Acaricidal activity of cinnamaldehyde and its congeners against Tyrophagus putrescentiae (Acari: Acaridae)

Abstract

The acaricidal activity of cinnamaldehyde and its 11 congeners against adults of Tyrophagus putrescentiae was examined using direct contact application and fumigation methods and compared with that of benzyl benzoate, N, N-diethyl- m-toluamide (DEET) and dibutyl phthalate. On the basis of 24 h LD 50 values, the compound most toxic to T. putrescentiae was cinnamyl acetate (0.89 μg/cm 2) followed by cinnamaldehyde (1.12 μg/cm 2), benzaldehyde (1.93 μg/cm 2), 3-phenylpropionaldehyde (2.08 μg/cm 2), cinnamyl alcohol (2.12 μg/cm 2), salicylaldehyde (2.75 μg/cm 2), and ( E)-2-hydroxycinnamic acid (4.32 μg/cm 2). These compounds were more potent than benzyl benzoate (10.03 μg/cm 2), DEET (13.39 μg/cm 2) and dibutyl phthalate (12.87 μg/cm 2). Very low activity (<60 μg/cm 2) was observed with cinnamic acid and ( E)-4-hydroxycinnamic acid. Moderate activity was obtained from cinnamic acid methyl ester, ( E)-3-hydroxycinnamic acid and 4-hydroxybenzaldehyde. These results indicate that hydrophobicity appears to play a crucial role in T. putrescentiae toxicity whereas a conjugated double bond and a length of CH chain outside the ring seem not to be implicated. In a fumigation test with T. putrescentiae adults, ( E)-cinnamaldehyde, cinnamyl alcohol and salicylaldehyde were much more effective in closed containers than in open ones, indicating that the mode of delivery of these compounds was largely due to action in the vapour phase. Natural and synthetic congeners of ( E)-cinnamaldehyde merit further study as potential T. putrescentiae control agents.