Ontogenic Changes in Haemolymph Biochemical Composition in the Silkworm, Bombyx mori L under Thermal Stress

The biochemical composition of haemolymph was studied during larval and pupal period in the mulberry silkworm, Bombyx mori. The silkworm is normally reared at 25±1°C and 70±5 % RH and 31°C and 36°C constitute temperature stress conditions for the domesticated silkworm. When the larvae and pupae were exposed to selected higher temperatures, a significant decrease in the protein levels of haemolymph was noticed and the order of decrease was found to be more at 36°C than at 31°C. Relatively higher increase in the free amino acid levels in the haemolymph presumably provides protective cover to tissues against high temperature by an increase in osmolarity and reduction in evaporative water loss. Despite fluctuations, metabolic homeostatic controls restrict the abnormal rise and drop in haemolymph sugar levels during actively feeding larval and quiescent pupal stages respectively. Regardless of higher trehalose levels, glucose is a readily available fuel resource for many somatic tissues. Trehalose, being a multifunctional molecule, undergoes changes in levels during larval and pupal development. Upon exposure to higher temperatures, monovalent cations like Na and + K were hyper-regulated and divalent cations like Ca and Mg were hypo-regulated in order to prevent + 2+ 2+ abnormal rise in the levels of hemolymph osmotic pressure. The lower levels of divalent cations in larval and pupal haemolymph at higher temperatures suggest that the divalent cations are sequestered by intracellular fluids to counteract osmotic desiccation of somatic cells at higher temperatures.