Monitoring of beet armyworm resistance to spinosad and methoxyfenozide in Mexico

摘要

BACKGROUND:Resistance to spinosad and methoxyfenozide has been studied in several insect pests,but there is a lack of information on Spodoptera exigua(Hubner)in Mexico.Therefore,evidence for the development of resistance in this pest to both compounds was examined.The effects of methoxyfenozide on reproductive parameters of S.exigua adults were also determined.RESULTS:Third instars from a field population were exposed for 24 h to the LC50 of spinosad or methoxyfenozide for over six generations(G2-G7).No significant reduction in susceptibility to either compound was detected for up to five generations.In G7,LC50 values for insects exposed to spinosad and methoxyfenozide were respectively 2.75-fold and 1.25-fold greater than for G1 larvae.Oral treatment with methoxyfenozide reduced the fecundity and fertility of G7 adults,confirming sublethal effects on reproduction.Finally,five populations(Se-La Floriza,Se-Lazareto,Se-Bachigualato,Se-Los Agustinos and Se-Villa de Arista)of S.exigua were collected from fields in three states of Mexico for resistance monitoring to spinosad and methoxyfenozide.With the exception of Se-Villa de Arista,the other populations showed significant resistance to spinosad,with resistance ratios between 16-and 37-fold,compared with a susceptible laboratory colony.In contrast,only one population(Se-Lazareto)showed significant resistance to methoxyfenozide(13-fold).CONCLUSION:Resistance management programmes should be established,particularly in areas where S.exigua has developed resistance to spinosad.