Temporal dynamics of rice insect pests and natural enemies in relation to weather variables in northern Bangladesh

Understanding the seasonal dynamics of insect pest and their natural enemies in relation to climatic variables is crucial for developing ecologically sound pest management strategies. This study monitored key pests and natural enemies by daily using light traps from January 2019 to December 2024, alongside the collection of meteorological data. The findings revealed moderate insect diversity (Shannon-Weiner index = 1.04) but low species evenness (Pielous' evenness = 0.406) reflecting the dominance of few species, particularly brown phanthopper (73.6%). Distinct climatic seasonality was observed, with the highest temperatures and rainfall occurring from March to October, corresponding with peak pest activity specifically May-July and September-November. The stem borer, rice leaffolder, brown and white-backed planthoppers (WBPH), green leafhopper, and zigzag leafhopper showed higher abundant during warmer months with maximum; minimum; mean temperatures ranging from 29.26 to 32.17°C; 17.68-26.70°C; 23.47-29.44°C, with high relative humidity ranging from 68.36 to 84.22%. The Aman (rain-fed) season exhibiting the peaked pest populations, followed by Aus (pre-monsoon) and Boro (irrigated) seasons except for rice bug, due to temperature and rainfall (p < 0.05). The Aus season was the hottest (maximum: 30.59-32.75°C, minimum: 24.08-24.96°C) with heavy rainfall (377.63 mm) followed by Aman (maximum: 30.10-31.66°C; minimum: 23.31-25.16°C; rainfall: 301.05 mm), and Boro (maximum: 26.64-28.44°C; minimum: 15.72-17.94°C; rainfall: 171.40 mm) respectively. Moreover, peak activity of most harmful insects was observed during the reproductive stage of rice. Among natural enemies, green mirid bug (GMB), carabid beetles, dragonflies, damselflies, and ladybird beetles exhibited strong seasonality, correlated with pest abundance and favorable climates. The maximum and mean temperatures were significantly & positively associated (p < 0.05) with most pests and predators, while rainfall had mixed effects, significantly enhancing WBPH (<0.05) and damselfly (p < 0.001) populations while suppressing GMB (p < 0.05) and others. Ladybird and carabid beetles were positively correlated with major pests. Transitional periods between cropping seasons (Boro-Aus and Aus-Aman) emerged as sensitive windows for pest emergence, management and natural enemy activity. These findings underscore the intricate interaction between climate and insect ecology and support the development of climate-resilient, season-specific Integrated Pest Management, incorporating with regular monitoring and habitat management.