Interactions between deet and anti-cholinesterasic compounds. a) and b) Toxic interactions between deet (μg/mg mosquito) and propoxur (μg/mg mosquito) for C. quinquefasciatus by topical application. The model including a synergistic interaction (b) between the two molecules provided a better description of the data than a model based on simply additive effects (a); see equations where ED is the effective dose, D the dose and ic the interaction coefficient. The interaction coefficient (ic = 3.07 ± 0.98) was significantly greater than 0, indicating that deet synergised propoxur toxicity in insects. c) Effects of propoxur (P) and deet (D), alone and in combination (P+D), on cockroach synaptic activity. All synaptic preparations were pretreated (10 min) with atropine (1 μM). NS not significant (P > 0.05). d) Effect of deet and neostigmine on the time course of full size EPPS recorded in mouse hemidiaphragm preparations. Mean values (± s.e.m, n = 6) of the half-decay time of EPPs (ms) under control conditions (2.8 ± 0.05 ms, blue column), 500 μM deet (6.1 ± 0.36 ms, red column) and in the continuous presence of deet and 3 μM neostigmine (10.5 ± 0.55 ms, yellow column). * denotes a significant difference from controls (P < 0.001). e) Examples of full size endplate potentials (EPPs) in response to a single or paired stimulus in the presence of 500 μM deet and in the presence of deet (upper part) and 3 μM neostigmine (lower part). * denote significant difference from control P < 0.001.