A REPORT ON FLIES ( DIPTERA : INSECTA ) AS FLOWER VISITORS AND POLLINATORS OF KOLKATA AND IT ' S ADJOINING

Dipterans are among the most common insects that visit flowers, and considered to be primitive pollinators with their suctorial or lapping mouthparts (Kevan and Baker 1983). In tropical areas, the diversity of Diptera can rival or exceed that of Hymenoptera (Inouye, 2001). A total of 42 families (Nematocera 12 and Brachycera 30) of Diptera are report.ed as flower visitors in the tropical world (Roubik, 1995), of them 37 families (Nematocera 12 and Brachycera 25) are present in India. Some of the more notable pollinating flies belong to the families Syrphidae, Bombyliidae, Tabanidae, Tephritidae, Stratiomyidae, Tachinidae, Calliphoridae, Pipunculidae, Muscidae. Bibionidae, Chironomidae, Culicidae, Empididae, Mycetophilidae, and Cecidomyiidae (Datta, 1998).

visited plant species.For this purpose 9 localities were studied during the year 2002-2004.As a result of this study 30 dipteran species under 23 genera of 9 families have been identified as flower visitors from Kolkata and it's adjoining areas.This is the first comprehensive as well as consolidated study made on the flower visiting dipterans in and around Kolkata or any other metropolitan city.

MATERIALS AND METHODS
The present study was conducted in 9 different localities of the south (Baruipur, Naren~rapur and Sonarpur), north (Madhyamgram, Badu, Duttapukur), east (Dapha east & Dapha west) and west (Howrah Botanical garden) of Kolkata in the districts of Howrah and 24 Parganas (North & South).Most' of the 10ca.1itiesare urban in nature and coming under Greater Kolkata, (Map 1).
The surveys were made at least twice in each station and observations taken throughout the day (from 6 am to 6 pm).The collections were made from different habitats like agricultural fields, orchards, medicinal plant gardens, nurseries, road side herbages, bushes, trees, seasonal flower gardens, managed gardens as well as from the wild.

FLIES
Generally the flies are minute to small soft-bodied insects; head highly mobile with large compound eyes, antennae of variable size and structure; suctorial mouthparts; prothorax and metathorax small and fused with large mesothorax; wings present only on mesothorax, the major morphological feature which distinguishes flies from other insects is their reduced hind wings, termed halteres (small, club-like structures that function as balancing organs during flight); legs with 5-segmented tarsi; abdomen with variable number of visible segments, female genitalia simple in most species, male genitalia complex and presence of cerci.

Family STRA TIOMYIDAE
The members of the family Stratiomyidae are commonly known as 'soldier flies' The flies are small to rather large, more or less flattened, and often colourfully white, yellow or metallic green.
They are mostly strong fliers, and are often seen sitting on flowers; the adults are pollen or nectar feeders.
Diagnosis: Head brilliantly metallic violet-blue to light green, bearing moderately dense grey pubescence on upper part, and more brownish about the middle; face and lower part of head, Map 1. : Map of Kolkata with adjoining areas (not to scale).
including proboscis, varying from brownish orange to pale yellowish with light yellowish pubescence; thorax with dorsum and scutellum brilliantly shining metallic green, bronze-green; abdomen metallic shining, yellowish bronze; legs pale yellow, with very short pale yellow setae in male or whitish in female; wings pale yellowish grey or pale brownish.

Remarks:
The species is reported for the first time as flower visitor of Bauhinia variegata yare candida.

Oplodontha rubrithorax (Macquart)
1838.Odontomyia rubrithorax Macquart, Mem. soc. sci. Agric. Lille,: 189.Diagnosis : The fly is small in size, with black thorax and yellowish abdomen; legs orange yellow with a brown ring on fore femora and brown streak on underside of middle femur.

Remarks:
The species was reported earlier as a flower visitor of Tagetes patula from West Bengal (Mitra, et al. 2003).During this present investigation, the species was found also from the same flower in Narendrapur and Baruipur of south 24 Parganas.
Diagnosis : This species is a small green metallic, with upper facets much larger than lower ones; legs pale yellow, hind femora with a broad median band and hind tibia with a broad apical band.

Remarks:
The species was also reported earlier as flower visitor of Tagetes patula from West Bengal (Mitra et. al., 2003).During this present investigation, like other species of the family Stratiomyidae, this specie~ was also collected from Narendrapur and Baruipur of south 24 Parganas.

Family TABANIDAE
Tabanids are relative~y large stout flies belonging to the suborder Brachycera.Body length ranges from 5-25 mm, compound eyes are well developed.As with most haematophagous Diptera it is only the females that suck blood in addition to nectar with the males being solely nectar feeders, the eyes are coloured and are also used to sex the flies.Males are hoI optic and the female's dichoptic.The antenna is stiff and projected forward.Adults are of the minor importance as mechanical transmitters of diseases.
Diagnosis: Small, slender flies; abdomen with inverted black markings on tergum 2, extensively yellowish; wing with posterior cell 5 having a large hyaline area up to hind margin; tibia never swollen (Fig. 11).

Remarks:
The species was collected from the yellow flower of Merremia vitifolia at Calcutta University campus, Baruipur.This flower visiting species was encountered only once throughout the survey.

Family BOMBYLIIDAE
The bombyliids or "bee-flies" are a group of moderate to large sized colourful and beautiful flies of the superfamily Asiloidea under the suborder Brachycera.These flies are actually considered as mimics of bees and as their bodies are clothed with a coat of soft, variegated hair and they are of great importance as conveyors of pollen.
Diagnosis: Small flies, frons and face quite black, with thick short black hair, antennae black, third joint shortly onion-shaped, basal joint with black bristles; thorax black with short yellow hairs, sides of thorax ash-grey, scutellum black; abdomen ovate, black with yellow hairs, dorsum bare, with microscopic black hairs; legs uniformly tawny yellow, with minute bristles; wings grey with costal cell yellowish, longitudinal vein 2 with a deep loop towards the tip, fork of third vein with distinct appendix, halters yellow, knob yellowish white with a black mark.

Remarks:
The species was collected from Naredrapur Ramakrishna Mission medicinal plant garden and Calcutta University campus, Baruipur.
Renlarks : The species is reported for the first time as flower visitor of Scaevola sericea Vahl.
Diagnosis: Medium size, black flies; antennal tip pointed ended with bristle; thorax dull black; scutellum with closely adhering black scales; abdomen black, 1st and 2nd segment rufous laterally, 7th segment with whitish pubescence laterally; clear iridescent wings.
Remarks : The species is reported for the first time as flower visitor of Scaevola sericea Vahl.

Family SYRPHIDAE
The family Syrphidae under the superfamily Syrphoidea of the infra order Cyclorrhapha in the section Aschiza is one of the largest and easily recognized groups of Diptera.The members of this family are commonly known as "flower flies" or "hover flies" Usually moderate to large sized flies, almost always bristleless, very brightly coloured flies and may be striped, spotted or banded yellow on a blue, black or metallic ground-colour.The black and yellow colouration often imparts to them a superficial resemblance to a wasp; other species are densely hairy and resemble bumblebees.Nearly all members of this family are attracted to flowers and may frequently be observed poised in air, their wings vibrating with extreme rapidity, hence the name of hover-fly.The venaspuria is one of their most characteristic features and is rarely found in other dipterans.It is a vein-like thickening of the wing membrane and may be distinguished from the veins in being fainter and terminating without association with other veins.These flies are pollinators of major significance.In some agro ecosystems, such as orchards, they out perform native bees in pollinating the fruits.
Diagnosis: A medium sized yeIIowish species; frons yeIIow, vertex black but both with black pubescence; thorax and scuteIIum covered with bright yellow pubescence; abdomen orange yellow with all the segments black banded at posterior margin; legs yellow (Fig. 6).
Remarks : This species was reported as the flower visitor of Cassia tora and COlnmelina sp.
from Gujarat (Mitra & Parui, 2002).This species is reported for the first time as flower visitor of Sida acuta.
Diagnosis: A medium sized yeIIowish species; antennal prominence yellowish with a small black dot above base of antennae; thorax blackish with 2 greyish stripes on fore part; scutellum yellow, pubescence on basal half, rest black pubescence; abdomen wholly orange with second to fifth segment indistinctly median spotten or black banded.

Diagnosis:
A medium sized blackish species with frons and face bright sulphur yellow; thorax shining black with side margins bright yellow from anteror margin of wing; abdomen black with a pair of yellow spots on second segment, third and fourth with a yellow band on each segment, fifth segment with greater part orange; legs yellow with a broad subapical black ring on hind femora.
Visiting plant species : Tagetes patula Linnaeus, Solanum melongena Linnaeus, CapSiCll111 Jrutescens Linnaeus.Diagnosis: Frons shining black dorsally and little yellowish ventrally; vertex black; face yellow with a clear bluish stripe on face from antennae to mouth; thorax metallic black with short golden yellow pile, humeri with yellow calli; scutellum yellowish brownish in middle; fore and mid legs bright yellow, hind femur with a median black band, tibiae black on apical half; wings clear; first segment of abdomen pale yellow, segment 2 very narrow, pale brown with a yellow band on hind margin, segment 3 with a reddish brown triangular mark on hind margin, segment 5 black.
Remarks: This species was collected for the first time as flower visitor of Helichrysum from the adjoining areas of Kolkata (Botanical garden, Howrah and Narendrapur).
Diagnosis : A small black species; eyes with three longitudinal stripes of white pubescence; thorax blue black with a pair of longitudinal grey stripes; scutellum black with serrated hind margin; abdominal segments reddish brown and black patterned; legs black and brown.

Eristalinus (Eristalinus) arvorum (Fabricius)
1787.Syrphus arvorum Fabricius, Mantissa Insect., 2 : 335. 9 Diagnosis : A large yellow and black species; frons covered with black pubescence and face with pale yellow pubescence; thorax with four longitudinal black stripes, whole thorax and scutellum covered with pale yellow pubescence; abdomen black, second and thrid segments with a pair of yellow spots; all tibiae black basally to a varying extent (Fig. 7).
Remarks: Earlier reported by Mitra et al., (2003) as the flower visitor of Tagetes patula.
During the present study, this species was found to visit the flowers of Santalum album and Mangifera indica at Calcutta University campus, Baruipur.
Diagnosis : A medium black species with reddish antennae; thorax black with 3 yellow longitudinal stripes; scutellum yellowish; third abdominal segment with a pair of quadrate yellowish spot on each side; tip of all femora yellow, front, mid and hind tibiae at base yellow, rest black (Fig. 8).
Remarks: This species was reported as flower visitor of Aegle marmelos and Tagetes patula from West Bengal (Mitra et at., 2003(Mitra et at., & 2004)).During this present survey, it was collected only from the flower of Tagetes patula at Dhapa east.
Visiting plant species: Tagetes patula Linnaeus.Diagnosis : Head light yellow; a median vitta on the posterior half of mesonotum; large spot on each side of metanotum; scutellum bearing two bristles; abdomen light yellow on first two segments, rest reddish yellow; wings hyaline; legs light yellow; hind tibiae reddish yellow or dark brown (Fig. 9).
Distribution : Throughout India.
Remarks: A good number of specimens were found as flower visitor of Cucurbita maxima in agricultural fields at Duttapukur.

Family MUSCIDAE
A family Muscidae is one of the most diversified and economically important group of the calyptrate Diptera belonging to the suborder Brachycera (Mc Alpine et al., 1989).Adult Muscidae are generally small to medium sized flies and seldom exhibit any striking developments of colour or form (Pont, 1972).
Diagnosis: Four black vittae on thorax, inner pair terminating towards posterior end, propleural depresson with find setulose hair; suprasquamal ridge without black setulae, all post dc strong; mid tibia without av and ad setae (Fig. 17).
Remarks: This species was reported earlier by Mitra et aI., (2004) as flower visitor of Weddelia calendulaceae from Narendrapur.
Remarks: This species was reported as the flower visitor of Zizyphus sp. and Anogeissus pendula from Gujarat by Mitra & Parui (2002).During this present survey, this species was collected from Dhapa (east & west), Sonarpur and Baruipur.
Diagnosis : Flies are wholly or partially metallic in colour; thorax metallic green with purple reflections, heavily dusted anteriorly and on the hypopleura; abdomen greenish to purple; genitalia hairy.Adults are oviparous and are attracted to dead animals, garbage and sometimes to flowering plants and fruits.
Remarks: During this present survey, this species was collected from Sonarpur and Baruipur and the first report as flower visitor of Santalurn and Psidiurn.

Table 1 .
: Dipteran flower visitors so far reported from adjoining areas of Kolkata with their visited plant species .

Table 1 .
: (Cont'd.)Mostspecies of fruit flies are highly ornamented with brightly contrasting colour patterns on their bodies and usually elaborate markings on the wings.Many species are of great economic importance and causes serious damage to commercial fruits and vegetables.

Table 2 :
Plant species and their flower visitors in and around Kolkata.Begonia sp.