Seasonal Variation in Species Richness and Diversity of Insects on West Himalayan Spruce, Picea smithiana as Compared to Silver Fir, Abies pindrow

Species Richness, Shannon Diversity and Pielou's Evenness indices of insects were studied seasonally in two natural forest stands (0.25 ha each) of West Himalayan Spruce, Picea smithiana and Silver Fir, Abies pindrow, at Narkanda (2,550 m) in Himachal Pradesh, for 4 successive years. A total of 40 species on insects (31 species on P. smithiana and 16 species on A. pindrow) were recorded on both the trees. Shannon Diversity and Pielou's Evenness indices both had greater values on P. smithiana as compared to A. pindrow for insects species in general. Shannon Diversity index peaked in May-June and then steadily declined to a minimum in October-November, on both the tree species. Amongst the 8 feeding groups found on P. smithiana, seasonal Shannon Diversity index and Species Richness of predators, defoliators, sap-suckers, sap-wood borers, rotten-wood borers, were synchronized and peaked in May-June. These two indices were also synchronized for cone-borers and parasitoids, but with peaks during October-November on Spruce. Similarly on A. pindrow only sap-suckers, defoliators and rotten wood borers were most prominent groups and these 2 indices for them were also synchronized in every season but peaked in August-September. One 'rare' insect species, Cucujus bicolor was also found on P. smithiana, in these forests.