The two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) has a wide range of host plants and is a serious pest of several crops worldwide (Tehri, 2014). T. urticae feeds mainly on the content of mesophyll cells, where it significantly reduces stomatal resistance, photosynthetic and respiratory rate, as well as growth, flowering and productive potential of crops (Goff et al., 2014). Due to the economic impact produced by the attack of T. urticae in different agricultural production systems, the control strategy is based, almost exclusively, on the use of agrochemicals; however, their effectiveness is variable (Modarres, 2012).

One of the main problems faced by chemical control is the rapid ability to create resistant populations after a few generations (Pascual, 2014). Given this circumstance and due to the degree of importance of this pest, it is necessary to know the levels of tolerance to pesticides, therefore, it is necessary to carry out toxicological studies to determine dose-mortality response lines and with it, identify the most efficient products and the most appropriate management recommendations. Therefore, the objective of the present research was to determine the susceptibility of four acaricides in three populations of T. urticae from rose crops of Tenancingo, State of Mexico.

The present research was carried out in the Laboratory of Toxicology of the Department of Agricultural Parasitology of the Antonio Narro Autonomous Agrarian University, Saltillo, Coahuila. Three acaricides were evaluated: Abamectin (Agrimec^® 1.8% EC), Acequinocyl (Kanemite^® 15 SC), Chlorfenapyr (Sunfire^® 2 SC) and Cinnamomum zeylanicum extract, (Cinnax^®), six doses of each product with three repetitions of each were evaluated. The populations used were mites from the greenhouse of Agricultural Parasitology free of selection pressure by pesticides for 10 years as a susceptible reference population, and three field populations with different management of acaricides, from greenhouses of three farms in rose crops of Tenancingo, State of Mexico: Rancho Los Pilares (L1) with acaricide rotation, Rancho Isoflor (L2) with acaricide rotation and Rancho Lizflor (L3) without acaricide use.

The collection in the field was carried out manually, they were placed in plastic containers and coolers for transfer to the Laboratory of Toxicology, where they were placed in plants of Phaseolus vulgaris of the Lima variety for feeding, they were kept under controlled conditions at a temperature of 25 ±2 °C, relative humidity of 60 to 70% and 12 h of daily light provided with white light bulbs. For the preparation of the different concentrations, distilled water and the Bionex^® product as a dispersant were used in a ratio of 1 ml: 1L water.

The range of concentrations used was 10 ppm to 10 000 ppm, except for abamectin which ranged from 0.01 ppm to 6 ppm due to the high specificity of the product. The leaf immersion technique was used for the evaluation of the acaricides. Mortality was evaluated at 24, 48 and 72 hours, as a criterion of death the mites were moved with a brush, those that did not respond to the action were considered dead. A completely randomized experimental design was used, with six treatments and a blank control which was water plus adherent, with three repetitions each and 30 to 45 adults for each repetition.

With the data obtained from the bioassays, a mortality correction was made with the formula proposed by Henderson and Tilton (1955). The results were subjected to a Probit Analysis (Finney, 1971), to obtain the curve of concentration-mortality response and thus determine the lethal concentration (LC50), by means of the statistical program SAS System for Windows 9.0.

Once the LC50 for the field lines and the susceptible line was obtained, the resistance ratio (RR) was determined by dividing the values of the LC50 of the field lines by the LC50 of the susceptible line (Georghiou, 1962). Table 1 shows the susceptibility to acaricides in the different populations of T. urticae. Under the influence of abamectin, the L1 population obtained an LC50 of 0.074 ppm, so it was more vulnerable since the susceptible line (SL) presented an LC50 of 0.29 ppm, while L2 and L3 showed an LC50 of 0.389 and 1.23 ppm, respectively. The results of the SL and L2 are consistent with those reported by Kwon et al. (2011), who indicated an LC50 of 0.24 ppm in a susceptible line exposed to abamectin; for their part, Choi et al. (2020) in two field lines, reported an LC50 of 0.065 and 0.56 ppm, similar in L1 and L3.

Regarding acequinocyl, the most susceptible population was L3, it obtained an LC50 of 15.49 ppm compared to SL, which needed 35.56 ppm, while L1 and L2 require 106.21 and 176 ppm, respectively. These results are similar to a field line exposed by Fotoukkiaii et al. (2019), where they mention an 18.09 ppm for T. urticae, similar to the L3 of this study. In the case of chlorfenapyr, the population that presented more susceptibility was L3 (442.14 ppm), followed by L2 and L1 (699.88 and 706.97 ppm), where SL (765.82 ppm) was the most tolerant to this acaricide, the above may be due to the fact that it has resistance genes.

However, these results resemble those mentioned by Ferreira et al. (2015) in a field population collected in crops of Rosa sp., in which they showed an LC50 of 735 ppm, close to L2 and L1. Regarding the C. zeylanicum extract, the most exposed population was L3 with an LC50 of 213.43 ppm, followed by L2 and SL (240.48 and 300.88 ppm), while in L1, 647.58 ppm are required, respectively, these results agree with Shahrima and Khalequzzaman (2015), where they reached a higher LC50 (510.53 ppm) when they applied C. zeylanicum oil to a laboratory line similar to L1 and SL.

Table 1 shows the results of the resistance ratio (R. R. 50) of the populations under study as a function of the susceptible line. This variable allows us to discriminate populations with resistance problems, those that have a factor of 10 times when comparing the field lines and the susceptible line are considered resistant. In this study, resistance to abamectin was found in L1 (0.25 times), L2 (1.3 times), while the L3 line (4.2 times), which coincided with Monteiro et al. (2015) in a field line exposed to abamectin for three consecutive years, where they reported a resistance that was 1.4 to 9.7 times. Therefore, L3 showed a tendency to develop resistance, so it is recommended to start with rotation of acaricide applications with different toxicological groups.

For the acaricide acequinocyl, the resistance ratios in L1 (2.98 times), L2 (4.9 times) and L3 (1.03 times) for T. urticae coincided with Yorulmaz and Saritas (2014), who reported a field line with a resistance ratio of 4.8 times, while Choi et al. (2020) mention that, in a population exposed for more than six consecutive years, the ratio of resistance is greater than 1 798.6 times. It is appreciated that L1 and L2 tend to develop resistance, this because constant applications of this product are made according to the log corresponding to the management of these populations in the field.

Regarding the acaricide chlorfenapyr, Kumari et al. (2017), when applying this product to the same species, mentioned a resistance of 82.67 times, for their part, Ferreira et al. (2015) indicate a resistance of 2.2, 570 and 3 600 times respectively, these data differ from those found in this study, where for L1 (0.92 times), L2 (0.91 times) and L3 (1.02 times). Regarding C. zeylanicum, in this study there was no resistance, where the lowest value was for L3 (0.7) and the highest corresponded to L1 (2.15 times), these data are similar to those presented by Noha (2019), where applying cinnamon oil caused a high ratio of mortality in T. urticae, for their part, Roya et al. (2013) concluded that the essential oil affected age-specific fertility, life expectancy and pre-adult developmental period and decreased longevity of adult female mites.