Contact application of Lamiaceae botanicals reduces bean weevil infestation in stored beans

Abstract

The bean weevil (Acanthoscelides obtectus, Say) is a serious pest of stored bean seeds. Bean weevil control relies heavily on the use of synthetic insecticides. In the search for a sustainable alternative, the residual contact toxicity and anti-oviposition activity of thyme (Thymus vulgaris L.), rosemary (Rosmarinus officinalis L.) and basil (Ocimum basilicum L.) essential oils as well as their dominant components (thymol, α-pinene, 1,8-cineole and linalool) were tested against A. obtectus adults. Out of the seven tested botanicals, T. vulgaris oil, thymol and linalool exhibited the highest toxic potential (>90% mortality). Females were less susceptible than males. The insecticidal activity of these botanicals was much greater when they were applied on glass compared to direct application to the bean. All tested botanicals reduced oviposition by bean weevil females. T. vulgaris oil, thymol and α-pinene also deterred bean weevil oviposition, as revealed by a two-choice test. Our research shows that T. vulgaris oil and thymol are promising and sustainable alternatives to synthetic pesticides for protecting stored beans against the bean weevil.

Toxic, Oviposition Deterrent and Oxidative Stress Effects of Thymus vulgaris Essential Oil against Acanthoscelides obtectus

“…Insecticidal efficacy of thyme EO was similar to the effects of some commercial botanical insecticides [94], but lower compared to conventional insecticides [95]. The main compounds of the thyme oil are oxygenated monoterpens thymol, carvacrol, and linalool, and non-oxygenated monoterpene p-cymene [71]. They are known for strong fumigant toxicity against A. obtectus and adult longevity reduction [70].…”

“…They are known for strong fumigant toxicity against A. obtectus and adult longevity reduction [70]. Additionally, contact application of thymol and linalool on glass [71] and essential oils of Clausena anisata (Willd.) J.D.…”

“…Many studies on storage and other pest insects recorded significant influence of thyme EO on pest survival and behavior [ 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ]. Lamiaceae EOs applied as fumigants have been extensively tested for the activity against A. obtectus [ 61 , 62 , 91 , 92 , 93 ] and several recent studies dealt with the effects of their application on bean seeds [ 63 , 67 , 71 ]. Here we evaluated efficacy of thymol chemotype of the thyme oil as residual contact insecticide and oviposition deterrent against A. obtectus .…”

“…We have previously shown that contact application of thyme EO might protect bean seeds as well. Namely, screening for contact toxicity and antioviposition activity against A. obtectus revealed that thyme EO was more efficient than other tested Lamiaceae EOs (basil and rosemary EO) [71]. Here we determined effective concentrations which halved adult survival and adult emergence, and concentration which led to three-fold lower oviposition on treated than on control bean seeds in a two-choice test.…”

“…Thyme oil was purchased from Sigma-Aldrich (St. Louis, MO, USA, #W306509) and its chemical composition was determined previously [71]. The major components of oil were thymol (43.52%), p-cymene (31.65%), linalool (5.38%) and carvacrol (5.11%).…”