The synergistic effect of piperonyl butoxide on the molluscicidal potential of monoterpenes and phenylpropenes against Theba pisana

The molluscicidal activity of six monoterpenes and two phenylpropenes against Theba pisana adults was evaluated using fumigation and direct contact methods. In the fumigant toxicity assay, (-)-citronellal showed the highest toxicity with LC50 value of 7.79 μl · l−1 air after 24 h of treatment, followed by (-)-terpinen-4-ol (LC50 = 12.06 μl · l−1), (-)-menthone (LC50 = 12.28 μl · l−1 air) and p-cymene (LC50 = 16.07 μl · l−1 air). Eugenol and trans-cinnamaldehyde were the most potent contact toxicants against T. pisana. Their LD50 values were 0.18 and 0.29 mg · snail−1 after 24 h of treatment, respectively. These two compounds were more toxic than a reference molluscicide, methomyl. In contrast, α-terpinene and (-)-citronellal were the least toxic compounds. In another experiment, the synergistic effect of piperonyl butoxide (PBO) on tested monoterpenes and phenylpropenes by topical application was examined. The results showed that the toxicity of the tested compounds was increased when mixed with PBO at a ratio [compound/PBO (1 : 2)] except for α-pinene and (-)-terpinen-4-ol in which the toxicity of binary mixtures was less than for single compounds. The synergistic effect of PBO improved with increased exposure time. The highest synergistic effect was observed with (-)-menthone and α-terpinene with synergistic ratios of 9.25 and 4.37, respectively. Monoterpenes and phenylpropenes and their mixtures with PBO described herein merit further studies as potential T. pisana control agents

Insecticidal properties of essential oils against <i>Tribolium castaneum</i> (Herbst) and their inhibitory effects on acetylcholinesterase and adenosine triphosphatases

<div><p>Essential oils from 20 Egyptian plants were obtained by using hydrodistillation. The chemical composition of the isolated oils was identified by gas chromatograph/mass spectrometer. Fumigant and contact toxicities of the essential oils were evaluated against the adults of <i>Tribolium castaneum</i>. In fumigation assays, the oil of <i>Origanum vulgare</i> (LC₅₀ = 9.97 mg/L air) displayed the highest toxicity towards the adults of <i>T. castaneum</i>. In contact assays, the oils of <i>Artemisia monosperma</i> (LC₅₀ = 0.07 mg/cm²) and <i>O. vulgare</i> (LC₅₀ = 0.07 mg/cm²) were the most potent toxicants against the adults of <i>T. castaneum</i>. Biochemical studies showed that the tested oils caused pronounced inhibition of acetylcholinesterase (AChE) and adenosine triphosphatases (ATPases) isolated from the larvae of <i>T. castaneum</i>. The oil <i>Cupressus macrocarpa</i> (IC₅₀ = 12.3 mg/L) was the most potent inhibitor of AChE, while the oil of <i>Calistemon viminals</i> (IC₅₀ = 4.4 mg/L) was the most potent inhibitor of ATPases.</p></div