Population fluctuation of planthoppers and their predators in rain-fed rice

Studies undertaken at Central Rice Research Institute (CRRI), Cuttack and in farmers’ field at Kandbindha, Dhenkanal during wet season indicated that mixed population of BPH and WBPH occurred in the field and among spiders Tetragnatha mandibulata was the dominant species. Population of planthoppers was low both at CRRI and Kandabindha during wet season of 2003–04. Population of spiders and the green mirid bug Cyrtorhinus lividipennis initially were at par with each other but the latter overtook the former in the second week of October and maintained the trend till the end. During wet season 2004–05 at CRRI the hopper population reached the peak level of 42 hoppers hill−1 in the first week of October. Population of spiders and C. lividipennis started concurrently along with the appearance of hoppers in the farmer's field at Kandabindha. Between the two predators, population of spiders fluctuated throughout the period of study. During both the years and at both the sites of trial the population of spiders was always lower than that of C. lividipennis. Under rain fed ecosystem, besides natural enemies, precipitation appears to play an important role in reducing the hopper population. Analysis of ratio of planthoppers to both the predators combined indicated that it was 4.5 and 2.5 in the beginning of hopper infestation and reached the maximum level of 23.9 and 12.4 and declined to 1.8 and 2.4 during 2004 at CRRI and Kandabindha, respectively.