Evaluation of larvicidal enhanced activity of sandalwood oil via nano-emulsion against Culex pipiens and Ades aegypti

Mosquito control with essential oils is a trending strategy using aqueous oil nano-emulsions to expand their performance. Sandalwood essential oil and its prepared nano-emulsion used to estimate their larvicidal activities against the 3rd instar larvae of Culex pipiens and Aedes aegypti and their effects on larval tissue detoxifying enzymes. Sandalwood nano-emulsion was characterized by homogeneous, stable, average particles size (195.7 nm), polydispersity index (0.342), and zeta potential (?20.1 mV). Morphologically showed a regular spherical shape in size ranged from 112 to 169 nm that confirmed via scanning electron microscopy. Oil analysis identified sesquiterpene alcohols, mainly santalols, terpenoids, aromatic compounds, fatty acid methyl esters, and phenolic compounds. Larvicidal activities of the oil and its nano-emulsion indicated dose, formulation, and exposure time-related mortality after 24 and 48 h in both species. After 24 h, 100% mortality was detected at 1000 ppm for the nano-emulsion with LC₅₀ of 187.23 and 232.18 ppm and at 1500 ppm for the essential oil with an LC₅₀ of 299.47 and 349.59 ppm against the 3rd larvae Cx. pipiens and Ae. aegypti, respectively. Meanwhile, an enhanced significant effect of the nano-emulsion was observed compared to oil exposure in decreasing total protein content and the activities of alkaline phosphatase and β-esterase enzymes, and increasing α-esterase and glutathione S-transferase activities in larval body tissues. Results demonstrated the enhanced larvicidal potential of sandalwood oil nano-emulsion over that of oil. The effect involved alterations in the detoxifying enzymes based on the existing natural active ingredients against Cx. pipiens and Ae. aegypti larvae.     

四种植物精油对黑翅土白蚁触杀和驱避作用

为筛选出高效防治黑翅土白蚁的天然植物精油,减少有机合成农药的使用,该文研究了大蒜精油、肉桂油、丁香油和印楝素油四种植物精油对黑翅土白蚁的触杀效果和驱避作用。结果表明:大蒜精油、肉桂油和丁香油的浓度为5和10 mg·m L~(-1)时,处理2 h后,黑翅土白蚁的校正死亡率达100%,而相同浓度的印楝素油和对照处理的黑翅土白蚁校正死亡率低于5%。随着处理时间延长,浓度为1.25和2.5 mg·m L~(-1)的大蒜精油、肉桂油和丁香油处理6 h时,黑翅土白蚁的校正死亡率仍达100%,而此时对应的印楝素油和对照处理的黑翅土白蚁校正死亡率仅为10%,说明大蒜精油、肉桂油和丁香油对黑翅土白蚁具有较强的触杀效果。大蒜精油、丁香油和肉桂油在处理黑翅土白蚁2 h后LC_(50)值(半致死量)分别为1.572、1.05和1.03mg·m L~(-1),说明肉桂油对黑翅土白蚁的毒性相对最大,触杀效果最好。此外,10 mg·m L~(-1)的大蒜精油、肉桂油、丁香油和印楝素油的驱避试验表明,处理4、6、8和12 h后,大蒜精油、肉桂油和丁香油三精油处理区的黑翅土白蚁数均显著低于对照区的,驱避率总体93%,而对应的印楝素油的驱避率总体28.5%,表明大蒜精油、丁香油和肉桂油三种植物精油对黑翅土白蚁均有显著的驱避活性。综上可知,四种植物精油中大蒜精油、肉桂油和丁香油在防治黑翅土白蚁方面应用潜力很好,是开发绿色环保白蚁防治药剂的可选材料。     

Larvicidal effects of some essential oils against Aedes aegypti (L.), the vector of dengue fever in Saudi Arabia

Essential oils are very popular among organic growers because they are ecologically safe, do not have mammalian toxicity, and cannot be resistant to a variety of contaminants. Four essential oils, Lemon, Lavender, Peppermint, and Neem, were tested for larvicide efficacy against the dengue fever vector Aedes aegypti larvae under laboratory conditions using dipping bioassay techniques. Among the essential oils tested, lemon, peppermint, and lavender oils showed high larvicidal activity against larvae of Ae. aegypti. Lemon oil showed the highest effects (LC₅₀ 10.676 ppm), while Peppermint, Lavender and Neem oil showed the lowest effects (LC₅₀ 21.380, 29.818 and 38.058 ppm, respectively). As a result, the mixture of lemon oil (LC₅₀) with Peppermint oil (LC₂₅) showed the highest co-toxicity factor, whereas the mixture of Lemon oil (LC₅₀) with Diesel oil (LC₂₅) showed the lowest co-toxicity factor. Based on the results of this study, it appears that essential oils may be useful as larvicides against Ae. aegypti larvae. In search of new natural larvicides, these compounds may provide an alternative to Synthetic insecticides as these are environmentally safe insecticides.     

Insecticidal and feeding deterrent activities of essential oils in the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae)

Ten essential oils were tested against the cabbage looper, Trichoplusia ni larvae for contact, residual and fumigant toxicities and feeding deterrent effects. Against third instar T. ni, Syzygium aromaticum (LD₅₀ = 47.8 μg/larva), Thymus vulgaris (LD₅₀ = 52.0 μg/larva) (the two positive controls) and Cinnamomum glanduliferum (LD₅₀ = 76.0 μg/larva) were the most toxic via topical application. Litsea pungens (LD₅₀ = 87.1 μg/larva), Ilex purpurea (LD₅₀ = 94.0 μg/larva), Cinnamomum cassia (LD₅₀ = 101.5 μg/larva) and Litsea cubeba (LD₅₀ = 112.4 μg/larva) oils were equitoxic. Thymus vulgaris (LC₅₀ = 4.8 mg/ml) and S. aromaticum (LC₅₀ = 6.0 mg/ml) oils were the most toxic in residual bioassays. Cymbopogon citratus (LC₅₀ = 7.7 mg/ml) and C. cassia (LC₅₀ = 8.5 mg/ml) oils were equitoxic followed by Cymbopogon nardus (LC₅₀ = 10.1 mg/ml) in this bioassay. The remaining five oils showed little or no residual effects. In a fumigation bioassay, L. cubeba (LC₅₀ = 16.5 μl/l) and I. purpurea (LC₅₀ = 22.2 μl/l) oils were the most toxic. Cinnamomum glanduliferum (LC₅₀ = 29.7 μl/l) and Sabina vulgaris (LC₅₀ = 31.2 μl/l) oils were equitoxic. Interestingly, S. aromaticum did not exhibit any fumigant toxicity. Cymbopogon citratus, C. nardus and C. cassia strongly deterred feeding by third instar T. ni (DC₅₀s = 26.9, 33.8 and 39.6 μg/cm², respectively) in a leaf disc choice bioassay. The different responses of T. ni larvae to the oils in different bioassays suggest that these essential oils exhibit different modes of action. Based on their comparable efficacy with essential oils already used as active ingredients in many commercial insecticides (i.e. clove oil and thyme oil), some of these essential oils may have potential as botanical insecticides against T. ni.     

Sublethal effects of essential oil of Cinnamomum zeylanicum Blume on life expectancy (ex) and age-specific fertility (mx) of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae)

Two-spotted spider mite, Tetranychus urticae Koch, is one of the most important pests of agricultural products that have a global distribution. Now, the control is dependent on the use of chemical pesticides. The effects of the sublethal concentrations (LC₁₀ and LC₂₅) of the essential oil of Cinnamomum zeylanicum were evaluated on some parameters of the life table of the pest, at the constant temperature of 30?°C, relative humidity of 40?±?5% and photoperiod of 16L: 8D. Our results showed that the essential oil of cinnamon is effective on female adult stage. Lethal concentration at which 50% mortality (LC₅₀) for the essential oils is from C. zeylanicum on female adult mite was 23.39?μl/L air. Sublethal concentrations of the essential oil of C. zeylanicum also impair the natural biology of the mite. Concentrations of sublethal of essential oil decreased age-specific fertility (m_x) of T. urticae compared with the control. Sublethal concentrations (LC₁₀ and LC₂₅) have reduced the life expectancy (e_x) in egg stage. Sublethal effects of the essential oil of C. zeylanicum and its impact on T. urticae management are discussed.     

Fumigant toxicity of Lavandula spica essential oil and linalool on different life stages of Tribolium confusum (Coleoptera: Tenebrionidae)

The confused flour beetle, Tribolium confusum, is a common and severe pest of stored products. Here, using fumigation tests during four different exposure times, we evaluated the toxicity of different doses of essential oil of spike lavender, Lavandula spica and one of its major constituents, linalool, on different life stages of T. confusum under laboratory conditions. The toxicity of the L. spica oil and linalool varied as a function of the developmental stage and treatment duration. Young larvae (L1) were the most susceptible to toxic effects, with LC₅₀ = 19.535 μl/L of air for L. spica oil and LC₅₀ = 14.198 μl/L of air for linalool after 24 h of exposure, whereas older larvae (L8) were affected only very little by fumigation. Linalool caused higher egg mortality than L. spica oil at equivalent doses, but lower mortality in pupae and adults. Emergence of intact adult insects from surviving eggs, larvae and pupae was further reduced as a function of dose and exposure time to both L. spica oil and linalool compared to control-treated insects. Our results show that L. spica oil and linalool might be suitable for biological control of T. confusum, but tests at a larger scale are necessary to confirm our results.     

Fumigant toxicity of Laurus nobilis and Myrtus communis essential oils on larvae and adults of the Red flour beetle,Tribolium castaneum Herbst (Col.: Tenebrionidae)

Considering the invasion to food commodities by insects and harmful effect of chemical pesticides, essential oils are among the best known substances tested against stored product pests. These compounds may act as fumigants, contact insecticides, repellents or anti-feedants. In present study, fumigant toxicity of essential oils from Laurus nobilis L. and Myrtus communis L. was assessed on larvae and adults of Tribolium castaneum Herbst at 27?±?2?°C, 60?±?5% RH in darkness. Each essential oil was tested in five concentrations with three replicates. The LC₅₀ values of L. nobilis and M. communis against adults of beetle were calculated 243.78 and 56.11?μl/l and LC₉₅ values for them were 685.85 and 144.01?μl/l, respectively. For the larvae of T. castaneum, the LC₅₀ values for L. nobilis and M. communis were 211.64 and 69.63 and LC₉₅ values were 656.84 and 183.65?μl/l, respectively. Results showed that these essential oils may have potential as botanical control agents against larvae and adults of T. castaneum.     

Larvicidal and adulticidal activity of essential oils from plants of the Lamiaceae family against the West Nile virus vector,Culex pipiens (Diptera: Culicidae)

Culex pipiens mosquitoes are the most widely distributed primary vector of the West Nile virus worldwide. Many attempts for investigation of botanical pesticides to avoid the development of pesticide resistance to conventional synthetic pesticides that are recognized as a threat to the diversity of ecosystems. The study aimed to determine the components of three essential oils of Lamiaceae family, lavender (Lavandula angustifolia), peppermint (Mentha piperita L.), and rosemary (Rosmarinus officinalis L.) by gas chromatography-mass spectrometry (GC–MS) analysis. Furthermore, aimed to validate the insecticidal activities of these oils as larvicidal agents against the third instar larvae of Culex pipiens using five different concentrations (62.5, 125, 250, 500, and 1000 ppm) for each oil in five replicates and as an adulticidal agent against approximately three-day-old female adults of Cx. Pipiens using 0.5, 1, 2, 4, and 5% concentrations in three replicates. The results generally showed a dose-related response. At 1000 ppm, rosemary oil showed the highest larvicidal (100%) (LC₅₀, 214.97 ppm), followed by peppermint oil (92.00% mortality and LC₅₀ (269.35 ppm). Lavender oil showed the lowest efficacy with 87.20% mortality and LC₅₀ (301.11 ppm). At 5% oil concentration, the highest knockdown rate at 1 h was recorded for lavender oil (95.55%), followed by peppermint oil (88.89%) and lastly rosemary oil (84.44%). After 24 h, rosemary oil showed the lowest adult mortality rate (88.89%; LC₅₀, 1.44%), while lavender and peppermint oils both showed a 100% mortality rate, with (LC₅₀, 0.81% and 0.91%, respectively). The chemical constituents of the oils consisted of monoterpenes and sesquiterpenes that determined their insecticidal activities against the target insect stage. The study proposed that rosemary essential oil may be useful for the control of Cx. pipiens larvae as part of an integrated water treatment strategy, and lavender and peppermint oils may be used in an integrated plan for adult’s control.     

Castor and camphor essential oils alter hemocyte populations and induce biochemical changes in larvae of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae)

Two plant essential oils; camphor and castor were tested for insecticidal and antifeedant activity against the 4th instar larvae of Spodoptera littoralis, a serious pest on cotton in Egypt. Also the impact of LC₁₀ of both oils on some physiological parameters in larvae was studied by using leaf dipping technique. Analysis of both oils using GC–MS revealed several insecticidal and antifeedant compounds. Our results showed higher insecticidal activity and antifeedant index of camphor oil against S. littoralis. The LC₅₀ and the antifeedant indices were 163.1, 246.8?mg/ml and 12.69, 6.62% for camphor and castor bean oil, respectively. The total hemocyte count (THC) and differential hemocyte count (DHC) were reduced significantly after 48?h of treatment compared to controls. Both oils reduced all types of hemocytes except plasmatocytes which were reduced only by castor oil. Camphor oil decreased total proteins and carbohydrates while castor oil targeted only carbohydrate content. Both oils didn't affect the amount of total lipids. Lipase, α-amylase and glucose-6-phosphate dehydrogenase (G6PD) enzyme activities were increased significantly in larvae treated with camphor oil than other treatments. These results clearly indicate that castor and camphor oils can affect the nutritional status in S. littoralis larvae, thereby changing the internal metabolic processes in the larvae which make them as potential control agents in IPM programs against S. littoralis.     

Toxicity of plant essential oils to different life stages of the poultry red mite,Dermanyssus gallinae,and non‐target invertebrates

Seven essential oils with potential as acaricides for use against the poultry red mite, Dermanyssus gallinae (De Geer) (Acari: Dermanyssidae), were selected for study. These products (essential oils of manuka, cade, pennyroyal, thyme, garlic, clove bud and cinnamon bark) were deployed against different life stages of D. gallinae in laboratory tests at the (lethal concentration) LC₅₀ level for adult mites. For all essential oils tested, toxicity to D. gallinae juveniles was as high as toxicity to adults, if not higher. However, at the LC₅₀ level determined for adults, some oils were ineffective in preventing hatching of D. gallinae eggs. The essential oils were also tested under laboratory conditions at their LC₉₀ levels for D. gallinae adults on two model non‐target species, the brine shrimp, Artemia salina (L.), and the mealworm beetle, Tenebrio molitor (L.). Results showed that not all essential oils were as toxic to A. salina and T. molitor as they were to D. gallinae, suggesting that it may be possible to select certain oils for development as acaricides against D. gallinae that would have minimal impact on non‐target organisms. However, the level of toxicity to A. salina and T. molitor was not consistent across the selected essential oils.     

Effect of Mentha piperita and Cuminum cyminum essential oil on Tribolium castaneum and Sitophilus oryzae

Essential oils are one of the known plant materials for insect pest control. The studies about essential oils application for control of insect pest population has been started in recent years. This study aims to investigate repellency effect and fumigant toxicity of Mentha piperita and Cuminum cyminum essential oil on Tribolium castaneum and Sitophilus oryzae. The results showed that the mortality rate of adult insects was increased with increase in essential oil concentration. The highest pest mortality rate in the case of M. piperita and C. cyminum on T. castaneum and S. oryzae was 64, 68, 82 and 78%, respectively. The average insect mortality was significantly different in various concentrations in most of the treatments. Amounts of LC₅₀ were 0.421, 0.271, 0.135 and 0.136 (ml/ml) for M. piperita and C. cyminum essential oil on T. castaneum and S. oryzae, respectively. Different concentrations of M. piperita and C. cyminum essential oil had different repellency effect on T. castaneum and S. oryzae. Repellency effect was increased with increase in essential oil concentration, and the highest repellency effect was belonged to the highest concentration. Essential oils of M. piperita and C. cyminum caused 61.2 and 66.4% repellency on T. castaneum. Meanwhile, their effect was found to be 55.2 and 60.4% repellency on S. oryzae at the highest concentration.     

Toxicity of basil and orange essential oils and their components against two coleopteran stored products insect pests

Two commercialized essential oils and their constituent compounds were investigated for fumigant and contact activities against two grain storage insects, adults of the maize weevil (Sitophilus zeamais) and the red flour beetle (Tribolium castaneum). The two commercialized basil and orange oils showed strong fumigant and contact activities against S. zeamais and T. castaneum. The constituents of the basil oil were linalool (21.83%), estragole (74.29%), and α-humulene (2.17%), and those of the orange oil were α-pinene (0.54%), sabinene (0.38%), β-myrcene (1.98%), limonene (96.5%), and linalool (0.6%). As a toxic fumigant, the basil oil was more effective (24-h LC₅₀ = 0.014 and 0.020 mg cm^− 3) than the orange oil (24-h LC₅₀ = 0.106 and 0.130 mg cm^− 3) against S. zeamais and T. castaneum adults, respectively. Among the constituents of the two essential oils, the toxicity of estragole was the highest (0.004 and 0.013), followed by linalool (0.016 and 0.023), limonene (0.122 and 0.171), α-pinene (0.264 and 0.273), and β-myrcene (0.274 and 0.275) based on 24-h LC₅₀ values (mg cm^− 3). Similar results were obtained in a contact toxicity test. The contact activity of basil oil was more toxic than orange oil, and estragole and linalool showed pronounced contact toxicity against S. zeamais and T. castaneum adults. Alpha-humulene had no activity as a fumigant at the tested doses, but it did have an effect as a contact poison, having 24-h LD₅₀ values of 0.040 and 0.045 mg adult^− 1 to S. zeamais and T. castaneum, respectively. Although basil oil, orange oil, and their components displayed both contact and fumigant toxicities, their effects were mainly exerted by fumigant action via the vapor phase. Thus, basil oil, orange oil, and their components could be potential candidates as new fumigants for the control of S. zeamais and T. castaneum adults.     

Chemical composition and larvicidal activity of essential oils from Piper species

The larvicidal activity of essential oils of four species of Piper from the Amazon Forest was tested using third-instar larvae of Aedes aegypti. The oils were extracted by steam distillation and analyzed by GC and GC–MS. The main components isolated from each Piper species were as follows: viridiflorol (27.50%), aromadendrene (15.55%) and β-selinene (10.50%) from Piper gaudichaudianum; β-selinene (15.77%) and caryophyllene oxide (16.63%) from Piper humaytanum; dillapiol (54.70%) and myristicin (25.61%) from Piper permucronatum; and asaricin (27.37%) and myristicin (20.26%) from Piper hostmanianum. Amongst all essential oils tested, the most active against larvae of A. aegypti was the oil extracted from P. permucronatum, with a LC₅₀ = 36 μg/ml (LC₉₀ = 47 μg/ml), followed by the essential oil of P. hostmanianum, with a LC₅₀ = 54 μg/ml (LC₉₀ = 72 μg/ml). The oils with higher content of arylpropanoids were more active against larvae of A. aegypti.     

Chemical composition and larvicidal activity of Piper capense essential oil against the malaria vector,Anopheles gambiae

Hydro-distilled essential oil from Kenyan Piper capense (Piperaceae) was analysed by gas chromatography mass spectrometry (GC–MS) and evaluated for larvicidal activity against the malaria vector, Anopheles gambiae. The oil consisted mainly of sesquiterpene hydrocarbons which accounted for 43.9% of the oil. The major sesquiterpenes were δ-cadinene (16.82%), β-bisabolene (5.65%), and bicyclogermacrene (3.30%). The oil also had appreciable amounts of monoterpene hydrocarbons (30.64%), including β-pinene (7.24%) and α-phellandrene (4.76%), and arylpropanoids (8.64%), including myristicin (4.26%). The oil showed larvicidal activity against third instar larvae of A. gambiae, with LC₅₀ and LC₉₀ values of 34.9 and 85.0 ppm, respectively. Most of the larvae died within the first few hours. The high larvicidal activity of this oil was indicated by the fact that over 80% mortality was observed at a concentration of 100 ppm after 24 h. These results compared favourably with the commercial larvicide pylarvex® which had LC₅₀ and LC₉₀ values of 3.7 and 7.8 ppm, respectively. Application of this oil or of products derived from it to larval habitats may lead to promising results in malaria and mosquito management programmes.     

Volatiles from Marina neglecta: Biocide effect on insect vectors of tropical diseases in Southern Mexico

Preventive measures based in the control of insect vectors are considered as the best choice to decrease the incidence of insect-borne diseases. Herein we report on the volatile content of the leaf essential oils from Marina neglecta, a medicinal plant distributed in the tropical regions of southern Mexico. In order to investigate the chemical variation of the essential oils, a volatile screening was performed during the four seasons of the years 2016–2019. Simultaneously, their biological activity was tested on distinct life stages of Meccus pallidipennis, M. bassolsae, Aedes aegypti and A. albopictus. Essential oils were mainly constituted of β-pinene (>30%) β-caryophyllene (>25%) and germacrene D (>13%). Dorsal-abdomen application of essential oils on triatomines, revealed an efficient LC₅₀ for nymphs of the stages I to III (4 µg/insect), nymphs of the stages IV to V (5–6 µg/insect), and adults (7–8 µg/insect). The LT₅₀ for the stages I to III was between 6 and 8 h, whereas that for the stages IV to V and adults oscillated between 12 and 16 h and 22 to 26 h, respectively. Fumigation experiments performed on nymph V, demonstrated that 300 µg L^?1 air produced 100% mortality after 72 h post-treatment. Among tested volatiles, β-pinene and β-caryophyllene produced a comparable mortality rate (p < 0.01) than that of essential oils in the stages assayed. Essential oils showed strong larvicidal (LC₅₀, 24–36 µg mL^?1) and adulticidal (35–48 µg mL^?1) activities in mosquito species with an LT₅₀ of 4.5 h and 25–35 min, respectively. The evaluation of β-pinene produced a significant mortality rate (p < 0.01) in larvae whereas germacrene D was the most effective volatile (p < 0.01) against adults of both mosquito species. According to our results, β-pinene was the most effective volatile against the four insect species evaluated and its effect was comparable to that of the essential oil.     

Nematicidal Activity of Plant Essential Oils against Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae)

The nematicidal activity and poisoning symptoms of 88 plant essential oils against Bursaphelenchus xylophilus were examined by an immersion bioassay. Results were compared with those of three trunk-injection nematicides: fenitrithion, levamisol hydrochloride, and morantel tartrate. As judged by 24 h LC₅₀ values, cinnamon bark oil (0.12 mg/ml) was the most effective nematicide, followed by coriander herb oil (0.14 mg/ml). Potent nematicidal activity was also observed with lemongrass, oregano, thyme red, and clove bud oils (LC₅₀, 0.57-0.88 mg/ml). Fenitrothion was ineffective (LC₅₀, > 10 mg/ml). In typical poisoning symptoms in B. xylophilus, these essential oils exerted rapid nematicidal action and the nematodes killed usually showed an extended shape, whereas levamisole hydrochloride and morantel tartrate usually exhibited semicircular and coiling shapes, respectively. The essential oils described merit further study as botanical nematicides for the control of pine wilt disease caused by B. xylophilus.     

Toxicity,repellent and oviposition deterrent effects of select essential oils against the house fly Musca domestica

Essential oils from plants may provide environment-friendly alternatives to conventional synthetic insecticides. Here, toxic, repellent, and oviposition deterrent effects of essential oils of six plants: Allium sativum L. (Alliaceae), Azadirachta indica A. Juss. (Meliaceae), Cinnamomum cassia (L.) (Lauraceae), Eucalyptus camaldulensis Dehnh. (Myrtaceae), Piper nigrum L. (Piperaceae), and Thevetia peruviana (Pers.) (Apocynaceae), were evaluated against different life stages of Musca domestica. Bioassays revealed that the essential oils of A. indica, T. peruviana and E. camaldulensis exhibited: a) the highest toxicity on larvae (LC₅₀ = 169.72, 182.23 and 277.01 ppm, respectively), pupae (LC₅₀ = 150.56, 164.84 and 164.87 ppm, respectively) and adults (LC₅₀ = 166.69, 139.15 and 302.75 ppm, respectively) of M. domestica; b) the highest repellency (91.44, 72.19 and 72.80%, respectively) and oviposition deterrent (90.36, 88.82 and 89.13%, respectively) effects on adults of M. domestica, as compared to the other essential oils. Moreover, the speed of mortality caused by essential oils of A. indica (LT₅₀ = 16.85 and 17.06 h for larvae and adults, respectively) and T. peruviana (LT₅₀ = 16.46 and 18.58 h for larvae and adults, respectively) was faster than the rest of the essential oils. On the whole, it might be expected that the essential oils of A. indica, T. peruviana and E. camaldulensis could be developed into a new type of environment-friendly insecticides and/or repellents for the management of M. domestica.     

Piperonyl butoxide synergizes the larvicidal activity of Origanum vulgare essential oil and its major constituents against the larvae of Aedes albopictus and Culex pipiens quinquefasciatus

Mosquitoes bite human beings and transmit many diseases, such as malaria, dengue fever, and Zika virus. Vector control of mosquitoes is an effective strategy for reducing the spread of disease. However, extensive use of insecticides (e.g. pyrethroids and organophosphorus) has caused resistance in mosquitoes, which weakens the effectiveness of mosquito control. Phytochemicals have been considered an alternative approach to mosquito control. Essential oil (EO) was obtained from the leaves and flowers of Origanum vulgare, and its synergistic activity with piperonyl butoxide (PBO) was tested against Aedes albopictus and Culex pipiens quinquefasciatus larvae. Thirty-seven compounds were identified, among which carvacrol and thymol were two major constituents (30.73 % and 18.81 %, respectively). O. vulgare EO had a significant toxic effect against fourth-stage larvae of Cx. p. quinquefasciatus and Ae. albopictus, with LC₅₀ values of 17.51 and 75.90 mg/L. Carvacrol and thymol also each appeared to be more effective against Cx. p. quinquefasciatus (LC₅₀ = 19.30 and 11.56 mg/L, respectively) than Ae. albopictus (LC₅₀ = 26.62 and 26.66 mg/L, respectively). PBO interacted synergistically with O. vulgare EO, carvacrol and thymol with 2.60–6.26 times as much of the active compound needed without PBO as against Cx. p. quinquefasciatus and Ae. albopictus larvae. Overall, our results contribute to the development of new natural mosquito insecticides.     

Progeny of the maize weevil,Sitophilus zeamais,is affected by parental exposure to clove and cinnamon essential oils

The interest in and utilization of botanical insecticides, particularly essential oils, has become increasingly relevant to the control of insect pests. However, the potential ecotoxicological risks or flaws (including sublethal effects on the targeted pest generation and its subsequent progeny) of this pest control tool have been neglected frequently. Here, we evaluated the effects of sublethal exposure to clove, Syzygium aromaticum (L.) Merrill & Perry (Myrtaceae), and cinnamon, Cinnamomum verum J. Presl (Lauraceae), essential oils on adult (F0) maize weevils, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and the physiology (e.g., body mass, respirometry, and grain consumption) and population dynamics (e.g., daily emergence and sex ratio) of their progeny. Longevities of the parents were negatively affected by the essential oils in a concentration‐dependent manner. Parental sublethal exposure to clove oil (0.17 μl cm^?2) accelerated offspring emergence but delayed the emergence of females compared to males. Parents that were sublethally exposed to clove (0.17 μl cm^?2) or cinnamon (0.35 μl cm^?2) essential oils produced heavier offspring. Parental sublethal exposure to cinnamon essential oil accelerated offspring emergence (at 0.70 μl cm^?2), delayed female emergence (at 0.17 μl cm^?2), and enhanced grain consumption (at 0.35 and 0.70 μl cm^?2) of the progeny. Thus, our findings indicate that sublethal exposure to clove and cinnamon essential oils is capable of promoting transgenerational effects in S. zeamais that can negatively impact the control efficacy of such products.     

Toxic effects of some insecticides,herbicides, and plant essential oils against Tribolium confusum Jacquelin du val (Insecta: Coleoptera: Tenebrionidae)

Cereals are staple food for many countries and are grown on millions of hectares of land, but much of the harvest is wasted due to losses by pests. To minimize these losses, many pesticides are used which are damaging to the environment and human health. There are debates to get rid of these chemicals but they are still in use at large scale. An alternative control strategy for insect pests in storage houses is the use of botanicals. In this study, four plant essential oils, two plant extracts, two herbicides, and two insecticides were used against Tribolium confusum and the comparison of toxicity was made by calculating LC₅₀ and LT₅₀ values. LC₅₀ values were higher for abamectin (2.09–10.23 mg/L) and cypermethrin (3.41–11.78 mg/L) insecticides followed by neem essential oil (7.39–19.24 mg/L) and citrus extract (10.14–24.50 mg/L). However, LC₅₀ values were maximum in case of jaman plant extract (22.38–176.42 mg/L) followed by two herbicides, Logran (19.66–39.72 mg/L) and Topik (29.09–47.67 mg/L) However, LC₅₀ values were higher for topic herbicide (24.098 ppm) and jaman essential oil (16.383 ppm) after four days of treatment. Abamectin and cypermethrin insecticides, neem essential oil and citrus plant extract also killed adults of T. confusum quicker as compared other essential oils, extracts and herbicides. Results revealed that botanical formulations being environmentally safe could be used instead of highly hazardous pesticides for stored products’ pests. This study also elaborates the non-host toxicity of herbicides commonly applied in our agroecosystem.