Diversity of Hymenopteran Egg Parasitoids in Organic and Conventional Paddy Ecosystems

M Gnanakumar,K Rajmohana,D Balan,C Bijoy,R Nishi

doi:10.4038/tar.v23i4.4865

Abstract

Organic farming; cultivation without chemical pesticides and fertilizers, has been known to promote the general plant diversity as well as animal diversity including many groups of animal taxa. The objectives of this study was to prepare a generic level systematic inventory of egg parasitoids, and compare the species diversity and richness between organic and conventional paddy ecosystems, which are two differently managed agroecosystems. The study also aimed to examine whether the differences in the management practices have any vital effect on the diversity of the functional groups, the hymenopteran egg parasitoids in particular, when the major physical parameters like soil, temperature and rainfall, remained constant. Altogether 40 species of egg parasitoids in 23 genera belonging to 5 families (Platygastridae, Mymaridae, Encyrtidae, Eulophidae and Trichogrammatidae) were identified in both paddy ecosystems. Out of the 40 species, 29 belong to 16 genera of family Platygastridae. The number of species found in organic and conventional ecosystems was 32 and 22, respectively. Simpson’s diversity index was also higher (0.978) in organic ecosystem compared to conventional paddy ecosystem (0.878).The functional group analysis of hymenopteran egg parasitoids reflected a uniform pattern of higher functional redundancy in all the functional groups in the organic ecosystem than in the conventional ecosystem. However, egg parasitoid communities present in both ecosystems share less taxonomic similarities. Tropical Agricultural Research Vol. 23 (4): 300-308 (2012) DOI:<strong> </strong><a href="http://dx.doi.org/10.4038/tar.v23i4.4865">http://dx.doi.org/10.4038/tar.v23i4.4865</a>

Highlights

Many studies in the recent past have suggested that organic farming enhances the biodiversity in agricultural landscapes compared with conventional farming
A total of 20 genera and 32 species under 5 families of hymenopteran egg parasitoids were recorded in organic paddy, where as only 22 species under 16 genera were identified in conventional paddy (Fig. 3)
Since a higher species richness and diversity reflects a healthier and a more stable state of an ecosystem, it can be concluded that the organic paddy ecosystem is a much more stable and healthier ecosystem than that of the conventional one

Summary

Introduction

Many studies in the recent past have suggested that organic farming enhances the biodiversity in agricultural landscapes compared with conventional farming. Though organic system enhances species richness and abundance, its effects are likely to differ between organism groups and landscapes (Hole et al, 2005; Bengtsson et al, 2005). Groups of species that perform similar roles in an ecosystem process are known as functional types or functional groups. Most of the ecosystem processes are driven by the combined biological activities of many species under same and varied functional groups (Naeem et al, 1999). The functional groups assessed in this study were egg parasitoids, the group often occupying the third strata in the trophic level/food web. Egg parasitoids are organisms that both attack and complete their development within a host egg (Mills, 1994).

Objectives

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Conclusion