Abstract: In this study, field trials were conducted to determine the effect of ecological factors on the incidence and development of leafhopper, Amrasca devastans at five different date of sowing on three varieties of cotton. The pest population was started from third week of February on third weeks old crop and acquired its peak in second week of March on six weeks old crop. Maximum pest population (9.30/3 leaves) was build up at temperature ranged from 21 to 31°C, relative humidity ranges from 82 and 55 percent, zero rainfall, wind velocity 4.5 km h-1, total sunshine hours (9.00 h week-1), evaporation (56.10 mm) and dewfall (1.491 mm). The highest incidence of leafhopper population was recorded in MCU 7 followed by SPCH 22 and SVPR 3. Leafhopper population was build up showed a significant and positive correlation with morning and evening relative humidity and rainfall whereas, it was significant and negative association with minimum temperature, wind velocity and dewfall. The determination of effects of different weather factors on population of leafhoppers in cotton was essential for effective pest management. This study will be very helpful not only for forecasting the out breaks of leafhopper population but also in formulating effective pest management strategies.
INTRODUCTION
Cotton (Gossypium spp.) being the king of natural fiber is grown in 111 countries all along the world. In India, it is cultivated in 8.97 million ha with a production of 21.3 million bales of seed cotton (Anonymous, 2005). Moreover, due to the top most position in Indian agriculture and it is also popularly known as white gold. Cotton fiber is an important raw material to the textile industries and plays a key role in national economy in terms of employment generation and foreign exchange up to 62.3-68.3% (Khan et al., 2003). The cotton is not only principal cash crop but also each and every parts of the cotton plant are useful to farmer in one way or the other (Shivanna et al., 2009). Unfortunately, cotton is highly vulnerable to insect pests. During growth period, 148 insect pests have been recorded on cotton crop, out of which only 17 species have been recorded as major insect pests of cotton crop (Abbas, 2001). Cotton pests can be primarily divided into sucking pests and bollworms. Among the sucking pests, leafhopper, Amrasca devastans (Dist.) is of major importance in cotton crop. Leafhoppers occur at all the stages of the crop growth and responsible for indirect yield losses. Since, these pests suck the sap from the plants which leads to reduction in growth and vigour of the plants. In severe case of infestation, the plants get dried up and eventually die (Madar and Katti, 2010).
Pesticides continue to play the key role in cotton arthropod pest management. Most of the farmers are marginal and small farmers with poor financial condition and therefore, cannot afford to buy costly pesticides and sprayers. Lot of spurious chemicals is entering into the market which is effective and result in development of insecticide resistance and resurgence of pests. This made cotton cultivation uneconomical resulting in suicide of large number of disappointed farmers in Andra Pradesh and Maharashtra (Saini et al., 2010). High populations of leafhoppers survive every year, despite extensive and intensive insecticide application. The incidence and development of these insect pests is very much dependent upon the prevailing physical environmental factors and crop stand. These insects multiply tremendously during the favorable weather conditions and take huge toll (Aheer et al., 1994). Climatic conditions largely influence the pest numbers and activity as well as several predators and parasites either directly or indirectly (Arif et al., 2006; Chaudhari et al., 1999). For developing a weather based pest forewarning system, information regarding population dynamics in relation to prevalent meteorological parameters (temperature, relative humidity, sun shine hours etc.) is needed. Moreover, the same meteorological parameters also influence the growth and development of crop. Therefore, a thorough understanding of interaction between the crop growth stage/meteorological parameters/pest dynamics is a pre requisite for weather based pest forecasting model. Hence, the present study was focused on location specific seasonal occurrence of leafhoppers at different crop growth stages and its relation with weather factors which is of great significance in formulating efficient pest management tactics.
MATERIALS AND METHODS
The field experiment was laid out at Pandit Jawaharlal Nehru College of Agriculture and Research Institute Karaikal during February and July in 2007 (Rice fallow cotton). The experiment was laid out in Factorial concept of Randomized Block Design (FRBD) comprised of 15 treatments (three treatments-varieties/hybrid-MCU 7, SVPR 3 and SPCH 22 and five sub treatments date of sowing-1st, 8th, 15th, 22nd February and 1st March) and designed in RBD. The factorial experiment has two or more factors but level of factors need not be same. Here, the set of three varieties were one factor and the set of five different date of sowing were another factor. Therefore, the fifteen treatment combinations were V1D1 V1D2, V1D3, V1D4, V1D5, V2D1, V2D2, V2D3, V2D3, V2D5, V3D1, V3D2, V3D3, V3D4 and V3D5. These treatment combinations were replicated force. This experiment was conducted with the above treatment combinations allotted to the ultimate experimental units. The plot size for each treatment was 5x4 m (20 m2) plots. The seeds of varieties MCU 7, SVPR 3 and SPCH 22 were sown at two plants per hole with a spacing 60x30, 60x30 and 120x60 cm, respectively. The interval between each sowing was seven days. The data on abiotic factors i.e., temperatures, relative humidity, wind speed, rainfall, sunshine hours, evaporation and dewfall were taken from Department of Agronomy, Pandit Jawaharlal Nehru College of Agriculture and Research Institute, Karaikal. The rainfall was calculated by self recorded rain gauge. It can gives as automatic record of rainfall without any bottle reading. The relative humidity can be obtained by hair hygrometer. The properties of human hair to increased the length with increased relative humidity and decrease with decrease the humidity. Increase relative humidity is used the instrument variation in length of human hair cause displacement of hook which is communicated by second arm of the liver to record the changes of graph paper. The circular drum makes one rotation in 24 h or once a week. The instrument is placement in the Stevenson screen in the observatory. The data on leafhopper population were recorded from 16th February to 30th July at weekly interval from following manner. Leafhoppers were counted as adult/nymph per leaf basis. Ten plants were taken from each treatment. The population of insects was counted from upper leaf of first plant, middle leaf of second plant, lower leaf of third plant and so on Arif et al. (2006).
Statistical analysis: At the end of season, the data obtained were subjected to proper statistical analysis. The correlations as well as regression between cotton leafhopper population and weather factors were estimated. Leafhoppers population was collected every week from the field. Weather factors were collected from Department of Agronomy (PAJANCOA and RI). Data was analyzed statistically by SPSS simple correlation worked out between population of leafhoppers and weather factors (maximum and minimum temperature, morning and evening relative humidity, sunshine hours, rainfall, evaporation and dewfall). The impact of weather factors on leafhoppers population fluctuation was determined through multiple linear regression models.
The regression equation was obtained:
where, Y1 is Leafhopper population and X1 is Morning relative humidity
RESULTS AND DISCUSSION
Population dynamics of leafhoppers: The incidence of leafhopper was observed during third week of February on third weeks old crop and acquired its peak incidence (9.30/3 leaves) was observed in second week of March on six weeks old crop. The population of leafhoppers was high during initial stage of crop growth with two peak population during 10th (9.30/3 leaves) and 16th (8.20/3 leaves) standard weeks (Table 1). The population of leafhoppers was maximum (9.30/3 leaves) during initial stages of crop growth with maximum temperature ranged from 31 to 33°C and minimum temperature ranged from 21 to 24°C, morning relative humidity 82 to 90 percent and evening relative humidity 55 to 66 percent, wind velocity 4.5 to 5.3 km h-1, sunshine hours 9.00 to 10.00 h and zero rainfall was favourable for multiplication of leafhoppers (Table 1). The present findings are in agreement with those of Prasad et al. (2008) and Kaur et al. (2009) who reported the maximum and minimum temperature ranged from 30.5 to 32.5°C and 20 to 23.5°C, respectively.
Correlation and regression between meteorological parameters and leafhoppers population: The population of leafhoppers showed significant positive correlation with morning and evening relative humidity and rainfall, while a significant and negative association with minimum temperature, wind velocity and dewfall. Whereas, maximum temperature, sunshine hours and evaporation had a non significant and negative association was recorded with leafhopper population (Table 1). The present findings are in agreement with those of Shitole and Patel (2009), Kaur et al. (2009), Prasad et al. (2008), Dhaka and Pareek (2008), Ramamurthy et al. (2000) and Rao et al. (2001) who reported significant positive correlation was found between the leafhopper population and relative humidity and rainfall. Similarly Ammar et al. (1986), Kavitha et al. (2003),Singh et al. (2004), Aheer et al. (2006), Shitole and Patel (2009) and Selvaraj et al. (2010) who reported the significant negative association with maximum temperature and sunshine hours.
| Table 1: | Incidence and correlation matrix of leafhopper, A. devastans with weekly mean abiotic factors in cotton |
| MSW: Meteorological standard week, Max: Maximum temperature, Min: Minimum temperature, *,**Significant at p = 0.05 and p = 0.01 level, respectively | |
A partial agreement with those of Arif et al. (2006) who reported that rainfall and temperature showed a significant and positive correlation with the jassid population, whereas, relative humidity showed a non significant effect. The present findings are in close conformity with those of Purohit et al. (2006) and Hegde et al. (2004) who reported that increase in jassid population showed a significant positive correlation with minimum temperature and evening relative humidity. The present results are in not agreement with those of Mahmood et al. (2002) who reported that minimum and maximum temperature was positively correlated whereas relative humidity and rainfall was negatively correlated with leafhopper population in brinjal. This difference may be due to different ecological condition and difference crop on which the experiment was conducted. The regression revealed that among the various abiotic factors morning relative humidity (X1) was found to be most influencing factor which contributed (R2 = 0.4751) 47% variation in leafhopper population. The prediction equation was obtained:
where, Y1 = Leafhopper population and X1 = Morning relative humidity
Effect of date of sowing on the incidence of leafhoppers: The incidence of leafhopper population was compared with different dates of sowing. The overall mean incidence of leafhopper population was 5.30/3 leaves for 1st February sowing, 4.93/3 leaves for 8th February sowing, 4.82/3 leaves for 15th February sowing, 4.62/3 leaves for 22nd February sowing and 3.93/3 leaves for 1st March sowing. The incidence of leafhoppers was highest (5.30/3 leaves) in the first sowing (1st February) while the incidence was least (3.93/3 leaves) in last sowing (1st March) in irrespective of varieties (Table 2). A gradual decrease of leafhopper population was observed when the sowing dates were progressed. The present results are not in agreement with those of Butter et al. (1992), Singh et al. (1978) and Agarwal et al. (1979) who reported higher population of cotton jassid on late sown cotton crop. The present results are not in agreement with those of Hassan et al. (2003), Oad et al. (2002) and Akhtar et al. (2002) who reported that seed cotton yield was declined in late sowing crop on different genotypes due to highest occurrence of leafhopper population. This may be due to effect of weather factors prevailing here.
| Table 2: | Effect of date of sowing on the incidence of leafhopper, A. devastans in cotton varieties |
| DAS: Days after sowing | |
| Table 3: | Correlations coefficient between the incidences of leafhopper, A. devastans in different varieties of cotton and various weather factors |
| *,**Significant at p = 0.05 and p = 0.01 level, respectively, Max: Maximum temperature, Min: Minimum temperature, RH: Relative humidity | |
| Fig. 1: | Effect of different varieties on the incidence of leafhopper, A. devastans Dist. in cotton |
This area weather factors is favourable for multiplication of pests only in early season of crop. Laterally, this weather factors are slowly affect the pest population. Therefore, weather factors are flexible from area to area and season to season and year to year.
Effect of varieties on the incidence of leafhoppers: The overall mean incidence of leafhopper was recorded in respect of three different varieties was maximum in 30th Days after Sowing (DAS). The highest incidence of leafhopper was recorded in MCU 7 (12.67/3 leaves) followed by SPCH 22 (11.20/3 leaves) and SVPR 3 (9.60/3 leaves). The mean incidence of leafhopper was least in SPCH 22 and maximum in MCU 7 (Fig. 1). The correlation analysis of mean data (Table 3) for all varieties revealed that maximum and minimum temperature and wind velocity showed highly significant negative influence of leafhopper population. Whereas, morning relative humidity and dewfall showed highly significant and have positive influence on the leafhopper population for all varieties, while the association was positive and non significant with other parameters. The present findings are in conformity with those of Aheer et al. (2006) and Riaz et al. (1987) who reported that maximum temperature affected jassid nymph negatively whereas, relative humidity affected positive and non significant for all genotypes.
The multiple linear regression analysis indicated that the influence of all the weather parameters was high and significant. It was 88.83% (R2 = 8883) in MCU 7, 63.15% (R2 = 6315) in SVPR 3 and up to 62.47% (R2 = 6247) in SPCH 22 on incidence of leafhopper population. The regression equation further indicated that the morning relative humidity had significant positive impact on the population of leafhoppers i.e. for one unit increase in morning relative humidity there will be 0.55, 0.38 and 0.31 units increased leafhoppers population in MCU 7, SVPR 3 and SPCH 22, respectively (Table 4).
| Table 4: | Multiple linear regression analysis between weather parameters and leafhopper, A. devastans in different varieties of cotton |
| X1: Morning relative humidity, X2: Minimum temperature | |
CONCLUSION
It may be concluded that climatic factors determine seasonal activity and population dynamics of leafhoppers in cotton. This information generated in present study would be helpful in developing efficient pest management strategies against insect pests of cotton crop for increased production efficiency, profit, besides safety to the environment.