Abstract
Tenebrio molitor is one of the main stored product pests. This study characterized oregano essential oil (OEO) by gas chromatography (GC/FID and GC/MS) and assessed its insecticidal properties against T. molitor. Mortality, survival, respiration, and behavioral response in larva, pupa, and adult of this insect were determined. The major components of OEO were carvacrol (25.6%), p-cymene (12.3%), linalool (8.71%), thymol (7.22%), γ-terpinene (7.21%), caryophyllene oxide (4.67%), α-pinene (2.71%), and eucalyptol (2.69%). OEO caused high contact toxicity in larvae (LD50 = 3.03 µg insect–1), pupae (LD50 = 5.01 µg insect–1), and adults (LD50 = 5.12 µg insect−1) of T. molitor. Survival rates were 100% in larvae, pupae, and adults of T. molitor not treated with OEO, declining to 65–54%, 38–44%, 30–23%, and 6–2% in insects treated with LD25, LD50, LD75, and LD90, respectively. Low respiration rates of T. molitor at different developmental stages was observed after OEO exposure. Additionally, OEO exposure affects behavioral avoidance response and causes repellency in larvae and adults. These findings show that OEO exerts insecticidal and repellent effects against T. molitor, suggesting a potent alternative to synthetic insecticides for controlling the beetle.
Highlights
The yellow mealworm beetle, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) is one of the main stored product pests of grains, flour, bran, and pasta worldwide
oregano essential oil (OEO) exposure affects behavioral avoidance response and causes repellency in larvae and adults. These findings show that OEO exerts insecticidal and repellent effects against T. molitor, suggesting a potent alternative to synthetic insecticides for controlling the beetle
A total of 25 components were identified in OEO, accounting for 95.79% of the total composition: carvacrol (25.28 ± 0.34%), p-cymene (11.9 ± 0.33%), linalool (8.71 ± 0.66%), thymol (7.23 ± 0.22%), γ-terpinene (6.88 ± 0.38%), caryophyllene oxide (4.67 ± 0.08%), α-pinene (2.71 ± 0.02%), eucalyptol (2.66 ± 0.27%), camphene (1.96 ± 0.01%), α-phellandrene (1.87 ± 0.02%), β-pinene (1.71 ± 0.02%), thymol methyl ether (1.68 ± 0.18%), camphor (1.67 ± 0.09%), β-bisabolene (1.64 ± 0.08%), carvacrol methyl ether (1.64 ± 0.01%), terpinen4-ol (1.56 ± 0.26%), borneol (1.46 ± 0.07%), α-thujene (1.42 ± 0.02%), terpinolene (1.37 ± 0.15%), aromandrene (1.35 ± 0.02%), cis-sabinene hydrate (1.35 ± 0.11%), α-terpineol (1.34 ± 0.19%), α-terpinene (1.23 ± 0.01%), cuminaldehyde (1.23 ± 0.01%), and β-myrcene (1.16 ± 0.02%) (Figure 1; Table 1)
Summary
The yellow mealworm beetle, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) is one of the main stored product pests of grains, flour, bran, and pasta worldwide. Some methods to control T. molitor include temperature treatment [4], sun treatment [5], controlled atmosphere [6], and fumigation of chemical insecticides [7]. Negative consequences such as development of insecticide resistance [8], environmental pollution [9], and residual toxicity [7] have limited the application of chemical control. The search for new strategies to pest control can be implemented to protection of stored products, considering the harmful effects of synthetic insecticides. Plant essential oils (EOs) are proposed for pest control in stored grains and display several insecticidal activities [10]. EOs can be applied on insects by contact (through the integumentary system) [14], inhalation (through the respiration system) [21], and orally (through the digestive system) [22]
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