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

Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2for both deltamethrin (Figure 1) and cypermethrin(Vassal et al., 1997; Vaissayre et al., 1998; Martin etal., 2000). Field data recorded for eight consecutiveyears (Figure 2) revealed that the pest infestationprofiles changed deeply from 1991 to 1998 (Ochou etal., 1998). Moreover, cases of ineffectiveness of thepest control programme against H. armigera have beenreported during exceptional pest outbreaks in Côted'Ivoire. With this regard, the routine calendar-basedprogramme applying six fortnightly sprays ofpyrethroid-organophosphate insecticide mixtures overthe whole cotton season has been questionned as thepyrethroid resistance in H. armigera was confirmed(Ochou & Martin, 2000). Similar cases of resistancewere reported in H. armigera in most West Africancountries (Benin, Burkina Faso, Guinea, Mali, Senegal,and Togo) (Anonymous, 1999).Development of the IRM strategy against H. armigera:To face pyrethroid resistance in the cottonbollworm, H. armigera, an Insect ResistanceManagement (IRM) programme, inspired from the"Australian" strategy (Sawicki and Denholm, 1987),was designed in Côte d'Ivoire. In practice, the strategyhas led to the determination of a pyrethroid-free seasonnationwide by using non-pyrethroid insecticides(endosulfan 700-750g/ha and profenofos 750 g/ha) in akind of "window" programme in order to lessenpyrethroid selection pressure. The pyrethroid-freeseason is established according to cotton growingzones (August 10 and August 20 respectively fornorthern and southern regions). The main picturewhich has come out from the nationwide adoption ofthe pyrethroid resistance management programme bycotton farmers is the important decrease in the fieldpopulations of H. armigera (Figure 2) since 1998(Ochou & Martin, 2002).Endosulfan has been widely used in the currentpyrethroid resistance management programme over thelast four years in Côte d'Ivoire, and so far, no resistanceto endosulfan has been detected (Martin et al., 2002).However, its recommendation is being actuallyquestioned with regard to its toxicity, environmentalissues, and farmer practices. To tackle this problem,investigations are being undertaken to adapt arelatively low dose of endosulfan (525 g/ha) to theactual field infestation of H. armigera (Ochou &Martin, 2000) and to assess microencapsulatedformulations of endosulfan, assumed safer than the ECformulations. At the same time, further investigationsfocused on new insecticides such as spinosad andindoxacarb as potential alternatives to endosulfan.Spinosad is a naturally produced mixture of theactinomycete Saccaropolyspora spinosa. Its mode ofaction is described as an activation of the nicotineacetylcholine receptor, but at a different site fromnicotine or imidachloprid. It is activated by contact andingestion, causing paralysis (Pesticide Manual, 12thedition, v2). Indoxacarb is an oxadiazine product wherethe active component blocks sodium channels in nervecells. It is activated by contact and ingestion, andaffected insects cease feeding, with poor co-ordination,paralysis, and ultimately death (Pesticide Manual, 12thedition, v2). Due to their novel mode of action, bothinsecticides appear ideal for resistance managementprogrammes. However, to be rationally used, there is aneed for a precise activity spectrum of these newinsecticides that proved as effective as endosulfan incontrolling H. armigera (Ochou & Martin, 2002).The present study is to assess the activity spectrumof spinosad and indoxacarb with regard to beneficialsand major components of the cotton pest complex inCôte d'Ivoire. The need to reinforce their activity byother insecticides will be also assessed. On the basis ofthe strength and weakness of these new insecticidesand with respect to cotton crop phenology and seasonaloccurence of main pests, appropriate recommendationswill be stated to justify their integration into thepyrethroïd resistance management programmes.76