Vertical Distribution of a Biting Midge, Culicoides oxystoma (Diptera: Ceratopogonidae) During Different Seasons in the Hooghly Estuary, Sagar Island, India

Abstract

Vertical distribution of different larval instars and pupae of Culicoides oxystoma in different depths in the mud and sandflats of Hooghly estuary were studied in relation to soil temperature and moisture at three stations in and around Sagar Island during March 1983 to February 1984. Temperature recorded higher in 0–3 cm depth and gradually decreased in subsequent depths. During the last part of the pre-monsoon (May and June) season, moisture was recorded minimum in 0–3 cm depth and gradually increased in greater depths, but in other seasons (monsoon and post-monsoon) the results were just opposite. Larval and pupal population showed a peak during post-monsoon then gradually declined in pre-monsoon and early monsoon. They were mostly encountered throughout the year from 0–3 cm depth except during summer months (May, June and July). First and second instar larvae were only recorded from 0–3 cm depth. Third and fourth instar larvae were distributed in all the depths, maximum in 0–3 cm. Pupae were never encountered from deeper depth (6–9 cm). Temperature and moisture act as important factors to control the vertical distribution of larvae and pupae of this species.