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 (Baythroid, ‘FCR 4545’ [both cyfluthrin], Karate [lambda cyhalothrin]) and insect growth regulators (Confirm [tebufenozide], ‘RH-2485’ [methoxyfenozide]) against the Mexican rice borer, Eoreuma loftini (Dyar), a key pest of sugarcane in south Texas. We also studied treatment effects on longevity and survivorship of its braconid parasitoid, Allorhogas pyralophagus Marsh. In the 1996 field season, Baythroid resulted in lower percentages of bored internodes compared with the other treatments. In the 1997 season, less borer damage was found in ‘FCR 4545’ (an isomer of Baythroid), relative to the other treatments. The differences may be partially attributed to the different application methods (tractor sprayer versus aerial). In both field seasons, no significant treatment effects could be found in any of the yield or juice quality measurements, suggesting that improvements must be made in application technology, or the biorational insecticides must be used in conjunction 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 generally most effective in reducing damage caused by E. loftini, although residual toxicity of Baythroid was higher than FCR 4545 against both E. loftini and A. pyralophagus. Comparisons between similar bioassays showed that Baythroid and tebufenozide were more toxic to E. loftini than to A. pyralophagus. Therefore, if A. pyralophagus or a similar parasitoid were to be used in conjunction with an insecticide, an effective approach may be to use a less 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.