Arthropod Fauna on Mung Bean (Vigna radiata L.) Under Rice Fallow in Southern Dry Zone of Sri Lanka.

Abstract

Mung bean (Vigna radiata L.) is a grain legume crop widely grown in the tropics as an intercrop, particularly with cereals. Intercrop provides'additional income to the farmers but could be a refuge for pests of previous crops by providing continuous food supply. The objective of the present study was to study the arthropod fauna broadly catergorized as natural enemies, pests of rice and pests of mung bean in mung bean cultivations grown under rice fallow in paddy fields in Marakadayaya, Weeraketiya in Hambantota district. Mung bean cultivation was maintained under common agronomic practices, with or without insecticide treatments to control mung bean pod borer in paddy fields, which were rotavated after the harvest. Randomly selected lm2 areas of mungbean cultivation in each farmer field were used for the observation of arthropod fauna in the selected catergories. A number of arthropod fauna was counted weekly and the number of arthropod fauna/m 2 of the vegetation in each field was recorded in three weeks after the crop establishment. The fauna which could be categorized as mungbean pests, possible pests of rice and natural enemies were selected and their categorical status were confirmed. Visual observations were made weekly from 07.30 h. to 09.30 h. and five replicates per each were done. Aphids and thrips were the most prominent insect species available throughout the cropping period. Paddy bugs were the prominent rice pest and with the highest diversity share. Other rice pests such as stem borers and leaf folder moths were also recorded but in low numbers. Minimum number of rice pest population was observed in the rotavated fields. Spiders were the most available natural enemies in all fields and populations of lady bird beetles and predatory wasps were low compared to spider population. Findings of the present study indicated rotavating of the paddy fields significantly reduced the rice pests, which could survive on mung bean vegetation grown under the rice fallow.