FIELD SELECTION FOR ENDOSULFAN RESISTANCE IN COFFEE BERRY BORER (COLEOPTERA, SCOLYTIDAE) IN NEW-CALEDONIA

A direct spray technique was used to monitor the frequency of endosulf an-resistant Hypothenemus hampei (Ferrari) in transects across individ ual coffee fields that had been sprayed from the road. A rapid decreas e in resistance frequency (phenotypic cline) away from the road was ev ident in one traditional low-density (shady) and two modern intensive (sunny) fields surveyed in 1988. Subsequent treatment of one sunny fie ld with two applications of endosulfan in 1989 resulted in an increase in the frequency of the endosulfan-resistant phenotype by an average of 61.4% across the field. In contrast, treatment of a second sunny fi eld with fenitrothion led to decreased frequency of the endosulfan-res istant phenotype by an average of 12% across the field. Concentration- mortality responses for beetles from particular locations in the field s (e.g., the roadside or most distant side) confirmed results obtained with the diagnostic concentration (LC99.95 of susceptible individuals ). After 1 year, frequency of the phenotype resistant to endosulfan al so declined an average of 18% in a shady field treated with fenitrothi on. Responses of beetles collected from the roadsides of other coffee fields confirmed that the frequency of the resistant phenotype decline d an average of 47.3% at sunny fields and 34.5% at shady fields in the second year, after fenitrothion began to be used. Further application s of endosulfan raised the resistance frequency in four of five fields in the second year. Changes in frequency of the resistance phenotype in the absence of the insecticide suggest that the frequency of endosu lfan resistance may not decline rapidly enough to justify reintroducti on of endosulfan within several years.