Seasonal Incidence of Sesame Webworm, Antigastra catalaunalis (Dup.) and Evaluation of Selected Cultural Control Practices, on Sesame Crop in Erbil City

Sesame (Sesamum indicum L.) belongs to the plant family Pedaliaceae (Bedigian, 2003) and is known as the queen of oilseeds due to its high content of oil and delicious flavor (Johnson et al., 1979) the percentage protein  reaches  to over 20 per cent and the per cent of oil to over 50% (Khan et al., 2009). Sesame seed is used for a wide array of edible products in both roasted and raw form and also used as animal feed (Bedigian, 2010) and its by-products are utilized as a mixture in Poultry feed (Sulaiman, 2017).
       
Sesame webworm, Antigastra catalaunalis (Duponchel)  is a key insect pest of the sesame crop throughout all life stages and is considered as one of the major obstructions of good sesame productivity in terms of quantity and quality (Selvanarayanan and Baskaran, 2000) causing 10-44 percent capsules infestation and resulting in about 70 percent seed yield loss (Ahirwar et al., 2010).
       
Different varieties are cultivated in Iraq, among them, the Variety Rafedeen is the most susceptible one which faces a high percentage of losses on various parts of the plant, The yield loss of sesame crop seeds per plant recorded as 22.2 and 18.1% in rafedeen variety, during 2001 and 2002 respectively (Al-Jorany and Al-Cerrawi, 2009).
       
Various management tactics have been attempted by previous authors, most of their studies have been focused on using insecticides to control the insect, however, the chemicals cause air and environmental pollution and health problems to humans (Weston et al., 2011, Ansari et al., 2014). 
         
Worldwide, some research has been done on cultural and other eco-friendly management methods to minimize the damages of this insect pest due to their safeness to the environment, however, to our knowledge very little work has been performed on the cultural methods to manage the sesame webworm on sesame crop in Iraq, So the present study aims to investigate the seasonal incidence of SWW, A. catalaunalis (Dup.) and evaluate the impact of three different dates of sowing and three various intercropping practices on the infestation percentage of sesame crop capsules and their role to minimize the losses of seed weight at harvest caused by the insect pest, in Erbil-Iraq.
 

Study location and cultivation
 
The studies were carried out in the Grdarasha research station field belonging to the College of Agricultural Engineering Sciences-Salahaddin University-Erbil-Kurdistan Region-Iraq during sesame growing season, 2020. For this study, sesame crop cultivar Rafedeen was sown in three different periods with a one-month interval between them, using (RCBD) design with 3 replicates, the dates of sowing were 16-5, 15-6 and 15-7-2020. For intercropping experiment, three different crop viz., cowpea, corn and sunflower were selected; the seeds have been sown between rows of sesame plants alternately, the average row number in plots was seven provided that both outer rows were trap crop. The sowing of sesame seeds was taken place on 15-6-2020, while seeds of intercropped plants had been sown previously fifteen days before sowing the main crop (Sesame Variety Rafedeen). The plots size was 1.5 X 2.5 Meters. The plants were sown in rows within plots; the row to row and plant to plant distances were 30 cm and 15 cm respectively.
 
Observations and sampling
 
Firstly, for seasonal incidence, sampling was taken place weekly for sesame plants (Variety Rafedeen) cultivated on three different dates of sowing (middle of May, Middle of June and Middle of July), by taking three plants, randomly, at each plot (Replicate) for all three dates of sowing starting from the first appearance of the caterpillars. Second, for evaluation of the effect of sowing dates of Sesame for management of Sesame webworm, Antigastra catalaunalis
(Dup.), the observation and data of per cent Capsule infestation per plant and seed weight of 25 capsules of Infested and intact ones were recorded at harvest time. 
       
The last experiment, for the intercropping systems, comparison between three different intercropping systems and the sole sesame plant was done by taking three plants (Sample) at harvest, from each treatment and replicate separately, the observations on capsule infestation percent at harvest and the yield (seed weight of 25 capsules) of infested and intact ones were recorded and compared with each other and with that of control (Sole sesame crop, Var. Rafedeen).
       
For calculating the per cent of capsule damages per plant, the following Formula was used.   


 
Statistical analysis
 
The obtained data were tabulated and subjected to analysis of variance and the Paired T-test has been used to calculate the amount of Seed weight losses then the means were compared with each other according to the (DMRT) Duncan test at 0.05 of significant level.

Seasonal incidence of sesame webworm
 
The data on larval population indicated that the larval population started after 2nd week of sowing when the plant was at the Leaves stage, which was 0.25,0.25 and 0.42 larvae/plant (22^nd, 26^th and 30^th meteorological week) for the first, second and third sowing dates respectively, the population of the caterpillar increased gradually and reached to its peak i.e., 2.31,2.50 and 2.83 larvae/plant in the 11^th week of sampling (32^nd, 36^th and 40^th meteorological week) for 1^st, 2^nd and 3^rd dates of sowing respectively, when the crop was at the flowering and capsule formation stage, in the year 2020. There after, the larval population of sesame webworm started to decrease gradually and the larval population reduced in number to 1.53, 1.67 and 1.94 larvae/plant at the last week of sampling before harvest, when the plants were at the capsule stage (35^th, 39^th and 43^rd SMW) for 1^st, 2^nd and 3^rd DOS respectively on all sesame varieties under the study (Fig 1). 


       
The findings of this study are more or less similar to that carried out by (Mishra et al., 2015) who mentioned that the population density of Antigastra caterpillars reached its peak (0.11) larvae/plant in the 35^th standard meteorological week and the present study results also supported by Mahadevan and Mohanasundaram (1986)who reported that the incidence of larvae of sesame webworm on flower stage was more than on leaf and capsule stage and the insect caused to just over 50 per cent loss in sesame seeds. However, Talpur et al. (2002) reported that the abundance and injuries of SWW larvae on pods were higher than leaf and flowering stage.
 
Effect of sowing date on capsule infestation at harvest
 
The data in Table(1) showed that the least capsule infestation percentage recorded on the sesame variety Rafedeen, was in the 1^st date of sowing with 16.75% capsules/plant, the highest percentage of capsule infestation at the harvest was in the third date with recording 23.84% as infestations/plant, in comparison to the 1^st date, it was about 7% higher than the percentage recorded in the 1^st date and the 2^nd date of seed sowing occupied the middle position in respect of capsule infestation at harvest with recording 22.08% capsule/plant.


       
Regarding capsule infestation at harvest, the 1^st date was differed from both other sowing dates significantly depending on the significant level (0.05) of DMRT. However, there was no significant difference between the 2^nd and 3^rd dates of sowing. The results of this study are in agreement with that reported by Kudher (1985) in Iraq who demonstrated that the infestation percentage in late sowing dates is higher than earlier dates. The present results are also supported by Gebregergis et al. (2018) who reported that the highest level of damage on leaf, flower and capsule due to SWW was recorded on the late sown sesame plants.
 
Effect of sowing date on seed weight losses at harvest
 
The data in Table (1) demonstrated that, the least percentage of seed weight loss was recorded on the sesame variety Rafedeen in the 1^st date of sowing with 22.27% /25 capsule yield, whilst the highest percentage of Seed weight loss was in the third date with recording 33.85% seed wight/25 capsule yield in comparison with the 1^st date, it increased just over 10. The 2^nd date of seed sowing was ranked in middle regarding the seed weight loss/25 capsules of sesame plant with recording 34.16% seed/25 capsules yield.
       
As an indication from DMRT at (0.05) significant level, the 1^st date was different from the other two dates significantly, however, there was no significant difference between 2^nd and 3^rd dates. 
       
Overall, it can be concluded that the May month provided the best time for sowing seed of sesame in the present study in comparison with the other two later months (June and July), as an indication to recording the least capsule infestation at harvest and seed weight loss of sesame plant variety rafedeen. The results of the present experiment are in line with those reported by Gebregergis et al. (2018) who mentioned that the least infestation of A. cataluanalis and better sesame seed yield was obtained in early sowing sesame, while the highest incidence of pest insect reached to 100 per cent and lower grain yield (69.1 kg/ha) were gained in the late sowing date of sesame. 
 
Impact of intercropping on percent damage on capsules at harvest time
 
According to data in (Table 2), all the trap crops plants reduced the damage percentage on capsules when compared with control plants which was 22.20±0.015% capsules/plant, the highest percentage of capsule infestation at harvest was on the sesame plants that intercropped with corn plants 20.20±0.006 % capsules/plant, hence, providing the least reduction in capsule damage percentage, while the lowest percentage of capsule damages recorded on sesame plants that intercropped with cowpea plants with 18.00±0.004% capsules/plant meaning it gave the highest percentage of damage reduction on capsules at harvest among the trap crops tested and the middle position, in terms of damage reduction capacity, occupied by the sesame plants intercropped with sunflower crop, with capsule damage 19.40±0.01% capsules/plant.


       
Duncan’s test revealed that the treatment with cowpea differed from the other two intercropped crops and the control plants significantly at the significant level (0.05), however, there was no significant difference between sunflower and corn plants with each other as far the capsule damage at harvest concerned. The findings of this study are in agreement with those mentioned by Behera and Jena (2013) who stated that intercropping systems has reduced the incidence of the larvae of Antigastra and also reported that among intercropped crops, the impact of Leguminous crop plants is greater than others to reduce the population density of the caterpillars of the pest moth. 
 
Impact of intercropping on per cent seed weight losses
 
The data provided in (Table 3) demonstrated that the minimum reduction in sesame seed weight loss was registered on the treatment of sesame intercropped with corn with the highest per cent of seed weight loss, among the present study treatments, with 27.60±0.002% / 25 capsule yields in comparison with that of sole sesame crop which was 33.40±0.004% seed weight loss/25 capsule yield. However, in the treatment of sesame intercropped with cowpea, the lowest percentage of losses was recorded 21.00±0.003% losses in seed weight/25 capsule yield; it means that the cowpea marked the most effective crop among intercropped plants with sesame as a trap crop and provided the highest percentage of reduction in seed weight losses of sesame seeds/25 capsules yield. Moreover, the sunflower crop provided a middle amount of protection against sesame webworm and recorded the second rank of seed weight losses among intercropped plants with 25.60±0.002% seed weight losses/25 capsule yield.


       
As an indicative from the Duncan test at a significant level of (0.05), there was a highly significant difference between all treatments and among intercropped trap crops the significant difference also was found high.
       
The order of crops capacity for the protection of the sesame plant seeds from seed weight losses due to sesame webworm, from highest to least capacity, was (sesame intercropped with cowpea > sesame intercropped with sunflower > sesame intercropped with corn > sole sesame). the results of the present study more or less are in concordance with the findings of the research conducted by Behera and Jena (2013) who reported that the sesame intercropped with cluster bean and black gram both in the family Fabaceae gave the highest yield equivalent in comparison with sorghum (SSG 59-3) and pearl millet (L-74) and provided the highest level of protection against insect damages due to sesame webworm on yield of sesame plants.

The present research indicated that the moth larvae started to appear at the leaf stage two weeks after sowings and reached to its peak at flowering and both cultural methods viz. sowing date and intercropping system have a great impact on the infestation and damages of sesame webworm, furthermore, the first date of sowing (sowing sesame seeds at May) is the suitable and most effective time to reduce the negative impacts of the insect pest with recording the least percentage of capsule damage and seed weight loss caused by sesame webworm. As for the intercropping system, the study concluded that the sowing cowpea intercropped with sesame seeds provided significantly highest protection against Antigastra catalaunalis (Dup.) with recording the least capsule infestation percentage and Seed weight loss/25 capsules of sesame caused by the pest insect larvae.