Abstract
Plant essential oils are considered as important bio-sources for the development of natural and environmentally safe pest control tools due to their multiple modes of action on insects. In this paper we have evaluated the activity of commercially available thyme oil and its constituents thymol, carvacrol, and p-cymene, as potential disruptants of the pheromone-mediated communication in the major pest moths Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae), and Grapholita molesta (Busck) (Lepidoptera: Tortricidae). In electroantennographic assays, the antennal response of males to thyme oil, thymol, and carvacrol was altered at high doses (103–104 µg), shifting the signal waveform into a biphasic negative–positive potential that caused a decay in the response. In wind tunnel assays, pheromone-mediated attraction of males of both species was interrupted in presence of thyme oil. Further trials demonstrated that thymol alone reduced the number of G. molesta and S. littoralis males landing on the pheromone source. This effect did not differ from that of thyme oil, although the latter provoked a significant reduction on downwind behavior steps in S. littoralis. Overall, our findings provide a preliminary basis for delving into the effect of thyme oil, and especially of its major constituent thymol, as potential mating disruptants of both species.
Highlights
Plant essential oils are considered as important bio-sources for the development of natural and environmentally safe pest control tools due to their multiple modes of action on insects
Significant differences in response were observed within thyme oil doses in both species, following a similar response pattern (G. molesta, χ2 = 17.726, df = 3, p = 0.001; S. littoralis, χ2 = 15.175, df = 2, p = 0.001)
Males exhibited a dose-dependent response at low doses (1–102 μg), and reached the maximum EAG amplitude at 1 02 μg (G. molesta, 1.12 ± 0.15 mV; S. littoralis, 0.69 ± 0.06 mV), with less than 60% of the antennae of both species responding at 1 μg
Summary
Plant essential oils are considered as important bio-sources for the development of natural and environmentally safe pest control tools due to their multiple modes of action on insects. In this paper we have evaluated the activity of commercially available thyme oil and its constituents thymol, carvacrol, and p-cymene, as potential disruptants of the pheromone-mediated communication in the major pest moths Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae), and Grapholita molesta (Busck) (Lepidoptera: Tortricidae). Essential oils are complex mixtures of secondary volatile compounds from plant metabolism, mainly composed of terpenes and terpenoids, and, to a lesser extent, by aliphatic and aromatic constituents of low molecular weight (aldehydes, alcohols, phenols, methoxy derivatives, and methylenedioxy compounds)[2] Their structural diversity has promoted a vast research on the bioactivity of EOs on insects, as they exert feeding[3,4] and oviposition d eterrence5,6, repellency[7], and toxicity in eggs[8], immature stages[9,10,11], and adults[12]. The effect induced by these chemicals on the male chemoreception system of both species was assessed by electroantennography (EAG), and the possible antagonism to the pheromone response of thyme oil, single compounds and binary/ternary mixtures was evaluated in a wind tunnel
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