Genetic diversity based on 28S rDNA sequences among populations of Culex quinquefasciatus collected at different locations in Tamil Nadu, India

The basis of the present study was to distinguish the existence of any genetic variability among populations of Culex quinquefasciatus which would be a valuable tool in the management of mosquito control programmes. In the present study, population of Cx. quinquefasciatus collected at different locations in Tamil Nadu were analyzed for their genetic variation based on 28S rDNA D2 region nucleotide sequences. A high degree of genetic polymorphism was detected in the sequences of D2 region of 28S rDNA on the predicted secondary structures in spite of high nucleotide sequence similarity. The findings based on secondary structure using rDNA sequences suggested the existence of a complex genotypic diversity of Cx. quinquefasciatus population collected at different locations of Tamil Nadu, India. This complexity in genetic diversity in a single mosquito population collected at different locations is considered an important issue towards their influence and nature of vector potential of these mosquitoes.

Detection of genetic polymorphism in the populations of brinjal shoot and fruit borer, Leucinodes orbonalis (Guenee).

In the present study six different populations of L. orbonalis were collected and subjected to analysis of genetic variability in terms of carboxylesterase isozyme pattern and DNA polymorphism using RAPD-PCR. Pattern of carboxylesterase revealed a similar isozyme cluster in the populations namely, sivaganga (population-3), dindigal (population-4), virudhunagar (population-5) and coimbatore (population-6). Similarly, the populations of L. orbonalis recorded 3 distinct randomly amplified polymorphic DNA markers in all populations grouped above. This pattern of genetic variability in the populations was also supported by the analysis of the similarity indices and UPGMA dendrogram.

Toxicity assessment of wild bean seed protein--arcelin on Asian armyworm, Spodoptera litura (Fabricius).

Arcelin, an anti-metabolic protein was purified from the seeds of wild bean, Lablab purpureus. The feeding assay containing arcelin at 5, 10 and 15 microg concentrations revealed no antifeedant effect against fifth instar larvae of S. litura. However, the enhanced activity of alpha- and beta-naphthyl esterases in the mid-gut samples of S. litura treated with arcelin suggests countermeasure against the toxic effect of arcelin.

Use of RAPD in assessing the genetic variability in Spodoptera litura.

A polymerase chain reaction based assay to distinguish six different ecotypes of the Spodoptera litura, a sporadic insect pest and a predominant defoliator of various crops was carried out. A total of 40 random primers were screened to reveal the existence of polymorphism between the populations. Among them eight showed scorable banding patterns and three primers (OPA-01, OPA-05, OPM-01) exhibited distinguishable banding patterns. However, Chengalpattu and Chennai populations revealed their closed relatedness and Coimbatore population stood distantly from others.

Resistance of legume seeds to the bruchid, Callosobruchus maculatus: metabolites relationship.

A study was initiated to categorize the seeds of various wild and cultivar legume varieties on the basis of their relative resistance to the bruchid, C. maculatus, and to correlate the important primary and secondary metabolites (non-protein anti-metabolites) in these seeds to the developmental parameters of the bruchid. In general, the wild seed varities showed greater amount of resistance to the bruchid attack when compared to that of the cultivar varieties. All the cultivar varieties studied showed higher amounts of primary metabolites, namely, proteins, carbohydrates, lipids and free amino acids thus showing a positive correlation between the primary metabolites content and the infestation rate. The wild varieties, however, showed significantly lower amounts of these primary metabolites and consequently a lower level of infestation. The non-protein anti-metabolites such as total phenols, ortho- dihydroxy phenols and tannis were significantly lower in the cultivars. The wild varieties, in contrast, revealed higher amounts of these secondary metabolites showing a negative correlation between these secondary metabolites content and the infestation rate. The study revealed that these non-protein anti-metabolites are important in conferring resistance to the seeds.

Changes of haemolymph protein profile in the larva of Pericallia ricini (Fabricius) parasitised by the Braconid Wasp, Apanteles taragamae Viereck (Hymenoptera: Braconidae).

Parasitism by the braconid wasp, A. taragamae caused alterations in the haemolymph polypeptides of woolly bear larvae of P. ricini. Analysis of haemolymph proteins by SDS-PAGE and densitometry showed that the quantities of haemolymph proteins were reduced dramatically in the parasitised larvae. Simultaneously, parasitism induced large amount of 95 kDa polypeptides in the haemolymph of the parasitised larvae. Also, a remarkable induction of 43 and 45 kDa polypeptides which are not detectable in non-parasitised larvae appeared in the parasitised larvae.