natural-products-in-plant-pest-management

184 M. Kostyukovsky and E. ShaayaNerve impulseHOCHCH 2 NH 2OCH 3 CH 3NCH 3 OCH 3AcetylcholineOHOctopaminePost-synaptic neuronalmembraneMuscularjunctionHemolymphNerve impulseMuscular contraction,other physiological,modulatory functionsFig. 8.1. Neurotransmitters in insect systems as possible sites of action of essentialoil toxicity.Table 8.10. Effect of essential oils in the absence and presence of the octopamineantagonist, phentolamine (10 –5 M), on intracellular cyclic-AMP levels.TreatmentWithoutphentolamineWithphentolamineConcentration(M)Intracellular cyclic – AMP levelspmol/abdominal segmentOctopamine SEM76 Pulegone d-limonene0 0.210 –8 0.39 0.027 0.023 –10 –7 0.58 0.42 0.88 0.020 0.1410 –8 0.18 0.17 – –10 –7 0.05 0.17 0.2 –10 –6 0.11 0.01 – –cyclic-AMP at low physiological concentrations of 10 –8 M (Table 8.10). Moreover,addition of the octopamine antagonist phentolamine strongly antangonizedthe response to octopamine, as well as to the essential oil SEM76 andpulegone, were strongly antagonized and no elevation in cyclic-AMP wasobserved (Shaaya, et al., 2001; Kostyukovsky et al., 2002b). These effects wereobserved at low dilutions of the essential oils (estimated at 10 –7 and 10 –8 M),levels that induced the overt behavioural toxicity responses in vitro (Table8.10; Kostyukovsky et al., 2002b). It should be mentioned that d-limonene,