Contact and fumigant toxicities of monoterpenes and phenylpropenes, and their possible mode of action to oleander aphid
2022
Hussein, Hanna S. | El-Deeb, Dalia A. | Tawfeek, Mohamed E. | Abdelgaleil, Samir A. M.
In the present study, ten monoterpenes and phenylpropenes were tested for their contact and fumigant toxicities against oleander aphid, Aphis nerii (Hemiptera: Aphididae). Also, the inhibitory effect of compounds on acetylcholinesterase (AChE) and adenosine triphosphatases (ATPases) activities was assessed in vitro to explore their possible modes of action. (-)-Menthol and (+)-camphor were the most potent contact toxicants among the tested compounds against A. nerii third nymphal instar with LC₅₀ values of 0.06 and 0.08 mg/L, respectively. In contrary, 1,8-cineole, p-cymene and α-pinene showed a weak or no contact toxicity where their LC₅₀ values were >10 mg/L. In fumigation assay, cuminaldehyde (LC₅₀ = 3.10 µl/L), (+)-camphor (LC₅₀ = 3.57 µl/L) and (-)-menthol (LC₅₀ = 3.59 µl/L) showed the highest toxicity against A. nerii, while eugenol (LC₅₀ >50 µl/L) was the less effective compound. (−)-Citronellal (IC₅₀ = 2.22 mM) and trans-cinnamaldehyde (IC₅₀ = 1.12 mM) caused the highest inhibitory effect on AChE and ATPases activity, respectively. In general, all compounds showed strong inhibitory effect on the activity of ATPases than AChE.
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