Predatory efficiency of dragonfly nymphs, Crocothemis servilia and Rhyothemis variegata against the mosquito, Culex quinquefasciatus Say

Abstract

This study compared the predatory potential of nymphs of two dragonfly species viz. Crocothemis servilia (Drury, 1773) and Rhyothemis variegata (Linnaeus, 1763) using the different larval instars and pupae of Cx. quinquefasciatus (Say, 1823) as preys in normal laboratory settings. Field-collected fed and 24 h starved nymphs of C. servilia and R. variegata were offered 1^st, 2^nd, 3^rd and 4^th instar larvae and pupae of Cx. quinquefasciatus to monitor the rate of predation. A 24 h starved nymph of C. servilia showed the highest predation on the 2^nd instar larvae (92.00±4.06%) followed by the 3^rd (83.00±5.61%), 4^th (80±6.89%) and 1^st (76.00±4.85%) instar larvae and the pupae (26.00±2.91), respectively, whereas, that of R. variegata exhibited the highest consumption of the 1^st instar larvae (90.00±3.54 %) followed by the  2^nd (88.00±5.61 %), 3^rd (82.00±3.74 %), 4^th (70.00±7.91 %)  larval instar and the pupae (23.00±4.63), respectively within 24 h exposure. In the same period, the fed nymphs of C. servilia showed maximum consumption of the 2^nd instar larvae (77.00±3.54%) followed by the 3^rd (76.00±4.58%), 4^th (64.00±4.00%) and 1^st instar (55.00±3.53%) larvae and the pupae (24.00±3.67), respectively, whereas, that of R. variegata exhibited highest consumption of the 1^st instar larvae (67.00±5.38 %) followed by the 2^nd (65.00±10.12 %), 3^rd (58.00±8.46 %) and 4^th (53.00±4.06 %) instar larvae and the pupae (21.00±2.92), respectively. The rate of predation was significant on all the larval instars and the pupae compared to their control counterparts (p<0.05) and the starved larvae and nymphs of both the dragonfly species showed higher predation compared to the fed nymphs. The aforementioned findings suggest that nymphs of both of the dragonfly species exhibited considerable predation potential against the immature stages of the Cx. quinquefasciatus mosquito. The present study recommends assessing the feasibility of using these species in large-scale mosquito control programs.