Bioactivity of Wild Hop Extracts against the Granary Weevil, Sitophilus granarius (L.)

The use of bioinsecticides, rather than synthetic compounds, appears a goal to be pursued in pest control, especially for species such as Sitophilus granarius (L.) which attack stored products. Since Humulus lupulus (L.) is a remarkable source of bioactive compounds, this study investigated the bioactivity of hop flower extracts against S. granarius adults by evaluating toxic (contact, inhalation, and ingestion), repellent, antifeedant, and nutritional effects as well as their anticholinesterase activity and olfactory sensitivity. Hop extracts were obtained by soaking dried and ground hop cones in solvents of decreasing polarity: methanol, acetone, and n-hexane. Dried crude extracts were resuspended in each solvent, and used in topical application, ingestion, and fumigation toxicity assays, as well as in contact and short-range repellency tests, in vitro anticholinesterase activity evaluation, and electroantennographic tests. No inhalation toxicity for the extracts was found. On the contrary, all extracts showed adult contact toxicity 24 h after treatment (LD50/LD90 16.17/33.20, 25.77/42.64, and 31.07/49.48 µg/adult for acetone, n-hexane, and methanol extracts, respectively); negligible variations for these values at 48 h were found. The anticholinesterase activity shown by all extracts suggested that the inhibition of this enzyme was one of the mechanisms of action. Interestingly, flour disk bioassays revealed a significant ingestion toxicity for the acetone extract and a lower toxicity for the other two extracts. Moreover, all extracts affected insect nutritional parameters, at the highest dose checked. Filter paper and two-choice pitfall bioassays showed repellent activity and a strong reduction of insect orientation to a highly attractive food odor source, with minor differences among extracts, respectively. Finally, the presence of volatile compounds in the different extracts that are perceived by insect antennae was confirmed by electroantennography. All these findings strongly suggest a possible use of hop cone extracts against S. granarius, thus further confirming this plant as an interesting species for pest control.

Essential oil composition of Callistemon citrinus (Curtis) and its protective assessment towards Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Essential oil (EO) was extracted from Callistemon citrinus leaves by hydro-distillation. The extracted oil was analysed by GC and Mass Spectroscopy. Analysis report showed that the major constituent of the essential oil was eucalyptol (40.44%). The EO of C. citrinus exhibited 100% fumigation toxicity (adult mortality) against adult and 95.8% larvicidal activity against Tribolium castaneum at 160 μL/L (12 hrs) and 320 μL/L (48 hrs), respectively. The effective concentration of 37.05 μL/L (adult) and 144.31 μL/L (larva) at 24 and 48 hrs respectively. A 100% repellent activity was observed at 20 μl for adult beetles and 93.3% for larvae of T. castaneum at 20 μl after 24 h. Exposure to C. citrinus EO significantly reduced beetle fecundity, ovicidal activity, egg hatching, larvae survival, and emergence of adult. The effect of EO on detoxification enzymes of T. castaneum adults was examined. Results indicated that the activity of detoxification enzymes drastically varied when compared with control. This EO had toxicant effects on all stages of the life of T. castaneum. Hence it may be used as fumigant instead of the use of using synthetic chemical fumigants.

Insecticidal and Enzyme Inhibitory Activities of Isothiocyanates against Red Imported Fire Ants, Solenopsis invicta

Contact and fumigation toxicity of four isothiocyanates (ITCs), including allyl isothiocyanate (AITC), 3-butenyl isothiocyanate (3BITC), 3-(methylthio) propyl isothiocyanate (3MPITC) and 2-phenylethyl isothiocyanate (2PEITC), were evaluated against the red imported fire ant worker, Solenopsis invicta Buren. 2PEITC and 3MPITC exhibited strong contact toxicity. The median lethal dose (LD50)value of AITC, 2PEITC and 3MPITC were 7.99, 2.36 and 2.09 µg/ant respectively. In addition, AITC and 3MPITC also showed strong fumigation toxicity but not 2PEITC. The median lethal concentration (LC50) values of AITC and 3MPITC were 32.49 and 57.6 µg/L, respectively. In contrast, 3BITC did not exhibit any contact and fumigation toxicity even at 100 μg/μL. Esterase (EST), glutathione S-transferase (GST) and acetylcholinesterase (AChE)-inhibiting activities were assessed for three ITCs in S. invicta workers. All three ITCs inhibited both EST and GST activities but not AChE. The in vitro half maximal inhibitory concentration (IC50)values of AITC, 2PEITC and 3MPITC for GST were 3.32, 0.61 and 0.66 µg/µL, respectively. These results suggested that naturally occurring ITCs might be potentially useful for developing fire ants control products.

Essential Oils Encapsulation into Nanoliposome and Novel Application of Nanoliposome as a Storage Pesticide

This study attempted to evaluate the physicochemical characteristics of essential oil nanoliposomes from three plants by two preparation methods including thin film sonication and heating. Also, the durability of fumigation toxicity of the essential oil nanoliposome and pure essential oil of Mentha pulegium against Tribolium castaneum Herbst adults were compared. The smallest mean size of the nanoliposome was prepared by the thin film sonication method (P<0.05). The encapsulation efficiency of the nanoliposome was higher than 96%. Nanoliposmes prepared by using two methods showed high stability during storage. The release profile of essential oils at the heating method showed that the essential oil diffusion from the nanoliposome was in the following order: Mentha pulegium > Ferula gummosa > Zattaria multiflora. These findings indicate that both preparation methods had the same effect on the formation of nanoliposomes, their characteristics, and their storage stability. The durability of fumigation toxicity of the nanoliposome M. pulegium essential oil had a significant effect on mortality of T. castaneum adults in comparison with pure essential oil of this plant. The result showed that nanoliposome encapsulation of M. pulegium essential oil significantly increased fumigation toxicity against T. castaneum. Therefore, essential oil encapsulation into a nanoliposome carrier can potentially be used in pest management.

Phytochemical Profile and Bioactivity of Essential Oil from Pimenta Dioica Leaves on Cowpea Beetle, Callosobruchus Maculatus (F.) (Coleoptera: Bruchidae): A Farmer Friendly Solution for Postharvest Pest Management

Pimenta dioica (Allspice) leaf essential oil was isolated using hydro-distillation and insecticidal properties were evaluated for their ability to suppress post-harvest insect pest Callosobruchus maculatus in storage legumes and pulses. Four concentrations of leaf oil (0.5, 0.6, 0.8 and 1.0 v/v% ) were tested to evaluate their contact and fumigation repellency as well as insecticidal activities. Volatile organic compounds of leaf oil were analyzed by headspace solid-phase micro extraction coupled with gas chromatography and mass spectrometry (HS-SPME/GCMS) using polar and medium polar fibers. All concentrations elicited significantly higher repellent effects on insects after 2 hour exposure when compared with those of the control with the highest concentration producing 98.0% and 92.0% contact and fumigation repellency effects. Contact and fumigation toxicity tests exhibited 100% mortality for the highest concentration after 6 and 12 hour exposure respectively giving low LC50 values of 0.3 (v/v%). Volatile oil analysis indicated that the leaf essential oil comprised of high amount of Eugenol (89.8%), Methyl eugenol (2.3%) and caryophyllene (4.1%) for the polar fiber. Eugenol (42.6%), Caryophyllene (27.9%), Humulene (6.8%) and 1,8 Cineol (8.1%) were obtained for the medium polar fiber. Results indicate that the leaf essential oil of P.dioica would be a safe, eco-friendly alternative botanical insecticide in managing C.maculatus during storage.

Composição química e toxicidade do óleo essencial de eucalipto sobre o ácaro-rajado

The spotted spider mite, Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) is a polyphagous pest which causes extensive damage to Brazilian agriculture. The control of this pest is usually performed by synthetic origin products. Thus, the essential oils with acaricide property can be resources considered as an alternative to control this pest. The objective of this study was to identify the chemical composition and evaluate the fumigation toxicity of Eucalyptus citriodora (Hook.) KD Hill & LAS Johnson essential oil on T. urticae. The essential oil extraction was performed by hydrodistillation, usinga Clevenger type apparatus . The compounds identification was made comparing the obtained mass spectra with the available spectra in the database of the spectral library Willey 330,000 and by the Kovats index (IK), calculated for each compound. Adult female spotted spider mite were subjected to doses of 3.57, 7.14, 10.71, 14.28 and 17.85 μL L-1 of the essential oil air in fumigation chambers during 24, 48 and 72 hours. Subsequently, lethal concentration (LC50) of the essential oil was estimated. Ten compounds were identified, being the citronellal (68.20%) the major compound. The LC50 value observed after 24, 48 and 72 hours of exposure to essential oil were 17.55, 17.00 and 10.50 μL L-1 of air, respectively, and the fecundity of T. urticae females reduced with an increase of the used concentrations.

FUMIGATION TOXICITY OF ESSENTIAL OILS AGAINST Rhyzopertha dominica (F.) IN STORED MAIZE GRAIN

ABSTRACT: The Rhyzopertha dominica F. (Coleoptera: Bostrichidae) is a primary pest of stored grains in many regions of the world. In this work we evaluated the fumigant activity of essential oils of Ocimum basilicum L., Citrus aurantium L., Mentha spicata L. and Croton pulegiodorus Baill on adult R. dominica in stored maize. Tests were conducted to determine lethals concentrations (CL50 and CL100) and mortality (fumigation).The fumigation test was done in containers made of glass containing 10 individuals of R. dominica, where essential oils were applied at different concentrations: O. basilicum and M. spicata (5, 10, 15, 20, 30 and 40µL/L of air), C. aurantium (10, 20, 30, 40, 50 and 60µL/L of air) and C. pulegiodorus (0, 20, 30, 50, 70 and 90µL/L of air). After 48 hours of exposure to the oils the percentage of insect mortality was evaluated. According to LC50 and LC100 the toxicity of essential oils decreased in the following order: O. basilicum> M. spicata> C. pulegiodorus> C. aurantium. The essential oil of O. basilicum exhibited strong fumigant toxicity against R. dominica adults, with a LC50 value of 17.67 µL/L air and LC100 value of 27.15 µL/L air. The C. aurantium essential oil required higher concentrations than O. basilicum, M. spicata and C. pulegiodorus to kill insects. However, all oils evaluated presented fumigating property to promote the control of R. dominica and demonstrated potential use in the management of this coleoptera.

Fumigation Toxicity of Essential Oil Monoterpenes to Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae)

The fumigant toxicity of eight essential oil components, 1-8-cineole, carvacrol, eugenol, (−)-menthone, (−)-linalool, S-(−)-limonene, (−)-β-pinene, and (+)-α-pinene, was tested against the cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae), at 0.25–60 µL/L air doses. 1-8-Cineole, carvacrol, and eugenol caused complete adult mortality at 10 µL/L air 24 h after treatment. 1-8-Cineole and carvacrol were the most toxic with LD50 values of 0.24 and 0.6 µL/L air at 24 h, respectively. (−)-β-Pinene and (+)-α-pinene were the least toxic with LD50 values of 31 and 31.4 µL/L air at 24 h, respectively. Toxicity was negatively correlated with vapor pressure. 1-8-Cineole and carvacrol caused 100% oviposition deterrence at all doses tested. Eugenol and (−)-menthone completely inhibited adult emergence. S-(−)-Limonene, (−)-β-pinene, and (+)-α-pinene were not effective at preventing oviposition or adult emergence, suggesting that a lethal dose of the three oil components would be necessary to control C. maculatus infestations.