Insecticidal effects of Thymus citriodorus L. (Lamiaceae) essential oil on two important stored product pests

Abstract

The aim of the present work was to evaluate the contact effect of essential oil of Thymus citriodorus L. (Lamiaceae) against adults of two important stored product pests, Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae) and Sitophilus granarius (Linnaeus, 1758) (Coleoptera: Dryophthoridae) under laboratory conditions. In the evaluation of contact toxicity, 2.5, 5, 10 and 15% (v/v) doses of plant essential oil were applied to test insects using a microapplicator (1µl/adult). Pure acetone (1 µl/adult) was used as negative control and K-Obiol® EC 25 (Bayer AG, Germany) containing 25 g/l deltamethrin and 250 g/l piperonyl butoxide was used as positive control at the dose recommended on the label. Mortality was recorded at 24, 48, 72 and 96 hours after aplications. As a consequence of the investigation, the essential oil demonstrated contact activity at varied rates depending on the insects and doses. In general, the effect of T. citriodorus essential oil against adults of T. casteneum was low and the highest effect was 14.49% at 15% (v/v) dose at the end of 24 hours. The effect of the same dose at the end of 96 hours could only reach 15.32%. S. granarius adults were more sensitive to T. citriodorus essential oil. Doses of 10% (v/v)  and 15% (v/v)  of the essential oil caused over 95% mortality of S. granarius adults after 48 hours. The study's findings indicate that T. citriodorus essential oil has the potential to be used in the management of S. granarius.