Monitoring of beet armyworm resistance to spinosad and methoxyfenozide in Mexico.
BACKGROUND
Resistance to spinosad and methoxyfenozide has been studied in several insect pests, but there is a lack of information on Spodoptera exigua (Hübner) 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 LC(50) of spinosad or methoxyfenozide for over six generations (G(2)-G(7)). No significant reduction in susceptibility to either compound was detected for up to five generations. In G(7), LC(50) values for insects exposed to spinosad and methoxyfenozide were respectively 2.75-fold and 1.25-fold greater than for G(1) larvae. Oral treatment with methoxyfenozide reduced the fecundity and fertility of G(7) 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).


CONCLUSIONS
Resistance management programmes should be established, particularly in areas where S. exigua has developed resistance to spinosad.
Osorio
Aniceto
A
Instituto de Investigaciones Agropecuarias y Forestales, Universidad Michoacana de San Nicolás de Hidalgo, Km. 9.5 Carr. Morelia-Zinapécuaro, 58880 Tarímbaro, Michoacán, Mexico.
Martínez
Ana M
AM
Schneider
Marcela I
MI
Díaz
Ovidio
O
Corrales
José L
JL
Avilés
Mayra C
MC
Smagghe
Guy
G
Pineda
Samuel
S
D000818:Animals; D027461:Beta vulgaris; D004338:Drug Combinations; D006834:Hydrazines / Q000494:pharmacology*; D007300:Insect Control; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007605:Juvenile Hormones / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology*; D008800:Mexico; D012098:Reproduction / Q000187:drug effects; D018411:Spodoptera / Q000187:drug effects*
D004338:Drug Combinations; D006834:Hydrazines; D007306:Insecticides; D007605:Juvenile Hormones; D018942:Macrolides; C406712:methoxyfenozide; C415329:spinosad