Optimization of the Use of Acaricides Fenazaquin, Propargite, and Fenpyroximate against Tetranychus Urticae

INTRODUCTION

Green plants, as the first level of energy production, are always attacked by a wide range of herbivores. Tartanychus urticae Koch is one of the most important agricultural pests [1, 2]. This mite can grow and spread on more than 1100 plant species [3, 4]. Tartanychus urticae starts to weave webs on the lower surface of the leaf and by feeding and sucking the cell sap, it destroys plant cells and leads to the appearance of yellow spots on the leaf surface. In this case, the chloroplasts of the leaves are gradually destroyed by the increase in the population of mites, feeding on the plant, the stomata of the leaf surface are closed and the reduction of transpiration leads to a decrease in production in the host plant [5-7].

The high growth and reproduction rate, short generation time, and high fertility and reproduction rate of Tartanychus urticae allow it to rapidly increase its population under appropriate conditions and cause increased damage and injury to the host plant [8, 9]. Due to the rapid increase in the population of Tartanychus urticae, farmers are forced to use acaricides in some cases. Therefore, it is necessary to pay attention to issues such as the use of specific and effective acaricides, the preservation of natural enemies, the prevention of resistance in the pest population, and chemical control is carried out with great care [10]. The most important challenge in the use of chemical pesticides is the persistence of these toxins in nature and plants. Excessive use of pesticides and their persistence in nature is one of the important sources of environmental pollution that negatively affects the health of living organisms, including humans [11-13].

Protecting the environment and its resources is one of the most important agricultural issues in the world, and therefore, modern agriculture is moving in a direction that creates the least risk from pesticides and achieves the highest yield in the crop [14, 15]. The acaricide fenpyroximate, with the trade name Ourtus, with a 5% suspension formulation, is a contact acaricide with a rapid impact effect on larvae, nymphs, and adult mites from the pyrazole group. Propargite, with the trade name Omite, with a 57% emulsifiable formulation, is from the sulfite group, which is a contact acaricide with a long-lasting and non-systemic effect that partially penetrates the outer layer of the leaf and, of course, remains mostly on the leaf surface. Fenazaquin acaricide, under the trade name Pride, is formulated as a 20% suspension from the quinazoline group. Its mode of action is an electron transport inhibitor that has a contact and digestive effect on larval, pupal, and adult tick stages and is used with a low dosage and a long-term effect on active stages and tick eggs [16].

Agricultural pesticide residues in fields may hurt farmers' health, and the long-term effects of pesticides can cause damage to liver and kidney tissue [17]. Achieving the best combination of factors affecting the process has always been one of the challenges for researchers. Optimization means using each input in the right amount and at the right time. Optimization refers to improving the performance of a product to achieve maximum benefit from it [18].

Managing the selection and optimal use of inputs and pesticides is one of the ways that reduce pesticide consumption. Given the adverse effects of pesticides and the resulting savings, the importance of optimizing the use of pesticides is becoming increasingly clear. One of the most important measures to increase the effectiveness and optimize the use of pesticides, including acaricides, is to use them at the appropriate dose and under appropriate temperature and relative humidity conditions [19, 20].

The response surface methodology is one of the optimization methods. This method began with the works of Box and Wilson in 1951 [21, 22]. Beans are among the most important legumes that are widely cultivated in the world and are consumed as an important source of nutrition. Beans contain 20 to 25% protein, which can be a good substitute for animal protein [23, 24]. Given the importance of legumes in various agricultural and food aspects, and given that no study has been conducted on optimizing the use of acaricides such as fenpyroximate, fenazaquin, and propargite against spider mites on beans, this study aimed to determine the optimal conditions for using the above three acaricides to control the spider mite Tetranychus urticae on cowpeas at different doses, temperatures, and humidity levels in laboratory conditions using the response surface methodology. This study aims to investigate the increase in mortality and the reduction in pesticide consumption.

MATERIALS AND METHODS

Bean plant cultivation

In this study, all laboratory studies were conducted using bean leaf discs with the scientific name Vigna unguiculata L. Bean seeds were soaked in a damp cotton cloth for 48 hours at a temperature of 27 °C and a light-to-dark ratio of 16 to 8 hours. After germination, 3 seeds were sown in each pot in a triangular shape in plastic pots with a diameter of 9 cm and a height of 10 cm containing a perlite substrate, and its surface was covered with a layer of sawdust [25]. The pots were placed in a growth chamber at a temperature of 25 ± 2 °C. The watering period of the pots was adjusted twice a week and macro and micro fertilizers were used as the plant went through the growth stages. The 3- to 4-leaf stage of the plant was used for experiments and the establishment of the Tartanychus urticae mite.

Tartanychus urticae mite cultivation

The population of Tartanychus urticae was established using bean plants. For this purpose, leaves infested with spider mites were collected from greenhouses and transferred to the laboratory. Using a 0.3 cm thin brush, mites were separated from the back of the leaves and placed on bean leaf discs that were placed in a plastic Petri dish containing cotton soaked in water to provide humidity. To prevent mites from escaping, a 3 mm high barrier was created around the leaves with cotton. The discs containing mites were transferred to several pots and placed at a temperature of 25 ± 2 °C and a relative humidity of 55 ± 5%. To increase the population of Tartanychus urticae, healthy pots were first separated from infected pots and the dried leaves of the infected pots containing spider mites were placed on healthy bean plants and reared for at least two generations in the laboratory [10]. During cultivation, mites, by feeding on leaf chlorophyll and growth and development, caused yellowing, drying, and browning of the leaf surface, and the destruction of the entire bean plant. Therefore, to maintain the colony of Tartanychus urticae, pots containing infected plants were replaced with healthy, uninfected pots every week.

 Age matching of ticks

To prepare a population of the same age of Tartanychus urticae mites to begin the experiments, the first 3-4 infected leaves were separated from the bean plant. To obtain a population of the same age of adult female mites, 60 adult female mites were separated from the infected pots using a small 0.3 cm brush and with the help of a stereomicroscope and placed on a bean leaf disc surrounded by wet cotton, with its back surface facing up and its upper surface on wet cotton in a plastic Petri dish with an opening diameter of 8 cm and a height of 1 cm. To create proper ventilation inside the Petri dish, part of the Petri dish lid was cut and covered with a double-layered silk mesh [26]. The adult female mites were given 24 hours to lay eggs. Then, the adult females were removed and the Petri dish containing the eggs laid by the adult mites was kept in a germinator at a temperature of 25 ± 2 °C, relative humidity of 55 + 5%, and a light-to-dark ratio of 16 to 8 hours until reaching maturity.

Determining the range of independent variables of the acaricides fenpyroximate, fenazaquin, and propargite

Based on the biology of the pest, the best and most desirable relative humidity and temperature (independent variables) were determined to be 55-60% and 25-30 °C, respectively. To determine the lethal concentrations that cause 25 to 75% mortality, the acaricides were bioassayed, which included concentrations of 125-1500 μL per liter of distilled water for fenpyroximate, 900-2300 μL per liter of water for propargite, and 69-2330 μL per liter of water for fenazaquin, as the minimum and maximum lethality. Bioassay data analysis for the lethal dose ratios for the tested acaricides and their ranges was performed using POLO-PC software. The most important issue in response surface studies is the interaction between factors. In the present study, the effects of independent variables including X1 temperature, X2 humidity, and X3 dose of application were evaluated (Table 1). Based on the number of variables, statistical design tables were determined for each acaricide with 14 experiments and six replications at the central point to calculate the repeatability of the process (Table 2). The optimization of the three-point overhead crane consumption was carried out using Design Expert 7.00 software and the Response Surface Method with Central Composite Design (CCD).

Table 1. Independent process variables and their values ​​for the experiments.

RESULTS AND DISCUSSION

Selecting the appropriate model: Lack of fitness test, coefficient of determination (R²), and adjusted coefficient of determination (R²adjusted) are used to check the correctness of the model. The significance of the lack of fit test for a model indicates that the points are not well located around the model and the model cannot be used to predict the values ​​of the function variables. As a result, when the lack of fit test becomes insignificant, it can be seen that the model can be well fitted to the data under test. The adjusted coefficient of determination confirms that the model can estimate the answers well and the coefficient of determination is the ratio of the changes described by the model to the total changes and is a measure of the degree of goodness of fit [10]. According to Table 3, the lack of fit test is not significant for all three pesticides, which indicates that the model shows the data trend well. The coefficient of determination and the adjusted coefficient of determination are given in Table 3. Comparison between the regression models of all three acaricides showed that the linear model was statistically significantly different from the other models (P < 0.0001). The significance index of the lack of fit test for a model indicates that the points are not well located around the model and the model cannot be used to predict the values ​​of the function variables. Therefore, with the lack of fit test being insignificant, it can be seen that the model can be well fitted to the data under study.

Table 2. Test pattern.

Table 3. Response surface variance analysis table for the linear model of mortality of adult female ticks treated with the acaricides fenpyroximate, propargite, and fenazaquin.