Effect of Dimethoate (Rogor 30% EC) on the brain neurosecretory cells of third instar grubs of Oryctes rhinoceros L. (Coleoptera : Scarabaeidae)

The brain neurosecretory cells of III instar grubs of Oryctes rhinoceros were exposed to insecticide Dimethoate (Rogor 30% EC) in the laboratory condition. The sublethal doses (0.125, 0.25 and 0.5%) of Rogor at time intervals of 8, 16 and 24 h have produced marked changes in the structure and the secretory activities of medial and lateral neurosecretory cells. Rogor stimulates the synthetic activity of these cells at the initial stages of its action and results in the accumulation of neurosecretory materials (NSM) in the cytoplasm. The decreased neurosecretion at later stages of the action was due to its transportation through the axons before the death of treated grubs. Similarly, vacuolization, shrinking and degeneration of cells were also observed in treated grubs.