Hoverflies of Assam (Diptera: Syrphidae): New records and their diversity

Abstract

Hoverflies, generally known as Syrphid flies belongs to family Syrphidae, which is one of the largest families of order Diptera. The adults use to feed on nectar and pollen of many flowering plants and larval stages of some species are predaceous to homopteran insects. The objective of the present investigation was focused on the assessment of the diversity and abundance of hoverfly at Assam Agricultural University, Jorhat, Assam during 2015-16. A total of 225 individual hoverflies were recorded during the study out of which 23 species belonging to 16 genera under 2 sub-families viz., Eristalinae and Syrphinae were observed. Among them, ten species viz., Eristalinus tristriatus, Eristalis tenax, Eristalodes paria, Lathyrophthalmus arvorum, Lathyrophthalmus megacephalus, Lathyrophthalmus obliquus, Phytomia errans, Pandasyopthalmus rufocinctus, Metasyrphus bucculatus and Sphaerophoria macrogaster were newly recorded from Assam. Among the species, Episyrphus viridaureus and Lathyrophthalmus arvorum were found to be the most abundant species with the relative abundance of 16.89 and 10.22% respectively. Two parasitoid viz., Diplazon sp. and Syrphophagus aeruginosus (Dalman) were also observed as natural enemies for the first time in Assam emerging out from parasitized pupa of hoverflies during the studies. Out of 23 species, 20 were found in horticultural ecosystem with total abundance of n= 119 followed by 18 species (n=106) in agro- ecosystem. The horticultural ecosystem recorded the highest diversity index and evenness (2.84 and 0.95) followed by agro-ecosystem (2.52 and 0.87). The highest number of species was recorded from horticultural ecosystem and the presence of such diversity reflects the composition of different food sources and also indicates the healthiness of the surrounding environment.