Neurosecretory cells occur in groups, medially, dorsally, dorsolaterally, laterally and midventrally, in the protocerebrum and tritocerebrum of adultPoekilocerus pictus. Mid-brain is devoid of such cells. On the basis of staining reactions the NS cells have been differentiated into A and B types. The median group consists of about 50–55 A and 30 B cells lying on either side of the midline in the parsintercerebralis. The other parts of the protocerebrum and tritocerebrum are filled with only B cells. Scant NSM is found in the NS cells of freshly moulted adult. Synthetic activity increases with age and after about 5 or 6 days the cells contain deep staining secretory vesicles.
Treatment of 1–6 day oldP. pictus with DDT for different periods showed that short incubation of 24 hr triggers the synthetic activity of NS cells, but prolonged incubation of 72 hr leads to a total depletion of NSM and to disruptive changes, like undulation of cell wall, cell shrinkage and ultimate cellular disruption.