Plant oil mixtures as a novel botanical pesticide to control gregarious locusts

Abstract

Abstract For thousands of years, large locust swarms have caused severe problems in agriculture. People fight against current outbreaks by using chemical pesticides or an insect fungus known as Green Muscle™. While chemical pesticides may be harmful for humans and non-target species, the sporulation of the fungus takes a long period of time and requires conditions of high humidity that are not always found in the field. In this study, we tested the toxicity of a linseed oil/bicarbonate emulsion against gregarious desert locusts and screened for plant essential oils that enhance its toxicity. Finally, we combined three essential oils to develop a novel formulation that is effective against the desert and migratory locust species after single spray treatment. Within 24 h, this formulation caused a mean mortality rate of 80% and 100% of desert and migratory locusts, respectively. Its toxicity is based on a synergistic effect resulting from the combination of caraway, orange peel and wintergreen oils. In addition, we tested this botanical pesticide on two beetle species regarded either as alternative or beneficial non-target species. The first species, mealworm beetles, did not suffer from the spray treatment and behaved normally after 8 days. In contrast, 67.7% of ladybird adults died in the same time span. Interestingly, the growth of wheat seedlings was almost unaffected by spraying this botanical pesticide. These results suggest this botanical pesticide can be used as a strong agent against desert and migratory locusts, but needs to be used with care to minimize unwanted side effects on the ecosystem.