Abstract
The Dysdercus peruvianus Guérin-Méneville is commonly known as the cotton stainer bug. In this study, it was evaluated the insecticide activity and mode of action of the essential oil from leaves of Ocotea elegans Mez and its nanoemulsion against D. peruvianus. Leaves of O. elegans were extracted by hydrodistillation. The essential oil obtained was analyzed by gas chromatography coupled with electron impact mass spectrometry and flame ionization detector. The essential oil toxicity measured by lethal dose 50 (LD50) and survival rate of insects were recorded. Lastly, an assay was carried out to assess the inhibition of the enzyme acetylcholinesterase to determine a possible mechanism of action of insecticidal activity. The sesquiterpene sesquirosefuran was the major compound detected and corresponds to 92% of the components of the essential oil. The nanoemulsion more stable showed hydrophilic lipophilic balance (HLB 11.74), droplet size 92±1.80 nm, and polydispersity index (PDI of 0.215±0.015). After the topical application of the O. elegans essential oil, significant decreases in the survival of D. peruvianus occurred in a dose-response manner with LD50 = 162.18 μg and the survival rate of the nanoemulsion in D. peruvianus was 10.0±5.47, a better value than in pure essential oil. The acetylcholinesterase inhibition presented inhibition concentration (IC50 = 1.37mg/mL) and mixed type of inhibition. This indicates that the essential oil of leaves from O. elegans and its nanoemulsion are promising candidates for use in integrated pest management programs.
Highlights
The cotton crop (Gossypium spp.) is one monoculture of great economic and social importance
Datura stramonium L., Eucalyptus camaldulensis Dehnh., Moringa oleifera Lam. and Nigella sativa L. were tested against T. castaneum, Trogoderma granarum Everts (1899) (Coleoptera:Dermestidae) and Cryptolestes ferrugineus Stephens (1831) (Coleoptera: Laemophloeidae) (Saleem et al, 2014), and essential oil of Orange activity was analyzed against T. castaneum (Kim & Lee 2014)
The IC50 (1.37 mg/mL) values obtained for the essential oil from O. elegans indicate a smaller inhibition than the essential oil from leaves (IC50 of 681 μg/mL) or flowers (IC50 of 1583 μg/mL) of Myrciaria floribunda (Tietbohl et al, 2014) and (IC50 of 1798 μg/mL) from leaves of Eugenia pruniformes, which were collected in the same locality (Albuquerque et al, 2012)
Summary
The cotton crop (Gossypium spp.) is one monoculture of great economic and social importance. In Gossypium spp., the latter pest provokes abnormal development of fruits, falling of new apples, the defective opening of buds, and staining of the fibers caused by insect excrement, reducing crop production by loss of weight, seed quality and oil content (Liu et al, 2014, Schaefer, 2015). To avoid such economic damage, control methods using chemical pesticides are usually employed, but these have high environmental toxicity due to the non-biodegradable properties (Jemâa, 2014). The present study, evaluates the effects of O. elegans essential oil and its nanoemulsion on D. peruvianus and analyzes its chemical composition and efficacy as an insecticide nanoemulsion
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