Population Dynamics and Prey Composition of Tetragnatha Spider in Semi-Organic Rice Field of Ranot Distritc, Songkhla Province, Southern Thailand

Abstract

Tetragnatha spiders are common predators in rice field ecosystems, which feed on various kinds of insects, but their population dynamics with the progress of rice growing stages are poorly understood. This study assessed the population dynamics and prey composition of Tetragnatha spiders in semi-organic rice fields in southern Thailand during four stages of rice plants, including vegetative growth stage, reproductive stage, ripening stage, and after harvesting stage. Spider and insect sampling was conducted at night between 1900h to 2200h because feeding activity of Tetragnatha spiders is highest. The results showed that species richness and abundance of Tetragnatha spiders were significantly higher in the reproductive stage than in the other stages. The main prey families captured by Tetragnatha spiders were different among stages of rice plants. Chironomidae, Corixidae and Baetidae were the main prey in the vegetative growth and the reproductive stages, while they were changed to Delphacidae thereafter. Insects with soft body and have high activity in the same period with building web of Tetragnatha spider tended to be caught in the web easily. It is concluded that both the spider populations and prey compositions are influenced by the stage of rice plants, which provided different food and habitat availability for spiders in rice ecosystems.