Analysis of the influence of wind on the spread of Thrips tabaci (Thys.: Thripidae) in the cotton fields of Golestan province

The onion thrips, Thrips tabaci Lindeman, one of the most important pests of vegetables, ornamentals and leafy crops, is widely distributed worldwide. Therefore, the study of factors contributing to the spread of this insect in agricultural ecosystems is of great importance. Considering the physiological conditions of this pest, wind is considered one of the most important factors for its spread. In this study, we investigated the effects of wind conditions on the spread of T. tabaci in Golestan province in 2021. We selected 48 cotton fields (at the cotyledon stage) in Golestan province and collected data on the relative population density of T. tabaci over a period from 10.03.1399 to 04.04.1399 (three times per week). The relative population density of thrips in each monitoring field (with a minimum size of one hectare) was estimated using the "shaking method" by placing white paper or plastic trays under randomly selected cotton plants, ensuring that they completely covered the lower leaves. We then counted the average number of thrips that fell on the white surface per plant and reported the results per hectare. Wind speed and direction during this period were analyzed using data from eight weather stations and wind rose diagrams were created. The data processing and wind statistics as well as the creation of the wind rose diagrams were carried out using WRPLOT software.  The average population density of T. tabaci in Golestan province during the specified period was 38.5 thrips per plant, with all stages recorded. No statistically significant difference was found between the districts of Golestan province in terms of relative population density of thrips. The percentage of frequency of windlessness (less than 0.54 m/s) was 69.86 to 84.48%. Spatial autocorrelation analysis (Moran's I) was used to identify hotspots (areas with a high probability of occurrence) of T. tabaci. The overall Moran's I values during the monitoring period (I = 0.35, p-value = 0.0174) indicated a random distribution of Thrips tabaci population density data collected in the fields. The map of relative density of T. tabaci in the cotton fields using inverse distance weighting method showed infestation centers in Gorgan, Kordkuy, Bandar Gaz and Aliabad regions.  Based on the results, it is possible to predict the dispersal patterns of onion thrips by obtaining information about the prevailing winds, which in this study came mainly from the west. By predicting the starting points of the infestation, certain control measures, such as the use of sticky traps along the prevailing wind directions, can be recommended to farmers.