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Population Dynamics of Sucking Pests with Relation to Weather Parameters in Bt Cotton in Buldana District, Maharashtra, India

Cotton (Gossypium sp.) is the leading natural fibre and oil seed crop which plays a key role in Indian economy with global position of second in production after China and offering livelihood security for the Indian farming community. It also plays a dominant role in the industrial and agricultural economy of the nation and has a unique place in social affairs. Many allied activities like ginning, fabric production, textile processing, garment manufacture and their marketing etc. provides employment about 6 million people. It also provides 65 percent raw material to textile industry and contributed 1/3 rd of total foreign exchange earning of India (Mayee and Rao, 2002).


Introduction
Cotton (Gossypium sp.) is the leading natural fibre and oil seed crop which plays a key role in Indian economy with global position of second in production after China and offering livelihood security for the Indian farming community. It also plays a dominant role in the industrial and agricultural economy of the nation and has a unique place in social affairs. Many allied activities like ginning, fabric production, textile processing, garment manufacture and their marketing etc. provides employment about 6 million people. It also provides 65 percent raw material to textile industry and contributed 1/3 rd of total foreign exchange earning of India (Mayee and Rao, 2002).
In India, the area under cotton crop is 121.91 lakh ha with production of 347.05 lakh bales (170 kg) and productivity of 484 kg lint/ha, however Maharashtra state comes under central zone occupies an area of 40.95 lakh ha with production of 73.75 lakh bales and productivity of 306 kg lint /ha (Anonymous, 2011). The sucking pests viz. Aphids (Aphis gossypii), Jassids (Amrasca biguttula biguttula) Whiteflies (Bemisia tabaci) and Thrips (Thrips tabaci) are most serious and destructive pests with regular occurrence. After introduction of Bt cotton hybrid a general shift in sucking pest complex towards thrips, aphids, jassids, white fly and other sucking pests was observed. These minor pests attained economic importance after introducing Bt cotton. The pest problems, particularly that of up till now minor pests, had not be monitored regularly and often remedial majors were undertaken only after they reached epidemic or causes heavy losses. A regular surveying of cotton pest, using preferably information communication technologies and development of suitable IPM strategies was the need of the hour, as it would have lay to better by all agencies involved in plant protection and issue proper advice to farmer based on actual pest problem. Amongst various reason of low productivity of Bt transgenic cotton, the sucking pests gain much importance due to havoc created by most of the sucking pest in the recent years. A broad range of insecticides available in market have proved as effective in reducing the pest population. However, negligence in following the principles of crop protection, indiscriminate and extensive use of synthetic insecticides led to development of insecticidal resistance, pest resurgence, residue, destruction of natural enemies etc. Hence, it is require moving on other molecules with different mode of action to overcome such types of consequences (Patel, et. al., 2014). Thus the present study was conducted to share the information on sucking pest scenario with farmer, state agencies and central agencies for developing appropriate management strategies.

Materials and Methods
The field survey was conducted in Buldana district (Maharashtra) under project entitled "National Information System for Pest Management-Bt Cotton" between the years 2008-09 to 2012-13. In the present study, 20 villages from five talukas of Buldhana district were selected. From these talukas two circles were preferred and from which two villages were selected and two Bt cotton growing farmer were chosen from each village. The observations were recorded in each week from these farmers field. Observations on aphids, jassids, thrips, whiteflies count were recorded by randomly selecting 20 plants from each field plot on top, middle and bottom leaves per plant. Sowing of cotton by project farmers was done from 15 th May to 1 st week of July at a different spacing under rain fed situation. For this purpose, different Bt hybrid varieties were selected for sowing purpose and regular agronomic practices were carried out. Data on weather parameters were obtained from the Meteorology unit, Regional Research Station, Buldana under Dr. PDKV, Akola. The relationship between weather parameters and sucking pests was established by using simple correlation coefficient and regression analysis.

Results and Discussion
The cumulative data on aphid was averaged out of between the years 2008-09 to 2012-13. Average population of aphid was ranged from 7.91 to 43.56 per cent on presence or absence basis. The maximum (43.56 % aphids) population was recorded in 33rd meteorological week; the aphid population was observed above ET level during 31 st to 37 th standard meteorological week, however it was lower (7.91 %) in 50th meteorological week. The peak population of aphid was increased at 33 rd standard meteorological week and thereafter the peak population goes decreasing up to 41 st week. Thereafter, the second peak of population was observed in 42 nd SMW after that the population continues decreasing up to 50 th SMW after that third peak of aphid was observed in 51 st SMW (Fig.  1). Dhobi and Bharpoda (2013) also reported that population of aphid (Aphis gossypii Glover) was appear during 37 th standard meteorological week and reached to a first peak during 39 th SMW.
The population of jassid was recorded during the same period of years. The result depicted in Figure 1 revealed that the population of jassid was ranged between 0.51 and 4.42. The peak period of jassid population was observed during 31 st to 41 th standard meteorological week which shows that the maximum (4.42 jassid per 3 leaves) population was recorded in five year average in 37 th meteorological week and it was observed minimum of 0.51 jassids/3 leaves/plant in 2nd meteorological week.
Reddy et al., (2011) showed that the peak incidence was observed from the second fortnight of October to first fortnight of November in 2009-10 (10.11 to 10.82/leaf) and in the season of 2010-11, the peak incidence was noticed in mid-September to first fortnight of October (6.02 to 5.48/leaf). Similarly, Bharpoda et al., (2013) concluded that the peak activity of jassid was recorded during 38 th to 45 th SMW to the tune of 3.17 to 4.82 per 3 leaves. These results are in line with the present findings.
Average population of thrips was ranged from 0.21 to 6.96 thrips per 3 leaves per plant. The peak activity of thrips was recorded during 34 th to 39 th SMW (Fig. 1) during which maximum population of 6.96 thrips/3 leaves was recorded in 36th meteorological week; whereas least in 2nd meteorological week i.e. 0.21 thrips/3 leaves /plant. The present findings are supporting the results of Bharpoda et al., (2013) who stated that the activity of thrips was concerned in Vadodara district to the tune of 0.06 (5 th SMW) to 4.30 (32 nd SMW). The population showed number of fluctuation in its activity. However, higher activity of thrips was noticed during 32 nd to 44 th SMW. Shivanna et al., (2009) reported that the maximum incidence of thrips population was noticed from April to May with a peak incidence of 26.81 per three leaves was recorded in April second fortnight.
The average population of white fly incidence was observed between the ranged of 0.82 to 6.57 whitefly per 3 leaves per plant during the five year in respective SMW. The peak activity of white fly was recorded during 36 th to 44 th SMW (Fig. 2) where the maximum (6.57 whiteflies/ 3 leaves) population was recorded in 37th meteorological week whereas, minimum of 0.82 whiteflies recorded in 31st meteorological week. These present findings are in line with the results obtained by Deb and Bharpoda (2013) who reported that the peak activity of white fly was observed during 46 th SMW (2 nd week of November).

Correlation studies
The five years (2008 to 2013) mean weekly counts of various sucking pests from 31 st std.
week were correlated separately with weather parameters and the correlation coefficients analysis is presented in Table 1.

Aphid
The maximum temperature did not show any significant impact on the A. gossypii as the correlation was negatively non-significant with the population of aphids (-0.102) but the minimum temperature had showed highly significant positive correlation with the population of aphid (0.725*) which showed that the minimum temperature was most favorable to the incidence aphids in Bt cotton ( Table 1). The rainfall showed highly significant positive impact on population buildup of aphid (0.773*) which reflects that the rainfall was very favourable for the positive population buildup of aphid.  Jassid Y 1 =5.528-0.346X 1 +0.475X 2 +0.009X 3 -0.034X 4 -0.023X 5 +0.406X 6 0.885 3.

Jassid
The maximum temperature did not show any significant impact on the A. biguttula biguttula. The correlation with jassid (0.358) population was positively non-significant and the minimum temperature (0.912) and rainfall (0.677*) had showed highly significant positive relationship with the population of jassid (Table 1). Relative humidity both in morning and evening was positively correlated with jassids. The average of morning (0.849*) relative humidity had positive relationship whereas, the relative humidity at the evening (0.789*) had showed highly significant positive relationship. The impact of BSH on the population of jassids revealed that the population was significantly negative correlated with aphid jassid (-0.471). Mohapatra (2008) reported that rainfall had a non-significant positive effect on population of A. biguttula biguttula (0.284).

Thrips
The maximum temperature was negatively non-significant correlated (0.124) population but minimum temperature was highly significant positive (0.685*) relationship with thrips ( Table 1). The rainfall showed highly significant positive impact on population buildup of thrips (0.784*) during all the years.
This shows that the rainfall was very favourable for the positive population buildup of thrips. The average of morning relative humidity had positive relationship (0.752*) whereas, the relative humidity at the evening had highly significant positive relationship with thrips (0.699*). The impact of BSH showed significantly negative correlation with thrips (-0.419). The present findings are in controversy with Selvaraj and Adiroubne (2012) who stated that thrips population build up showed a significant and positive correlation with BSH.

Whitefly
The maximum (0.691*) and minimum (0.584*) temperature exhibited highly significant positive correlation with population of whitefly (Table 1). The population of whitefly showed the nonsignificant positive relationship (0.217) with the rainfall. The average of morning relative humidity had positive relationship (0.460*) but at the evening it showed non -significant positive (0.262) correlation with the population of whitefly. The impact of BSH on the population of whitefly showed the nonsignificant positive correlation (0.136). Shera et al., (2013) found that the population of B. tabaci was positively correlated with maximum and minimum temperature during all the years; however, it was significant with minimum temperature. Meena et al., (2013) concluded that whitefly population exhibited positive correlation with maximum, minimum and mean temperature on chilli.

Regression studies
Based on regression analysis by taking sucking pest population (Y) as a dependent variable and weather parameters (X) as independent variables following equations were fitted for the year 2008-2013 (Table 2). The regression equation indicated that an increase in 1ºC of maximum temperature increases the aphid population by 5.658 per 3 leaves per week and the population decreases by 4.321 per 3 leaves as the 1ºC of minimum temperature increases. The increase of 1% morning and evening relative humidity increases the aphid population by 0.390 and 1.360 per 3 leaves per week. Increase in 1% maximum temperature resulted for decreasing the jassid population by 0.346 per 3 leaves similarly, 1% increasing of morning and evening relative humidity the population of jassid were decreases by 0.034 and 0.023 per 3 leaves, respectively. Whereas, in case of thrips, the population were decreased by 0.120 and 0.021 per 3 leaves as the 1°C of maximum temperature and 1% evening humidity were increased, respectively. Due to the increase in maximum temperature of 1ºC whitefly population almost reduces by 0.433 and similarly whitefly population reduction (0.111 per 3 leaves) was also observed at increasing of evening humidity by 1%.
The prediction of sucking pests of Bt cotton were made by developing multiple regression equations by using regression models. The results of regression models and the coefficients of determination (R 2 ) indicated that the sucking pests viz., aphid, jassid, thrips and whitefly were predicated to an extent of 84, 88, 74 and 77 per cent, respectively. The correlation and regression analysis clearly showed the importance of weather factors in predicting the sucking pest incidence in Bt cotton.