Effects of dietary monocrotophos on the marsupial Sminthopsis macroura and the Australian native rodents Notomys alexis and Notomys mitchelli

Laboratory-bred Sminthopsis macroura, small (20–30 g) insectivorous marsupials, ingesting quickly (in less than 4 min) a large dose (80–100 mg kg⁻¹ body weight) of monocrotophos [1-[N-methylcarbamoyl)propyl-en-2-yl dimethyl phosphate], died within 30 min with cholinesterase (ChE) activity in their brain tissues inhibited by 66–69%; those that had ingested a much smaller dietary dose (2 mg kg⁻¹ body weight) at intervals during 18 days survived despite a higher ChE inhibition (92% on the 18th day). Notomys alexis and N. mitchelli, two species of small (30–50 g) rodents native to Australia, survived for 5 days on a diet of hulled millet containing 668 mg kg⁻¹ monocrotophos despite a 64% and 58% inhibition of ChE activity by the 5th day and a drastic reduction in food consumption reflected by a 14% and 12% loss of body weight respectively. These responses are discussed in terms of their effects on toxicity studies.