An analytical study of the neurosecretory cells of the brain of the mature larvae and diapause pupae of Amsacta collaris Hampson (Lepidoptera: Arctiidae) under different temperature regimes.

The neurosecretory cells (NSCs) of the brain of the mature larvae and 3 months old diapause pupae of Amsacta collaris Hampson (Lepidopera: arctiidae) have been studied under different temperature regimes (0, 7, 18, 37, and 42 degrees C), using paraldehyde fuchsin and performic acid resorcin fuchsin staining techniques. The 0 degree C is fatal to the larvae, and at 7 degrees C, within 24 h the quantity of NSM reduced considerably in all the subtypes of A-cells; activity started 3rd day onwards, and on 5th day, the A1-cells appeared loaded with NSM, the A2-cells moderately filled, but no change in A3-cells was observed. At 0 degree C, within 48 h or chilling, the NSCs of diapause pupae (DP) revealed a moderate amount of NSM with numerous, large vacuoles in the A1-cells and in some insects, the cells appeared gigantic in form; the A2- and A3-cells were moderately filled with NSM. After 1 week of chilling, at 0 degree C, the A1-cells appeared almost empty. The A1-cells of DP-kept at 7 degrees C and 18 degrees C respectively, discharged quickly all the previously stored NSM, within 2 days, hence appeared poorly filled. 3rd day onwards, a gradual increase in NSM was observed. After 15 days, a moderate amount of NSM in A1-, a large amount in A3-, and increased amount in A2-cells of the medial and lateral groups was observed. The 37 degrees C appeared to be the most suitable temperature at which all the cells show maximum activity in mature larvae and DP both, and contain a moderate amount of NSM in them. At 42 degrees C, the A1-cells in larvae and DP contain a moderate amount of NSM, A2-cells of the medial group a poor, and A2-cells of the lateral group, a depleted amount of NSM, the A3-cells, however, appeared heavily loaded. Later, the NSM decreased gradually in all the subtypes of A-cells. On 15th day, at 42 degrees C the A1-cells in DP revealed depletion of NSM, the A2-cells become totally inactive and lack NSM; the A3-cells a poor amount of NSM in them. The significance of these changes at different temperature regimes is discussed.