Host searching behavior and potential of an aquatic ichneumonid pupal parasitoid of rice caseworm (Parapoynx stagnalis) in an upland rice paddy agro-ecosystem of the Western Ghats, India

Abstract

Parapoynx stagnalis (Zeller) (=Nymphula depunctalis (Guenée), is a sporadic rice paddy pest of south and southeast Asian rice paddy fields, and widely known as rice caseworm. A recent outbreak of the pest was observed in the upland rice paddy agro-ecosystem of the central Western Ghats, India. No potential natural enemies of this pest have so far been reported, mainly due to the semi-aquatic behavior of the larvae and pupae. However, an undescribed aquatic ichneumonid wasp species (belonging to a genus near Litochila) is reported as a potentially useful early stage pupal parasitoid of this pest in our study. The host searching behavior and potential of the parasitoid wasp was studied in detail using both field and laboratory experiments. The adult female wasps usually dive into the water in search of the host pupae, remaining under water for a maximum of 90.2s, while searching for rice caseworm pupae. In field and laboratory experiments, we found 73% of the parasitized pupae of P. stagnalis kept under water yielded adult parasitic wasps. However, no parasitoids emerged from parasitized host pupae maintained in dry terrariums. Sex ratio was 2.8:1. The present discovery of the semi-aquatic parasitoid wasp could aid in better management of the rice caseworm population in rice paddy fields.

Keywords:

• Rice caseworm
• upland rice paddy agro-ecosystem
• aquatic ichneumonid wasp
• Western Ghats
• India

Acknowledgements

Without the cooperation of the farmers of Sringeri, the study would have suffered a lot, our sincere gratitude to the entire farmer community of Sringeri. PAS wishes to thank Professor C. A. Viraktamath (Gandhi Krishi Vignan Kendra, University of Agricultural Sciences, Bangalore), Professor Shen Horn Yen (National Sun Yat-Sen University, Taiwan), and Dr Donald Quicke (Imperial College, London) for their valuable comments, suggestions, and also for providing me with the necessary reprints, which have improved the overall performance of this study. Kiran M. C. is gratefully acknowledged for preparing the map. The financial assistance by ICAR, New Delhi through NATP/CGP/PIMIII is gratefully acknowledged by PDR.