Management of Rice Yellow Stem Borer Scirpophaga insertulas (Walker) using Different Formulations of Insect Sex Pheromone in West Bengal

Yellow stem borer Scirpophaga insertulas (Walker) devastated the rice crop in both vegetative and reproductive growth stages during monsoon and summer seasons of West Bengal. A field trial was conducted for evaluating the efficacy of pheromone lure against rice yellow stem borer in farmers’ fields under Gopalpur co-operative society, Burdwan during rainy 2011-2013. The field trials consisted of six treatments including control viz. T1= 50 pheromone traps/ha installed at 10 DAT where lure was not replaced, T2= 50 pheromone traps/ha installed at 10 DAT and lure replaced at 45 DAT, T3= 50 pheromone traps/ha installed at 10 DAT and lure replaced at 45 and 60 DAT, T4= 80 Exosex YSBtab per hectare @ 20 mg installed at 15 DAT, T5= as per farmers practice where cartap hydrochloride @ 750 g a.i/ha used at 45 and 60 DAT and T6= untreated control. Here both the dispenser (lure) and Exosex YSBTab containing (Z)-11 hexadecinal and (Z)9 hexadecinal at 3:1 ratio was used. This experiment, resulted that the two peaks were found (27th August and 1st October) during rainy season. The Exosex YSBTab @ 20 mg had significantly exhibited minimum oviposition by female as well as significantly managed the yellow stem borer as compared to other pheromone treatments.

West Bengal is one of the rice growing states, cultivating rice over 5.69 m ha which constitutes 12.99 percent of total rice area of India, producing 14.75 m tons forming 15.80% production of country with an average productivity of 2.59 tons/ha of milled rice (2006-07).Typical rice production seasons are Aus/Bhadri (autumn rice) -April/May to August/September, Aman (Kharif), June/July to November/December and Boro (like Rabi) November/December to April/May.Kharif rice is grown under diverse rice growing situations -irrigated, Rainfed (upland, Shallow-land, Semideep water, Deep water) (Anon., .Catling and Islam (1995) studied the borer species composition in deep water rice in Bangladesh and found that Scirpophaga incertulas was the dominant borer species in deep water rice in the field stubbles during the growing season.Alam and Bhuiyan (1964) reported that in Bangladesh 3 to 20% of crop was lost due to rice stem borer annually and severe causing about 60% damage may occur (Catling and Islam, 1981).The intensive studies on yield losses of deep water rice in Bangladesh showed that yellow stem borer Scirpophaga incertulas was responsible for 10-15% loss of rice crop with catastrophic outbreak causing upto 60% damage (Catling and Islam, 1981;Daryaei, 2005).On the other hand the application of insecticide increased the paddy yield of Basmati 385 by 42.6% to 54.5% over control (Khan et al., 2010).Deep circular stem feeding was observed for 81.94% larvae incidence of partially emerged white head (59.19%) dominated the field in West Bengal (Satpathi et al., 2012).The use of pesticides that often have stronger effect on natural enemies and often have a stronger effect on natural antagonists than on the target species because of widespread insecticide resistance (Pimentel et al., 1992;Elzen and Hardee, 2003;Oerke, 2006).Even some agrochemical industries now have reached the view that a further increase is not feasible and thus they support the development of mating disruption and mass trapping of rice stem borer in order to maintain a sustainable level of pesticide use (Cork et al., 2005).Keeping above background in mind, our aim was to evaluate the pheromone lure for sustainable management against rice yellow stem borer.

MATERIALS AND METHODS
A field experiments were conducted on farm trials at Gopalpur Co-operative field, Burdwan of West Bengal, India during 2012 and 2013 kharif (rainy) seasons.Each treatment with assigned three hectare was separated from other treatment demarcated with 100 m gap or more.Farmers' practice plots which belonged to different farmers were located adjacent to the treated plots.Treatments were replicated 2 km apart and farmers' practice plot and pheromone plots were located at 200 m apart from each other.Separate monitoring funnel traps were deployed throughout treated and control plots @ 3 traps ha -1 .The field trial was conducted for studying optimization of doses of pheromone which consists of five treatments viz.T 1 = 50 pheromone traps ha -1 at 10 days after transplanting (DAT) where lure was not replaced, T 2 = 50 pheromone traps ha -1 at 10 days after transplanting (DAT) but lure was replaced at 45 DAT, T 3 = 50 pheromone traps ha -1 at 10 days after transplanting (DAT) subsequently lure was replaced at 45 and 60 DAT, T 4 = EXOSEX YSB Tab 20 mg at 15 DAT, T 5 = Cartap 4 G @ 750 g a.i ha -1 (twice at 25 and 45 DAT) along with Chlorpyriphos 50% EC + Cypermethrin 5% EC @ 250-350 g a.i ha - 1 and Chlorantraniliplore 18.55% W/W @ 25 g a.i ha -1 , T 6 was untreated plot.
Dispenser for YSB containing (Z)-11 hexadecinal and (Z)-9 hexadecinal in 3:1 ratio was obtained from pest control India, Bangalore, India.Each dispenser was loaded with 5 mg pheromone chemical.The observations for borer damage were recorded from 50 randomly selected hills/sub plots at weekly interval.The damage caused at peak incidence only was taken into consideration. .In all fields were adopted almost similar cultivation practices were adopted.In Exosex YSB Tab @ 20 mg pheromone tablets were loaded into the groove of the biodegradable plastic hangers which were tied to the bamboo sticks of 1.5 m length.Such sticks were fixed and placed in the transplanted field in 11 × 11 m matrix at the rate of 80 per ha.Tablets were installed at 15 DAT.The trap height was adjusted during the lure replacement in such a way that the trap canopy remains just above the crop height level.
Damage due to stem borer was assessed in term of dead heart (DH) and white ear (WE) by counting total number of tillers or total number of panicle bearing tillers and number of DH or WE in each selected hill at vegetative stage or heading stage.Randomly were selected 400 hills in each treatment and 100 hills considered as a replication.Damage assessment data were recorded at 30, 45 and 60 DAT at vegetative phase and 90 and 110 DAT at reproductive phase using formula 1. Grain yields were estimated on Gobindabhog (aromatic variety) through 5 × 5 meter area crop cuts from each treatment of each replication and converted in to yield per hectare.Calculating egg mass index were examined 400 hills in each treatments in diagonal way at 10, 20, 30 and 40 DAT using formula 2.

Estimation of egg mass index (IE%)
In order to find the oviposition preference of YSB on different treatment on long duration scented rice an experiment was conducted on rice variety Govindbhog in irrigated lowland areas of West Bengal and the results were presented in Tables 1 to 3. It is evident from the observations that the average egg mass index (IE %) in pheromone treated plots of irrigated rice field was significantly lower than plots with farmer's practices.The average egg mass index (IE %) during the oviposition period was found to be 0.153 % in T 4 , 0.171 % in T 3 , 0.173 % in T 2 , 0.180 % in T 1 and 0.418 % in T 5 whereas reduction of IE over control were 29.83 %, 33.50 %, 33.74 %, 35.21 % and 81.66 % in respective treatments during 2012 (Table 1).During 2013, the average egg mass index figures were 0.133 %, 0.154 %, 0.164 %, 0.176 % and 0.428 % in T 4 , T 3 , T 2 , T 1 and T 5 respectively whereas percent reduction of egg mass index were 25.54 %, 29.64 %, 31.57%, 33.98 % and 82.41 % over control in the respective treatments (Table 2).Different oviposition preferences of YSB were recorded in both coarse and fine rice where the mean number of egg masses/m 2 were statistically higher on fine grain variety than scented fine rice variety in Pakistan (Rustamani, 2002).
The pooled egg mass index (IE %) value for the year 2012 and 2013 could be arranged in ascending order as T4 > T3 > T2 > T1 > T5 where the reduction of IE over control were 27.67 %, 31.55 %, 32.65 %, 34.59 % and 82.04 % respectively (Table 3).The result is in accordance with Mishra and Sharma (2012) where the pheromone based Integrated Pest Management (IPM) module against YSB in scented rice (Basmati rice) showed that the incidence of YSB at vegetative stage ranged from 2.43 to 5.70 % in IPM plot as compared to 3.12 to 13.07 % dead heart in non -IPM (farmers' practice) plots during kharif 2008 respectively.However at maturity stage, the damage ranged between 1.15 to 5.10 % in IPM plots against 3.73 to 11.01 % white ear head in non -IPM plots in 2008.The pooled data showed that the maximum infestation were 5.19 and 12.35 % dead heart at vegetative stage whereas 4.91 and 10.58 % white ear head at maturity in IPM and non-IPM plots respectively.It is a common phenomenon that the adult moth mates between 7 to 10 AM and lay eggs in clusters after mating.According to Pathak (1967) the adult of YSB emerges during the evening or night.Jadhao and Khurad (2012) reported that one female moth lays eggs early at night in small masses of about 50 to 80 eggs near the leaf blade.The moth deposits only one egg mass per night and oviposition takes place for one to two days after emergence and die within two to three days after oviposition.From the present investigation it is observed that the fecundity is dependent not only on the temperature but also on relative humidity.Both male and female were found in tail to tail position for 30 minutes over the surface which ultimately lead to on oviposition by female (Plate 13).Doke (1936) studied the effect of temperature and humidity on ecology of stem borer.Here it is found that the sex pheromone is used for disruption of mating, which is achieved by placing high concentration of pheromone throughout the field.This high concentration of pheromone saturated the area resulting in males failing to find the female, thus preventing mating and laying of egg for multiplication of insect.This result is agreement with Islam (2012) who reported about the pheromone use for insect control in Bangladesh.

Monitoring of male YSB using insect sex pheromone
The relative attractiveness of the crop for shelter and oviposition was found to be foliage of the host plant, depending on density.To find out the influence of different treatments of pheromone for management of YSB in scented rice the experiments were conducted in irrigated lowland areas at Gopalpur, under the district of Burdwan     It is evident from Fig. 1 that the male moths were trapped from 13 th August to 26 th November with two distinct peaks on 27 th August and 1 st October regardless of the treatment in scented rice cv.Gobindobhog grown in irrigated areas of Gopalpur under the district of Burdwan, West Bengal during 2012.Although the trapped population was high on 5 th November but an uniform level of trapping was found subsequently from second peak to till the crop was harvested.The trapping was mostly identical in 2013 too when the maximum number of male moths were trapped in the last week of August and first week of October respectively without considering the treatment as given Fig. 2. The pooled data of 2012 and 2013 exhibited three peaks of which former two are distinct but the later one in very short during the first week of November as given in Fig. 3.

Management of YSB cause crop damage using insect sex pheromone
Yellow stem borer (Scirpophaga incertulas Walker) devastated the crop in all seasons.Larval feeding of YSB from inside stem (Pseudostem) severs central part of tiller at its base resulting in drying of the central whorl and rendering the tiller non productive.Damage thus caused by the borer in this way is typically termed as dead heart (DH) during vegetative stage.Similar nature of damage is seen at heading or reproductive stage, the panicle becomes chaffy (with empty grains) which is called as white ear head (WE).
Insecticides is primary method of control which generally applied at a minimum of two prophylactic rounds in a crop season to control YSB, which often results in the secondary pest resurgence, needing additional pesticide usage.Besides, pesticides are known to cause different types of health hazards to human beings and domestic animals through handling, contamination of food chain and environment as a whole.Further, success of insecticide application depends upon the detection of the pest incidence/ intensity.Among effective alternatives, insect sex pheromones have been proved to provide promising tool for management of YSB, both in monitoring and direct control of pest as well as minimizing pesticide load in rice ecosystem.
Table 4 suggests that the treatments could be arranged according to the subsequent DH% and WE% as ranging from 0.294 to 0.736% with average 0.451% and 1.730 to 3.816% with average 2.773 in T 4 , followed by 0.314 to 1.295% with average 0.681% and 2.052 to 4.018% with average 3.132% in T 3 , 0.335 to 1.373% with average 0.712% and 2.120 to 4.144% with average 3.132% in T 2 , 0.338 to 1.66% with average 0.855% and 2.217 to 4.464% with average 3.341% in T 1 .Here, the entire plot treated with pheromone exhibited numerically close to farmers practice or T 5 (DH ranges from 0.431 to 1.581% with average 1.104% and WE ranges from 3.090 to 7.608% with average 5.349%) but it was significantly better than control where the average dead heart and white ear head varied from 1.659% and 8.071% respectively during 2012.Similar results were also obtained in 2013 too where DH% varied from 0.155 to 1.032% with average 0.526% inT 4 which was very much close to T 3 (0.211 to 1.104% with average 0.577%), T 2 (0.267 to 1.174% with average 0.624%), T 1 (0.224 to 1.216% with average 0.659%).Average white ear head was observed from 90 DAT with 2.372%, 2.529%, 2.699% and 2.851% in T 4 , T 3 , T 2 and T 1 respectively.Numerically the value of T 5 is close to pheromone plots with average 0.886% DH and 4.654% WE but it was found that all treatments were significantly lower than control where average DH was 1.372% and 0.499% WE was recorded as given in Table 5.
The variation of damage due to YSB was ultimately reflected in yield as T 4 exhibited its supremacy in both the years with 3997.3 kg/ha and 4273.7 kg/ha as mentioned in Tables 4 and 5.The yields of all the plots treated with pheromones were close to farmers' practice or T 5 but it was significantly better than control (T 6 ).
The pooled data of 2012 and 2013 were calculated and found that all the treatments could be arranged with respect to minimum damage and maximum yield as T 4 > T 3 > T 2 > T 1 > T 5 > T 6 .Here the initial damage of dead heart reflected as subsequent white ear head and ultimately yield of rice crop cv.Gobindobhog as given in Table 6.Here, T 4 exhibited 0.225 to 0.884% DH with average 0.488% subsequently 1.446 to 3.699% WE with average 2.572% in the same field and it ultimately gave highest yield 4115.5 kg/ha of scented rice (Gobindobhog) in irrigated areas of Gopalpur under the district of Burdwan, West Bengal.Consequently T 6 exhibited maximum damage 0.730 to 2.495% DH with average 1.516% and 3.527 to 11.043% WE with average 7.285% which ultimately gave minimum yield (3665.0 kg/ha) in same field of Gopalpur.Numerically all the pheromone treatments were close to farmers' practice (T 5 ) but it was significantly higher than control (T 6 ).
The present finding are in agreement with result of the work on evaluation of Exosex YSB tab for management of rice yellow stem borer through pheromone mediated auto confusion technology (Anon., 2010-2011) where a comparative study of Exosex YSB tab @ 20 mg and farmers' practice (FP) or chemical control as per routine practice was made at the same field of Gopalpur on Gobindobhog during 2010 and found that in one trial the DH incidence ranged 0.56 to 0.88% and 0.85 to 1.73% in FP, the highest being FP at 45 and 60 DAT.Although numerical values of DH in two treatments were closer to Exosex YSB Tab treatment was found to be significantly superior to FP. However incidence in all the treatments was below economic threshold level and thus both the treatments were effective in suppressing YSB damage during vegetative stage.White ear head incidence in Exosex YSBtab 3.2 mg (AC-2) and FP was registered as 1.28 to 2.90% and 3.28 to 11.35% respectively.In respect of yield, AC-2 gave higher yield than farmers' practice.In another treatment dead heart incidence was recorded in Exosex YSB Tab and FP treatments which ranged from 0.34 to 0.80% and 1.90 to 2.25% respectively.Here both the treatments controlled the pest damage effectively and maintained it below economic threshold level.Although DH incidence in both the treatments was numerically very similar, Exosex YSB tab treatment was found to be superior to farmers practice.A similar trend was observed in respect of WE incidence at heading stage.Mean WE incidence ranged from 1.80 to 7.63%, the highest infestation was registered in FP.YSB pheromone tablet successfully controlled YSB damage while FP failed by registering 11.67% WE during second observation.At both observations YSB pheromone tablets were significantly superior to farmers practice.WE incidence in AC-2 (1.60% and 1.82%) was significantly less than FP.Overall YSB damage at both vegetative and heading stages was kept in check by YSB pheromone tablets and were found to be superior to FP in all observations.Among YSB pheromone tablet a single application of 20 mg at 15 DAT was managing the pest effectively.
Yield registered by AC-2 (4013 kg/ha) of Gobindobhog was significantly higher than that of farmers practice (3678 kg/ha).In third trial AC-2 and FP treatments effectively suppressed the pest incidence during vegetative stage of crop with DH% ranging from 0.12 to 2.62%.However, DH level in FP was significantly higher than that found in YSB pheromone.DH% level in AC-2 ranged from 0.30 to 2.05% as against the highest record of 10.81% in FP at 110 DAT.Thus YSB pheromone tabs effectively protected the crop from YSB at heading stage while the FP of chemical control was not successful (Anon., 2010-2011).The mean YSB infestation level at vegetative stage of the crop in AC-2 was reflected in 0.16 to 0.52% DH as against 1.57 to 2.20% in FP.However, the level of DH was significantly lower in Exosex YSB tab than the farmers practice.Mean pre-harvest YSB damage accounted for 11.28% WE incidence which was considered as fairly high level of damage and indicated failure of FP involving use of three rounds of insecticide to control the pest.Grain yields were estimated with the help of crop cutting experiments.Exosex YSB tab recorded significantly higher yields over farmers method which varied from 3.0 to 4.5 q/ha (Anon., 2010 -2011).

CONCLUSION
From the result of this experiment, it is to be concluded that auto-confusion technology (T 4 = 80 Exosex YSB tab @ 20 mg) could more effectively control the YSB population than the other application of pheromone in rice ecosystem as it utilizes the natural behavior of the male insect to control the matting of the insect as opposed to preventing the natural behavior of male insect.
Pheromone traps/hectare at 10 DAT where lure was not replaced, T2 = 50 Pheromone traps/hectare at 10 DAT but lure was replaced 45 DAT, T3 = 50 Pheromone traps/hectare at 10 DAT but lure was replaced 45 and 60 DAT, T4 = 80 Exosex YSBtab 20 mg at 15 DAT, T5 = Use two rounds of chemical pesticide at 25 and 45 DAT and T6 = Untreated control.*Figures are parentheses in angular transformed values.during 2012 and 2013.The results are presented in Fig. 1 to 3.

Table 1 .
Average egg mass index (IE%) value in different treatments of pheromone in long duration scented rice (Gobindobhog) at Gopalpur, Burdwan during 2012

Table 2 .
Average egg mass index (IE%) value in different treatments of pheromone in long duration scented rice (Gobindobhog) at Gopalpur, Burdwan during 2013

Table 4 .
Average crop damage due to yellow stem borer in different treatments of pheromone in rice cv.Gobindobhog at Gopalpur, Burdwan, West Bengal during kharif 2012 *Figures are parentheses in angular transformed values.

Table 5 .
Average crop damage due to yellow stem borer in different treatments of pheromone in rice cv.Gobindobhog at Gopalpur, Burdwan, West Bengal during kharif 2013 *Figures are parentheses in angular transformed values.

Table 6 .
Overall crop damage due to yellow stem borer in different treatments of pheromone in rice cv.