Entomology, Ornithology & Herpetology: Current Research
Open Access

Seasonal Incidence of Pink Bollworm Pectinophora gossypiella (Saunders) in Bt cotton

Rahul B Dake^*, Latpate CB and Zanwar PR ^*Correspondence: Rahul B Dake, Department of Agricultural Entomology, College of Agriculture, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, India, Email:

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Introduction

Cotton is a major fibre crop of global significance, cultivated in more than seventy countries in the world. Cotton crop is playing an important role in economic, political and social affairs of the world. Cotton belongs to the family “Malvaceae” and genus “Gossypium”. Cotton crop as commercial commodity plays an important role in industrial activity of nation, in terms of both employment generation and foreign exchange, Hence it is popularly known as “White Gold” and “Friendly Fibre”.

The major threat to the continued success of Bt crops is evolution of resistance by pests. While most target pest populations remain susceptible, resistance to Bt crops has been reported in one of the most devastating pests of cotton globally recently, the pink bollworm, evolved resistance to transgenic cotton that produces Bt toxin Cry 1 Ac in western India. Bt cotton is specially developed for the bollworms but sucking pests are emerging as prime insect pests causing severe losses in yield. Among major insect pests of cotton population of sucking pests was higher in Bt hybrids [1].

There are several reasons attributed to this low yield, losses due to pests assume significant importance as cotton crop is a heaven for insects. A total of 1326 species of insects have been recorded on cotton. The pest spectrum of cotton crop is quite complex comprising several species of the insects. pink bollworm (Pectinophora gossypiella Saunders) account for a considerable yield loss to the extent of 36.2% [2].

In cotton, population buildup of various insects’ pests has been found to be influenced by different parameters of climate. The insect being the member of biotic community interacts with other non- living (abiotic) components of the environment. The outcome of these interactions is population dynamics, the positive and negative growth of the population. Hence, the life system and abundance of insect can be understood by study of interaction between insect and abiotic factors. Appropriate manipulation of agro-ecosystem can aid in preventing economic damage by the insects. New technology to be developed in future for the management of insect pests will necessarily depend on knowledge of pertinent agro-ecosystem under particular situation. The determination of effect of different environmental factors on incidence of sucking pests and bollworm complex in cotton is essential for effective pest management. It may be possible to predict their occurrence on the basis of meteorological factors well in advance. This may help in making an effective and most economic use for farmer pest management armory. Timely preventive measures can be undertaken with less use of chemical insecticides and thus reducing harmful side effects on human being. Hence, attempt can be made for development of database useful for pest forecasting. This study will be very useful not only for forecasting the outbreak of bollworms but also in formulating effective management strategies.

Materials and Methods

The field experiment with Bt cotton crop using variety RCH-659 BG-II was conducted at Research Farm of Department of Agril. Entomology, College of Agriculture, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani (MS)-India during Kharif 2018 and Kharif 2019. The experiment was conducted in unprotected plot with 10 m x 10 m size which was non-replicated and the plot was divided in four quadrants. Ten plants were randomly selected from each quadrant for observations. Observations were recorded during morning before 8.00 am in each meteorological week from untreated plot of RCH-2 BG –II cotton hybrid. The observations recorded during the course of investigation are seasonal activity of pink bollworm with different parameters.

Pheromone trap catch

TFive pherosensor sleeve traps were erected at 1-2 m height in plot depending on the crop stage for monitoring the pink bollworm adult emergence from the first week of July, till the end of December during both seasons. Every week adult male moth catches in the pheromone traps were recorded.

Percent rosette flowers

The observations on rosette flowers due to pink bollworm infestation were recorded at weekly interval. In each week, after the initiation of flowers, ten plants were randomly selected for counting the total number of flowers and number of rosette flowers. Finally, per cent rosette flowers were worked out by using the following formula,

Percent green boll damage

Observations on the incidence of pink bollworm in green bolls were made at weekly intervals. For this purpose, 20 green bolls of three-week old, 20 green bolls from plot were plucked randomly and brought to the laboratory. In laboratory, the number of damaged bolls was counted and expressed in terms of per cent green boll damage using formula,

Pink bollworm larval population in green bolls

Observations on the incidence of pink bollworm in green bolls were made at weekly interval. For this purpose, 20 cotton green bolls were collected for estimating green boll damage and these bolls were cut opened along with ridges of the locules with the help of sharp cutter carefully and pink bollworm larvae of all the age groups were counted. Then total number of pink bollworm larvae per 20 bolls was worked out.

Percent locule damage in green bolls

Observations on the locule damage in green bolls by pink bollworm were made at weekly interval. For this purpose, 20 cotton green bolls collected were cut opened along with ridges of the locules with the help of sharp cutter carefully and then total number of locules and damaged locules were counted and expressed in terms of per cent locule damage using formula,

Meteorological data on weekly basis for Kharif seasons during the year 2018 and 2019 were obtained from meteorological observatory, Department of Agril. Meteorology, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani from the same campus.

The data pertaining to seasonal activity of major insect pests was correlated with various weather factors. The relation between weather parameters and major insect pests in Bt cotton was studied. Simple correlation, simple regression and multiple regression studies were carried out.

Results and Discussion

The data on moths trapped per trap, percent rosette flower, percent green boll damage, larval population per twenty bolls and percent locule damage in twenty green bolls during Kharif 2018 and Kharif 2019 in Bt cotton are presented in Table 1.

Table 1: Seasonal incidence of pink bollworm in Bt cotton.

During the kharif 2018, the adult trap catch of pink bollworm started from the month of July and it’s ranged from 03.00 to 125.00 moths/trap/week. Thereafter, there was gradual increase in adult trap catches and a sudden sprut in moth emergence was observed from first week of November, corresponding to 44^th MW (85.00 moths/trap/week) and continued at high level till the end of December corresponding to 52nd MW (57.00 moths/trap/week). First peak of moth catch was observed in 45th MW (123.00 moths/ trap/week). Second peak with the highest trap catch was observed during 51^st MW (125.00 moths/trap/week) then onwards the pink bollworm population gradually declined.

During Kharif 2019 the adult trap catch of pink bollworm started from the month of August and it’s ranged from 01.00 to 86.00 moths/trap/week. The adult trap catch of pink bollworm increased gradually reaching to its first peak with the highest trap catch in the last week of November (47^th MW) (86.00 moths/trap/week) and thereafter gradually declined till the end of season.

The findings of earlier workers are more or less in the line of present work [3] who reported that the pink bollworm infestation during October. Monitoring with the pheromone traps indicated that the activity of PBW advanced to as early as August month (2004-2005). However, the peak activity of the pest was consistently high during end of the season [4]. The [5] reported the adult trap catches of pink bollworm was started from the month of September and its build up was more or less steady till the second week of November. While, [6] reported that the peaks of moth populations of pink bollworm were recorded during 41-52nd MW corresponding with larval population in field. The [7] reported maximum trapped moths were in the last week of November.

Rosette flowers due to pink bollworm P. gossypiella (Saunders)

During Kharif 2018 the data on rosette flowers due to pink bollworm in Bt cotton ranged from 3.65 to 17.25 per cent occurring from 38^th MW. The rosette flowers were noticed from the period 38^th MW to 02nd MW. The highest incidence was noticed in 46^th MW (17.25 per cent). Thereafter it gradually declined to 3.27 per cent in 02nd MW and become nil at 3rd MW.

The rosette flowers during Kharif 2016 Table 1 in Bt cotton ranged between 7.14 to 38.18 per cent. The rosette flowers started from 38^th MW (7.14 per cent). The first peak with highest incidence was recorded in 44^th MW (38.18 per cent). The second peak incidence was observed in 52nd MW (28.57 per cent).

However, the results of present findings are in contrast with [8] who reported that the maximum numbers of rosette flowers observed on 30 July. As per [9] the pink bollworm, P. gossypiella infestation on flowers found higher in 2nd week of September with intensity of 7 larvae per 30 flowers. According to [10] the peak of flower resetting was observed during 47^th. In the same way, he reported that the percent rosette flowers due to P. gossypiella were highest in 41st MW.

Green boll damage by pink bollworm P. gossypiella (Saunders)

The data on per cent green boll damage due to P. gossypiella in Bt cotton during Kharif 2018 Table 1 ranged between 5.00 to 40.00 per twenty bolls occurring from 39^th MW (5.00 per cent per twenty bolls). The peak incidence was noticed in second forth night of November (46^th and 47^th MW) i.e. 40.00 per cent per twenty bolls. Thereafter per cent green boll damage gradually declined with second peak in 52nd MW 30 per cent per twenty bolls.

During Kharif 2019 per cent green boll damage due to P. gossypiella in Bt cotton ranged between 10.00 to 70.00 per cent per twenty bolls. The incidence was observed from second week of October 38^th MW with 10.00 per cent per twenty bolls. The peak incidence was noticed in 48^th MW with 70.00 per cent per twenty bolls and gradually declined till end of the season.

The findings of earlier workers are more or less in the line of present work. [11] Who reported that infestation of pink bollworm was recorded on Bt-cotton in September (12th week) of crop. According to (2018) the peak green boll damage was observed in 46^th, 47^th and 48^th MW. As per [12] the incidence in green bolls was noticed from the first fortnight of September (34^th SMW) and rose gradually to reach its zenith during the second fortnight of December (48^th SMW). [13] Reported that per cent green boll infestation due to P. gossypiella is highest (125%) in 48^th MW.

Larval population of pink bollworm P. gossypiella (Saunders) in green bolls

The number of pink bollworm larva in green bolls were recorded at weekly interval starting from first week of September to third week of January and data are presented in Table 2.

Table 2: Seasonal incidence of pink bollworm in Bt cotton.

During Kharif 2018, the larval incidence on green bolls in Bt cotton varied from 2.00 to 21.00 larvae per twenty green bolls. The incidence started from last week of September (39^th MW) 2.00 larvae per twenty green bolls and later, the larval population increased gradually with first peak of 21.00 larvae per twenty bolls during 46^th MW. The second peak was recorded 52nd MW (11.00 larvae per twenty green bolls).

During the succeeding year (Kharif 2019) the larval incidence on green bolls in Bt cotton documented ranged from 2.00 to 40.00 larvae per twenty green bolls. The incidence noticed from first week of October (40^th MW) to till the end of season (03rd MW) 2.00 larvae per twenty green bolls. The highest occurrence recorded in 47^th MW 40 larvae per twenty green bolls and later on gradually declined.

Locule damage in green bolls due to pink bollworm P. gossypiella (Saunders)

The per cent locule damage in green bolls made by pink bollworm larvae was recorded from twenty green bolls and the data are presented in During Kharif 2018 of investigation, the per cent locule damage in green bolls ranged from 1.23 to 55.56 in Bt cotton. Maximum of 55.56 per cent locule damage in green bolls were noticed during peak boll developmental period (up to November). Whereas, highest locule damage in green bolls also registered in the same period (46^th MW). Followed by November per cent locule damage decreased up to the end of season.

In the second year (Kharif 2019) of study, similar trend in the highest locule damage was noticed with 62.50 per cent locule damage in developmental period (up to November). The per cent locule damage in green bolls ranged from 1.25 to 62.50 in Bt cotton. The per cent locule damage in green bolls gradually increased up to 47^th MW and gradually declined to the till the end of season.

The findings of earlier workers are more or less in the line of present work. The [10] who reported that the locule damage in green bolls were observed during 47^th MW. As per [12] locule damage ranged from (24.71 to 39.35 %) with a mean of (39.05 %).

Relationship between weather parameters and pink bollworm in Bt cotton Pheromone trap catch

Simple correlation studies: The data on correlation between weather parameters and pheromone trap catch during Kharif 2018 and Kharif 2019 presented in Table 3.

Table 3: Seasonal incidence of pink bollworm in Bt cotton.

The pheromone trap catch in Bt cotton were positively significant and non-significant relationship to bright sun shine (r=0.388*) and evaporation (r=0.168), respectively. The pheromone trap catch in relation to minimum temperature (r=-0.512**), morning RH (r=- 0.570**) and evening RH (r=-0.455*) were negatively significant. The pheromone trap catch negatively non-significant in relationship to maximum temperature (r=-0.079), rainfall (r=-0.224) and wind speed (r=-0.231) during Kharif 2018.

Although, during Kharif 2019, the pheromone trap catch in Bt cotton were positively significant relationship to bright sun shine (r=0.563**). The pheromone trap catch in relation to minimum temperature (r=-0.655**), evening RH (r=-0.670**), rainfall (r=- 0.398*) and wind speed (r=-0.655**) were negatively significant. The pheromone trap catch were negatively non-significant in relationship to maximum temperature (r=-0.186), morning RH (r=- 0.347) and evaporation (r=-0.072)

Multiple regression studies

The partial regression coefficients for different weather parameters and pheromone trap catch during Kharif 2018 and Kharif 2019 were worked out and presented in Tables 4 and 5. The multiple regression equation fitted with weather parameters in order to predict pheromone trap catch in Bt cotton was as below

Table 4: Multiple correlation and regression between weather parameters and moth catches (trap) of pink bollworm during 2018.

Table 5: Multiple correlation and regression between weather parameters and moth catches (trap) of pink bollworm during 2019.

Kharif 2018: Y=66.21+0.797 X₁ -0.091 X₂ -1.000 X₃ +0.001 X₄ +0.053 X₅ +0.301 X₆ +0.191 X₇ -1.663 X₈ with coefficient of determination (R2) 0.62.

Kharif 2019: Y=-333.91–10.75 X₁ +6.414 X₂ -1.030 X₃ – 0.137 X₄ +0.103 X₅ +3.369 X₆ -13.000 X₇ +1.639 X₈ with coefficient of determination (R2) 0.69.

Where, X₁ =maximum temperature, X₂ =minimum temperature, X₃ =morning RH, X₄ =evening RH, X₅ =rainfall, X₆ =bright sun shine, X₇ =wind speed, X₈ =evaporation and R2=Coefficient of determination.

The coefficient of determination (R2) represents the proportion of common variation in the two variables. The present investigations shown that the weather parameters contributed for 62.00 and 69.00 per cent of total variation in the rosette flowers in Bt cotton during Kharif 2018 and 2019 and of both years, respectively indicating that the predictions of the rosette flowers by using weather parameters were reliable.

Green boll damage by pink bollworm P. gossypiella (Saunders)

Simple correlation studies: The data on correlation between weather parameters and green boll damage during Kharif 2018 and Kharif 2019 presented in Table 3.

The green boll damage positively significant in relationship to bright sun shine (r=0.542**). The green boll damage positively non-significant in relationship to maximum temperature (r=0.017) and evaporation (r=0.123). The green boll damage in relation to minimum temperature (r=-0.682**), morning RH (r=-0.694**) and evening RH (r=-0.692**) and wind speed (r=-0.513**) were negatively significant and rainfall (r=-0.321) negatively non-significant during Kharif 2018.

While, during Kharif 2019, the green boll damage in relation to bright sun shine (r=0.603**) was positively significant. The green boll damage negatively significant in relationship to minimum temperature (r=-0.610**), evening RH (r=-0.632**) and wind speed (r=-0.677**). The green boll damage in relation to maximum temperature (r=-0.115), morning RH (r=-0.372), rainfall (r=-0.367) and evaporation (r=-0.038) were negatively non-significant (Tables 6 and 7).

Table 6: Multiple correlation and regression between weather parameters and rosette flower during 2018.

Table 7: Multiple correlation and regression between weather parameters and rosette flower during 2019.

Multiple regression studies

The partial regression coefficients for different weather parameters and green boll damage during Kharif 2018 and Kharif 2019 were worked out and presented in Tables 8 and 9. The multiple regression equation fitted with weather parameters in order to predict green boll damage in Bt cotton was as below.

Table 8: Multiple correlation and regression between weather parameters and green boll damage during 2018.

Table 9: Multiple correlation and regression between weather parameters and green boll damage during 2019.

Kharif 2018: Y=243.36 – 0.849 X₁ +0.387 X₂ -2.411 X₃ – 0.068 X₄ +0.090 X₅ +1.784 X₆ -0.037 X₇ -6.106 X₈ with coefficient of determination (R2) 0.63.

Kharif 2019: Y=-139.59+0.1602 X₁ –0.888 X₂ -1.198 X₃ – 0.601 X₄ +0.079 X₅ +1.147 X₆ -7.102 X₇ -5.34 X₈ with coefficient of determination (R2) 0.79.

Where, X₁ =maximum temperature, X₂ =minimum temperature, X₃ =morning RH, X₄ =evening RH, X₅ =rainfall, X₆ =bright sun shine, X₇ =wind speed, X₈ =evaporation and R2=Coefficient of determination.

The coefficient of determination (R2) represents the proportion of common variation in the two variables. The present investigations shown that the weather parameters contributed for 63.00 and 79.00 per cent of total variation in the green boll damage in Bt cotton during Kharif 2018 and 2019 and of both years, respectively indicating that the predictions of the green boll damage by using weather parameters were reliable.

Larval population of pink bollworm P. gossypiella (Saunders) in green bolls

Simple correlation studies: The data on correlation between weather parameters and larval population of pink bollworm during Kharif 2018 and Kharif 2019 presented in Table 3.

The larval population of pink bollworm in Bt cotton positively significant in relationship to bright sun shine (r=0.534**). The population of pink bollworm larvae positively non-significant in relationship to maximum temperature (r=0.127) and evaporation (r=0.166). The larval population of pink bollworm in relation to minimum temperature (r=-0.602**), morning RH (r=-0.699**), evening RH (r=-0.665**) and wind speed (r=-0.512**) were negatively significant and rainfall (r=-0.311) negatively non-significant during Kharif 2018.

Whereas, during Kharif 2019, the larval population of pink bollworm in relation to bright sun shine (r=0.619**) was positively significant. The larval population of pink bollworm negatively significant in relationship to minimum temperature (r=-0.573**), evening RH (r=-0.602**), rainfall (r=-0.388*) and wind speed (r=- 0.650**). The larval population of pink bollworm in relation to maximum temperature (r=-0.045), morning RH (r=-0.346) and evaporation (r=-0.024) were negatively non-significant.

Multiple regression studies

The partial regression coefficients for different weather parameters and larval population of pink bollworm during Kharif 2018 and Kharif 2019 were worked out and presented in Tables 10 and 11. The multiple regression equation fitted with weather parameters in order to predict larval population of pink bollworm in Bt cotton was as below.

Table 10: Multiple correlation and regression between weather parameters and larval population pink bollworm during 2018.

Table 11: Multiple correlation and regression between weather parameters and larval population pink bollworm during 2019.

Kharif 2018: Y=5.02+0.021 X₁ -0.005 X₂ -0.064 X₃ +0.005 X₄ +0.002 X₅ +0.048 X₆ +0.008 X₇ -0.169 X₈ with coefficient of determination (R2) 0.61.

Kharif 2019: Y=-0.31+0.165 X₁ -0.065 X₂ -0.023 X₃ –0.015 X₄ +0.001 X₅ +0.045 X₆ -0.032 X₇ -0.277 X₈ with coefficient of determination (R2) 0.56.

Where, X₁ =maximum temperature, X₂ =minimum temperature, X₃ =morning RH, X₄ =evening RH, X₅ =rainfall, X₆ =bright sun shine, X₇ =wind speed, X₈ =evaporation and R2=Coefficient of determination.

Locule damage due to pink bollworm P. gossypiella (Saunders) in green bolls

Simple correlation studies: The data on correlation between weather parameters and locule damage during Kharif 2018 and Kharif 2019 presented in Table 3.The locule damage in relation to bright sun shine (r=0.475**) was positively significant. The locule damage positively non-significant in relationship to maximum temperature (r=0.137), morning RH (r=0.137) and evaporation (r=0.118). The locule damage in relation to minimum temperature (r=-0.535**), evening RH (r=-0.585**) and wind speed (r=-0.485*) were negatively significant and rainfall (r=-0.275) was negatively non-significant during Kharif 2018.

Whereas, during Kharif 2019, the locule damage positively significant in relation to bright sun shine (r=0.602**). The locule damage in relation to minimum temperature (r=-0.602**), evening RH (r=-0.599**), rainfall (r=-0.395*) and wind speed (r=-0.644**) were negatively significant. The locule damage in relation to maximum temperature (r=-0.093), morning RH (r=-0.093) and evaporation (r=-0.041) were negatively non-significant.

Multiple regression studies

The partial regression coefficients for different weather parameters and locule damage during Kharif 2018 and Kharif 2019 were worked out and presented in (Tables 12 and 13). The multiple regression equation fitted with weather parameters in order to predict locule damage in Bt cotton was as below.

Table 12: Multiple correlation and regression between weather parameters and locule damage in green bolls during 2018.

Table 13: Multiple correlation and regression between weather parameters and locule damage in green bolls during 2019.

Kharif 2018: Y=3.07+0.032 X₁ -0.024 X₂ -0.047 X₃ +0.010 X₄ +0.002 X₅ +0.028 X₆ +0.003 X₇ -0.091 X₈ with coefficient of determination (R2) 0.59.

Kharif 2019:Y=34.48+4.426 X₁ -2.024 X₂ -0.786 X₃ –0.412 X₄ +0.016 X₅ +1.161 X₆ -1.487 X₇ -7.815 X₈ with coefficient of determination (R2) 0.57.

Where, X₁ =maximum temperature, X₂ =minimum temperature, X₃ =morning RH, X₄ =evening RH, X₅ =rainfall, X₆ =bright sun shine, X₇ =wind speed, X₈ =evaporation and R2=Coefficient of determination.

The coefficient of determination (R2) represents the proportion of common variation in the two variables. The present investigations shown that the weather parameters contributed for 59.00 and 57.00 per cent of total variation in the locule damage in Bt cotton during Kharif 2018 and 2019 and of both years, respectively indicating that the predictions of the locule damage by using weather parameters were reliable.

Lingren who concluded that higher temperatures delayed moth emergence, while lower temperatures resulted in early trap capture. Maximum and minimum temperature thresholds for trap capture were 30.30C and 12.30C, respectively. [6] Reported that the pheromone trap catches of pink bollworm showed negative significant correlation with minimum temperature. However it showed non-significant negative with maximum temperature, morning relative humidity, evening relative humidity, rainfall and rainy days. However, reported the larval density of pink bollworm had highly significant and negative correlation with changes of the temperature of both seasons. However, the correlation between number of larvae and changes of the relative humidity was insignificant and negative in both seasons. Maximum temperature, minimum temperature and wind shear showed a significantly negative correlation with population of pink bollworm [10].

As per [9] Larval population on flowers shows negative correlation with maximum, minimum (temperatures) and evening relative humidity, while, had positive correlation with morning relative humidity and rainfall. However, larval population on bolls had negative correlation with maximum, minimum (temperatures) and rainfall but had positive correlation with morning, evening relative humidity. The trap catches had a negative and non-significant relationship with rainfall and a negative and significant relationship with maximum temperature reported by [12]. While, [13] reported that the rosette flowers by P. gossypiella showed that positively non- significant with rainfall, minimum temperature, bright sun shine, and wind velocity then negatively significant with maximum temperature. While, negatively non-significant correlation with morning RH and evening RH.

Conclusion

The coefficient of determination (R2) represents the proportion of common variation in the two variables. The present investigations shown that the weather parameters contributed for 61.00 and 56.00 per cent of total variation in the larval population of pink bollworm in Bt cotton during Kharif 2018 and 2019 and of both years, respectively indicating that the predictions of the larval population of pink bollworm by using weather parameters were reliable.

Acknowledgement

While, Kumar reported the maximum temperature had negative and significant association with trap catches of pink bollworm, while minimum temperature, morning and afternoon relative humidity were positive and non-significantly correlated with trap catches. Whereas, total rainfall had non-significant negative influence on PBW trap catches.

Conflict of Interest

The author declares there is no conflict of interest

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