author(s)
RK Patel and GG Radadia

abstract
Investigations on population dynamics of cotton jassid, Amrasca biguttula biguttula (Ishida) and natural enemies were carried out under field condition during Kharif 2015 and 2016 at Regional Cotton Research Station, Navsari Agricultural University, Maktampur farm, Bharuch, Gujarat. Population dynamics study revealed that cotton jassid was observed throughout the crop period during both seasons. Jassid population crossed economic threshold level during 36^th and 35^th Standard Meteorological Week (SMW) and continuously found above ETL till 2^nd SMW (19 weeks) and 51^st SMW (17 weeks) during 2015-16 and 2016-17, respectively. The peak population of jassid was recorded in 43^rd SMW (37.22 jassids/3 leaves) and 46^th SMW (38.48 jassids/ 3 leaves) during 2015-16 and 2016-17, respectively. Among natural enemies, lady bird beetle was observed during 38^th to 4^th SMW (0.04 to 1.34/ plant) and 33^rd to 2^nd SMW (0.06 to 1.60/ plant) with its peak in 48^th SMW and 50^th SMW whereas, chrysoperla was observed during 37^th to 2^nd SMW (0.04 to 0.48/ plant) and 36^th to 51^st SMW (0.04 to 0.36/ plant) with its peak in 46^th SMW and 40^th SMW during 2015-16 and 2016-17, respectively. The population of spider was found almost entire crop period ranging from 0.06 to 0.46 per plant and 0.08 to 0.54 per plant with its peak in 45^th SMW and 43^rd SMW during 2015-16 and 2016-17, respectively. The jassid population showed significant positive correlation with maximum temperature, evaporation and sunshine hours whereas, significant negative correlation with wind speed and rainy days. The jassid population showed highly significant positive correlation with chrysoperla and spider population while, non-significant positive correlation with lady bird beetle population on cotton crop. The population of lady bird beetle had highly significant negative correlation with minimum and average temperature, morning, evening and average relative humidity, wind speed, rainfall and rainy days while significant positive correlation with sunshine hours and evaporation. The chrysoperla and spider population had significant positive correlation with maximum temperature and evaporation while significant negative correlation with wind speed and rainy days. The spider population also showed significant positive correlation with sunshine hours. The step wise regression analysis indicated that the influence of weather parameters was upto 69.0 percent, 49.6 percent and 42.5 percent on the incidence of jassid during kharif 2015, kharif 2016 and mean of two seasons, respectively.