INFLUENCE OF TEMPERATURE AND RELATIVE HUMIDITY ON OVIPOSITION AND FECUNDITY OF OLIGONYCHUS BIHARENSIS (HIRST) (ACARI: TETRANYCHIDAE)–A PEST ON CASSAVA

Sangeetha G. Kaimal; N. Ramani

Volume : III, Issue : IX, September - 2014

INFLUENCE OF TEMPERATURE AND RELATIVE HUMIDITY ON OVIPOSITION AND FECUNDITY OF OLIGONYCHUS BIHARENSIS (HIRST) (ACARI: TETRANYCHIDAE)–A PEST ON CASSAVA

Sangeetha G. Kaimal, N. Ramani

Abstract :

The impact of temperature and relative humidity on the oviposition and fecundity of the spider mite, Oligonychus biharensis (Hirst) infesting Manihot esculenta, was studied under 3 constant temperature–humidities combination of 35+2oC & 60+5%RH, 30+2oC & 70+5%RH and 25+2oC & 80+5%RH. Shortest pre–oviposition period (0.5+0.12 days) was noted at 35 + 2oC & 60 + 5% RHfollowed by 30 + 2oC & 70 + 5% RH (1.6+0.1 days) and highest at 25 + 2oC & 80 + 5% RH (1.9+0.07 days). Humidity had little influence on the pre–oviposition and post–oviposition periods when compared to temperature. Fecundity was recorded highest at 35 + 2oC & 60 + 5% RH (75.6+0.9 eggs per female) followed by 30+2oC & 70+5%RH (58.7+0.9 eggs per female). Lowest number of eggs was laid at 25+2oC & 80+5%RH (26.7+0.6 eggs per female). Higher humidity had negative impact on the egg laying capacity as shown by adult females. A decrease in the duration of oviposition period was recorded at low temperatures and higher humidities. Of all the different temperature–humidity conditions provided, the combination of 35+2oC & 60+5%RH was found to be best suited for the successful survival and development of the mite O. biharensis on M. esculenta in alarming rates so as to acquire the status of a major pest This is almost in agreement with the temperature and humidity conditions prevalent during summer months when the population density of O. biharensis has attained the peak level in the field. The study elucidates that higher temperature and low relative humidity prevailing in the state of Kerala owing to global warming has beyond doubt elevated the status of these mites as dreadful pests well beyond threshold level.