Spatial dynamics of teak defoliator (Hyblaea puera Cramer) - Cochin ...

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showed that outbreaks do not occur simultaneously in all places. Based on a ground survey conducted in roadside teak plantations along the Western Ghats in Kerala and part of Kamataka, Nair and Sudheendrakumar (1986) showed that moths emerging from an outbreak site moved at least 4 km before causing another outbreak. They suggested a short-range, gypsy-type of movement of H puera populations resulting in a south to north progression in the incidence of outbreaks in course oftime. A later study at Nilambur (Nair and Mohanadas, 1996), showed that the first outbreaks during an year occur in a few small patches, 0.5-1.5 ha in area, which are widely separated. It was suggested that these early patches serve as epicentres where the population builds up and spread to other areas. Except the above few studies, most studies on H puera populations were concerned with temporal changes in population. Study of the spatial distribution of outbreaks is important to: (1) understand the cause-effect relationship between previous and subsequent outbreaks, and (2) examine the spatial preference of defoliator outbreaks. Detailed investigation made into the spatial distribution of outbreaks in about 1000 ha ofteak plantations at Kariem - Muriem during a period of three years, are described and analyzed in this Chapter. The pattern of outbreaks and its relationship with the topography ofthe area was examined using Geographic Information System (GIS). It was examined whether populations of the insect noticed within the study area could cause the subsequent outbreaks in the area. 4.2. METHODS GIS was used to map the sites of infestation and relevant site characteristics such as elevation and aspect within the study area and to make relevant analysis of data. GIS is a computer software that store, retrieve, transform, display, and analyze spatial data (Anonymous, 1995). Georeferenced data, such as insect densities, crop type, or soils can be incorporated in a GIS to produce map layers (Liebhold et al., 1993). A map layer, generally composed ofonly one type ofdata, thus has a theme. The GIS serves as a tool for analyzing interactions among and 16
within these various spatially referenced data themes. The software used was ARC/INFO in a UNIX platform. The methods used to prepare the maps and the procedure ofanalysis are given below. 4.2.1 Preparation ofmaps 4.2.1.1 Outbreak maps Defoliator outbreaks were mapped in the scale 1:50,000 as described in Chapter 3. These maps were digitized in individual layers ofthe GIS database. To understand the frequency of defoliator outbreaks in different sites within the study area, all the defoliation maps of a particular year were overlaid to produce a composite map. Information on the number oftimes that a particular site was under outbreak was generated in the database ofthe composite map. This information was used to produce the outbreak frequency map. FigA.1. Map of Kariem Muriem showing the layout of grids. 17
Page 1 and 2: SPATIAL DYNAMICS OF TEAK DEFOLIATOR
Page 3 and 4: CERTIFICATE This is to certify that
Page 5 and 6: Mr. Rajan James, Mr. A. Moosa, Mr.
Page 7 and 8: 4.3.5. Correlation between outbreak
Page 9 and 10: CHAPTER I INTRODUCTION Insects are
Page 12 and 13: covering the entire plantations of
Page 14 and 15: Burma and recommended that providin
Page 16 and 17: In a two-year light trap study at J
Page 18 and 19: during 1983-94 and 1987-89 recorded
Page 21 and 22: area of 50 ha. A group of ten grids
Page 23: CHAPTER IV STUDIES ON THE SPATIAL D
Page 27 and 28: 4.2.3. Correlation between outbreak
Page 30: 4.3. 2. Outbreak pattern, 1993 The
Page 33 and 34: 4.3.3. Outbreak pattern, 1994 Table
Page 35 and 36: _ 0 _ 1 0 2 _ 3 _ 4 _ 5
Page 37 and 38: _ 0 _ 1 0 1 _ 3
Page 39 and 40: Table 4.7. The relationship between
Page 41 and 42: Fig. 8. Location of first outbreak
Page 43 and 44: Table 4.9. Elevation and aspect oft
Page 45 and 46: aspect and outbreak frequency. The
Page 47 and 48: map. The methodology adopted for da
Page 49 and 50: The sixth outbreak occurred on 26 M
Page 51 and 52: explained as caused by progenies of
Page 55 and 56: Fig.5.3. Map ofNilambur teak planta
Page 61: Fig.5.9. Map ofNilambur teak planta
Page 67 and 68: Fig.5 .15. Map ofNilambur teak plan
Page 71 and 72: Fig.5.l9. Map ofNilambur teak plant
Page 73 and 74: Fig.5 .21. Map ofNilambur teak plan
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6.2. METHODS In this study, post em
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was observed at around 06.15 h on t
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Two moths (one male and one female)
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Aggregations of the moths were pred
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CHAPTER VII DEVELOPMENT OF OUTBREAK
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-.-.-._ --- _--. Black light tube -
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Table 7.1. Correspondence between l
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foliage. If folds are detected, obs
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study has considerable bearing on t
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maximum of 13 ha (see Section 5.2,
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c) Variation in plant quality I ava
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away places. These populations seld
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Berryman, A. A. (1987) The theory a
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Nair, K. S. S., Mohanadas, K and Su
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APPENDIX A ALGORITHM: FOR COMPUTATI
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Date *No. of Incidence Local Date *
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Date "No. of Incidence local Date "
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