Effect of Temperature on Hemocytic Immune Responses of Tropical Tasar Silkworm, Antheraea mylitta D

Insect blood cells (Hemocytes) are very vital component of the insect immune system but elaborate studies on hemocyte profile of economically very important sericigenous insect A. mylitta under altered physical conditions were unnoticed by researchers. Hence, an attempt was made to investigate the effects of high, low and cyclic temperature treatment/stress on cellular (hemocyte) immune responses such as Total Hemocyte Count (THC), Differential Heamocytes Count (DHC) and related changes in cell contour/morphology in fifth instar larvae of A. mylitta. Based on morphology staining reaction and response towards temperature stress six types of hemocytes were identified in A. mylitta. They are prohemocytes (PRs), plasmatocytes (PLs), granulocytes (GRs), spherulocytes (SPs), oenocytoids (OEs) and adipocytes (ADs). Besides, vermicytes (Ves) and podocytes (POs) were occasionally observed in smears of moulting phase of late fifth instar larvae. Presence of POs is unique in the present insect and it has not been reported earlier. Variations in Differential Hemocyte Counts (DHC) were observed when the ambient regime of temperature 26±1°C was changed to Chilling (4°C), heating (50°C) and cyclic 20, 26 and 32°C to cause temperature stress. Reduction in PLs and GRs were observed during Cyclic Temperature Treatment (CTT) in comparison to normal temperature but chilling and heating temperature did not showed the similar trends. Decrease in PLs and increase in GRs were observed after chilling temperature and increase in PLs and decrease in GRs were noticed after heating temperature. More mitotically dividing PRs were seen during elevated temperature stress. Low temperature lead to clumping of hemocytes and high temperature to its spread and nuclear fragmentation. Significant drop in THC was observed at low temperature but surprisingly at heating temperature significant increase was noticed. THC was found to decline in 120 h CTT larvae.