The repellency of lemongrass oil against stable flies, tested using video tracking

Preferences for livestock bedding as a development substrate of the stable fly, Stomoxys calcitrans L. (Diptera: Muscidae), and potential application of entomopathogenic nematodes for controlling stable fly larvae

The stable fly, Stomoxys calcitrans L. (Diptera: Muscidae), is a significant insect pest with global veterinary implications due to its capacity to both cause nuisance and transmit disease-causing pathogens to livestock. This study aimed to determine the livestock bedding preferred for use as a development substrate by S. calcitrans larvae and field-collected adults. The result showed that S. calcitrans larvae exhibited a preference (26.7%) for 7-day-old cow manure. Gravid females displayed a pronounced preference (55.0%) for fresh cow manure. As there were eight choices, indifference would result in 12.5% for each bedding substrate. Furthermore, the efficacy of four entomopathogenic nematodes (EPNs), namely Heterorhabditis bacteriophora (Poinar), Heterorhabditis indica Poinar, Karunakar & David (Rhabditida: Heterorhabditidae), Steinernema siamkayai Poinar, Karunakar & David and Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), against S. calcitrans larvae and the persistence after application to livestock bedding substrates were evaluated under laboratory conditions. In filter paper bioassays, all four EPNs caused 76.7%-100.0% mortality in the second instar larvae of S. calcitrans when applied at 50 and 100 infective juveniles (IJs)/cm2 within 5 days after exposure. For the third instar larvae of S. calcitrans, only H. indica induced high mortalities of 86.6% when applied at 100 IJs/cm2 within 5 days after exposure, while the other EPNs resulted in mortalities of less than 70%. The data further demonstrated that H. bacteriophora, H. indica and S. siamkayai remained present in the substrates linked to S. calcitrans larvae for as long as 7 days after the application of EPNs. This study demonstrates the potential of EPNs as a biologically based control agent against larvae of S. calcitrans, a serious pest and significant vector for various livestock animals.

Larvicidal activity of β-Citral: An In-vitro and In-silico study to understand its potential against mosquito

Tropical and subtropical regions face millions of deaths from mosquito-borne illnesses yearly. Insecticides prevent transmission but pose health risks like dermatitis and allergies. The primary objective was to mitigate the recurring dependence on synthetic insecticides, thereby curbing the development of mosquito resistance. Leaves of Cymbopogon flexuosus (lemongrass) was collected from Mayurbhanj, India, processed, then extracted by steam distillation for essential oils & analyzed spectroscopically. Larvicidal assays were performed across varying concentrations, revealing the significant mortality induced by the Cymbopogon flexuosus extract against Anopheles stephensi larvae. 3D structure was modelled by using G protein-coupled receptors (GPCR) sequence and structural stability was also validated. After docking the binding free energy was determined from GPCR protein with β-citral complex. Molecular dynamics (MD) study was conducted on the docked pose that displayed an optimal interactome profile. The larvicidal assay at the 12th and 24th hour revealed the highest LC50 (lethal concentration) of 23.493 ppm and 19.664 ppm . β-Citral has a high binding affinity and an identifiable binding site, which suggests that it may play a larvicidal role in regulating the receptor's function by creating stable complexes with it. β-Citral from lemongrass oils has potential larvicidal activity and effective against GPCR family 1 of mosquito and highly effective repellents against mosquito-borne diseases.

Contributions of γ-Aminobutyric Acid (GABA) Receptors for the Activities of Pectis brevipedunculata Essential Oil against Drosophila suzukii and Pollinator Bees

The γ-aminobutyric acid (GABA) receptors play pivotal roles in the transmission of neuronal information in the nervous system of insects, which has led these proteins to be targeted by synthetic and natural products. Here, we assessed the insecticidal potential of the essential oil of Pectis brevipedunculata (Gardner) Sch. Bip., a neotropical Asteraceae plant used in traditional medicine, for controlling Drosophila suzukii (Matsumura) adults by feeding exposure. By using in silico approaches, we disentangle the contribution of GABA receptors and other potential neuronal targets (e.g., acetylcholinesterase, glutathione-S-transferases) in insects that may explain the essential oil differential activities against D. suzukii and two essential pollinator bees (Apis mellifera Linnaeus and Partamona helleri Friese). Neral (26.7%) and geranial (33.9%) were the main essential oil components which killed D. suzukii with an estimated median lethal concentration (LC50) of 2.25 µL/mL. Both pollinator forager bee species, which would likely contact this compound in the field, were more tolerant to the essential oil and did not have their diet consumptions affected by the essential oil. Based on the molecular predictions for the three potential targets and the essential oil main components, a higher affinity of interaction with the GABA receptors of D. suzukii (geranial -6.2 kcal/mol; neral -5.8 kcal/mol) in relation to A. mellifera (geranial -5.2 kcal/mol; neral -4.9 kcal/mol) would contribute to explaining the difference in toxicities observed in the bioassays. Collectively, our findings indicated the involvement of GABA receptors in the potential of P. brevipedunculata essential oil as an alternative tool for controlling D. suzukii.

A critical review of current laboratory methods used to evaluate mosquito repellents

Pathogens transmitted by mosquitoes threaten human health around the globe. The use of effective mosquito repellents can protect individuals from contracting mosquito-borne diseases. Collecting evidence to confirm and quantify the effectiveness of a mosquito repellent is crucial and requires thorough standardized testing. There are multitudes of methods to test repellents that each have their own strengths and weaknesses. Determining which type of test to conduct can be challenging and the collection of currently used and standardized methods has changed over time. Some of these methods can be powerful to rapidly screen numerous putative repellent treatments. Other methods can test mosquito responses to specific treatments and measure either spatial or contact repellency. A subset of these methods uses live animals or human volunteers to test the repellency of treatments. Assays can greatly vary in their affordability and accessibility for researchers and/or may require additional methods to confirm results. Here I present a critical review that covers some of the most frequently used laboratory assays from the last two decades. I discuss the experimental designs and highlight some of the strengths and weaknesses of each type of method covered.

Insect Bite Hypersensitivity in Horses: Causes, Diagnosis, Scoring and New Therapies

Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic disease of horses. It is most often caused by sensitivity to the saliva of Culicoides spp. of biting midges; however, it can also be caused by hypersensitivity to other insect species. The prevalence of IBH in horses is reported to be as high as 60% in some parts of the world. Due to the severe pruritus and effects of secondary self-trauma, IBH has animal welfare concerns, and there is currently no cure. Management of this condition is life-long, time consuming and costly. New grading systems to document disease severity are being validated, which will allow the comparison of clinical trial results of new and existing therapies. Management involves the minimisation of insect bites by use of stabling, fans, rugs and repellents. Symptomatic therapy involves the administration of systemic or topical corticosteroids, systemic antihistamines, and creams and sprays to promote skin healing and decrease inflammation. New immune-mediated therapeutics including vaccines, in addition to desensitisation procedures, show promise at controlling hypersensitivity reactions. This article will review aetiologic agents, pathophysiology, scoring systems and current and new therapies.

Control of red flour beetle (Tribolium castaneum) in feeds and commercial poultry diets via using a blend of clove and lemongrass extracts

The insects' infestation decreases the nutritive value of the stored grains and causes losses in its weight, quality, or economic values. The aim of the present study was to investigate the efficiency of a natural product of clove and lemongrass extracts in controlling of red flour beetle (Tribolium castaneum) in different feedstuffs and commercial poultry diets. Different concentrations of the tested product (5, 10, 20, 50, 100 mg) were mixed with 10 g of different feedstuffs and poultry diets, and incubated at different time points. The percent repellency (PR), toxicity effect, and antifeedant activity of the plant extracts compound were assessed. The PR was detected depending on the choice method. It was found that the PR was dose and time dependent. The highest doses (50 or 100 mg/10 g feed) achieved the highest repellency effect reaching 70% at 24 h post-application (PA). The minimal PR was reported by the lowest dose of 5 mg/10 g feed reaching 50% at 24 h PA. Moreover, the PR was found to decrease by time. The toxicity effect of this natural product on T. castaneum was cumulative, not acute, in which it was recorded after 1 month of application. Besides, this effect needs high doses of the product (at dose 500 or 1000 mg/50 g feed). The used product achieved a clear antifeedant activity against T. castaneum, as the feeding deterrent index (FDI %) for corn grains was 98.5% at 1.0 and 2.0% concentration, whereas for wheat grains there was a significant difference between both concentration (96.0 vs. 74.4%). In addition, the weight loss of control corn and wheat grains was higher than the treated ones, and it was about 3.15% and 2.0% per month for corn and wheat, respectively. In conclusion, the clove and lemongrass extracts had a repellency effect reaching to 70%. Moreover, it had a lethal effect on T. castaneum. In addition, it can reduce the weight loss of the infested feeds and consequently increasing its FDI %. Therefore, the clove and lemongrass extract blend can be used to protect the feedstuffs from the damage by this insect.

Essential oil based controlled-release non-toxic evaporating tablet provides effective repellency against Musca domestica

Housefly, Musca (M) domestica L. (Diptera: Muscidae) is a pervasive insect that transmits a variety of pathogens to humans and livestock. Although numerous synthetic pesticides are available to combat houseflies, their ecological and toxicological concerns have led to the exploration of natural products as safer alternatives. The present work was designed to develop an essential oil based controlled-release evaporating tablet (EO-CRT) and investigate its repellency against M. domestica. This study assesses the toxicological impacts of the EO-CRT following its sub-chronic inhalation exposure. Briefly, repellent activity of fourteen essential oils viz. lemon grass, bergamot, mentha, basil, camphor, lavender, clove, patchouli, rosemary, cinnamon, eucalyptus, citronella, jasmine and wild turmeric against M. domestica were screened using the 'Y'-tube olfactometer. The synergistic activity of the best four oils, under preliminary screening, were further evaluated by double and triple blending. The best combination of three oils were finalized for optimization with 17-run, 3-factor, 3-level Box-Behnken design. This was then employed to construct polynomial models and predict the best optimized formulation EO-CRT. EO-CRT was characterized by Differential Scanning Calorimetry (DSC) and Gas Chromatography-Mass Spectroscopy (GC-MS). The efficacy of the EO-CRT against M. domestica was assessed by attraction and repellent assay. Chest X-ray, histopathology and scanning electron microscopy of the exposed lung was performed to study EO-CRT's sub-chronic toxicity on Wistar rats. The EO-CRT showed slow release up to a period of 10 days at room temperature, exhibited 100% repellency (%Error=1.237) against M. domestica and was found to possess all the characteristics of an ideal formulation. Sub-chronic toxicity study further revealed the non-toxic nature of the EO-CRT. Thus, our study provides an assurance that the formulated EO-CRT could be effective not only in repelling the nuisance pest, M. domestica, in human dwellings, but also in minimizing the mechanical transmission of pathogens by it.

Essential oil spray reduces clinical signs of insect bite hypersensitivity in horses

OBJECTIVE

To assess the efficacy of an herbal spray combining various essential oils, with a claim of mast cell stabilisation, antipruritic, anti-inflammatory, and insect repellent effects on the clinical presentation of insect bite hypersensitivity (IBH) in horses.

DESIGN

Double-blinded, placebo-controlled, randomised, cross-over clinical trial.

METHODS

Twenty adult horses with clinical IBH were treated with a daily application of herbal spray or placebo for 28 days in a randomised, cross-over fashion, separated by a>28-day washout period. Horses were examined and scored prior to and after the completion of each treatment. Histopathology was performed on four horses. Owners kept daily diaries of observations.

RESULTS

The herbal spray significantly reduced the severity of all assessed parameters (pruritus, excoriations, lichenification and alopecia; P < 0.05) compared with baseline values (pretreatment) and with placebo. Owners reported improvement of pruritus in 19/20 horses (95%) with complete resolution in 17 horses (85%) following treatment. Skin biopsies showed resolution of orthokeratosis in 4/4 horses, reduced thickness of the stratum spinosum in 2/4 horses and complete resolution of histopathological abnormalities in 1/4 horses after treatment, compared with either no change or deterioration of histopathologic lesions after placebo. No side effects were observed.

CONCLUSIONS

The tested herbal spray may be an effective treatment for the management of equine IBH.

A Historical Review of Management Options Used against the Stable Fly (Diptera: Muscidae)

The stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), remains a significant economic pest globally in situations where intensive animal production or horticultural production provide a suitable developmental medium. Stable flies have been recorded as pests of livestock and humans since the late 1800s to early 1900s. Over 100 years of research has seen numerous methodologies used to control this fly, in particular to protect cattle from flies to minimise production losses. Reduced milk production in dairy cows and decreased weight gain in beef cattle account for losses in the US alone of > $2000 million annually. Rural lifestyles and recreation are also seriously affected. Progress has been made on many control strategies against stable fly over a range of chemical, biological, physical and cultural options. This paper reviews management options from both a historical and a technical perspective for controlling this pest. These include the use of different classes of insecticides applied to affected animals as toxicants or repellents (livestock and humans), as well as to substrates where stable fly larvae develop. Arthropod predators of stable flies are listed, from which potential biological control agents (e.g., wasps, mites, and beetles) are identified. Biopesticides (e.g., fungi, bacteria and plant-derived products) are also discussed along with Integrated Pest Management (IPM) against stable flies for several animal industries. A review of cultural and physical management options including trapping, trap types and methodologies, farm hygiene, scheduled sanitation, physical barriers to fly emergence, livestock protection and amendments added to animal manures and bedding are covered. This paper presents a comprehensive review of all management options used against stable flies from both a historical and a technical perspective for use by any entomologist, livestock producer or horticulturalist with an interest in reducing the negative impact of this pest fly.

Lemon Grass Essential Oil Does not Modulate Cancer Cells Multidrug Resistance by Citral-Its Dominant and Strongly Antimicrobial Compound

With strong antimicrobial properties, citral has been repeatedly reported to be the dominant component of lemongrass essential oil. Here, we report on a comparison of the antimicrobial and anticancer activity of citral and lemongrass essential oil. The lemongrass essential oil was prepared by the vacuum distillation of fresh Cymbopogon leaves, with a yield of 0.5% (w/w). Citral content was measured by gas chromatography/high-resolution mass spectrometry (GC-HRMS) and determined to be 63%. Antimicrobial activity was tested by the broth dilution method, showing strong activity against all tested bacteria and fungi. Citral was up to 100 times more active than the lemongrass essential oil. Similarly, both citral and essential oils inhibited bacterial communication and adhesion during P. aeruginosa and S. aureus biofilm formation; however, the biofilm prevention activity of citral was significantly higher. Both the essential oil and citral disrupted the maturated P. aeruginosa biofilm with the IC₅₀ 7.3 ± 0.4 and 0.1 ± 0.01 mL/L, respectively. Although it may seem that the citral is the main biologically active compound of lemongrass essential oil and the accompanying components have instead antagonistic effects, we determined that the lemongrass essential oil-sensitized methicillin-resistant S. aureus (MRSA) and doxorubicin-resistant ovarian carcinoma cells and that this activity was not caused by citral. A 1 mL/L dose of oil-sensitized MRSA to methicillin up to 9.6 times and a dose of 10 µL/L-sensitized ovarian carcinoma to doxorubicin up to 1.8 times. The mode of multidrug resistance modulation could be due to P-glycoprotein efflux pump inhibition. Therefore, the natural mixture of compounds present in the lemongrass essential oil provides beneficial effects and its direct use may be preferred to its use as a template for citral isolation.

Spatial repellency, antifeedant activity and toxicity of three medium chain fatty acids and their methyl esters of coconut fatty acid against stable flies

BACKGROUND

Stable flies are one of the most detrimental arthropod pests to livestock. With changing climates and agronomic practices, they expand their roles as pests and disease vectors as well. Their painful bites reduce livestock productivity, annoy companion animals, and interfere with human recreational activities. Current management technologies are unable to effectively control stable flies. The present study reports new results concerning the contact, spatial repellency, and toxicity of a bio-based product, coconut fatty acid and their methyl ester derivatives of free fatty acids of C_8:0 , C_10:0 and C_12:0 to stable flies.

RESULTS

Three medium chain fatty acid methyl esters (C_8:0 , C_10:0 and C_12:0 ) showed strong antifeedant activity against stable flies and their strengths were dose-dependent. Only the C_8:0 acid, C_8:0 - and C_10:0 methyl esters elicited significant antennal responses. Laboratory single cage olfactometer bioassays revealed that coconut fatty acid and C_8:0 methyl ester displayed active spatial repellency. All three methyl esters showed strong toxicity against stable flies.

CONCLUSION

Antifeedant activity is the main method through which coconut fatty acid deters stable fly blood-feeding. The C_8:0 , C_10:0 and C_12:0 methyl esters act not only as strong antifeedants, but also possess strong toxicity against stable fly adults. Limited spatial repellency was observed from coconut fatty acid and C_8:0 methyl ester. © 2019 Society of Chemical Industry.

Entomology in the 21st Century: Tackling Insect Invasions, Promoting Advancements in Technology, and Using Effective Science Communication-2018 Student Debates

The 2018 student debates of the Entomological Society of America were held at the Joint Annual Meeting for the Entomological Societies of America, Canada, and British Columbia in Vancouver, BC. Three unbiased introductory speakers and six debate teams discussed and debated topics under the theme 'Entomology in the 21st Century: Tackling Insect Invasions, Promoting Advancements in Technology, and Using Effective Science Communication'. This year's debate topics included: 1) What is the most harmful invasive insect species in the world? 2) How can scientists diffuse the stigma or scare factor surrounding issues that become controversial such as genetically modified organisms, agricultural biotechnological developments, or pesticide chemicals? 3) What new/emerging technologies have the potential to revolutionize entomology (other than Clustered Regularly Interspaced Short Palindromic Repeats)? Introductory speakers and debate teams spent approximately 9 mo preparing their statements and arguments and had the opportunity to share this at the Joint Annual Meeting with an engaged audience.

Transmission of pathogens by Stomoxys flies (Diptera, Muscidae): a review

Stomoxys flies are mechanical vectors of pathogens present in the blood and skin of their animal hosts, especially livestock, but occasionally humans. In livestock, their direct effects are disturbance, skin lesions, reduction of food intake, stress, blood loss, and a global immunosuppressive effect. They also induce the gathering of animals for mutual protection; meanwhile they favor development of pathogens in the hosts and their transmission. Their indirect effect is the mechanical transmission of pathogens. In case of interrupted feeding, Stomoxys can re-start their blood meal on another host. When injecting saliva prior to blood-sucking, they can inoculate some infected blood remaining on their mouthparts. Beside this immediate transmission, it was observed that Stomoxys may keep some blood in their crop, which offers a friendly environment for pathogens that could be regurgitated during the next blood meal; thus a delayed transmission by Stomoxys seems possible. Such a mechanism has a considerable epidemiological impact since it allows inter-herd transmission of pathogens. Equine infectious anemia, African swine fever, West Nile, and Rift Valley viruses are known to be transmitted by Stomoxys, while others are suspected. Rickettsia (Anaplasma, Coxiella), other bacteria and parasites (Trypanosoma spp., Besnoitia spp.) are also transmitted by Stomoxys. Finally, Stomoxys was also found to act as an intermediate host of the helminth Habronema microstoma and may be involved in the transmission of some Onchocerca and Dirofilaria species. Being cosmopolite, Stomoxys calcitrans might have a worldwide and greater impact than previously thought on animal and human pathogen transmission.