Mode of infestation and biocontrol potential of Hexamermis viswakarma Dhiman, a parasitoid of Leptocoris augur (Fabr), a pest of Kusum Plant, Schleichera oleosa lour

Abstract

Hexamermis vishwakarma Dhiman (Nematoda – Mermithidae) is a parasitoid of Kusum tree pest Leptocoris augur (Fabr). The pest severely causes damage to the seeds, bark and leaves of this tree. The parasitoid infests the bug population in large number during rainy season July to September at Saharanpur and Jharkhand forest area. Its mode of infestation and biocontrol potential is studied during present course of investigation. The parasitoid occurs in eggs, preparasite and post parasitic phases during its life cycle. The infective stage of parasite are preparasitic juveniles which are hatch out from the laid eggs after first rain of rainy season in first week of July. The preparasites are very active and emerges out in large number on soil and even reach on herbs under Kusum tree by undulating movement in search of host. On getting host (Ist to Vth instar nymphs as well as adults of L. augur). These move on host surface and search weak body points for entrance which are usually coxal joints, wing axillaries under surface of wing pods of nymphs, genital region and joints of abdominal tergites, sternites and pleurites. For penetration mouth stylet (penetration tooth) is used by preparsite and penetration lasts for about 15 to 35 minutes. Finally, these reach in the haemocoelomic cavity of host and begins to feed on host tissues such as haemocoelomic fluid, adipose tissue, body muscles, reproductive organs etc. and grow rapidly to become parasitic stage. Impact of parasitization on host is analysed which revealed that physical, anatomical and physiological changes are caused in host. The parasitized bug turns restless, its abdomen swells up resume biconvex shape, flight ability reduced feeding requirement of   host greatly increased, copulation and oviposition stop, cuticle of abdomen turns transparent and coils of parasitic stage are externally visible. Depletion of haemocoelomic fluid, fat bodies and muscles starts and becomes distorted. Lipids and proteins content greatly decreases. Ecdysis in nymph stops and nymph prolong their duration till emergence of parasitic stage. After completing parasitic life within the host, it emerges out making a hole in weak body part of host and enters into moist soil to become adult after moulting. The host dies after emergence of parasitic stage within 10 to 15 minutes. Thus, cent percent mortality occurs due to parastitization which is good for biocontrol potential.