Species Richness, Density and Diversity Indices (Simpson and Shannon Weiner) of Grasshoppers Fauna (Orthoptera: Pyrgomorphidae) in Maize-Wheat Cropping System of South-Western Rajasthan (India)

Survey conducted in the five districts of Rajasthan viz., Banswara, Dungarpur, Rajsamand, Sirohi and Udaipur during 2005-06 and 2006-07 yielded four different species Chrotogonus trachypterus (Blanchard), Chrotogonus oxypterus (Blanchard), Atractomorpha crenulata Fabricius and Pyrgomorpa bispinosa Walker. Based on the mean density data recorded during the investigation, the two species of Chrotogonus (C. trachypterus and C. oxypterus) had the highest mean density in the month of February with (12.88 & 12.13/ 180 ft²) at Udaipur and lowest mean density in the month of October with (2.30 & 1.88/ ft²) at Rajsamand, respectively. In the south-western regions of Rajasthan, the maximum mean density was during February in maize-wheat cropping system. The relative density of C. trachypterus and C. oxypterus was the maximum during the month of May (50.56 & 48.41 % respectively) at Dungarpur district. Due to sparse vegetation during May in most parts of Rajasthan the geophilus species, Chrotogonus had relatively the highest relative density as compared to the other pyrgomorphids. The mean density for Atractomorpha crenulata happened to be the maximum during the month of August with 4.38 per ft² and relative density was the highest in September (31.10 %) at Banswara. The grasshopper, Pyrgomorpha bispinosa had the maximum mean density (3.88/ ft²) during the month of August at Banswara. The relative density (28.39 %) was the highest during September at Banswara. The Simpson Diversity Index and Shannon Weiner Diversity Index values were the maximum in August during both the years. This conspicuously indicates the fact that the monsoon season (August-September) happened to comprise greater diversity of the Pyrgomorphids than the spring season (February-March). Based on the habitat preference and their behaviour, the Pyrgomorphids could be grouped as the geophilus and arboreal types. A comparison within the geophilus species showed that the relative density was nearly equal depicting a 1: 1 ratio at all districts and the diversity indices were 1.915 to 2.00 during both the year. Similarly, comparison between the arboria species indicated that their relative density was also nearly equal depicting a similar 1: 1 ratio and the diversity indices were 1.00 to 1.997 during both years.