Abstract:

Present investigation was carried out in the year 2011-12 to study natural parasitism dynamics, competitive interaction between parasitoids and behavioral response of Pieris brassicae (L.) and its parasitoids under the influence of both plant and herbivore volatiles. Parasitism by Hyposoter ebeninus (Grav.) was noticed from early October, 2011 and it was found to be highest (67.00%) during second week of January, 2012; whereas it was lowest (2.00%) in the fourth week of March and completely disappeared by early April, 2012. Seasonal variation in the development of two parasitoids showed inverse relationship between temperature and developmental time. No correlation was observed between percent females in the progeny of H. ebeninus (Grav.) and weather parameters. Competitive interaction between H. ebeninus and Cotesia glomerata revealed significantly higher total parasitism when both parasitoids were released together for 24 hours. Furthermore, precocious mortality was observed to be maximum (24.00%) in the treatment 'C. glomerata (L.) followed by H. ebeninus'. Egg-larval period was also highest in the same treatment. However, per cent pupation was highest in the treatment, H. ebeninus alone and C. glomerata alone. Behavioral response of both the natural enemies on plant and herbivore volatiles indicated that mechanically damaged plant + larvae + larval excreta of P. brassicae was found most attractive to the parasitoids which was followed by mechanically damaged plant + larval excreta. In contrast, P. brassicae visits were higher on healthy or undamaged plant.