Insecticidal properties and grain protective efficacy of essential oils against stored product insects

Essential oils of three plants, namely Haplophyllum tuberculatum , Psidium guajava and Pinus roxburghii were obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC/MS). Contact toxicity assay was used to evaluate the insecticidal potential of isolated essential oils against three stored product insets, Sitophilus oryzae , Tribolium castaneum and Trogoderma granarium . The efficacy of the oils for controlling S. oryzae in stored wheat at three application rates (0.5, 1.0 and 5.0 g/kg grain) was also evaluated. GC/MS analyses confirmed the main compounds to be cis -sabinene hydrate (27.21%) in H. tuberculatum , d-limonene (30.73%) in P. guajava , and α-pinene (39.16%) in P. roxburghii . The oil of H. tuberculatum revealed the highest contact toxicity against the adults of T. castaneum , T. granarium and S. oryzae displaying LC 50 values of 0.13, 0.048 and 0.11 mg/cm 2 , respectively. Likewise, the oil of H. tuberculatum showed higher toxicity to T. granarium larvae than P. guajava and P. roxburghii oils. In grain protectant assay, the three oils induced complete adult mortality of S. oryzae after 7 days of exposure to treated wheat with 5.0 g/kg. Furthermore, the oils induced significant progeny decrease of S. oryzae after 45 and 90 days of treatment with complete suppression (100%) of progeny at 5.0 g/kg. The essential oils also prevent wheat damage for 90 days. According to the results described here, the three essential oils may be developed as a biorational tool to protect the stored products against insects.