G. it. Ent., 6 (35): 459-463
December 31, 1993
Some enzymatic changes in the metabolism of the armyworm,
Mythimna separata (Walker) (Lepidoptera, Noctuidae)
by
GHANASHYAM TRIPATHI & PARAS NATH
Abstract - The cytoplasmic malate dehydrogenase (cMDH), mitochondrial malate dehydrogenase (mMDH) and lactate dehydrogenase (LDH) were studied in the different larval instars of the armyworm, Mythimna separata under normal and experimental conditions. The activities of cMDH, mMDH and LDH gradually increased from the 1st to the 4th instar, and then declined slowly in the 5th and 6th instars. This indicates a gradual enhancement in energy production, gluconeogenesis and lipogenesis in larval forms, probably due to increased feeding to meet the increased demand of metabolic activities as a function of growth and development. The subsequent decline in the carbohydrate metabolism capacity may be explained with the cessation of feeding in the 5th and 6th larval instars. In spite of changes in their activities, the ratio between mMDH and cMDH remained more or less constant in all larval instars, while that between mMDH and LDH varied substantially in the different instars showing the fluctuations in the aerobic and anaerobic capacities during the larval development. The exposure of the 4th instar larvae to two organophosphate insecticides (quinalphos and monocrotophos) at their LC50 for 24 hours significantly reduced the activities of cMDH, mMDH and LDH, which is probably due to either the direct binding of the insecticides, of their metabolites, with the enzymes and/or by blocking the enzyme syntheses.
