Plant Extracts and Essential Oils Against Major Pests of Citrus and Red Fruits: Trends, Limitations and Knowledge Gaps.

Ecotoxicity of plant extracts and essential oils: A review

Mosquitoes control and personal protection from mosquito's bites is one of the serious ways for preventing of contagious diseases distribution. Mosquitoes in addition to the localsymptoms (itching, redness and irritation) can cause transmission of fatal and dangerous disease especially in tropical areas. In recent years, interest in plant-based products has been revived because of the development of resistance, cross-resistance and possible toxicity hazards associated with synthetic insecticides and their rising cost. Various plant-based products as herbal repellents are safe and biodegradable alternatives to synthetic chemicals for use against mosquitoes. In the present study, essential oils and extracts of six plants "Melissa officinalis, Rosmarinus officinalis, Lavandula officinalis, Citrus limonum, Eucalyptus globulus and Ocimum basilicum" were evaluated compared against mosquitoes of Anopheles Stephensi. Finally, repellant properties of essential oils and extracts as experimental groups and of N, N-diethyl 3 - methylbenzamide (DEET) as a positive control group were compared.We used Duncan's multiple range tests to determine the significant differences at 1% level between the experimental group and the control group. Results of statistical analysis showedsignificant differences between the extracts and essential oils. Essential oils indicated moreeffectiveness rather than extracts.   Key words: Malaria, Anopheles stephensi, insect repellent, essential oil, plant extract. &nbsp

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The chemical compositions and larvicidal potential against mosquito vectors of selected essential oils obtained from five edible plants were investigated in this study. Using a GC/MS, 24, 17, 20, 21, and 12 compounds were determined from essential oils of Citrus hystrix, Citrus reticulata, Zingiber zerumbet, Kaempferia galanga, and Syzygium aromaticum, respectively. The principal constituents found in peel oil of C. hystrix were beta-pinene (22.54%) and d-limonene (22.03%), followed by terpinene-4-ol (17.37%). Compounds in C. reticulata peel oil consisted mostly of d-limonene (62.39%) and gamma-terpinene (14.06%). The oils obtained from Z. zerumbet rhizome had alpha-humulene (31.93%) and zerumbone (31.67%) as major components. The most abundant compounds in K. galanga rhizome oil were 2-propeonic acid (35.54%), pentadecane (26.08%), and ethyl-p-methoxycinnamate (25.96%). The main component of S. aromaticum bud oil was eugenol (77.37%), with minor amounts of trans-caryophyllene (13.66%). Assessment of larvicidal efficacy demonstrated that all essential oils were toxic against both pyrethroid-susceptible and resistant Ae. aegypti laboratory strains at LC50, LC95, and LC99 levels. In conclusion, we have documented the promising larvicidal potential of essential oils from edible herbs, which could be considered as a potentially alternative source for developing novel larvicides to be used in controlling vectors of mosquito-borne disease.

Mosquitoes (Diptera: Culicidae) pose a serious threat to humans worldwide, known to transmit various pathogens that cause infectious diseases and arboviruses, which are viral diseases such as chikungunya, dengue, Rift Valley fever, yellow fever, malaria, elephantiasis, Murray Valley encephalitis, Japanese encephalitis, Saint Louis encephalitis virus, West Nile virus, Eastern equine encephalomyelitis virus, Highlands J virus, Everglades virus, and crosse encephalitis virus. The emergence of widespread insecticide resistance and the potential adverse environmental problems associated with synthetic insecticides have highlighted the need for alternative methods to control the spread of mosquito populations, making it an important research priority. Safe and innovative tools, such as plant-based repellents, have recently been implemented to enhance mosquito management strategies. Plant-based repellents play a crucial role in the development of natural products as alternatives to chemical control methods. Plant extracts and essential oils, which are biodegradable, target-specific, eco-friendly, and have potent effects against mosquitoes, are reviewed in this article. These plant-based repellents offer promising potential for effective mosquito management, providing a safer and environmentally friendly approach to control mosquito populations and reduce the spread of mosquito-borne diseases. Properly formulated and used in combination with other integrated vector management strategies, plant-based repellents can contribute to sustainable and effective mosquito control efforts. Keywords: Essential oils, dengue, repellents, malaria mosquito, bio-products, management, biocontrol.

The objective was to evaluate aromatic plants’ effects on the acceptance, preference, egg load, and life span of females of the twospotted spider mite (TSSM) in laboratory experiments and TSSM population under aromatic plants’ intercropping in greenhouse experiments. The pseudofruits production was also evaluated. For the laboratory, basil’s, Chinese chives’, chives’, and garlic’s influence on TSSM were tested on strawberry leaves. Four laboratory experiments were conducted: (1) Multiple choice test; (2) T-shaped arena test; (3) host–plant acceptance on aromatic plant or strawberry leaves; and (4) performance of TSSMs on strawberry leaves under aromatic plant influence. For the greenhouse experiments, assessments of the TSSM populations were realized by observing TSSM with a 10× magnifying glass on strawberry leaves in a monocrop or intercropped with Chinese chives, chives, garlic, or onion. Pseudofruit production was evaluated. Our results show that strawberry leaves were strongly preferred by TSSM. The T-shaped arena test revealed that all aromatic plants repel the TSSM. The test with the performance of TSSM females revealed that aromatic plants affected the mite’s biological parameters. Chinese chives reduced the number of eggs laid per day by 33.22%, whereas garlic reduced the number by 17.30% and chives reduced it by 12.46%. The total number of eggs was reduced by 34.79% with Chinese chives and 25.65% with garlic. Greenhouse experiments showed that chives reduced TSSM populations on two cycles and Chinese chives and garlic reduced TSSM populations on the first cycle only. With our findings, we suggest that Chinese chives, chives, and garlic are the primary candidates for intercropping use against TSSM. Chinese chives and garlic reduced the total number of eggs, but only garlic reduced female mite longevity. However, none of the intercropping plants improved strawberry pseudofruit production.

Botanicals are various plant-based products like plant extracts or essential oils. Anti-fungal activities of selected essential oils were tested on the pathogen causing potato and tomato late blight (Phytophthora infestans). Tests to evaluate anti-oomycete activities of commercial essential oils and their major compounds were carried out in vitro in microplate in liquid media. Anti-oomycete activities on Phytophthora infestans strain were obtained from essential oils/major compounds: Eucalyptus citriodora/citronellal; Syzygium aromaticum (clove)/eugenol; Mentha spicata/D-Carvone, L-Carvone; Origanum compactum/carvacrol; Satureja montana (savory)/carvacrol; Melaleuca alternifolia (tea tree)/terpinen-4-ol, and Thymus vulgaris/thymol. As an active substance of mineral origin, copper sulfate was chosen as a control. All selected essential oils showed an anti-oomycete activity calculated with IC50 indicator. The essential oils of clove, savory, and thyme showed the best anti-oomycete activities similar to copper sulfate, while oregano, eucalyptus, mint, and tea tree essential oils exhibited significantly weaker activities than copper sulfate. Clove essential oil showed the best activity (IC50 = 28 mg/L), while tea tree essential oil showed the worst activity (IC50 = 476 mg/L). For major compounds, three results were obtained: they were statistically more active than their essential oils (carvacrol for oregano, D- and L-Carvone for mint) or as active as their essential oils sources (thymol for thyme, carvacrol for savory, terpinen-4-ol for tea tree) or less active than their original essential oils (eugenol for clove, citronellal for eucalyptus). Microscopical observations carried out with the seven essential oils showed that they were all responsible for a modification of the morphology of the mycelium. The results demonstrated that various essential oils show different anti-oomycete activities, sometimes related to a major compound and sometimes unrelated, indicating that other compounds must play a role in total anti-oomycete activity.

The generalist predatory mite Amblyseius swirskii is a widely used natural enemy of phytophagous pests. Due to the negative effects of conventional pesticides on non-target organisms, the development of selective natural and eco-friendly pesticides, such as essential plant oils, are useful pest control tools to use in synergy with biological control agents. Essential oils of Nepeta crispa, Satureja hortensis, and Anethum graveolens showed promising results to control Tetranychus urticae. Hence an experiment was carried out to evaluate the effects of these essential oils on the biochemical and demographic parameters of A. swirskii. A significant reduction of carbohydrate, lipid, and protein contents of oil-treated predatory mites was observed. However, essential oils of S. hortensis and A. graveolens had no effect on lipid reserves. The glutathione S-transferase activity of A. swirskii was influenced by A. graveolens oil treatment. In addition, the enzyme activity of the α-esterases was elevated by all treatments. The essential oils showed no effect on β-esterases activity compared to the control treatment. None of the concentrations of the different tested oils affected the population growth parameters of A. swirskii. However, a significant reduction was observed in oviposition time and total fecundity of predatory mites. A population projection predicted the efficacy of predatory mites will likely be decreased when expose to the essential oils; however, population growth in the S. hortensis treatment was faster than in the other two treatments not including the control. The results presented in this study may have critical implications for integrated pest management (IPM) programs. However, our observations show that using the tested essential plant oils requires some caution when considered as alternatives to synthetic pesticides, and in combination with A. swirskii. Semi-field and field studies are still required to evaluate the effects on T. urticae and A. swirskii of the essential oils tested in this study, before incorporating them into IPM strategies.

Simple SummaryEssential oils show considerable acaricidal activity against pests. This study investigated the effects of three essential oils on T. urticae, one of the most serious pests in the world. The quality of the host plant and growth conditions affect the reproduction of Tetranychus urticae Koch, reducing their population levels very quickly. Research is ongoing to find eco-friendly insecticides or natural bioactive compounds against spider mites under greenhouse and field conditions. Clove EO was found to be the most toxic, while basil and peppermint EOs were the least effective, and immature stages were more sensitive to EOs than mature stages. It can be concluded that cucumber cultivars are effective in regard to the biological aspects and reproduction of two spot spider mites (TSSM), and the tested oils are good alternatives to control T. urticae in the protected cultivation of cucumbers.The two spotted spider mite (TSSM), Tetranychus urticae Koch, is a cosmopolitan mite. It rapidly reproduces and can develop resistance to chemical pesticides. This study aims to evaluate the toxicity and acaricidal activity of three essential oils from basil, clove, and peppermint against T. urticae reproduction, which is grown on three cucumber cultivars, Chief (SC 4145), Raian (CB898), and Toshka (SC 349), under laboratory conditions at 27 + 3 °C and 70 + 5% RH. GC-MS characterized the volatile oils of basil, clove, and peppermint. Methyl cinnamate, eugenol, and menthol were the main essential oils in basil, clove, and peppermint, respectively. The results indicated significant differences in the duration of development between T. urticae feeding on the three cucumber cultivars (p ≤ 0.05), including eggs, protonymph, and deutonymph time. The Toshka (SC 349) cultivar recorded the lowest developmental time. The longevity period exhibited the same trend with non-significant differences between Raian (CB898) and Toshka (SC 349). Moreover, the lethal concentration (LC50) and LC90 values in tested essential oils (EOs) showed that clove EOs were the most toxic. In contrast, basil and peppermint EOs were the least effective, and immature stages were more sensitive to EOs than adult stages. The infected Toshka (SC 349) discs treated with essential oils and abamectin under in vitro conditions indicated that clove oil is comparable to abamectin regarding its effect on the egg numbers (18.7 and 17.6 egg), immature development time, longevity, life span, and life cycle (20.6 and 20.8 days) of T. urticae. We conclude that the resistant cultivation of cucumber plants can be recommended in integrated pest management programs. The most effective of the tested oils, clove EOs, should be used as alternatives to pesticides to control T. urticae in the protected cultivation of cucumbers.

A variety of endo and ectoparasites can affect livestock, causing poor animal performance and low welfare conditions. Haemonchus contortus (Trichostrongyloidae), Rhipicephalus microplus (Ixodidae), Cochliomyia sp. and Lucilia sp. (Calliphoridae) are some of the most important parasites to livestock in Brazil and in many other tropical and subtropical countries, where farmers need to be vigilant. Although a constant parasite control uses large-spectrum anthelmintics or synthetic insecticides, giving a timely potent reduction of the infections, they also represent a threat to the lifespan of these compounds due to drug-selected parasites. Thus, the development of plant-based therapies is a solid alternative for standard, agroecological, and holistic farming systems, as well as it is an important ally to combat drug resistant parasite populations. In this article, we discussed the scientific literature on plant extracts, notably hydroalcoholic extract or essential oils, used for the control of the above livestock parasites published in the last 13 years. Our objective was to pinpoint the most important issues for this promising area of research, exploring the potential and the challenges that are facing us by examining more than 150 in vitro and in vivo studies. Almost all the authors reported positive data from plants or isolates, the most important challenges that were faced during our search were the lack of a proper experimental study design, and the deficiency in the characterization of the plants used. It is our opinion that plant-based products may be a solid choice for parasite control in livestock animals achieving high welfare standards and mitigate farming input (i.e. use of chemicals and their waste into the environment).

This study aimed to investigate the biological activities of eight essential and five vegetable oils against Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), a major insect pest of a wide variety of fruit and some vegetable crops in Australia. Currently, synthetic insecticides are mostly used to control this pest but insecticides of botanical origin are generally safer to humans and the environment. Therefore, botanical insecticides represent a potential alternative to the synthetic insecticides. Under laboratory conditions, repellency and oviposition deterrence effects of essential and vegetable oils were evaluated against female B. tryoni, using artificial substrates and apple fruits. The results showed that vegetable oils were more effective than essential oils in deterring oviposition. The oil with most potential was from safflower, Carthamus tinctorius (Asterales: Asteraceae). This vegetable oil at a concentration of 10 mL/L significantly reduced oviposition in apples by 56.4% in a choice test, but none of the essential and vegetable oils tested had a significant effect on oviposition in apples in a no choice test. The likely mechanism is that safflower and other vegetable oils created a slippery surface and females were unable to make punctures in the fruit for egg deposition. Essential oils especially lemon-scented tea tree Leptospermum petersonii (Myrtales: Myrtaceae), peppermint Mentha piperita (Lamiales: Lamiaceae), honey myrtle Melaleuca teretifolia (Myrtales: Myrtaceae) repelled female B. tryoni, but their persistence on apple fruits was very low, only for a few hours (2-4 hours). Safflower oil was further investigated for its mechanism and effectiveness against female B. tryoni. In a laboratory test, safflower oil treatments (2.5 mL/L and 5.0 mL/L) reduced the number of fly punctures on treated artificial fruits no matter whether prepunctures were present or absent. Safflower oil treatments also reduced the number of fly landings and eggs laid, but only when the treated artificial fruits were without prepunctures. These results confirmed that safflower oil is active against female B. tryoni mainly by physically preventing this fruit fly from making oviposition punctures, not by discouraging them from depositing eggs or by repelling them. Further tests using fruit bearing tomato plants (a no choice test) in a glasshouse situation revealed that safflower oil application at concentrations of 10 mL/L and 15 mL/L reduced the number of oviposition punctures but failed to reduce the number of eggs laid. The fumigant toxicities of the eight essential oils against B. tryoni eggs and larvae were evaluated in the laboratory using a filter paper method with a 950 ml glass jar as the fumigation chamber. During fumigation, eggs were put on a moistened black filter paper, whereas larvae were placed in carrot-based diet. The results of a 24 hour exposure test showed that peppermint oil had strong fumigant effect on eggs. However, this oil showed low fumigant effect against the larval stages. Broad-leaved peppermint (Eucalyptus dives) (Myrtales: Myrtaceae) oil showed low fumigant effect against eggs but a strong fumigant effect on the first and second instars. None of the tested essential oils showed fumigant effects on third instars. Further investigations were conducted on the effects of fumigation with essential oil alone or when followed by cold storage on survival of the fruit fly in “Gala” variety apples. Efficacy was based on the number of pupae recovered from treated and untreated fruits and on phytotoxic effects. In a 24 hour fruit fumigation test, peppermint oil applied at 100 and 200 µL/L air was found to be active against B. tryoni eggs, whereas broad-leaved peppermint oil was active against both eggs and larvae but only at the highest dose tested (200 µL/L air). However, both peppermint and broad-leaved peppermint oils sometimes had a phytotoxic effect on the apples. In a 6 hour fruit fumigation test, an equal mixture of peppermint and broad-leaved peppermint oil (100 µL/L air) did not cause phytotoxic effect but had only a slight effect on B. tryoni eggs and no effect on the larvae. There was no synergism or additive effect when this essential oil mixture was applied in combination with subsequent cold storage. Cold storage (4 + 1oC) alone was confirmed to be a very effective treatment against B. tryoni larvae and eggs in “Gala” apple without causing fruit damage. Contact and oral toxicities of eight essential and five vegetable oils were evaluated against female B. tryoni. In the contact toxicity tests, the oils were sprayed onto females at a concentration of 10 mL/L, whereas in the oral (ingestion) toxicity test, the oils were incorporated into fruit fly baits at a concentration of 20 mL/L bait. The results of contact toxicity tests showed that honey myrtle was the most potent oil. This essential oil at the concentration tested had moderate toxicity against female B. tryoni. However in oral toxicity tests, none of the oils had a significant mortality effect on female B. tryoni.

Botanical insecticides, derived from plant-based bioactive compounds with insecticidal activities, have been used to protect crops for more than a century. Synthetic insecticides have become essential in modern agricultural practices because they act quickly, are cost-effective, easy to use, and effective against a wide range of harmful species of insects and pests. Synthetic insecticides, once beneficial, have now become a threat to human health and the environment due to their toxic nature and environmental impact, and hence, botanical pesticides can be utilized as a substitute to synthetic chemical pesticides. Botanicals are easily available, biodegradable, have a broad spectrum of activity, are inexpensive, and have low toxicity to humans and non-target organisms. Various plants species including neem, pyrethrum, garlic, citrus, etc., contains various types of plant secondary metabolites including alkaloids, flavonoids, terpenes, essential oils, glycosides, esters, etc., were popular botanicals. These metabolites exhibited different physical/chemical characteristics and mechanisms of action and affect the insects in various ways such as insecticides, repellents, antifeedants, toxicants, growth retardants, herbicides, and attractants. This chapter describes the in-depth knowledge of various classes of bioinsecticides and their possible mode of actions.

Background. Malaria is one of the deadliest mosquito-borne diseases in sub-Saharan Africa and Ethiopia. Owing to their costs and environmental issues, synthetic insecticides are poor choices to control mosquitoes. Plant-based products can be considered as safe and biodegradable alternatives. The present study aimed to test the toxicity and oviposition deterrent activities of Thymus serrulatus and Thymus schimperi essential oils (EOs) against Anopheles arabiensis. Methods. Thyme EOs were extracted by hydrodistillation using the Clevenger-type apparatus. They were named Tar, Ala, and Yil after the areas of thyme collection Tarmaber, Alamata, and Yilmana Densa, respectively. Laboratory-based tests were used to determine the larvicidal, adulticidal, oviposition deterrent, and half lethal dose (LD50) of each EO. Results. The concentrations of 100 μl/L and 50 μl/L resulted in complete mortalities of larvae and adults, respectively, for all the three Eos considered. The EOs exhibited high repellency with oviposition activity index of −1 (OAI = −1) at concentrations of 50 μl/L (Tar), 100 μl/L (Ala), and 200 μl/L (Yil). Conclusions. The EOs of T. serrulatus and T. schimperi were effective against larvae and adult mosquitoes at small doses and resulted in oviposition deterrence at doses from 50 to 200 μl/L. Thus, these EOs are promising mosquitocides and oviposition deterrents. But, further tests both in the presence of already known and effective deterrents and field trials are required.

New pesticides based on plant extracts and essential oils (EO) are the modern approach to control insect pests and diseases and replacing synthetic pesticides. Therefore, a preliminary screening of nine indigenous plants containing essential oil for antifungal and insecticidal impacts on selected microorganisms and insect pests was evaluated during 2018-19 at Kadoorie Agricultural Research Center (KARC), Palestine Technical University. The biological properties of the plant extracts and EO were tested in vitro. Results showed that clove, thyme and eucalyptus oil significantly inhibited the growth of A. niger, B. cinerea, A. flavus, P. ultimum, P. digitatum and F. oxysporum 24 and 48 hr post-application. EC50 and EC90 values were significantly the lowest for eucalyptus, thyme then clove. LC50 and LC90 values against green peach aphid and two-spotted red spider mite were calculated from log-dose probit mortality regression. EO bioassay on aphid showed no significant impact of aphid mortality among all the EO, but a significant effect on the two-spotted red spider mites mortality. Mustard, sage and bitter-cucumber oil applications have high mortality on aphid, while mustard, mint and sesame oil application have high mortality on the two-spotted red spider mite. EO showed no significant impact on plant enzyme activities as in expression values of PPO and POX. The biological activity of the EO investigated on several microorganisms, and insect pests suggested that clove, eucalyptus and thyme showed the highest antifungal activities, while mint, mustard and sesame have the highest insecticidal and acaricidal activities.

BackgroundAedes albopictus is an epidemiologically important vector for the transmission of viral pathogens of yellow fever, dengue fever, chikungunya, zika, and filariasis. Plant-based products can provide environmentally safe mosquito control agents. Therefore, the efficacy of essential oils (EOs) extracted from Eucalyptus globulus, Ageratum conyzoides, and Cymbopogon citratus was determined against the larvae of A. albopictus.ResultsThe highest larvicidal action was illustrated by the EO of E. globulus with an LC50 value of 46.58 ppm, followed by A. conyzoides with LC50 of 69.51 ppm. The efficacy of combinations of the EOs of the three plants at different ratios showed the combination of A. conyzoides with C. citratus at a 1:1 ratio to be the most effective with LC50 value of 13.05 with a 95% confidence limit of 10.54–15.32. The composition of the EOs analyzed using GC–MS showed precocene II and β-caryophyllene as major compounds of EO of A. conyzoides. We further evaluated the efficacy of the combination of EO with a binary combination of synthetic insecticides and detected the highest efficacy in a combination of A. conyzoides with malathion–cypermethrin and malathion–temephos.ConclusionTherefore, the EO of A. conyzoides, through synergistic action with organophosphate and pyrethroid synthetic insecticides, can effectively act against the vector of dengue, zika, and chikungunya. The EO of A. conyzoides or its major compounds can be explored for the development of mosquitocidal formulation using effective synthetic insecticides.