Evaluation of three bioassay techniques for citrus thrips resistance and correlation of the leaf dip method to field mortality.

Abstract

Three bioUHSUy methods were compnrcd for cvulullting citrus thrips, Scirtothrips citri (Moulton), insecticide resistance with susceptible and Ouvolinate resistant laboratory strains. The leaf dip technique at the LC:;o was 2to 3.B-fold more sensitive to both dimethoate and nllvalinate than the leaf sproy t.echniQue, whereas topical application was least sensitive (up to 19-foJd). As the leaf dip metJlod was more sensitive llnd easier to perfonn, morlnlitics obtained in the laboratory bioassay were correlated with actual field mortalities at various dosages of Ouvalinate and fonnetanate to e\'aluate t.he suitability of this technique for monitoring and predicting field failures caused by insecticide resistance. Mortalities obtained by the dip method were ca. 2-fold higher than those observed at the same dosage in the field, and this method can therefore be used to conservatively estimate acmal field mortalities for purposes of citrus thrips resistance management. The importance of an appropriate field dosage for new insecticides to prevent early field failures is discussed as part of a general resistance management strategy.