Ovidio Díaz-Gómez

Susceptibility of Females and Males of Bemisia tabaci (Gennadius) B-Biotype and Trialeurodes vaporariorum (Westwood) to Thiamethoxam

Abstract. Differences in susceptibility to insecticides based on adult insect sex indicate that males are more susceptible than females. Hence, it may be necessary to sex the insects before a bioassay is conducted, but this activity is tedious, takes time, and this manipulation might cause harm to the insects. Monitoring the evolution of resistance to the neonicotinoid insecticides in field whitefly populations is important and usually based on adult exposure to these toxicants. The aim of this study was to correlate the susceptibility to thiamethoxam with sex in susceptible populations of Bemisia tabaci (Genn.) B-Biotype and Trialeurodes vaporariorum (West.). Five-day-old males, females, and a mixture of female and male (80:20) adults were evaluated to determine log doses-Probit lines for this insecticide. In B. tabaci, the CL50 ranged of 1.4 mg [lA] L-1 to 2.8 mg and the relative proportion RR50 ranged from 1.0 to 2x. The CL95 ranged from 12.3 to 16.7 mg and the RR95 values varied from 0.8 to 1.0x. In T. vaporariorum, the CL50 fluctuated from 14.2 to 30.3 mg and the value of RR50 between 1.0 and 2.1x. The CL95 ranged of 180.4 to 314.0 mg and the RR95 from 1.0 to 1.7x. In both species, no differences were found between insect sex and susceptibility to thiemathoxam. Hence, to conduct bioassays with thiamethoxam on these species, the use of one sex or the other is irrelevant.

Resistencia de Tetranychus urticae Koch a Acaricidas Usados en la Producción de Rosal de Invernadero en México

Abstract. In the State of Mexico, Mexico, Rosa sp. production is one of the most important economic activities. However, the two-spotted mite, Tetranychus urticae Koch, is a pest that limits this crops productivity, and its control is carried out mainly with acaricides. Therefore, we estimated the levels of resistance to six acaricides in three field-collected populations of T. urticae from greenhouses of this growing region, and compared their response with a susceptible population of the same species. The products tested were abamectin, fenbutatin oxide, chlorfenapyr, amitraz, bifenthrin, and propargite. Significant differences were found in the response to the applied concentrations of acaricides. The levels of resistance were high to all tested acaricides, except fenbutatin oxide, in the Villa Guerrero and Tenancingo populations. The Coatepec population was susceptible to fenbutatin oxide and abamectin and had higher levels of tolerance to bifenthrin, amitraz, and chlorfenapyr. The RR50 values in resistant populations, ranged from 10 (propargite in Tenancingo population) to 6.400-fold (amitraz in Villa Guerrero population), in comparison to the susceptible reference. Amendments to both pest management strategies and the use of acaricides against T. urticae in Rosa sp. are proposed.