Plant oils as potentiation agents of monoterpenes for protection of stored grains against damage by stored product beetle pests

Plant oils (coconut, sunflower, sesame and mustard) at 10 and 5 ml/kg were tested alone and in combination with 1,8 cineole, eugenol or camphor at 0.5, 1.0 and 5.0 mu l or mg/kg against Sitophilus granarius (L.), S. zeamais (Mots.), Tribolium castaneum (Herbst) and Prostephanus truncatus (Horn) in wheat and maize-treated grains stored for 3 h or 10, 30, 60 and 90 days. All treatments with either plant oils alone or in combination with each chemical caused significant mortality compared with untreated grain. Plant oils when used alone were less effective against the beetles than oils combined with either 1,8 cineole, eugenol or camphor. Mortality significantly decreased with the time after application except in treatments combining plant oils and chemicals, which achieved complete control of all beetles exposed after 90 days storage following application. Treatments with plant oils and each chemical either alone or in combination inhibited progeny production by S. granarius, S. zeamais and P. truncatus, irrespective of dosage used or of storage interval following application.