Investigating the effect of weather factors on the population trends of cotton pests at the initial growing stage in Fars province

Cotton seedlings are attacked by several sucking pests such as cotton thrips (Thrips tabaci Lindeman), cotton aphid (Aphis gossypii Glover), green leafhopper (Empoasca sp.), and cotton whitefly (Bemisia tabaci Gennadius), which cause significant damage if not adequately controlled. Climatic factors such as temperature and relative humidity are among the most important external factors regulating insect populations. Since pests can cause severe damage to cotton fields in the early stages of cotton cultivation, the present study investigated pest population fluctuations and their relationship with weather factors. The results may be useful for integrated management of cotton pests.

This project was conducted in 2020 and 2021 at Darab Agricultural Research Station. The experimental field was divided into five replicates. From each replicate, 5 seedlings were randomly taken. The sampling unit was the number of pests on a cotton seedling. Sampling was done weekly. The meteorological data recorded on a daily basis was obtained from the Darab Meteorological Station, which is located 200 meters away from the project site. Using the correlation analysis, linear and non-linear regression, the relationship between the population of each pest and meteorological variables was investigated.

In the first year, with the germination of cotton seedlings, thrips infection also started (0.41 thrips per seedling) and then the thrips population density increased more than six times until the middle of June (2.74 thrips per seedling). When the weekly average maximum daily temperature exceeded 42 degrees Celsius, thrips population decreased. The results of the correlation analysis between the weekly average maximum daily temperature and the weekly average density of thrips showed that this correlation is negative and significant (P = 0.008; R = -0.68). By combining the data of both years of the experiment, the results of linear regression analysis showed that there is a significant relationship between the weekly average of whitefly density and the weekly average of daily relative humidity. The results of the present research showed that the most important weather factor influencing the cotton aphid population is the air temperature, so that when the air temperature is higher than 30 degrees Celsius, the activity of the aphid decreases drastically.

The results of this research showed that cotton seedling is faced with a wide range of pests, and weather factors, especially temperature and relative humidity, are effective on the onset of pest infestation at the initial growing stage of cotton, as well as on the density and fluctuations of the cotton pest population. Therefore, the results of this study can play an important role in the planning and application of integrated pest management programs for the cotton pests at the initial growing stage.