure interval and concentration increased; however, except for month 0, mortality after 2 wk on untreated wheat was usually <25% for all bioassays on wheat treated with 1 and 2 ppm cyfluthrin. Although the number of F1 rice weevils was dependent on initial exposure interval and concentration, the exposure intervals were not sufficient to prevent oviposition. Progeny production also increased as the residues aged. Results of this study indicate that lesser grain borers and rice weevils will survive if exposed for 24 h or less on wheat treated with cyfluthrin EC.