A Key for Identification of Deltocephaline Genera ( Hemiptera : Cicadellidae : Deltocephalinae ) Associated with Vegetable Ecosystem in Sri Lanka

Members of the subfamily Deltocephalinae include many vector species transmitting pathogens among economically important crops. Species of ten genera belonging to seven tribes namely, Exitianus Ball, Nephotettix Matsumura, Deltocephalus Burmeister, Hecalus Stål, Balclutha Kirkaldy, Cicadulina China, Hishimonus Ishihara, Orosius Distant, Changwhania Kwon and Doratulina Melichar were detected in a survey carried out during 2007-2008 in Mid Country associated with the vegetable ecosystems of Sri Lanka. An illustrated dichotomous key based on the morphology and genitalia characters is presented here for easy identification of field collected leafhoppers at generic level.


INTRODUCTION
Deltocepahlinae is the largest subfamily in the family Cicadellidae (leafhoppers), and members of this subfamily occur in all zoogeographic areas and many species are capable of transmitting pathogens among economically important crops.The subfamily is divided into 23 tribes and of these, 9 tribes were reported in Sri Lanka (Omen et.al., 1990).Deltocephalines feed on the phloem sap of a wide variety of vascular plants, and the members of about 14 tribes feed only on grasses or sedges (Viraktamath, 2005a).Of the leafhopper vectors of the plant diseases, 63% of the species belongs to subfamily Deltocephalinae (Nielson, 1979).The species of Nephotettix Matsumura, Deltocephalus (Recilia) Burmeister, Orosius Distant and Hishimonus Ishihara have been reported as important vectors in India (Viraktamath, 2005a).Study of the species diversity leafhoppers in agroecosystems in Sri Lanka, has revealed 25 species of Deltocephalines belonging to 10 genera in 7 tribes including vector species (Gnaneswaran et al., 2006).Presence of vector species associated with the crop ecosystem must be monitored with care to avoid economic loss in the future.For which all species must be identified correctly.Taxonomic studies of Leafhoppers in Sri Lanka had not been carried out after Distant (1918).Occurrence of the species of some genera namely: Deltocephalus (Racilia), Nephotettix (Gnaneswaran et al., 2008b;Wilson and Claridge, 1991) and Idioscopus (Gnaneswaran et al., 2007) were reported from Sri Lanka with taxonomic notes but not other genera.There is a great need to develop illustrated simple keys to vectors and other economically important species of leafhoppers for use by entomologists who are dealing with crop protection strategies.

MATERIALS AND METHODS
A field survey was conducted in vegetable ecosystems selected in Mid Country Wet Zone and Low Country Dry Zone of Sri Lanka, during 2007-2008 to collect leafhoppers from vegetables and grasses.The insect specimens were collected by using sweep nets and aspirators.The collected specimens were curated (Oman et al., 1949) and deltopcephalines were sorted out by examining their morphological characters (Viraktamath, 2005a & b) under binocular stereoscopic microscope (X 10) and mounted singly on card points.The abdomen of each specimen was dissected to study the genitalia (Knight, 1965) and then identified by consulting published taxonomic keys and related literatures (Morrison, 1973;Webb, 1987;Rao and Ramakrishnan, 1990;Dietrich, 2005 andViraktamath, 2005 a &b).
Identities of the specimens were confirmed by Dr. C. A. Viraktamath, Department of Entomology University of Agricultural Sciences, Bangalore, India.A key to the Deltocephaline genera associated with vegetable ecosystem in mid country Sri Lanka, was prepared based on the morphological variations.
Although considerable damage was noticed on vegetable crops by the species of typhlocybine leafhopper (Gnaneswaran et al., 2008a), no damage symptoms were observed due to the presence of Deltocephaline species.Several of the well known vector species were found in very few numbers.They were: Hishimonus phycitis (Distant) was collected from brinjal (7/field) which has been known to transmit phytoplasma which causes little leaf of brinjal (Nielson, 1979), and Orosius albicinctus Distant, a vector for Phyllody of sesame and gram, and potato purple top roll in brinjal, collected by sweeping grasses in the ecosystem (2/field).Deltocephalus dorsalis (Motschulsky) a vector of rice stunt disease and Cicadulina bipunctata (Melichar) vector for ragi streak virus.Regular monitoring of these vector species is essential in this ecosystem in order to forecast and minimize the damage.Therefore, a simplified taxonomic key is prepared for a correct identification of the species which is a pre prerequisite for easy monitoring and manipulation of this group of insect.

Key to separate leafhopper genera associated with vegetable ecosystem in mid country region of Sri Lanka (after Viraktamath 2005 a & b).
Deltocephalinae.Small to medium sized insects (2-8 mm) with ocelli either on anterior margin of head or close to anterior margin of head on crown of vertex .Clypeus not extended laterally over bases of antennae to form antennal pits.In Macropterous form front wing possess cross vein r-m1.
Cicadulina China 4 Body depressed; head strongly produced; ocelli on crown near margin, very close to eyes.-HecaliniiFace and thorax green to yellowish green with Concentric parabolic orange fasciae on head and pronotum.
Hishimonus Ishihara 7 Male connective linear fused to aedeagus Deltocephalini Stout body.vertex more than twice as broad as long male plate fused at the base linear male connective, fused to aedeagus.