The synergistic effects of Carum copticum essential oil on diatomaceous earth against Sitophilus granarius and Tribolium confusum

• The toxicity of Carum copticum essential oil decreased in wheat commodity.
• Combination of essential oil with diatomaceous earth (DE) seems to be synergistic.
• The essential oil significantly increased insect's locomotion.
• Insect's hyperactivity increased their contact with DEs and cause higher mortality.
• Essential oil and DEs have binary activity which complements their effects.

In this study, synergistic/antagonistic interaction between Carum copticum (L.) powder and essential oil with diatomaceous earths (DEs) was assessed against Tribolium confusum Jacquelin du Val. and Sitophilus granarius (L.) adults. The obtained synergistic interaction was interpreted by measurement of insects' locomotor activity when exposed to C. copticum essential oil. Essential oil had strong fumigant toxicity against adult insects; however, toxicity diminished in the presence of wheat commodity. Plant essential oil synergized the performance of DE samples such that they generally became more insecticidal than DE alone. However, plant powder effects were antagonistic; effects were not as severe as predicted in terms of the insect mortality. Insects' locomotor activity increased significantly when exposed to C. copticum essential oil. These results support the hypothesis that essential oil can enhance the efficacy of DE, at least by increasing locomotor activity and insect-contact toxicity of DE particles. Therefore, combination of essential oil with DE could have potential for use in integrated stored-product pest-management programs.

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