ASSESSMENT OF ARTHROPOD DIVERSITY IN PADDY FIELDS AND ASSOCIATED WEED PATCHES IN THE KANDY DISTRICT, SRI LANKA

Abstract

Arthropods form a crucial component of agricultural ecosystems, playing essential roles as herbivores, predators, parasitoids and pollinators. Their interactions contribute to important ecological processes such as pest control, pollination and nutrient cycling. Paddy fields and surrounding weed patches provide distinct but interconnected habitats that vary in structure, plant composition and microclimatic conditions. These differences influence the composition and abundance of arthropods, especially during the different growth stages of rice, ranging from seedling vegetative stages through to flowering and ripening. Weed patches, which often harbour higher plant diversity and offer refuge throughout the cultivation period, can serve as significant reservoirs for arthropod biodiversity. This preliminary study explores the diversity and distribution of arthropods in paddy fields and adjacent weed patches across four sites Pamunuwa, Hepana, Gangoda and Lankathilaka in the Kandy District of Sri Lanka during the Maha season that extended from October 2024 to February 2025. Arthropods were sampled using sweep netting, quadrat sampling and pitfall trapping methods, while weed density was assessed using quadrat sampling. Across all sites, the study recorded arthropods belonging to 8 different orders, 59 families and 99 genera. The sampled arthropods were categorized into four functional groups based on their ecological roles. The study revealed that arthropod diversity and abundance were significantly higher in weed patches compared to paddy fields, with weed patches recording 99 species and 7,512 individuals vs 78 species and 6,519 individuals in paddy areas. Hemiptera (24%) and Coleoptera (21%) were the most dominant orders, while predator groups like Araneae and Odonata showed notable presence, particularly in weed habitats. Functional group analysis showed a higher representation of herbivores and predators in weed patches, supporting greater ecological roles. Paddy field growth stages also influenced arthropod presence, with pests like planthoppers and grasshoppers increasing in vegetative and reproductive phases, and predator abundance rising in later stages. Diversity indices such as the Shannon (3.849), Simpson (0.9697) and Margalef (10.98) indices were consistently higher in weed ecosystems, indicating that weed patches support a more complex and balanced arthropod community structure than managed paddy fields. This study showed that the heterogeneous diversity of plants has an effect on arthropod diversity