Investigating the Effectiveness of Using Sex Pheromones in Population Control and Damage Reduction of Chilo suppressalis

INTRODUCTION

Chilo suppressalis Walker is one of the most important pests of rice worldwide. The damage caused by this pest is particularly significant in temperate rice-growing regions of Asia such as Japan, Korea, and China. In the Middle East, this pest causes serious damage to rice crops, while in Europe it is only considered a pest of rice in Spain [1-3]. This pest attacks rice plants at various stages of growth and development, causing damage such as the death of central buds and whitened panicles [4, 5].

In the rice agroecosystem, if pesticides are used, the water of the fields contains chemical pesticide residues that can enter the food chain and cause great harm to living organisms, especially animals living in these areas. Therefore, today, the use of insecticides in the control of insect pests is problematic. Although chemical insecticides are of particular importance in the control of harmful insects of agricultural products, the use and selection of compounds with less or no effect on natural enemies and the environment, such as sex pheromones, is of particular importance. Therefore, it is necessary to review the efficiency and use of low-risk, safe, and environmentally friendly compounds in the rice field to reduce the process of developing pest resistance to common insecticides in the rice field [6-8].

Since Chilo suppressalis is considered an important pest in rice fields, it is necessary to control the abundance of this pest and maintain the rice crop. Chemical pesticides, especially granular insecticides. Also, if not managed properly, this pest can reduce rice yield by one-third. On the other hand, to control this pest, between 4000 and 8000 tons of granular insecticides are introduced into the rice agroecosystem annually [9-11]. The Integrated Rice Pest Management Program in Indonesia in 1986, by decree of the then president, banned the use of 57 insecticides in rice fields and, by training millions of farmers in non-chemical pest management, ultimately reduced the use of chemical insecticides by 60% [12, 13]. Therefore, rice farmers need to introduce and use new and usable compounds. One of the safe and appropriate methods of combating Chilo suppressalis is the use of synthetic sex pheromones, which is now considered one of the main foundations of mass pest management.

In recent decades, due to population growth and the need to ensure food security, pressure on natural resources has increased, especially in developing countries, which has resulted in increased agricultural production in many parts of the world through the use of high-yielding seeds, inorganic fertilizers, pesticides, and water, which in turn has led to an increase in production costs. Also, excessive and inappropriate use of agricultural chemicals has caused water pollution and reduced genetic diversity of living organisms, and soil quality [14, 15]. One of the most successful methods is the use of chemical communicators for pest control, which has been used in recent decades. This method involves the release of large amounts of synthetic pheromones to prevent or delay the mating of pest insects. This method was first used about 30 years ago to control the pest Trichoplusia ni (Hubner) [16].

Vacas et al. [3] showed that the effectiveness of 3 pheromone diffusers per hectare or a batch of inactive diffusers (total dose: 6.6 to 7.9 g/ha) was as effective as 30 pheromone diffusers per hectare (5 g/ha). They also reported that disruption of Chilo suppressalis mating reduced damage caused by the pest to less than 10%. The results of field experiments showed that the synthetic sex pheromone mixture was very effective for hunting Chilo suppressalis. The results of Raut et al. field study on the use of sex pheromones showed that the use of sex pheromones can reduce egg laying and also damage the pest in the vegetative and reproductive stages. Also, their observations showed that the average egg mass index in pheromone-treated plots in the rice field was significantly less than in the plots where the farmer had not used the pheromone [17, 18].

The present study aimed to determine the effectiveness of the Chilo suppressalis sex pheromone by mass trapping as a control method in the form of integrated management of Chilo suppressalis in the rice agroecosystem.

MATERIALS AND METHODS

This experiment was conducted in a rice research field. Thus, five treatments were performed, including sex pheromone with 1 trap per hectare, sex pheromone with 3 traps per hectare, sex pheromone with 5 traps per hectare, sex pheromone with 7 traps per hectare, and control (granular spraying with diazinon 10% at a rate of 15 kg per hectare). The concentration of Chilo suppressalis sex pheromone for all treatments was 2 mg.

For the present study, sampling was carried out in different generations and different stages of the rice plant. The first sampling was carried out from the dead central buds of the rice plant in the vegetative stage of the rice plant and the first generation of the pest. For sampling at this stage, 10 plants were randomly selected and examined from each experimental plot with a 1×1 meter square.

Sampling was carried out in the reproductive stage and the second generation of the pest from the white heads of rice one week to ten days before harvest. The operation of this sampling stage was similar to the sampling of dead central buds. The desired pheromone traps were installed from the beginning of the emergence of Chilo suppressalis in the experimental field until the rice harvest stage. After installing the traps, the number of moths caught by the traps was counted daily.

Pheromone traps were installed in the field on an area equivalent to 5 hectares. To carry out this experiment, pheromone traps were installed in a delta shape and the desired number in the field on wooden stands and slightly above the level of the rice plant. The height of the traps was adjusted according to the growth of the rice plant and the increase in plant height using a wooden stand. In this study, for the treatment of one trap, one trap containing the desired sex pheromone was installed in the middle of the one-hectare field, for three traps at three points in the field, for five pheromone traps at five points, and for seven traps at seven points of the experimental field (the distance between the traps was 1000 meters).

Collection of adult insects from traps continued from the first catch to the last catch of moths in each generation in the field. Also, the duration of attraction of traps, the duration of durability, and the stability of pheromones were investigated in this experiment. In this study, the control treatment was separated from the control treatment by spraying 10% diazinon granules at a rate of 15 kg/ha and without pheromone traps in the field and was carried out at a distance. In addition, all practices including the type of rice variety, nursery, preparation of rice seedlings, planting time of rice seedlings, irrigation, weed control, and control of plant pathogens were carried out according to the conventional program. In addition, the number of live larvae inside the stem was randomly determined in 10 frames in experimental plots with a size of 1×1 meters, and then the number of live larvae inside the infected stems was counted. To determine the yield of the crop, the plants were uprooted from each plot with an area of ​​5 square meters from 5 points and collected in the field after one day of sun exposure. Next, the threshed rice clusters were weighed with a digital scale with an accuracy of 0.01. The weight moisture of the product was determined with a moisture meter, and then based on the weight percentage table (14%), the final weight of each plot was taken.

The graphs were drawn using Excel software. Statistical calculations and data analysis related to the tested treatments were performed using the T-test in SAS ver. 9 software.

RESULTS AND DISCUSSION

The results of this study showed that the largest population of Chilo suppressalis caught by pheromone traps was during the third to sixth week, and the peak flight of the first generation was 161, which can be seen in Figure 1.

According to Figure 1, the largest number of moths caught by the treatment with seven traps per hectare was in the sixth week, and after that, it was associated with five pheromone traps per hectare (143). The lowest number of moths caught was associated with the spraying treatment (trap without pheromone). In this regard, it should be noted that the number of moths caught in the spraying treatment was very low (one to two). In the same figure and the first generation, the three-trap treatment attracted 52 Chilo suppressalis. Also, the treatment with one trap in the same generation attracted 33 moths. In the second generation of the pest, the highest number of moths caught by pheromone traps was in the ninth week with seven pheromone traps per hectare and 129 moths. The five-trap pheromone treatment in the same generation attracted 58 moths. The three-trap treatment also caught 51 moths and the one-trap pheromone treatment caught 32 moths. The peak flight of the third-generation Chilo suppressalis moths occurred in the fourteenth week (70 Chilo suppressalis) (Figure 1). According to Figure 1, the lowest number of captured Chilo suppressalis moths in all generations was related to the treatment sprayed without pheromone traps.

In this regard, the results of Kanno et al. [19] studies comparing pheromone bait traps with light traps showed that the number of Chilo suppressalis moths caught by pheromone traps was very high over two generations. They also stated that the number of moths caught in pheromone traps was about three to five times higher than in light traps.

Table 1 shows the comparison of the average data. As can be seen, the dead central buds in the tested treatments are significantly different from each other at the 0.01 probability level. The highest percentage of dead central buds in the treatments of one and three pheromone traps per hectare was 26.31% and 26.2%, respectively, and they were classified in group a. The percentage of dead central buds infection in the treatment of five and seven pheromone traps per hectare was 17.15% and 16.57%, respectively, and statistically, the two traps were not significantly different from each other and were placed in group ab. The results of this study showed that the infection of dead central buds in the control treatment (spraying with diazinon granules) had the lowest value (11.18%) and was placed in group b.

The results of Table 1 showed that with the increase in the number of pheromone traps per hectare, the percentage of dead central buds decreased and a negative slope was observed (-3.19). Also, the linear equation showed that R² = 0.85 and there was a positive relationship between the number of traps and the decrease in the percentage of infection in the first generation of the pest. Also, Table 1 shows the infection of whitened clusters related to the traps. In this table, the highest percentage of bleached clusters contamination related to the treatment with one pheromone trap with 20.66%, followed by the treatment with three pheromone traps with 15.36% contamination were placed in two groups a and b, respectively, and the treatment with 5 and 7 pheromone traps along with the control treatment were placed in one group, and the lowest amount of contamination was 8.57% and 7.79%, respectively, in group c.

Table 1. Comparison of the evaluated indicators averages.

*Means with the same letter or letters in each column are not significantly different at the 0.01 probability level.