Monday, December 11, 2006

Comparing arthropod community structure in a monocot [finger millet (Eleusine coracana l.)] versus dicot crop [pigeonpea (Cajanus cajan. Millsp)] from GKVK, Karnataka, India

Byju N. Govindan,, Krishnappa Chandrashekara,, and A. R. V. Kumar, University of Agricultural Sciences, Department of Agricultural Entomology, GKVK, Bangalore, Karnataka, India

Arthropod community diversity in pigeonpea, a dicot crop and finger millet, a monocot crop was examined at GKVK, Hebbal, Karnataka, India. Active and passive sampling methods were employed at biweekly intervals across different crop phenological stages. The seasonal variation in species richness, abundance and diversity of insects (Shannonís and Simpsonís index) corresponding to the changes in the crop phenology in both crops at the community and the trophic level are presented.

Arthropod sampling on finger millet yielded 16,403 individuals in 181 species where as that on pigeon pea yielded 6332 individuals in 217 species. The communities appear to be in non-equilibrium state in finger millet but in equilibrium in pigeonpea. In both crops, the species accumulation curves and the non-parametric cumulative species richness estimate Chao 1 did not reach an asymptote. The total arthropod species richness, diversity indices and evenness values dipped and the abundance peaked around the flowering time in finger millet; also the proportions of biting and sucking insects (phytophages) varied out of phase throughout the crop phenological phases in finger millet where as no such distinct patterns were noticed in pigeonpea. Analyzed at the trophic level, significant differences were noticed in the community composition in distinct crop phenological phases in two crops, as is also revealed by the Morisita-Horn index of similarity analysis. The high levels of parasitoid abundance and diversity reached during the later flowering and grain maturation stage respectively suggests the possibility of using finger millet as an element in agro-ecosystem diversity to support parasitoids.