Changes in the Haemolymph Cationic Concentration in Larvae of the Silkworm Bombyx mori L. Exposed to Selected High Temperature Regimes

The effects of high temperature on cationic composition of haemolymph of the three selected races of the silkworm, Bombyx mori, viz., PM, NB4D2 and CSR2 during 4 moult and 5 instar larval development were th th investigated. Haemolymph cation levels increased significantly throughout the feeding period from 1 to 6 day st th in all the three races and showed a significant decrease on 7 day. Mg and K ions were present at relatively th 2+ + higher levels followed by Ca and Na both in the leaf and larval haemolymph. Among the races, haemolymph 2+ + cation levels were higher in NB4D2than CSR2 and PM. K levels of bivoltine races were about 30% higher than + the multivoltine PM. The rates of elimination of cations were least during feeding stage than during non feeding stages resulting in higher cation levels during feeding stage. Despite increased feeding activity during active growth period, the cation levels showed significant drop in silkworm excreta suggesting that the cations are more completely absorbed during growth phase. When larvae were exposed to higher temperatures, monovalent cations like Na and K are hyper-regulated and divalent cations like Ca and Mg are hypo-regulated in order + + 2+ 2+ to prevent abnormal rise in the levels of haemolymph osmotic pressure. The lower levels of divalent cations in both haemolymph and excreta in larva haemolymph at higher temperatures suggest that the divalent cations are sequestered by intracellular fluids to counteract osmotic desiccation of somatic cells at higher temperatures.