SPIDER POPULATION AND THEIR PREDATORY EFFICIENCY IN DIFFERENT RICE ESTABLISHMENT TECHNIQUES IN ADUTHURAI, TAMIL NADU.

Abstract

ABSTRACT The role of spiders in regulation of insect pests has been studied in the rice ecosystem ADT 39 cultivated by different Rice Establishment Techniques, namely Transplantation (T1), System of Rice Intensification (T2), Integrated Crop Management (T3), Drum Sowing (T4), Random Planting (T5) and Seedling Throwing (T6). The study was carried out in Tamil Nadu Rice Research Institute (TRRI), Aduthurai between December 2005 and March 2006. Two aspects, namely population of spiders and pests, and role of spiders in the reduction of insect pests were studied. The number of spiders and pests found in the field were recorded by sweeping net and visual observation. A total of five spiders, namely Lycosa pseudoannulata, Callitrichia formosana, Tetragnatha javanas, Argiope catenulata and unidentified Plexippus species were identified from all the six different technique plots. Among them, Integrated Crop Management, showed the maximum percentage (20.93%) of spiders, whereas the minimum was observed in Seedling Throwing (8.58%). The population of spiders fluctuated during different days after transplantation (DAT). Lycosa pseudoannulata and Callitrichia formosana were the maximum during 42 DAT to 53 DAT, while Argiope catenulata was predominant from 88 DAT to 113 DAT. Six different insect pests, namely Nephotettix virscens, Scripophaga incertulas, Cofana spectra, Cnaphalocrosis medinalls, Nilaparvata lugens and Leptocorisa acuta were recorded in all the six technique plots. The population of pests in the different treatments showed rise and fall during the observation. The Maximum population of pests was recorded during 66 DAT. Among the techniques, Drum Sowing (25%) showed the highest percentage, whereas the minimum was recorded in Transplantation and Random Planting (11% each). All the spiders showed the positive correlation with rice pests Nilaparvata lugens and Leptocorisa acuta and negative correlation with Cnaphalocrosis medinalls. High population of spider in the different treatment plots limits the exponential growth of pest population.