Latest Research News on Lepidopteran: Feb 2021

Immunity in Lepidopteran Insects

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential practical significance. An early response to infection in lepidopteran larvae is the activation of hemocyte adhesion, leading to phagocytosis, nodule formation, or encapsulation. Plasmatocytes and granular cells are the hemocyte types involved in these responses. Infectious microorganisms are recognized by binding of hemolymph plasma proteins to microbial surface components. This “pattern recognition” triggers phagocytosis and nodule formation, activation of prophenoloxidase and melanization and the synthesis of antimicrobial proteins that are secreted into the hemolymph. Many hemolymph proteins that function in such innate immune responses of insects were first discovered in lepidopterans. Microbial proteinases and nucleic acids released from lysed host cells may also activate lepidopteran immune responses. Hemolymph antimicrobial peptides and proteins can reach high concentrations and may have activity against a broad spectrum of microorganisms, contributing significantly to clearing of infections. Serine proteinase cascade pathways triggered by microbial components interacting with pattern recognition proteins stimulate activation of the cytokine Spätzle, which initiates the Toll pathway for expression of antimicrobial peptides. A proteinase cascade also results in proteolytic activation of phenoloxidase and production of melanin coatings that trap and kill parasites and pathogens. The proteinases in hemolymph are regulated by specific inhibitors, including members of the serpin superfamily. New developments in lepidopteran functional genomics should lead to much more complete understanding of the immune systems of this insect group. [1]

Lepidopteran Sex Pheromones

As a consequence of the diversity of Lepidoptera, including 150,000 described species, interesting species-specific sex pheromone systems are exhibited in this insect group. The quite varied pheromones, which have been identified from female moths of nearly 530 species from around the world, are classified into groups of Type I (75%), Type II (15%), and miscellaneous (10%), according to their chemical structures. Additionally, many pheromones produced by male moths and butterflies have been known. While new sex pheromones from about 70 lepidopteran species have been reported in the last five years utilizing GC-EAD, GC-MS, LC, and NMR, our information about the pheromones is still rudimentary, and these kinds of semiochemicals remain an exciting research target for natural product chemistry. In addition to the overview of their chemical structures, this chapter deals with current methods for their identification. Furthermore, an actual application of the synthetic pheromones for pest control is briefly introduced. [2]

Structural and functional diversities in lepidopteran serine proteases

Primary protein-digestion in Lepidopteran larvae relies on serine proteases like trypsin and chymotrypsin. Efforts toward the classification and characterization of digestive proteases have unraveled a considerable diversity in the specificity and mechanistic classes of gut proteases. Though the evolutionary significance of mutations that lead to structural diversity in serine proteases has been well characterized, detailing the resultant functional diversity has continually posed a challenge to researchers. Functional diversity can be correlated to the adaptation of insects to various host-plants as well as to exposure of insects to naturally occurring antagonistic biomolecules such as plant-derived protease inhibitors (PIs) and lectins. Current research is focused on deciphering the changes in protease specificities and activities arising from altered amino acids at the active site, specificity-determining pockets and other regions, which influence activity. Some insight has been gained through in silico modeling and simulation experiments, aided by the limited availability of characterized proteases. We examine the structurally and functionally diverse Lepidopteran serine proteases, and assess their influence on larval digestive processes and on overall insect physiology. [3]

Parasitization of Helicoverpa armigera (Lepidoptera: Noctuidae) by four Indigenous Trichogrammatid Species/Strains in a Mixed Cropping System of Tomato and Okra

Aims: Egg parasitoids, Trichogramma are recognised as natural enemies of many lepidoptera pests worldwide. In Kenya, a number of indigenous parasitoids species have been recovered. We evaluated the relative preference (parasitism) by four Trichogrammatid egg parasitoid species/strains, namely, T. sp. nr. mwanzai (L), T. sp. nr. lutea (H), T. sp. nr. mwanzai (M) and T. sp. nr. lutea (M) for the African bollworm Helicoverpa armigera on two of its host plants, tomato and okra usually intercropped in smallholder farms in Kenya.

Study Design: Host parasitism on host plants.

Methodology: Evaluations of parasitism for H. armigera by Trichogrammatid species/strains on Tomato and Okra in bioassays in both laboratory and field cages, in choice and no-choice conditions were undertaken.

Results: In general, species/strains exhibited significant differences in parasitism for the host (F=2.8; df =3, 7; P= 0.05) but neither the host plant nor host plant x species/strain interaction affected parasitism. Chi-square analyses showed no significant preference by species/strains between the two host plants although there was greater tendency by the parasitoids to go for H. armigera on okra than tomato.

Conclusion: The results give useful insights in planning for augmentation biological control of H. armigera in mixed farming agroecosystems. The four Trichogrammatids could effectively be used in augmentation programs in the tomato-okra cropping systems. [4]

Evaluating Ecofriendly Botanicals of Barleria longiflora Linn. F. (Acanthaceae) against Armyworm Spodoptera litura Fab. and Cotton Bollworm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

This study to investigate the crude extracts effect of Barleria longiflora against fourth instar larvae of Spodoptera litura and Helicoverpa armigera. Antifeedant, larvicidal, and the inhibitory activities of B. longiflora were observed with different solvent extracts of petroleum ether, chloroform and ethyl acetate. Significant effect has been observed in ethyl acetate extracts of B. longiflora compared with other solvent extract and control. Even though ethyl acetate extracts of B. longiflora showed higher percentage of antifeedant (79.40 and 77.36%) and larvicidal activities (70.96 and 68.70%) against S. litura and H. armigera,respectively. Percentage of deformed larvae, pupae and adults were high on ethyl acetate extract. Percentage of successful adult emergence was deteriorated by extract treated larvae. Preliminary phytochemical analysis showed the presence of Coumarin, saponins, steroids and tannins in ethyl acetate extract. [5]

Reference

[1] Jiang, H., Vilcinskas, A. and Kanost, M.R., 2010. Immunity in lepidopteran insects. Invertebrate immunity, pp.181-204.

[2] Ando, T., Inomata, S.I. and Yamamoto, M., 2004. Lepidopteran sex pheromones. The chemistry of pheromones and other Semiochemicals I, pp.51-96.

[3] Srinivasan, A., Giri, A.P. and Gupta, V.S., 2006. Structural and functional diversities in lepidopteran serine proteases. Cellular & molecular biology letters, 11(1), pp.132-154.

[4] Kalyebi, A., Hassan, S., Sithanantham, S. and M. Mueke, J. (2014) “Parasitization of Helicoverpa armigera (Lepidoptera: Noctuidae) by four Indigenous Trichogrammatid Species/Strains in a Mixed Cropping System of Tomato and Okra”, Advances in Research, 2(4), pp. 188-194. doi: 10.9734/AIR/2014/8377.

[5] Chennaiyan, V., Sivakami, R. and Jeyasankar, A. (2016) “Evaluating Ecofriendly Botanicals of Barleria longiflora Linn. F. (Acanthaceae) against Armyworm Spodoptera litura Fab. and Cotton Bollworm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)”, Annual Research & Review in Biology, 10(3), pp. 1-9. doi: 10.9734/ARRB/2016/23691.

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