Ecological Studies of Drosicha mangifera
Seasonal Abundance and Population Dynamics of Drosicha mangifera on Mangifera indica at different study stations in Jammu from January, 2014 to December, 2015:
The mango mealy bug Drosicha mangifera was found infesting and causing considerable damage to the Mangifera indica in various districts of Jammu region. Keeping in view, the significant damage being caused by Drosicha mangifera to mango plantations has became important to study various ecological parameters in relation to this noxious pest at different stations to determine and recommend the damage control measures of these pests in the area of the investigator.
Studies were undertaken to investigate the influence of various abiotic factors on the population build up of Mangifera indica under agro-climatic conditions at different study stations of Jammu viz. Udheywala, Kharot and Majalta. The data related to seasonal population of Drosicha mangifera from January, 2014 to December, 2015 by the present investigator are presented in Tables. Nymphs as well as adult counts of Drosicha mangifera during monthly intervals for the two consecutive years i.e. 2014-2015 at threee different stations (Udheywala, Kharot and Majalta) were taken into consideration. Presented tables further depicts that pest population disappears during winter months and show maximum presence during January to May. The seasonal abundance of the pest at various stations and its correlation with weather parameters viz. Maximum Temperature, Minimum Temperature, Average Temperature, Average Relative Humidity and Average Rainfall have also been recorded in the following pages at different study stations.
Station Udheywala (District Jammu)
Seasonal abundance and population dynamics of Drosicha mangifera on mango plantations (Mangifera indica) at Udheywala during January, 2014 to December, 2015
The seasonal abundance and population fluctuation of Drosicha mangifera at Udheywala (District Jammu) for two consecutive years i.e. January, 2014 to December, 2015 on Mangifera indica indicated that the pest become active from January till May.
During Jan., 2014- Dec. 2014, it is realized from the graph that the first infestation was obtained in the first fortnight of January (3.30 nymphs per plant) when the average temperature and average relative humidity were 10.62?C and 74.75 resp.
The mean population of the bug showed a gradual increase during second fortnight of January (6.00 nymphs per plant), first and second fortnight of February (11.30 nymphs per plant and 12.80 nymphs per plant) when the average temperature, average Humidity and average rainfall were 13.05 and 73.20 and 50 mm, 15.54, 73.00 , 30.00 mm and 14.57, 71.99 and 31.00 mm. After February the population decreases in the first fortnight of March (8.00 nymphs per plant) and then showed a regular trend of increase in the second fortnight of March (15.00 nymphs per plant), April (22.30 nymphs per plant, 24.70 nymphs per plant) and afterwards the population showed a decline in the first fortnight of May (18.70 nymphs per plant) and then in the second fortnight of May least population was recorded (8.80 nymphs per plant). The highest population peak was observed in second fortnight of April (24.70 nymphs per plant) and least infestation was observed during the first fortnight of January (3.30 nymphs per plant). However, there is a final disappearance of the pest from June to December during all the studied years. Thus, only one peak of Drosicha mangifera nymphal population was observed during April on mango.
In the year January, 2015 to December, 2015, the highest population peak was observed in second fortnight of April (26.70 nymphs per plant) and afterwards there is a decline in the first and second fortnight of May. During both two years, the pest population is observed to disappear by the end of May and again reappeared in January in the study area.
Correlation and Regression Analysis of the Population of Drosicha mangifera with Weather Parameters at Udheywala (District Jammu) between January, 2014 to December, 2015. (Table-…….)
Pearson correlation coefficient between Drosicha mangifera population and weather pararmetres viz. temp. (Max., Min., Avg.), Avg. relative Humidity and Avg. Rainfall during 2 consecutive years viz. Jan. 2014 to Dec. 2015 at Udheywala (District Jammu) have been presented in Table…….. . Correlation analysis for Mealy bug population densities indicated a significant positive correlation with Max. Temp. (R=0.661; P? 0.037), a highly significant positive correlation with Min. Temp. (R= 0.772; P? 0.009) and a significant positive correlation with average temperature. (R=0.730; P?0.016). However, a population showed a significant negative correlation with Avg. relative humidity. (R=-0.646; P? 0.044) and an insignificant negative correlation with Avg. Rainfall (R=-0.019; P= 0.958) during Jan. 2014 to Dec. 2014 (Table……..)
During Jan. 2015 to Dec. 2015, (Table……..) the mango mealy bug population shows a highly significant positive correlation with Min. Temp. (R= 0.765; P? 0.010) whereas population has a significant positive correlation Max. Temp. (R= 0.644; P?0.044) and Avg. temp. (R= 0.718; P? 0.019). Population showed a significant negative correlation with average relative Humidity (R= -0.642; P?0.045) and an insignificant negative correlation with average rainfall (R= -0.011; P=0.976).
Linear regression equation of each weather factors during the 2 consecutive years study have been presented in Table…………..which shows that the population of Drosicha mangifera had a positive association with Max., Min., and Avg. Temp. during both the studied years whereas average relative Humidity and Avg. Rainfall showed a negative association towards the population.
Multiple regression models showed that during all the 2 consecutive years, Avg. Rainfall has a positive association with mealy bug population. On the contrary, average relative Humidity and avg. rainfall had a negative association with the Drosicha mangifera.
The Coefficient of determination (R2) values for various weather factors was 0.789 during 2014 and 0.772 during 2015 thereby revealed that these weather conditions played a significant role in the population build up of Mango mealy bug at Udheywala area of Jammu region.
Mean pooled population of Drosicha mangifera during Jan. 2014-dec 2015.
While studying the mean percentage infestation of 2 consecutive years from Jan. 2014- Dec. 2015, it was evident that the pest remains active in field for 5 months of the year starting from first fortnight of January to 2nd fortnight of May. Peak infestation was observed in the 2nd fortnight of April while least infestation was recorded in the January (3.65 nymphs per plant). A similar observation was made by Bhau (2012) who also reported 1 peak of Mango mealy bug population during April on mango. However, she has recorded the data at weekly intervals starting from Ist standard week till the last week of May. She has observed that the mean nymphal population was increasing heavily till 16th standard week with a maximum of of 23.33 nymphs per plant. A highly significant positive correlation occurred between weekly minimum, maximum temperature and mealy bug population. However with relative humidity and rainfall a non significant negative correlation existed. More or less similar report was made by Chakraborty et al. (2015) in West Bengal who found that at 07 SMW, the population was very low. It then increased gradually from 11 SMW to 16 SMW and then started to disappear at about 20 SMW. At 15 SMW a single peak of Drosicha mangiferae population was observed. Population showed an insignificant positive relation with the Tmax. While a significant positive effect with Tmin. With the Tavg an insignificantly positive relation was found in 2012, 2013 and 2014, while in 2011 relations were significantly positive.
Correlation and regression analysis of the population of Drosicha mangifera with weather parameters at Udheywala during Jan. 2014- Dec. 2015 (Table-).
Analysis of Pearson correlation between population of Drosicha mangifera and different abiotic factors (Table-) revealed that maximum temperature (R= 0.653; P?0.041) and average temperature (R=0.724; P?0.0018) had a significant positive correlation with the mealy bug population whereas, minimum temperature (R= 0.768; P?0.009) had a highly significant positive correlation towards the population. However, a significant negative correlation with average relative humidity (R= -0.644; P?0.044) and an insignificant negative correlation was noted with average rainfall (R= -0.015; P= 0.967) with the mealy bug population.
The linear regression equations of each weather parameter during the study period revealed that the infestation of Drosicha mangifera showed a positive association with maximum, minimum and average temperature. However, average relative humidity and average rainfall showed a negative association towards the population.
Multiple regression analysis revealed that only average temperature had a positive association with the population whereas, average relative humidity and average rainfall showed a negative association with the population of Drosicha mangifera.
Coefficient of Determination (R2) was 0.781, thereby indicating that as much as 78.10 % variation in the population of Drosicha mangifera was caused by cumulative meteorological factors viz. average temperature, average relative humidity and average rainfall affecting the Mangifera indica at Udheywala during Jan. 2014-Dec. 2015 (Table-…).