Pollinator Distribution in Pesticide-Applied and Pesticide-Free Vegetable Growing Areas in the Mid-Hill of Bagmati Province, Nepal

Insect pollinators play an important role in vegetable production. However, both farming practices and local environmental conditions can impact pollinator communities. The application of pesticides in vegetable farming has been increasing recently to fulfil the growing demand for vegetables due to population growth. The excessive use of pesticides, along with variations in elevation and ecological gradients, may influence insect pollinators. However, there seems to be limited previous research in this field. Thus, the present study examined pollinator diversity and networks in vegetable-growing areas with and without pesticide application in the Kavrepalanchok and Dhading districts. For this purpose, we selected four municipalities: Dhunibesi and Benighat Rorang from Dhading, and Panauti and Banepa from Kavrepalanchok. In total, 80 plots (40 m x 40 m) were established, encompassing 20 plots (10 with pesticide applied and 10 pesticide-free) from each municipality. The field observations and insect collection were carried out using sweeping nets and hand picking in the peak vegetable-growing season (October, 2023 to May, 2024). The specimens were identified using a stereoscopic microscope. The results showed significant differences in species richness, abundance, diversity, and plant-pollinator network characteristics in pesticide-applied and pesticide-free sites. By district, Kavrepalanchok revealed higher species richness (38 in pesticide-applied and 48 in pesticide-free sites) and Shannon diversity index (3.25 and 3.27, respectively) than Dhading. Similarly, the results revealed higher connectance (0.34), web-asymmetry (0.77), and nestedness (24.55) in pesticide-free sites of Kavrepalanchok. However, Dhading showed mixed results. These findings suggest the influence of agricultural practices and ecological gradients on pollinator distribution and interactions in vegetable farms. For understanding the impact of pesticide application, further extensive work with large spatial coverage along the different altitudinal gradients needs to be carried out.