Effectiveness of monoterpenes and phenylpropenes on Sitophilus oryzae L. (Coleoptera: Curculionidae) in stored wheat

Six monoterpenes, ((−)-citronellal, p-cymene, (−)-menthone, α-pinene, α-terpinene and (−)-terpinen-4-ol) and two phenylpropenes, (trans-cinnamaldehyde and eugenol) were tested for their insecticidal activity against the rice weevil, Sitophilus oryzae under laboratory conditions. The bioassays were carried out on wheat at the concentrations of 0.5, 1.0 and 5.0 g/kg. Adult mortality was assessed after 14 days of exposure. After this interval, the treated wheat was retained for an additional period of 90 days, in order to evaluate progeny production and wheat loss. At the concentrations of 0.5 and 1.0 g/kg, trans-cinnamaldehyde and eugenol achieved highest adult mortality. At 5.0 g/kg, all compounds except for p-cymene and α-pinene caused complete (100%) adult mortality. Generally, trans-cinnamaldehyde was the most potent compound causing complete inhibition of progeny at the three concentrations. Similarly, no progeny were observed in the wheat treated with (−)-citronellal, eugenol, p-cymene, (−)-menthone, and (−)-terpinen-4-ol at 5.0 g/kg after 45 and 90 days. Similar trends were noted for wheat weight loss and damage as the treatment with monoterpenes and phenylpropenes at the highest rate preserved the wheat intact and free from damage by S. oryzae for 90 days. Our findings suggest the tested compounds except p-cymene and α-pinene could be recommended for use as part of an integrated pest management program for S. oryzae control in stored wheat. [Display omitted] •Four monoterpenes and two phenylpropenes were found to cause significant adult mortality of S. oryzae in stored wheat.•Highest adult mortality was observed with trans-cinnamaldehyde and eugenol.•No progeny were produced in wheat treated with trans-cinnamaldehyde after 90 days.•Monoterpenes and phenylpropenes treatments reduced wheat weight loss caused by S. oryzae.