Population dynamics and insecticide efficacy of <i>Bemisia tabaci</i> (Hemiptera: Aleyrodidae) on cucumber in relation to climatic variables under field condition

The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a major pest of cucumber (Cucumis sativus L.), causing significant yield losses through phloem feeding, honeydew production, which encourages mould formation, and the spread of economically significant plant viruses. The objective of this field study was to investigate the ecological dynamics and population density of B. tabaci on cucumber plants throughout the two growing seasons (2024 and 2025) in Etay El-Baroud District, El-Beheira Governorate, Egypt. The seasonality studies are important to know which season had more favorable climatic conditions for insect growth and development. This study also evaluated the relationship between cucumber plant age and whitefly population density using the third-degree nonlinear equation during the two growing seasons. Moreover, correlation and regression analyses were conducted to examine the relationship between cucumber plant age and selected weather variables. In addition, correlation between the percentages of damaged cucumber leaves and B. tabaci population density was analyzed. In parallel, four insecticides were evaluated under field conditions: Spiromesifen (Koffex 24% SC), Etofenprox (Primo 10% SC), Thiamethoxam (Tulbert 24% SC), and Spinetoram (Radiant 12% SC) against the immature (Egg and nymphal instars) and adult stages of the whitefly. The field study showed that infestation was first on cucumber plants 15 days after planting, and the percentage of damaged leaves increased markedly, reaching peaks of 43.33% and 45.00% in late April during the two seasons, respectively, before gradually declining until June. Thus, control measures should be initiated during the seedling stage before the pest reaches its peak population density. The results of the insecticide evaluation revealed that insecticides provided strong suppression of the different developmental stages of the whitefly during the early assessment periods, whereas their efficacy declined with time. Overall, across both seasons, Koffex was the most effective treatment against whitefly eggs, whereas Primo, Tulbert, and Radiant showed comparatively lower and less persistent effects.