Effect of Different Synthetic Pesticides Against Pink Bollworm Pectinophora gossypiella ( Saund . ) On Bt . and non-Bt . Cotton Crop

The field studies were conducted at the farmer’s field in 2015-2016 to determine the effect of three different insecticides (triazon, radiant and polytrin C) on Bt. and non-Bt. cotton varieties against pink bollworm. The results revealed that triazon was observed the most effective pesticide against PBW on both cotton varieties. The mortality reduction percent of 33.99 to 30.45% was recorded at triazon, 27.72 to 26.95% at radiant and 24.68 to 14.48% at polytrin C respectively, in 2015. However, in 2016 the mortality reduction percent decreased but effective trend of these selected pesticides were observed same with mortality reduction percent of 28.15 to 25.46% at triazon, 21.95 to 23.52% at radiant and 19.96 to 16.37% at polytrin C in Bt. and non-Bt. cotton varieties. In present investigation, triazon was observed the most effective pesticide than radiant and polytrin C on larvae of PBW in both Bt. and non-Bt. varieties.


INTRODUCTION
Pink bollworm Pectinophora gossypiella (Saunders) is considered as one of the most serious insects pest of cotton crop attacking on fruiting bodies which may result indirect losses of yield and indirectly damage of cotton fiber quality.It has been estimated that the total losses first time caused by this insect pest was over one million in Egypt [1] which further advanced with time in different cotton growing countries of the world.The major constraint in controlling the pest through pesticides is the habitat of pest larvae feeds and develops inside of bolls [2] and difficult to get direct exposure of many pesticides.The recent introduction of microbial pesticides such as Spinosyn particularly against many lepidopteron pests have given a great solution as bio-control [3][4][5][6].However, an application of repeating similar pesticides did not impact well in controlling the bollworm complex [7][8][9] and resulted in insect resistance.The great example in this regard was an introduction of Bacillus thuringiensis that previously provided an effective insecticidal activity against various lepidopterous species but such effect was later evolved in term of pest resistance particularly in P. gossypiella [10].
In country like Pakistan, where cotton is considered as golden fiber and most of the economy relies on cultivation of single crop, it is essential to know the preference of P. gossypiella on different varieties of Bt. and non-Bt.cotton.Only few studies, have been *Address correspondence to this author at the Department of Entomology, Faculty of Crop Protection, Sindh Agriculture University, Tandojam, Sindh, Pakistan; Tel: 0301-3454358; E-mail: ranaimran234@gmail.compreviously attempted however there is still lacking in regard to know the resistance development of pink bollworm on various commercial varieties of cotton available particularly in Sindh province.Therefore, this study was designed to observe the effect of different synthetic pesticides against PBW on Bt. and non Bt. cotton crop.

MATERIALS AND METHODS
The comparative effect of different pesticides against pink bollworm on cotton varieties was carried out during two consecutive growing years (2015 and 2016).The cotton varieties "Bt.MNH-886 and non-Bt.FH-1000 were used throughout the experiment at farmer's field of district Sanghar.The cotton was grown in area of half acre which was further divided into four blocks (Figure 1) and each block was replicated four times and similar layout was applied in non-Bt.cotton crop.
The experiment was consisted of three pesticides (Trizon 40% EC, Radiant 120% SC and Polytrin C 440 EC) and one control plot as treatments.These pesticides were used at experimental plot according to their recommended doses (Table 1).
These pesticides were applied four times at the interval of 15 days to both Bt. and non-Bt.cotton varieties.To observe the efficacy of selected pesticides against pink bollworm, 50 bolls from each replication (200 bolls/treatment) were observed before and after each spray.The pre-treatment observations were recorded at 24 hours before spray, however the posttreatment observations were taken at different hours (24, 48, 72 and 96), one week and two weeks of each pesticides spray, respectively.The data were later compared to control plot within both Bt. and non-Bt.varieties.

Data Analysis
The experiment was selected as Randomized Complete Block Design (RCBD) with four treatments and replications.The collected data were subjected to statistical analysis using three factorial analysis of variance (ANOVA).The analyzed means of all treatments were further compared through LSD (Least Significance Difference) at p value (0.05) using statistical software SAS (ver.9.1).Moreover, the reduction percentage (%) of pink bollworm population was also calculated using following formula described by Abbot (1925).

RESULTS
The results regarding the efficacy of different pesticides spray against larval population of pink bollworm varied significantly at different intervals (24 hrs F= 209.60;48 hrs F=281.89;72 hrs F=282.83;96 hrs F=406.17,1week F=777.53;and 2 weeks F=1312.09,dF=3 at P<0.05).The results in Tables 2 and 3 further indicated the reduction percentage in larval population of pink bollworm on Bt. and non-Bt.cotton crops.The highest reduction percentage of 36.74 was recorded on Bt. cotton with pesticide application of triazon followed by radiant 27.72 % and polytrin C 24.68 %.However, similar effect of these pesticides was also observed on non-Bt.cotton with less reduction percentage as compared to Bt. cotton.A maximum mean reduction in larval population of 30.51% at triazon followed by radiant 27.33 % and polytrin C 16.23 %was recorded on non-Bt.cotton in 2015 shown in (Figure 2).The trend of results in 2016 was observed with similar findings, however the overall maximum mean reduction population decreased and recorded 28.15 % at triazon followed by radiant (21.95%) and polytrin C (19.96%) in Bt. cotton crop and 25.46% at triazon followed by radiant (23.52%) and polytrin C (16.37 %) in non-Bt.cotton crop were respectively recorded (Figure 3).

DISCUSSION
Pink bollworm P. gossypiella is a sever pest of cotton crop which affecting mostly fruiting bodies and huge losses of cotton production including lint qualities.Although, the introduction of Bt. cotton varieties have      indicated significant resistance against bollworm complex but reported resistance of P. gossypiella against Bt.cotton crop has opened a new gate of challenges for cotton growers.In this regards, the present study consisted of collective information of two (2015 and 2016) cotton growing years showing resistance of P. gossypiella against different pesticides on Bt. and non-Bt.cotton crops.The pesticides used in this study were observed more effective on Bt. cotton as compared to non-Bt.cotton crop in both years.It could be due to the less population of P. gossypiella was observed as compared to non-Bt.cotton crop.Thus, Bt. cotton showed deterrent against larval attack of P. gossypiella due to having Bacillus thuringiensis inside it and performed bio-insecticidal effect.
Overall, the maximum toxic effect persisted up to 24 hrs after application of all pesticides of different selected groups in both years of study on Bt. and non Bt. cotton crops.It could be possible due to developed resistance against long term usage of pesticides.Similarly, the less persistence of most pesticides has also been recorded previously against P. gossypiella on Bt. cotton [11].The development of pest resistance against various pesticide in the field condition has also been reported by [12].Thus, it showed that the repetition of similar application of pesticides generates pest resistance mainly and may also results in insect pest outbreak.However, maximum mean reduction percentage of P. gossypiella after application of these different pesticides was varied.The pest population in 2015 was observed much reduced on Triazon, as compared to Radiant and Polytrin C. in Bt. and non-Bt.cotton crops.Such findings showed that Triazon was much affected in controlling pink bollworm meanwhile more or less reduction percentage of pest was also observed on other pesticides.In addition, the results in 2016 were observed with similar findings in which the maximum mean reduction population percent was observed after application of triazon.Furthermore, [13] successfully managed the bollworms complex in cotton with timely spray schedule of synthetic pesticide with less repetition.Meanwhile, these insecticides may lost their effect if applied as a response to high pest population [14,15].Nevertheless, spinosyn, pyrethroids and other organophosphorus class of insecticides were reported frequently used against lepidopteran particularly bollworm complex [16] but the evolution of synthetic insecticides resistance has been developed worldwide as the most serious threat to the development of sustainable Integrated Pest Management practices [17].Therefore, similar resistance indicated by P. gossypiella observed in this study against most these popular groups of insecticide on both Bt. and non-Bt.cotton crops at different intervals particularly after 24 hours of pesticide application in both years.

CONCLUSION
It is concluded through present investigation that the population of P. gossypiella was less observed on Bt. cotton as compared to non-Bt.cotton.Furthermore, from selected pesticides, the Triazon was observed much effective in controlling the larval population of P. gossypiella with maximum reduction percentage in both years from Bt. cotton fields.

Figure 2 :
Figure 2: Reduction percentage of larval populations after application of different pesticides in Bt. and non-Bt.cotton during 2015.

Figure 3 :
Figure 3: Reduction percentage of larval populations after application of different pesticides in Bt. and non-Bt.cotton during 2016.