Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2of cross-resistance with pyrethroids(Martin et al., 2002). It is the same for theprofenofos that did not show any resistancein H. armigera field populations (Fig. 6).This organophosphorus compound wasused since 1977 in mixtures withpyrethroids to control the mites. It wasused alone for 2000 as pyrethroidsalternative. No cross-resistance wasdetected with pyrethroids (Martin et al.,2002).these populations has been surveyed in each year since1985 (Fig. 4). Three plateaux appeared showingschematically the apparition of pyrethroid resistance inH. armigera populations from Bouaké: susceptibility(1985-1988), decrease of susceptibility (1989-1995)and resistance (1996-2001).Concerning the survey of pyrethroid alternatives,dose-mortality regression lines for endosulfan andprofenofos have been done annually since 1999 inBouaké populations. Endosulfan LD50s of fieldpopulations were at the same level than BK77 (Fig. 5).Thus endosulfan did not show any resistance in H.armigera cotton field populations. This cyclodiene isused from the 1970's in mixtures with DDT andmethyl-parathion. It was replaced by pyrethroids in1984. But from the development of pyrethroidresistance, endosulfan was reused alone with success(Ochou and Martin, 2002). From this result, it appearsthat this success partially originates from the absenceDISCUSSION Results obtained on larvaewith the application of discriminatingdoses by vial test method confirmed thepresence of resistant H. armigera in all thefield populations collected in Côte d'Ivoire.The larva vial test was not an accuratemethod. However, results obtained directlyin the field were indicators of thepyrethroid resistance and could beconfirmed with the bioassay method.Bioassays results showed that thedeltamethrin resistance level in H.armigera populations could be consideredas low in Côte d'Ivoire (in average RF