Monitoring cotton bollworms through synthetic sex pheromone traps

Bollworms are most serious pests of cotton crop which do not only cause losses by devouring foliage and fruiting bodies of cotton which results in low yield but also deteriorate its lint quality. Their management relies on application of pesticides but recent introduction of synthetic pheromones for mass trapping of their adult moths have given better solution for recording and monitoring their population. We used five different components of synthetic sex pheromone installed in funnel type traps (4 traps/per acre) at different localities of district Sanghar. The components were (0E, 12E)-10, 12 Hexadecadienal for Earias insulana (Boisduval), Z7, Z11-16AC (50), Z7, E11-16AC (50) Hexadecadienyle Acetate for Pectinophora gossypiella (Saunders), D, Z11-16AL (97), Z9-16 AL (3) Hexedecenal for Helicoverpa armeigera (Hubner) and (Z, E)-9,11and (Z, E)-9, 12-tetradecadienyl acetate (Z9, E11-14: Ac; Z9, E12-14: Ac) for Spodoptera litura (Fabricius). All these bollworm species in different localities were successfully trapped with significant different population. A maximum population of P. gossypiella and H. armigera were at Tando Adam, E. insulana at Shadadpur and S. litura at Jam Nawaz Ali. P. gossypiella trapped maximal in the month of October, E. insulana in September, H. armigera in August and S. litura in November, respectively. Based on the results, it is recommended that these pheromone lures should be introduced at different timings and pest species according to their presence.


Introduction
Cotton Gossypium hirsutum L. is one of the important cash crops grown in Pakistan. It contributes substantially (1.4%) to the national economy and possess a primary source of livelihood for rural people [1]. During the current year 2018, cotton production was 9.86 million bales, with a decrease of 17.5 percent over the production of 2017 (11.946 million bales).
This below expectation performance of the cotton crop was largely due to reduction in the cultivated area on account of less economic incentive given to the farmers [2]. There are number of factors responsible for lower cotton yield but insects are ranked at the top, which do not only deteriorate the quality of cotton but also reduce the yields [3]. Cotton crop is mostly attacked by the insect pests from seedling to harvesting but the maximum losses (30-40%) are recorded by bollworms [4]. In bollworms, army worm Spotdoptera litura (Fabricius), spotted bollworm Earias insulana (Fabricius), american bollworm Helicoverpa armigera (Hubner) and pink bollworm Pectinophora gossypiella (Saunders) are the major pests of cotton crop [5]. Among these bollworms, P. gossypiella is the most serious pest because it damages the reproductive part of crop during immature stage (larvae), remains inside bolls and very difficult to control with by insecticides. The pest is widely distributed all over the world particularly in India and Pakistan. The other two species of bollworms tend to cause more conspicuous damage particularly to the newly developing fruiting bodies and the terminal shoots. Meanwhile, these bollworms badly affect the quantity and quality of the lint. Control of these pest species with conventional insecticides is very difficult due to high cost and inaccessibility [6]. The use of sex pheromone lures for insect monitoring and reducing their population by adult moth trapping nowadays is the common practice by various cotton research institutes of Pakistan. Some progressive growers are also well familiar with application of different pheromones in cotton crop, as these are inexpensive and eco-friend strategy in integrated pest management tools [7]. Since few years, it has been well documented that synthetic pheromones are better to monitor and control the cotton bollworms population as compared to other control measures [8]. In Sindh province, few studies regarding use of pheromone have been previously conducted [9], but there is still lack of studies conducted in district Sanghar, which is to be considered as hub of cotton growing and processing area of Sindh province. Therefore, the aim of present experiment was designed to observe the population of cotton bollworms through synthetic sex pheromone traps in the various locations of district Sanghar, Sindh, Pakistan.

Figure 1. Funnel type pheromone trap
The synthetic sex pheromone traps for each species were replaced after every 15 days and data were recorded fortnightly. Trapped adults were brought and counted in separate Petri dishes (11x15 mm).

Data analysis
The experiment was laid out in Randomized Complete Block Design (RCBD) with four treatments and four replications. The data were subjected to analysis by using ANOVA statistical test and the means were separated by using Fisher's Least Significant Difference (LSD) at 5% level. All the statistical tests were done by using SAS (Ver. 9.2).

Results and discussion
The population of P. gossypiella in different localities were significantly different (DF=3; F=11.76; P< 0.05). The highest mean population was 8.49±0.26 at Tando Adam followed by 8.26±0.22 at Shahdadpur with non-significant difference and the lowest was 4.87±0.19 at Sinjhoro followed by 5.17±0.14 at Jam Nawaz Ali also with non-significant difference. However, the collective weekly population of P. gossypiella at all localities was highest (31.65±3.1) in the second week of October ( Table 1). The population of H. armigera were nonsignificantly different at different localities (DF=3; F=5.09; P> 0.05). The maximum population of H. armigera was 0.91±0.09 at Tando Adam followed by 0.82±0.05 at Sinjhoro, 0.72±0.03 at Shahdadpur and minimum 0.68±0.11 at Jam Nawaz Ali. The collective weekly population of H. armigera at all localities was highest (6.42±0.23) in the last week of August ( Table 2). The population of E. insulana were nonsignificantly differentat different localities (DF=3; F=5.09; P> 0.05). The maximum population of E. insulana was 1.77±0.15 at Shahdadpur followed by 1.70±0.13 at Jam Nawaz Ali, 1.62±0.13 at Tando Adam, and 1.42±0.11 at Sinjhoro. The collective weekly population of E. insulana at all localities was highest (9.37±1.09) in the third week of September as in (Table 3).
The population of S. litura in different localities were non-significantly different (DF=3; F=6.09; P> 0.05). The highest mean population was 2.46±0.89at Jam Nawaz Ali followed by 2.11±0.73 at Tando Adam, 2.06±0.31 at Sinjhoro and 1.98±0.21 at Shahdadpur. However, the collective weekly population of S. litura at all localities was highest (10.24±1.31) in the first week of November (Table 4). The results of sex pheromone traps in (Fig.  2 & Table 5), showed that the adult population of bollworms was varied at the different localities. The results showed that the maximum number of adults were collected from Tando Adam, followed by Shahdadpur, Jam Nawaz Ali, and Sinjhoro. Comparison between adult species and the maximum number of P. gossypiella adults were trapped as compared to S. litura, E. insulana, and H. armigera. The population of P. gossypiella was correlated with abiotic factors, that it showed positive correlation (r = 0.812, p<0.05) with highly significant difference with temperature and relative humidity was significantly different (0.69, p<0.05) and further showed non-significant different (0.52, p>0.05) with dates. The population of E. insulana was correlated with abiotic factors, that it showed positive correlation (r = 0.50, p<0.05) with lowest significant difference with temperature and relative humidity was lowest significantly different (0.49, p<0.05) and further showed nonsignificant different (0.49, p>0.05) with dates. The population of S. litura was correlated with abiotic factors, that it showed positive correlation (r = 0.63, p<0.05) with lowest significant difference with temperature and relative humidity was lowest significantly different (0.55, p<0.05) and further showed non-significant different (0.51, p>0.05) with dates. The population of H. armigera was correlated with abiotic factors, that it showed positive correlation (r = 0.51, p<0.05) with lowest significant difference with temperature and relative humidity was lowest significantly different (0.48, p<0.05) and further showed non-significant different (0. 50

Conclusion
On the basis of present research work on monitoring the adult population of cotton bollworms through synthetic sex pheromone traps it has been concluded that the highest population of P. gossypiella and H. armigera were found in Tandoadam, E. insulana was found in Shadadpur, and S. litura was found in Jam Nawz Ali.