A recent increase in the Calocoris trivialis populations associated with premature olive blossom dropping in Crete coupled with ineffective control by organophosphate and pyrethroid insecticides resulted in resistance development speculation. A stem-dip assay was developed to evaluate C. trivialis susceptibility to dimethoate and beta-cyfluthrin against nymphal and adult insect stages. Susceptibility of C. trivialis populations collected from two Cretan orchards with no (AGRK) and extensive spray history (SPL) to both insecticides was evaluated and compared. Dimethoate LC50 values of the AGRK population were 17.47 and 33.37 mg L-1 for adults and nymphs and 45.85 and 20.08 mg L-1 for SPL respectively. C. trivialis was significantly more susceptible to beta-cyfluthrin as indicated by LC50 values for AGRK, SPL adults (0.53, 0.73 mg L-1) and nypmphs (1.44, 2.21 mg L-1). No evidence for resistance development was found in any of the insecticide cases. Adult insects were significantly more sensitive than nymphs in both insecticide/population combinations. Ratios of nymph: adult LC50values were 1.91, 2.71 for dimethoate and beta-cyfluthrin in AGRK and 2.28, 3.02 in SPL population. Susceptibility data and evidence of differential stage-dependent response of C. trivialis to both insecticides should be taken account for the establishment of effective control strategies.
Keywords: Beta-cyfluthrin; Dimethoate; Insecticide sensitivity; Mirid; Olive fruit.