Laboratory and field evaluations of biorational insecticides against the Mexican rice borer (Lepidoptera : Pyralidae) and a parasitoid (Hymenoptera :Braconidae)

We compared laboratory and field efficacies of pyrethroid insecticides (Bay throid, 'FCR 4545' [both cyfluthrin], Karate [lambda cyhalothrin]) and inse ct growth regulators (Confirm [tebufenozide], 'RH-2485' [methoxyfenozide]) against the Mexican rice borer, Eoreuma loftini (Dyar), a key pest of sugar cane in south Texas. We also studied treatment effects on longevity and sur vivorship of its braconid parasitoid, Allorhogas pyralophagus Marsh. In the 1996 field season, Baythroid resulted in lower percentages of bored intern odes compared with the other treatments. In the 1997 season, less borer dam age was found in 'FCR 4545' (an isomer of Baythroid), relative to the other treatments. The differences may be partially attributed to the different a pplication methods (tractor sprayer versus aerial). In both field seasons, no significant treatment effects could be found in any of the yield or juic e quality measurements, suggesting that improvements must be made in applic ation technology, or the biorational insecticides must be used in conjuncti on with other control agents, such as biological controls. Efficacy may be improved if applications can be timed to windows of susceptibility based on either plant phenology or pest lifecycle. Baythroid and FCR 4545 were gene rally most effective in reducing damage caused by E. loftini, although resi dual toxicity of Baythroid was higher than FCR 4545 against both E. loftini and A. pyralophagus. Comparisons between similar bioassays showed that Bay throid and tebufenozide were more toxic to E. loftini than to A. pyralophag us. Therefore, if A. pyralophagus or a similar parasitoid were to be used i n conjunction with an insecticide, an effective approach may be to use a le ss toxic biorational, such as the insect growth regulator tebufenozide, or to time the release of the parasitoids after residual toxicity has declined in a biorational such as FCR 4545.