Development of Management Stratigies Against Red Ant (Dorylus Orientalis Westwood) of Potato

Several management approaches against red ant of potato Dorylus orientalis (Westwood) were studied at farmer’s field near Hill Agricultural Research Station, Khagrachari during 2008-09 and 2009-10 cropping seasons to find out the most effective management technique. Dursban 20 EC and Sevin 85 WP reduced red ant damage significantly. From both the season (2008-09 and 2009-10), three times application of Dursban 20 EC @ 5ml/lit of water around the root zone starting from 45 days after sowing of potato tuber at 10 days interval gave the lowest tuber infestation (17.28% and 10.68%) with (62.77% and 56.60%) infestation reduction over control closely followed by 3 times application of Sevin 85 WP @ 3 gm/lit of water (20.14% and 13.73%) with (85.77 % and 81.71%) infestation reduction over control. Both the season the highest infestation (46.41% and 75.06%) was recorded from the control treatment.


Introduction
Potato (Solanum tuberosum L.) belongs to the family Solanaceae is used as the most important food for a large number of people in the world. It is the most important non-cereal food crop and ranks fourth in terms of total global food production after maize, wheat and rice [1]. It is one of the important vegetables as well as cash crop in Bangladesh which achived 11 th position in the world in terms of potato production in 2008 [2]. Owing to promotional effort of government it is being placed as a third crop next to rice and wheat [3] [4]. It is a staple food in the developed countries and which accounts for 37% of the total potato production in the world [5]. Considering the trend of population growth and consequently the increased demand for food in the country and dwindling cultivable land area, the potato is likely to play a very important role in the future. Potato is a popular and important vegetable in Bangladesh. For the whole year, it is used as main vegetable and also represents about 53% of the total edible vegetables.
Potato crop is attacked and damaged by a number of insect pests which directly cause damage to the tubers. Among these, Red ants (Dorylus orientalis), is one of the most important soil pests of potato reducing the yield up to 35-40% in West Bengal [6]. The pest made hole on the surface of tuber which reduced tuber yield as well as market quality [7]. The insect is reported causing 70-90% damage at harvest to potatoes in farmer's fields in Bihar [8]. Dorylus orientalis has long been known as an important pest of potato in middle and higher hills of Nepal [9] and it causes serious damage to potato, radish, carrot, cauliflower, cabbage and many solanaceous and cruciferous vegetables in Nepal [10]. [11] reported that red ant severely damaged the marketable potato tuber yield in Nepal. Red ants are reported as a pest of potato, cauliflower, cabbage, groundnut, sugarcane, and coconut seedlings in the North-Eastern states, Bihar, and Uttar Pradesh [12]. The pest appears during December and remains active until April, causing more than 10% of the damage in irrigated potato crops. High temperatures and dry weather favor population build-up [13]. The pest damages mainly the potato stems and tubers by chewing holes and in case of severe attack plants become wilt in direct sunlight and will eventually dry up [14].
In Bangladesh red ant is reported as a serious problem in the hilly areas of Khagrachari district. During winter season it attacks potato crop just after tuber formation and infestation in continued upto harvesting of potato unless any management approach is taken. From assessment report the highest 90.3 % infestation was found by numbers, while by wt. the highest 54.91 % infestation was recorded from red ant damage [15].
This pest is generally controlled by the application of pesticides in the soil. Spraying of infested potato fields with chlorpyrifos (Dursban) 20 EC @ 2.5 L/ha checked the further spread of infestation in Bihar [16]. However, in Bangladesh there is no comprehensive information available in the literature regarding the management of red ant. There Universal Journal of Plant Science 1(3): 74-77, 2013 75 is a need to develop a strategy to control the pest. Therefore, the present investigation was carried out to find out the suitable management approach for controlling potato red ant.

Materials and Methods
The experiment was carried out at farmer's field near Hill Agricultural Research Station, Khagrachari during 2008-09 and 2009-10 cropping seasons. Diamant variety of potato was used in the experiment. Plot size was 3m×3m and spacing was maintained as 60cm×40cm. Recommend dose of fertilizer was applied under recommendation of fertilizer recommendation guide and other intercultural operation were done with irrigation uniformly. The experiment was laid out in randomized complete block design (RCBD) with 4 replications. There were seven treatments: T 1: Application of Neem oil cake @ 300 kg/ha during final land preparation, T 2: Application of Poultry manure @ 3 ton/ha during final land preparation, T 3: Application of Dursban 20 EC @ 5 ml/lit of water for 3 times, T 4: Application of Sevin 85 WP @ 3 gm/lit of water for 3 times, T 5 : Application of Kerosine @ 5 ml/lit of water for 3 times, T 6 : Application of Furadan 5G @ 40 kg/ha for 3 times and T 7 : Untreated control.
Neem oil cake was applied at final land preparation; insecticides and kerosine were applided 3 times at 10 days interval starting from 45 days after sowing. During final harvest data were taken on weight of healthy and infested tuber and percent infestation was calculated using the following formula:

% Infestation=
Weight of infested potatoes x 100 Total weight of potatoes Yield data of different treatments were recorded. Marketable yield was determined calculating the weight of healthy tuber only. The experimental data were analyzed by MSTAT-C software. Mean comparisons for treatment parameters were compared using Dun-can's Multiple Range Test [17] at 1% level of significance. The marginal benefit cost ration (MBCR) was calculated on the basis of prevailing market price of potato, insecticides, Neem oil cake, poultry manure and spraying cost. Marginal benefit cost ratio was calculated as follows: Marginal BCR= Benefit on control Cost of treatment

Effect of Different Management Approaches Against Red Ant Damage and Yield
From two consecutive sessions (2008-09 and 2009-10) results indicated that three times application of Dursban 20 EC @ 5ml/lit of water around the root zone starting from 45 days after sowing of potato tuber at 10 days interval gave the lowest tuber infestation (17.28% and 10.68%) closely followed by 3 times application of Sevin 85 WP @ 3 gm/lit of water (20.14% and 13.73%). Both the season the highest infestation (46.41% and 75.06%) was recorded from the control treatment (Table 1 and 2).
During both the cropping season the highest red ant infestation reduction over control (62.77% and 85.77%) was recorded from Dursban 20 EC followed by Sevin 85WP (56.60% and 81.71%). Highest marketable yield was also obtained from application of Dursban 20 EC (21.37 ton/ha and 17.47 ton/ha) closely followed by Sevin 85 WP (19.82 ton/ha and 16.03 ton/ha). The lowest marketable yield was recorded from control treatment (6.55 ton/ha and 7.10 ton/ha). The similar result was also observed by [13], that chlorpyrifos (Dursban) 20 EC @ 2.5 L/ha could control the pest very effectively. [8] also concluded that spraying of infested potato fields with chlorpyrifos (Dursban) 20 EC checked the further spread of infestation in Bihar. [16] recommended that mixture of carbaryl and lindane were superior to the other treatments and equally effective in reducing infestation and damage to tubers by the ant. Application of chlorpyrifos emulsifiable concentrate mixed with sand granules and applied to the soil before planting at the rate of (2000 g a.i./ha to 2500 g a.i./ha) was effective to control red ants [15].

Economic Analysis
The net income and marginal benefit cost ratio was varied depending on cost of pesticidal application (table 3). The highest net income (Tk. 55900/ha) was recorded from Dursban 20 EC treated plots followed by Sevin 85 WP treated plots (Tk. 47310/ha). The marginal benefit cost analysis of insecticidal application revealed the highest monetary benefit from Dursban 20 EC treated plots. For each taka spent, Dursban 20 EC gave on an average the profit of Tk. 9.73 followed by Tk. 5.78 in Sevin 85 WP treated plots.

Conclusion
From two year experiment it can be concluded that application of Dursban 20 EC @ 5ml/lit of water for 3 times or Sevin 85 WP @ 3gm/lit of water for 3 times at 10 days interval starting from 45 days after sowing of potato can minimize red ant infestation in potato significantly. However, Dursban 20 EC to the best tool in managing red ant infestation in potato considering efficacy, profitability.