Biomedical subjects
Publications and source records attributed to K Ilango.
The hexane extract and ethyl acetate soluble fraction of methanolic extract of the fruit pulp of Momordica dioica exhibited moderate and concentration dependent antifeedant activity against Spodoptera litura.
Females of phlebotomine sandflies (Diptera: Psychodidae) possess highly variable spermathecae that present several important taxonomic characters. The cause of this diversity remains a neglected field of sandfly biology, but may possibly be due to female post-mating sexual selection. To understand this diversity, a detailed study of the structure and function of the spermathecal complex in at least one of the species was a prerequisite. Using scanning and transmission electron microscopy, described here is ultrastructure of the spermathecal complex in the sand fly, Phlebotomus papatasi Scopoli. The spermathecal complexes are paired; each consists of a long spermathecal duct, a cylindrical spermathecal body, and a spherical spermathecal gland. Muscle fibres, nerves, tracheoles, and vascular sinuses connect the spermathecal body and duct through the epithelial layers. Spermathecal gland is formed by a typical insect epidermis and consisting of an epithelial layer of class-1 epidermal cells and elaborate glandular cells of class-3 epidermal cells, each having both receiving and conducting ductules (i.e. "end apparatus") and a "cytological apodeme", which is a newly described cell structure. The spermathecal body and duct are lined by class-1 epidermal cells and a cuticle, and are enveloped by a super-contracting visceral muscular system. The cuticle consists of rubber-like resilin, and its fibrillar arrangement and chemical nature are described. A well-developed neuromuscular junction exists between the spermathecal gland and the spermathecal body, which are connected to each other by a nerve and a muscle. The spermathecal complexes of the sandfly are compared with those of other insect species. The physiological role and possible evolutionary significance of the different parts of spermathecal complex in the sandfly are inferred from the morphology and behaviour. Post-mating sexual selection may be responsible for the structural uniqueness of the spermathecal complex in phlebotomine sandflies.
The spermathecal complex of Phlebotomus papatasi Scopoli (Diptera: Psychodidae) undergoes histological and physiological changes during its gonotropic cycle. The present histochemical study revealed a mucopolysaccharide secretory mass in the spermathecae of the newly emerged sandfly. Sperm competition occurs when two or more males compete to fertilize an ovum in the female reproductive tract. In this study, spermatophores of two or more competing males were deposited at the base of the spermathecal ducts, which originate from the female bursa copulatrix. This suggests that females play a role in sperm displacement, which is defined as any situation in which the last male to mate with a female fertilizes maximum number her eggs. A blood meal ingested by the female for ovary development and egg laying stimulates the release of sperm from the spermatophore. The spermatozoa then migrate to the lumen of the spermatheca. The ultrastructure of spermatozoa comprises a head with double-layered acrosomal perforatorium, an elongate nucleus, and the axoneme with a 9 + 9 + 0 flagellar pattern. This axomene differs from the flagellate axoneme of other Psychodinae. Morphological changes, such as the casting off of the acrosomal membrane, and histological changes in the spermatophore are also described. Mating plugs that have been described previously in sandflies appear to be artefacts. Females of P. papatasi may be inseminated more than once during each gonotrophic cycle, and additional inseminations may be necessary for each cycle. The relationships between the volumes of the sperm and the spermatheca were calculated to determine sperm utilization and fecundity of P. papatasi. As the females of P. papatasi mate polyandrously, the anatomical and physiological complexity of the spermathecal complex may be related to post-copulatory sexual selection.
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The morphology of insect genitalia is often highly species-specific, and its variation has been suggested as an important impetus for evolution. Structural variation of the male genitalia and the female spermathecae in Phlebotomine sand flies is unique among the blood sucking Diptera. We describe the fine structures involved in mating for Phlebotomus papatasi (Scopoli). Relationships among the length of the spermathecal duct and aedeagal filament were studied in 26 species of Old World phelebotomine sand flies comprising 12 subgenera. In most taxa the aedeagal filaments were very long allowing direct insemination into the spermathecae, indicating that intrasexual competition among males occurs as sperm precedence. There was a positive correlation between the lengths of the spermathecal ducts and aedeagal filaments, indicating that an evolutionary "arms race" occurs between males and females over the control of fertilization. The pattern of genitalia variation in phlebotomine sand flies also indicated that differences in the lengths of the spermathecal ducts and aedeagal filaments are distributed unevenly among closely related species. Genital differences do not seem to occur in populations of the Phlebotomus argentipes Annandale & Brunetti complex, whereas differences showed strongly in closely related Phlebotomus papatasi and P. bergeroti Parrot, and in sympatric Phlebotomus martini Parrot and P. celiae Minter.
Using light microscope and scanning electron microscope, the external morphological characteristics of the antennal flagellum and its sensilla are described in the sandfly, Phlebotomus argentipes Annandale and Brunetti sensu lato, a well known vector of visceral leishmaniasis in India. A revised terminology is given for the antennal segments to bring phlebotomine more in line with other subfamilies and families while a description of antennal sensilla is provided for the first time in phlebotomine sandflies. Each flagellum consists of scape, pedicel, flagellomeres I to XIII and apiculus. The antennal segments contain scales and sensilla and the latter consist of sensilla trichodea, s. basiconica, s. auricillica, s. coeloconica and s. chaetica and their putative functions are discussed. The sensilla chaeticum hitherto known as antennal ascoid in the phlebotomine sandflies was used to differentiate within and between species. Differences in its relative size to the flagellomere between the populations of P. argentipes collected from the endemic and non-endemic areas in Tamil Nadu state, southern India were established. These differences are considered to be a character displacement as means of premating reproductive isolating mechanism among the populations/members of species complex.
The Phlebotomine sandfly fauna of Tamil Nadu and Pondicherry in South India is described. Two morphologically different forms of Phlebotomus argentipes, the vector of Indian visceral leishmaniasis, are reported from Madras, a known focus of visceral leishmaniasis. A new species, Sergentomyia shettyi sp. nov., is described and Sergentomyia babu and Sergentomyia insularis stat. nov. are considered distinct species on the basis of their parapatric distribution. Phlebotomus papatasi and P. argentipes were the most abundant species around houses (37% and 29% of the catch, respectively), based on 1 year's sampling in villages near Pondicherry. The incidence of visceral leishmaniasis in Tamil Nadu since 1903 is summarized.