EUCHARITID WASPS

         The order Hymenoptera consists of most widely recognized insects such as ants, bees and wasps. This also contains far more, and more diverse, species than the ants, bees and wasps. Most of the Hymenoptera belong to groups unknown to the common people. These are small (usually less than 5 mm long) parasitic species that go about their lives unnoticed by the general public except insect taxonomists, biological control workers, ecologists or naturalists. One such group is the little known and rarely distributed eucharitid wasps.

     The eucharitid wasps belong to the family Eucharitidae under the Superfamily Chalcidoidea. This family is the largest and most diverse group of hymenopteran parasitoids of eusocial insects (Heraty, 2002). They are parasitic on ants. It comprises the most bizarre forms in the Superfamily Chalcidoidea. Most of the members of this family are brilliantly coloured and strikingly attractive. They are moderately sized individuals measuring approximately about 4-5 mm in length.

      The eucharitids are probably most closely related to the Perilampidae, the only other family of the Chalcidoidea in which the prepectus is fused with the lateral part of the pronotum. The Eucharitidae can be easily distinguished from other families by the reduced pronotum and the elongated sickle-shaped mandibles. The other important diagnostic characters of the family are: in several species, apex of scutellum often produced posteriorly into a fork or horn or stump; malar sulcus absent; labrum with single row of 4-16 marginal digits; in some species the flagellar segments serrate or ramose; fore wing with usually well developed marginal vein but in some cases veins not discernible; notauli usually present; tarsi 5 segmented; gaster often with a long petiole in many species; first gastral tergum usually more than half as long as remaining part of gaster; ovipositor concealed or exserted, if exserted then either acicular or expanded.

      The members are distributed in almost every zoogeographical region of the world. They are not reported from New Zealand and a few of smaller oceanic islands and are relatively poorly represented throughout the Palaearctic region (Heraty, 2002). The eucharitids are most abundant and specious in the tropics.

      Eucharitids have remarkable host relationships with ants. The eggs are laid on plants and the primary larva (planidium type) attaches itself to the worker ants and so are carried into the ant nest where it is transferred to the ant larva. It waits till the host larva reaches prepupal or pupal stage before it starts to feed and completes its development.

     The Eucharitidae is an economically important group of insects since in their positive role they are beneficial parasites of pest ants and in their negative role, they themselves are pests of beneficial plants. In India Orasema assectator Kerrich deposits its eggs into incisions in the leaf tissue of tea bushes and secondary fungal disease "sewing leaf-blight" occurs in these incisions (Das, 1963; Kerrich, 1963). In Argentina Orasema aenea Gahan was reported to transmit the bacterium Pseudomonas savastanol (E. Smith) that caused tubercular infections on leaves of olive (Nicolini, 1950). Orasema costaricensis Wheeler & Wheeler cause "Brown spot" on young banana fingers in Costa Rica as a result of their oviposition punctures (Tocchetto, 1942; Roberts, 1958; Evans, 1966).

      Sexual dimorphism is usually strongly visible among eucharitid wasps. Sexes are readily distinguishable based on the relative length of the petiole, the shape of the gaster, sometimes the shape and number of antennal segments and the presence or absence of an ovipositor or genitalia that are usually visible externally. More subtle differences can also be observed. Males are usually less robust than females, the mesosoma is slightly smaller in proportion to body size, sculpture may be more prominent, colouration is darker and metallic reflections, if present, tend to be more extensive.

     Though relatively more work on the eucharitids have been done on the fauna of foreign countries, our information on the fauna of Indian subcontinent is very scanty and fragmentary. Only 31 valid species under 11 genera are present in India till date. They are as follows: Indosema indica Husain & Agarwal, 1983, Orasema assectator Kerrich, 1963, Orasema delhiensis Narendran & Girish Kumar, 2005, Orasema initiator Kerrich, 1963, Orasema nirupama Girish Kumar & Narendran, 2007, Anorasema manii Heraty, 1992, Gollumiella antennata (Gahan, 1940), Gollumiella longipetiolata Hedqvist, 1978, Neolosbanus laeviceps (Gahan, 1940), Neolosbanus palgravei (Girault, 1922), Psilocharis hypena Heraty, 1994, Ancylotropus keralensis Girish Kumar & Narendran, 2008, Ancylotropus manipurensis (Clausen, 1928), Cherianella narayani Narendran, 1994, Stilbula ashokai Narendran, 1996, Stilbula bangalorica Girish Kumar & Narendran, 2008, Stilbula indica (Mani, 1935), Stilbula lata Narendran, 1996, Stilbula minispina Heraty, 2002, Stilbula mysorensis (Mani & Dubey, 1974), Stilbula nilgiri Heraty, 2002, Stilbula tanjorensis (Mani & Dubey, 1974), Schizaspidia andamanensis (Mani, 1944), Schizaspidia brevifuniculata Narendran, 1986, Schizaspidia coromandelica (Mani & Dubey, 1974), Schizaspidia furcifera Westwood, 1835, Schizaspidia malabarica Narendran, 1986, Schizaspidia sabariensis (Mani & Dubey, 1974), Schizaspidia sitarami Narendran, 1986, Schizaspidia travancorensis (Mani, 1944) and Chalcura deprivata (Walker, 1860).

References

P. Girish Kumar and *T.C. Narendran
Zoological Survey of India,
M- Block, New Alipore, Kolkata- 700 053
      West Bengal, India,
E- mail: kpgiris[at]gmail[dot]com

* Systematic Entomology Laboratory,
Department of Zoology,
University of Calicut,Kerala- 673 635, India.
E- mail: drtcnarendran@yahoo.com