Academic Journal of Entomology 5 (1): 41-46, 2012 ISSN 1995-8994 © IDOSI Publications, 2012 DOI: 10.5829/idosi.aje.2012.5.1.61267

Spatial Distribution of Nymphula depunctalis Guenée Larvae (: Pyralidae), an Early Vegetative Pest of Oryza sativa L.

12Hiren Gogoi and Dipsikha Bora

1Department of Zoology, Silapathar Science College, Silapathar-787059, Assam, India 2Department of Life Sciences, Dibrugarh University, Dibrugarh-786004, Assam, India

Abstract: Rice caseworm, Nymphula depunctalis Guenée is a serious pest of paddy that attacks young rice plants in waterlogged paddy fields. Present study was designed to determine the spatial distribution of N. depunctalis larvae in ten farmer’s rice fields of Dhemaji district, Assam, India and in 13 cultivars of Oryza sativa 22 L. in a controlled experimental field. Results of the variance to mean ratio (S /m), index of dispersion (ID ), test, Z test and Lloyd’s mean crowding indicated highly aggregated spatial distribution pattern of N. depunctalis larvae. In farmers field condition, only two occasions in booting period showed uniform distribution pattern. In controlled experimental field, degree of aggregation was comparatively low than the farmers field condition. Only one occasion in stem elongation and five occasions in booting period showed uniform distribution pattern.

Key words: Nymphula depunctalis Guenée Spatial Distribution Index of Dispersion (ID ) and Lloyd’s Mean Crowding

INTRODUCTION blade to construct larval case. Cut leaf piece trends to roll due to lack of turgor pressure which is further secured by Spatial distribution of a population that is the the larvae with silk. A new case was constructed position that individuals occupy in environment one immediately after each moult or when it was accidently relative to the others at a given time is a central issue in removed from the case. population dynamics studies. A population may show Each female laid 300-400 eggs, 200-300 eggs and three basic patterns of distribution: random, uniform 50-70 eggs in day 2, day 3 and day 4 respectively. N. (regular) and aggregated (clustered). Pattern may change depunctalis larvae need water for respiration and in time, among developmental stages of a same species or movement from plant to plant and the prefer to lay even occur superposed in a given population [1, 2]. eggs on the underside of leaves that are floating on the Identification of the distribution pattern is essential to water surface [15]. Egg desiccates if laid on aerial portion develop sampling programs, especially those involving of the leaves [16]. species considered pests [3]. Present study was designed to determine the spatial Rice caseworm, Nymphula depunctalis Guenée distribution of N. depunctalis larvae in ten farmer’s rice (=Parapoynx stagnalis Zeller) (Lepidoptera; Pyralidae) is fields of Dhemaji district, Assam and in 13 cultivars of O. a serious pest of paddy that attacks young rice plants in sativa in a controlled experimental field. waterlogged paddy fields [4-9] and is reported from South and South East Asia, China, Japan, Australia, South MATERIALS AND METHODS America (Argentina, Brazil, Uruguay, Venezuela), Central Africa (Madagascar, Malawi, Mozambique, Rwanda and The study was conducted in Dhemaji district, Assam, Zaire), East Africa and several West African countries India during the year 2008, 2009 and 2010. Study site was and probably occurs throughout West Africa [10-14]. geographically situated between the 94° 12' 18'' E and 95° Larvae crawl and grip with the aid of 6 thoracic legs, 41' 32'' E longitudes and 27° 05' 27'' N and 27° 57' 16'' N while the crochets are used to cling to its case. latitudes. It is basically plain area lying at an altitude of Second instar larvae cut leaves near the tip of the leaf 104 m above mean sea level.

Corresponding Author: Hiren Gogoi, Department of Zoology, Silapathar Science College, Silapathar-787059, Assam, India. 41 Acad. J. Entomol., 5 (1): 41-46, 2012

To study the spatial distribution pattern of were selected for each cultivar in the controlled N. depunctalis larvae, population density was estimated experimental field. Spatial distribution of N. depunctalis both in farmer’s field condition and in controlled field larvae was determined by index of dispersion and Lloyd's condition. Larvae were identified by their larval case; mean crowding. presence of branched tracheal gills, shorter than segment’s length; and thorax with dorsal gill group [17]. Index of Dispersion: Dispersion of a population can be Study was conducted during tillering, stem elongation classified through calculation of the variance to mean and booting stage in the months July and August; ratio; namely: S2 /m = 1 random, < 1 regular and > 1 September and October respectively. For the studies in aggregated. Departure from a random distribution can be farmer’s field condition, ten number of farmer’s paddy tested by calculating the index of dispersion (ID ), where n fields were selected in the district and study was denotes the number of samples: conducted irrespective of hill density of rice plants and 2 water level of the field. Controlled experimental field was ID= (n-1) S /m situated in Bakal Gaon Pathar of the district. 2 ID is approximately distributed as with n-1 degrees

Farmer’s Field Condition: In farmer’s fields, three types of freedom. Values of ID which fall outside a confidence of hill density viz. 16 hills per m22 , 20 hills/m and interval bounded with n-1 degrees of freedom and 25 hills/m2 and water level of range 0-30 cm were selected probability levels of 0.95 and 0.05, for instance, considered at random. Eight to nine cultivars of O. sativa would indicate a significant departure from a random were recorded in each farmer’s field. distribution. This index can be tested by Z value as follows: 1/2 1/2 Controlled Field Condition: In controlled experimental Z = (2ID -(2 -1) field, seedlings 25 DAS (days after sowing) were = n-1 transplanted at a hill density 20 hills per m2 with 4 seedlings per hill. Water level of 10-15 cm for tillering If 1.96 Z -1.96, the spatial distribution would be stage, 5-10 cm for stem elongation stage and 0-5 cm for random but if Z <-1.96 or Z > 1.96, it would be uniform and booting stage was maintained during the experimental aggregated, respectively [19]. period. Thirteen cultivars of O. sativa were transplanted in the controlled experimental field in an area of 100m2 per Lloyd's Mean Crowding X*: Mean crowding (x*) was cultivar. proposed by Lloyd to indicate the possible effect of mutual interference or competition among individuals. Environmental Parameters: In both farmer’s field Theoretically mean crowding is the mean number of other condition and controlled field condition environmental individuals per individual in the same quadrate: parameters, rainfall, relative humidity and air temperature were same. Mean rainfall of 20.67-26.85 X* = m + (S2 /m)-1 mm/day, 4.56-15.45 mm/day and2.31-5.19 mm/day; relative humidity of 89.55-90.84 %, 83.63-91.10 % and 81.58-85.32% As an index, mean crowding is highly dependent and air temperature of 27.59-28.66°C, 27.46-29.29°C upon both the degree of clumping and population and 25.69-26.51 °C were recorded during tillering, stem density. To remove the effect of changes in density, elongation and booting period. Lloyd introduced the index of patchiness, expressed as the ratio of mean crowding to the mean. As with the Population Density in Farmer’s Field: Population density variance-to-mean ratio, the index of patchiness is of N. depunctalis larvae was estimated in ten number of dependent upon quadrate size x* / m= 1 random, <1 farmer’s paddy fields. For this, 45-55 quadrats [18] were regular and >1 aggregated [20]. selected in each field depending on the number of rice cultivars, considering five quadrats for each cultivar. RESULT AND DISCUSSION

Population Density in Different Cultivars of O. sativa: Population density, considered as the mean number Density was also estimated in 13 cultivars of O. sativa of larvae per square meter (m), variance to mean ratio 22 traditionally cultivated by the farmers of Dhemaji district, (S /m), chi square value ( ), index of dispersion (ID ) Assam (India) in an experimental field. For this, 5 quadrats and Lloyd mean crowding are shown in Table 1-6.

42 Acad. J. Entomol., 5 (1): 41-46, 2012

22 Table 1: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in farmer’s rice fields during tillering period of O. sativa 2008 2009 2010 ------2 2 2 2 22 Rice field n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Akajan Patiri 45 29.42 101.35 238.71 4459.25 85.11 129.77 9.69 22.97 86.67 1010.81 35.64 31.66 21.07 49.69 114.04 2186.15 56.80 69.76 Arsi Lason 55 18 91.93 299.55 4964.11 89.30 108.93 18.60 52.72 358.58 2847.05 65.12 70.32 17.95 80.05 276.53 4322.92 82.64 97.00 Balikata Miri 45 21.76 182.03 245.00 8009.46 117.24 202.79 2.24 8.83 132.80 388.65 18.55 10.07 10.27 91.43 181.60 4023.00 80.37 100.70 Fulbari Asomia 45 61.24 116.99 145.00 5147.67 92.14 177.23 41.47 81.25 183.80 3575.09 75.23 121.72 38.33 84.16 106.58 3703.15 76.73 121.49 Galowa 50 42.35 161.74 86.80 7925.13 116.05 203.09 8.19 20.87 285.24 1022.64 35.38 28.06 32.86 74.71 121.36 3660.86 75.72 106.57 Jalakia Suti 55 14.45 90.22 191.27 4871.94 88.37 103.67 16.69 50.06 146.22 2703.25 63.18 65.75 13.71 47.20 269.73 2548.63 61.05 59.91 Kulajan 55 24.87 89.44 114.53 4829.95 87.94 113.31 9.65 40.93 172.73 2210.20 56.14 49.58 16.62 38.98 119.80 2105.10 54.54 54.60 Mesu 55 27 162.22 216.36 8759.70 122.02 188.22 14.76 107.44 82.20 5801.55 97.37 121.20 30.02 102.21 209.00 5519.15 94.72 131.23 Sila Gaon 45 16.58 42.73 277.44 1880.29 52.00 58.31 22.72 69.09 215.40 3040.08 68.65 90.81 30.89 102.55 111.93 4512.19 85.67 132.44 Sissi Borgaon 45 15.69 50.12 129.07 2205.49 57.09 64.81 21.16 90.41 229.89 3978.15 79.87 110.57 13.38 58.20 177.44 2560.86 62.24 70.58 P value of 2 < 0.01 in all cases; n = number of quadrats

22 Table 2: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in farmer’s rice fields during stem elongation period of O. sativa 2008 2009 2010 ------2 2 2 2 22 Rice field n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Akajan Patiri 45 3.27 22.45 156.40 987.80 35.12 24.72 6.82 42.40 145.89 1865.46 51.75 48.22 1.47 10.90 127.98 479.45 21.64 11.37 Arsi Lason 55 4.8 29.56 276.66 1596.00 46.15 33.36 4.42 18.60 68.27 1004.35 34.47 22.02 4.69 18.52 176.86 1000.18 34.38 22.21 Balikata Miri 45 8 21.61 40.07 951.00 34.28 28.61 22.80 81.23 69.33 3574.26 75.22 103.03 6.29 26.15 118.44 1150.48 38.64 31.44 Fulbari Asomia 45 3.09 18.80 132.71 827.37 31.35 20.89 4.38 14.54 105.27 639.73 26.44 17.92 2.49 9.45 66.88 415.95 19.52 10.94 Galowa 50 4.67 14.05 231.60 688.61 27.26 17.72 11.73 26.49 79.60 1298.01 41.10 37.22 4.30 17.27 136.68 846.16 31.29 20.57 Jalakia Suti 55 8.91 44.87 185.58 2422.76 59.27 52.78 2.96 13.87 98.80 749.06 28.36 15.83 2.53 25.72 218.27 1388.73 42.36 27.25 Kulajan 55 3.41 11.10 73.95 599.54 24.28 13.51 5.7 27.80 102.66 1501.45 44.45 32.50 2.69 29.12 207.00 1572.27 45.73 30.81 Mesu 55 7.13 44.03 284.31 2377.64 58.61 50.16 7.05 53.43 138.09 2885.43 65.62 59.48 3.93 35.75 214.84 1930.53 51.79 38.68 Sila Gaon 45 8.38 23.45 54.11 1031.85 36.10 30.83 13.04 32.12 58.60 1413.32 43.84 44.16 8.71 14.51 76.18 638.41 26.41 22.22 Sissi Borgaon 45 4.87 35.51 168.89 1562.30 46.57 39.38 11.18 76.14 133.00 3350.09 72.53 86.32 6.98 47.85 124.07 2105.39 55.56 53.83 P value of 2 < 0.01 in all cases; n = number of quadrats

22 Table 3: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in farmer’s rice fields during booting period of O. sativa 2008 2009 2010 ------2 2 2 2 22 Rice field n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Akajan Patiri 45 0.13 3.27 78.40 144.00 7.64 2.40 1.11 3.12 100.24 137.20 7.24 3.23 0.24 1.52 80.07 66.73 2.22 0.76 Arsi Lason 55 0.05 0.96 43.66 52.00 -0.15 0.01 1.64 7.95 121.89 429.44 18.96 8.59 0.62 4.04 136.46 218.35 10.55 3.66 Balikata Miri 45 0.42 1.78 62.11 78.11 3.17 1.20 8.8 33.47 163.33 1472.64 44.94 41.27 0.07 0.95 33.80 42.00 -0.16 0.02 Fulbari Asomia 45 0.4 1.98 40.13 87.00 3.86 1.38 2.69 9.53 162.33 419.37 19.63 11.22 0.84 6.24 212.96 274.63 14.11 6.08 Galowa 50 2.46 21.64 202.00 1060.33 36.20 23.10 8.70 55.58 135.92 2723.28 63.95 63.28 12.14 137.95 137.20 6759.64 106.42 149.09 Jalakia Suti 55 0.8 3.31 85.09 178.50 8.55 3.11 1.24 4.58 74.44 247.44 11.90 4.82 2.40 31.77 152.85 1715.50 48.23 33.17 Kulajan 55 0.6 2.01 85.09 108.67 4.40 1.61 1.95 7.76 107.36 418.84 18.60 8.71 0.44 3.80 126.00 205.17 9.91 3.24 Mesu 55 0.11 1.59 87.31 85.67 2.75 0.70 6.95 55.80 117.91 3013.03 67.28 61.75 5.44 48.19 137.93 2602.39 61.80 52.63 Sila Gaon 45 0.18 1.35 57.73 59.50 1.58 0.53 11.36 40.99 152.51 1803.37 50.73 51.35 0.27 1.26 44.40 55.50 1.21 0.53 Sissi Borgaon 45 0 0.00 - 0.00 -9.33 -1.00 3.33 11.82 49.00 520.20 22.93 14.15 1.33 6.72 78.36 295.50 14.98 7.05 P value of 2 < 0.01 in all cases; n = number of quadrats

22 Table 4: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in cultivars of O. sativa during tillering period 2008 2009 2010 ------2 2 2 2 22 Rice cultivar n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Bahadur 5 66.8 30.67 0.00 153.36 14.87 1013.50 118.6 5.46 0.60 27.29 4.74 147.40 179 32.06 0.00 160.31 15.26 1206.00 Bogilahi 5 7 5.83 0.00 29.15 4.99 40.00 12.7 2.25 0.60 11.26 2.10 16.78 86 47.22 0.00 236.11 19.09 2315.00 Bor Jahingia 5 34 10.15 0.00 50.74 7.43 136.00 4 3.91 0.60 19.56 3.61 17.70 62.4 39.18 0.00 195.91 17.15 1596.70 Ijong 5 135.5 19.15 0.00 95.77 11.19 505.80 30.8 16.18 0.60 80.89 10.07 291.50 40 9.97 0.00 49.87 7.34 138.50 Kati Neoli 5 111 23.01 0.60 115.05 12.52 639.50 31.6 5.59 0.60 27.97 4.83 61.90 12.4 8.20 1.60 41.02 6.41 78.70 Kekua 5 225.6 69.13 0.00 345.63 23.65 4977.30 69.2 20.87 0.60 104.37 11.80 503.90 149 15.31 0.00 76.57 9.73 382.50 Kola Joha 5 16 8.17 0.00 40.86 6.39 81.70 58 13.49 0.00 67.45 8.97 242.20 76.6 6.31 0.00 31.54 5.30 115.40 Ranjit 5 112.4 40.56 0.00 202.81 17.49 1756.70 120.4 7.37 0.60 36.84 5.94 173.70 121 26.08 0.60 130.38 13.50 800.00 Ronga Bora 5 17.6 5.59 0.00 27.97 4.83 47.90 103.5 32.32 0.60 161.61 15.33 1139.80 82 21.97 0.00 109.83 12.18 563.50 Saru Jahingia 5 34.8 24.31 0.00 121.57 12.95 622.30 6.2 5.36 0.00 26.79 4.67 33.90 20.6 10.09 0.60 50.45 7.40 121.40 Solpuna 5 7.6 10.53 0.00 52.67 7.62 117.80 3.27 2.51 0.60 12.55 2.36 8.57 3.4 3.21 0.00 16.05 3.02 12.70 Suagmoni 5 7 7.28 0.60 36.39 5.89 55.70 20.6 10.92 0.60 54.61 7.81 138.90 151.6 9.04 0.60 45.22 6.86 232.40 Toraboli 5 13.4 4.25 0.00 21.27 3.88 29.90 5.4 5.50 0.40 27.52 4.77 34.70 9.8 8.14 0.00 40.68 6.37 75.00 P value of 2 > or = 0.5 in all cases; n = number of quadrats

43 Acad. J. Entomol., 5 (1): 41-46, 2012

22 Table 5: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in cultivars of O. sativa during stem elongation period 2008 2009 2010 ------2 2 2 2 22 Rice cultivar n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Bahadur 5 0 - - - - - 127.2 6.14 0.00 30.70 5.19 163.90 92 34.39 0.00 171.94 15.90 1273.50 Bogilahi 5 2 2.83 1.6 14.14 2.67 9.00 7.30 3.27 0.00 16.36 3.07 17.00 62 21.97 0.00 109.83 12.18 543.50 Bor Jahingia 5 67 12.04 0.00 60.21 8.33 211.00 21.4 7.83 0.60 39.15 6.20 81.70 20.4 20.18 0.60 100.91 11.56 426.70 Ijong 5 0 - - - - - 43.5 30.21 0.00 151.07 14.74 948.80 7.4 10.29 1.60 51.43 7.50 112.20 Kati Neoli 5 3.2 2.39 0.00 11.94 2.24 7.90 18.2 8.20 0.00 40.99 6.41 84.40 7.6 7.92 0.00 39.62 6.26 69.40 Kekua 5 0 - - - - - 61.2 9.18 0.00 45.88 6.93 144.40 70.2 41.12 0.60 205.62 17.63 1760.40 Kola Joha 5 57.4 16.70 0.00 83.49 10.28 335.20 66.5 13.41 0.00 67.04 8.93 245.25 40 9.97 0.00 49.87 7.34 138.50 Ranjit 5 0 - - - - - 22 21.08 0.60 105.42 11.87 465.50 3.4 3.21 0.00 16.05 3.02 12.70 Ronga Bora 5 1.8 3.49 1.6 17.46 3.26 13.00 91.8 13.45 0.00 67.25 8.95 276.00 56.4 14.57 0.60 72.85 9.43 267.70 Saru Jahingia 5 3.8 2.77 0.00 13.87 2.62 10.50 32.4 11.76 0.60 58.80 8.20 169.70 4.4 1.52 0.60 7.58 1.25 5.70 Solpuna 5 1.6 2.30 1.60 11.51 2.15 5.90 4.8 0.78 0.40 3.89 0.14 4.50 5.2 3.27 0.60 16.36 3.07 14.90 Suagmoni 5 4.2 1.30 0.60 6.52 0.97 4.90 29 20.02 0.00 100.12 11.51 429.00 22.8 21.25 0.00 106.27 11.93 473.50 Toraboli 5 26.8 4.82 0.00 24.08 4.29 49.00 16.2 9.63 0.60 48.14 7.17 107.90 4.2 1.30 0.60 6.52 0.97 4.90 P value of 2 > or = 0.5 in all cases; n = number of quadrats

22 Table 6: Mean population density of N. depunctalis larvae per square meter (m), variance to mean ratio (S /m), chi square value ( ), index of dispersion (ID ), Z value and Lloyd mean crowding (x*) in cultivars of O. sativa during booting period 2008 2009 2010 ------2 2 2 2 22 Rice cultivar n m S /m ID Z X* m S /m I DD Z X* m S /m I Z X* Bahadur 5 0 - - - - - 23 11.87 0.00 59.37 8.25 163.00 0 - - - - - Bogilahi 5 1.2 1.79 1.60 8.94 1.58 3.40 5.13 2.75 0.00 13.75 2.60 10.63 0 - - - - - Bor Jahingia 5 3.2 3.42 0.60 17.10 3.20 13.90 5.1 6.59 0.60 32.97 5.47 45.30 22.8 21.25 0.00 106.27 11.93 473.50 Ijong 5 0 - - - - - 19.33 7.11 0.00 35.57 5.79 67.13 7.4 6.35 0.00 31.74 5.32 46.70 Kati Neoli 5 0 - - - - - 12.8 5.81 0.00 29.03 4.97 45.50 3 2.74 0.00 13.69 2.59 9.50 Kekua 5 0.8 0.84 - 4.18 0.25 0.50 50.8 7.66 0.00 38.31 6.11 108.50 0 - - - - - Kola Joha 5 1.2 0.84 0.40 4.18 0.25 0.90 68.14 7.64 0.00 38.20 6.10 123.84 54.4 15.24 - 76.21 9.70 285.70 Ranjit 5 0 - - - - - 9.6 2.30 0.60 11.51 2.15 13.90 4.6 4.56 0.60 22.80 4.11 24.40 Ronga Bora 5 0 - - - - - 75.8 96.99 0.00 484.93 28.50 1224.30 106.6 89.22 0.00 446.09 27.22 8065.40 Saru Jahingia 5 0.6 0.55 0.20 2.74 -0.31 -0.10 7.8 9.63 0.60 48.14 7.17 99.50 0.8 0.84 0.40 4.18 0.25 0.50 Solpuna 5 0 - - - - - 4.4 1.40 0.60 7.01 1.10 5.70 3.8 3.83 0.40 19.17 3.55 17.50 Suagmoni 5 0.8 0.84 0.40 4.18 0.25 0.50 13 4.69 0.00 23.45 4.20 34.00 3 3.24 0.60 16.20 3.05 12.50 Toraboli 5 1.2 1.30 0.60 6.52 0.97 1.90 3 2.74 0.00 13.69 2.59 9.50 0.6 0.55 0.20 2.74 -0.31 -0.10 P value of 2 > or = 0.5 in all cases; n = number of quadrats

During study period, 1485 quadrats were sampled from period in the year 2008. No population was recorded in farmer’s field and 195 quadrats were sampled from the Bahadur, Ijong, Kati Neoli, Ranjit, Ronga Bora and controlled experimental field. Solpuna in the year 2008 and in Bahadur, Bogilahi and Results of the variance to mean ratio (S2 /m), index of Kekua in the year 2010 during booting period. Maximum dispersion (ID ), Z test and Lloyd mean crowding indicated aggregation was observed in Ronga bora during booting highly aggregated spatial distribution pattern of N. stage in the year 2008 and 2009. Kekua, Kola Joha, Saru depunctalis larvae. All rice fields of farmers showed Jahingia and Suagmoni in the year 2008 and Saru Jahingia aggregated pattern of distribution during tillering and and Toraboli in the year 2010 showed uniform distribution stem elongation period. During booting stage, Arsi lason during booting stage. Unlike farmers field condition in the year 2008 and Balikata miri in the year 2010 showed similar trend of distribution was observed during tillering, uniform distribution. Degree of aggregation was highest stem elongation and booting stage in controlled during tillering stage and then decreases gradually during experimental field. stem elongation and booting stage. Aggregation observed in both studies may be result- 2 Index of dispersion (ID ), value, Z test indicated a ant of intrinsic behavior of the individuals, response to significant departure from a random distribution in all the the food and habitat resources distribution, water level rice fields. and hill density of the rice field. Concentration of a Degree of aggregation was comparatively low in suitable resource in some areas has been considered as controlled field than that of farmer’s field. All cultivars the prevailing cause of aggregation of most organisms showed aggregated pattern of distribution during tillering [21]. In case of N. depunctalis, comparatively lower stage. No infestation was recorded in four cultivars, aggregation pattern in different cultivars in controlled Bahadur, Ijong, Kekua and Ranjit during stem elongation experimental field indicated the role of varietal preference

44 Acad. J. Entomol., 5 (1): 41-46, 2012 in aggregation. However, aggregation pattern within the 2. Elliott, J.M., 1983. Some methods for the statistical same cultivar in the controlled experimental field indicated analysis of sampling of benthic invertebrates. the intrinsic behavior. Moth prefers to lay egg on the Freshwater Biological Association, Cumbria, pp: 176. underside of leaves floating on water [15]. Therefore, the 3. Davis, P.M., 1993. Statistics for describing moth aggregates in such places to oviposit. Larvae crawl populations. In: L.P. Pedigo and G.D. Buntin, and grip with the aid of 6 thoracic legs, while the crochets Handbook of sampling methods for in are used to cling to its case and are not able to migrate to agriculture. CRC Press, Boca Raton. distant places without the aid of water. This resulted in 4. Shroff, K.D., 1919. Notes on miscellaneous pests in aggregated distribution pattern of the larvae. Burma. Proceedings of 3rd entomological meeting, N. depunctalis larvae need water for respiration and Pusa, pp: 341-354. movement from plant to plant [15]. Egg desiccates if laid 5. Sison, P.L., 1938. Some observations on the life on aerial portion of the leaves [16]. In areas without water, history and control of the rice caseworm, most of the larvae were unable to survive and these may Nymphula depunctalis Guenee. Philippines Journal result higher density in areas with water and lower density of Agriculture, 9: 272-301. in areas without water. 6. Alum, A.Z., 1967. pest of rice in East Pakistan. Venugopalrao et al., Heinrichs et al. and Oyediran et Major insect pests of rice plant. John Hopkins press, al. [22-24] reported higher infestation of N. depunctalis pp: 633-655. with higher hill density. This was another factor that 7. Grist, D.H. and R.J.A.W. Lever, 1969. Pest of rice. contributed to the higher degree of aggregation in London: Longmans, Greens and Co. Ltd., pp: 520. farmer’s field condition. 8. Chi, T.T.N., B.T.T. Tam, H.X. Dau, N.T. Khoa, In farmer’s field condition, there was diversity in N.T.P. Lan and T.R. Paris, 1995. Current status of rice habitat pattern due to water resource, hill density and rice pest management by farmers in direct-seeded rice and cultivar. It also resulted in aggregated pattern of transplanted rice area. Omonrice, 4: 42-50. distribution. During stem elongation and booting period 9. Vromant, N., A.J. Rothuis, N.T.T. Cuc and F. Ollevier, water level was almost same in the rice fields, it was also 1998. The effect of fish on the abundance of rice a cause for decrease of the degree of aggregation in these caseworm Nymphula depunctalis (Guenee) periods compared to tillering stage. During booting stage (Lepidoptera: Pyralidae) in direct-seeded, water resources near the rice field may results in high concurrent rice-fish fields. Biocont. Sc. and Techn., density of larvae and higher aggregation. 8: 539-546. Sometime low infested areas during tillering stage 10. Pathak, M.D., 1975. Insect pests of rice. may be a choice for the moth and the larvae during stem Manila (Philippines): International Rice Research elongation and booting period as observed in Ronga bora Institute. during booting stage in the year 2008 and 2009. 11. Brenière, J., 1983. The principal insect pests of rice in Based upon the obtained results it may be concluded West Africa and their control. Monrovia (Liberia): that the spatial distribution of N. depunctalis larvae was West Africa Development Association. aggregated. N. depunctalis larvae distribution pattern was 12. Reissig, W.H., E.A. Heinrichs, J.A. Litsinger, determined by the oviposition pattern of the adults, type K. Moody, L. Fiedler, T.W. Mew and A.T. Barrion, of rice cultivar, water level and hill density. The results 1985. Illustrated guide to integrated pest management indicate that use of sampling strategy that incorporate in rice in tropical Asia. Los Banos, the Philippines: spatial distribution information will help to model crop IRR, pp: 411. loss more accurately strengthening IPM decision making 13. Hill, D.S., 1987. Agricultural insect pests of the and that spatially targeted applications of insecticide will tropics and their control (2nd ed.). Cambridge reduce the cost of management of N. depunctalis and will University Press, Cambridge, pp: 746. also reduce the risk of toxicity from synthetic insecticides. 14. Dale, D., 1994. Insect pests of the rice plant-their biology and ecology. In: E.A. Heinrichs, REFERENCES editor. Biology and management of rice . New Delhi: Wiley Eastern, pp: 363-485. 1. Southwood, T.R.E., 1978. Ecological methods, 15. Bandong, J.P. and J.A. Litsinger, 1981. with particular reference to the study of insect Ovicidal activity of insecticides on the rice caseworm populations. Chapman and Hall, London, 2nd. ed., Nymphula depunctalis. Int. Rice Res. Newsl., pp: 524. 6(1): 17-18.

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16. Patgiri, P., 1997. Bioecological studies 21. Ricklefs, R.E. and G.L. Miller, 2000. of Nymphula depunctalis (Guenee) Ecology. W.H. Freeman and company, New York, (Pyralidae: Lepidoptera) and its management. 4th edition, pp: 822. Dissertation, Ph.D. Assam Agricultural University, 22. Venugopalrao, N., B.H.K. Rao and P.S. Reddy, 1982. Jorhat. Note on the effect of cultural practices on the 17. Zeller, 1852. Lepidoptera microptera quae, incidence of insect pests of rice. Indian J. Agric. Sci., J.A. Wahlberg in cafrorum terra collegit, Lepid. micr. 52(1): 48-50. Caff. 23. Heinrichs, E.A., D.E. Johnson and A.A. Sy, 1993. 18. Pound, R. and F.E. Clements, 1898. A method of Seedling age and plant spacing effects on insect determining the abundance of secondary species. pests in lowland irrigated rice. In WARDA annual Minn. Bot. Studies, 2: 19-24. report 1993. Bouaké (Côte d’Ivoire), West Africa Rice 19. Patil, G.P. and W.M. Stiteler, 1974. Concepts of Development Association, pp: 43-44. aggregation and their quantification: A critical review 24. Oyediran, I.O. and E.A. Heinrichs, 1999. with some new results and applications. Res. Pop. Seasonal abundance of rice feeding insects and Ecol., 15: 238-254. spiders in continuously cropped lowland rice in 20. Lloyd, M., 1967. Mean crowding. J. Anim. Ecol., West Africa. Insect Science. Appl., 19: 121-129. 36: 1-30.

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