Diminished Activity of Larval Midgut Transaminases and Phosphatases in Helicoverpa armigera Hübner (Lepidoptera) Induced by Dietary Stem Extracts of Thevetia neriifolia

Abstract

Helicoverpa armigera Hubner (Noctuidae) is a common crop pest causing extensive loss of crop yields despite several efforts and diverse measures taken. As utilization of synthetic pesticides in the fields have caused ecological disturbances and lethal effects on humans and organisms; present studies explore Thevetia neriifolia (Apocynaceae), a widely used ornamental plant, against H. armigera as an alternate control measure. The study investigates the dietary effects of hexane and methanol extracts of T. neriifolia stems (HSE, MSE) on the activity of midgut enzymes of H. armigera, the alterations in which could hamper its growth and development. Different concentrations of the stem extracts, ranging from 0.001% to 0.02%, were incorporated in the diet of early IV instars of H. armigera. Effect of each extract was assessed by estimating the activity of four midgut enzymes; alanine aminotransaminase (ALT), aspartate aminotransaminase (AST), acid phosphatase (ACP) and alkaline phosphatase (ALP) of cotton boll worm. Investigations showed that dietary stem extracts resulted in significant and dose-dependent reduced activity of all the enzymes. The percent inhibition of the enzymatic activity was higher with dietary MSE of T. neriifolia as compared to the hexane stem extract. Also, the enzyme inhibition effects of extracts were more pronounced on phosphatases in comparison to transaminases. Larval feeding with T. neriifolia MSE diminished ALT activity by 26.95% to 49.79% and AST activity by 11.02% to 56.53%, whereas the ACP and ALP activity decreased by 44.65% to 87.61% and 21.97% to 85.97%, respectively. On the other hand, HSE inhibited ALT activity by 29.43% to 41.67% and AST activity by just 2.72% to 47.08%. However, a respective reduction of 14.58% to 78.44% and 32.73% to 78.07% was noticed in ACP and ALP activity with dietary HSE. The GC-MS analysis of the stem hexane and methanol extracts of T. neriifolia reveals the presence of 39 and 30 phyto-chemicals, respectively. Investigations showed the possible use of T. neriifolia extracts as a growth regulatory agent against H. armigera. Identification and isolation of bioactive compounds require further investigations.