Spatial distribution of alfalfa weevil, Hypera postica Gyllenhal (Coleoptera: Curculionidae) in cold arid region (Ladakh) of Jammu and Kashmir

Abstract

Spatial distribution of alfalfa weevil, Hypera postica Gyllenhal in alfalfa crop was studied during the cropping seasons of 2005-06, 2006-07, 2007-08 and 2008-09 at Regional Agriculture Research Sub Station Kargil, Jammu and Kashmir, India. The various parameters of dispersion viz., variance mean ratio, exponent k, common k (Kc), Lloyd’s index of mean crowding (x*), patchiness index (x* / x) and Taylor’s power law were applied to determine the nature of distribution of H. postica. In the pursuance of various index, it was observed that the alfalfa weevil exhibits aggregate or contagious pattern of distribution in the field. The value of Taylor’s aggregation index (b), i.e. 1.5279, 0.2378, 1.2941 and 1.1869 during the year 2005- 06, 06-07 and 08-09, respectively, was greater than one (>1) which indicates aggregated nature of distribution of alfalfa weevil. In Iwao m* - m relationship contagiousness coefficient value (β = 1.3817, 1.1991, 1.1523 and 1.3092, respectively) was found to be > 1 which also justify that weevil populations approached aggregate or negative binomial distribution pattern. The intercept (5.8296, 2.4226, 2.3361 and 2.2460) also justify that alfalfa weevil followed contagion nature of distribution instead of dispersion.