Physicochemical Characteristics of Four Limonene-Based Nanoemulsions and Their Larvicidal Properties against Two Mosquito Species, Aedes albopictus and Culex pipiens molestus

Synthesis of eco-friendly layered double hydroxide and nanoemulsion for jasmine and peppermint oils and their larvicidal activities against Culex pipiens Linnaeus

Mosquito-borne diseases represent a growing health challenge over time. Numerous potential phytochemicals are target-specific, biodegradable, and eco-friendly. The larvicidal activity of essential oils, a jasmine blend consisting of Jasmine oil and Azores jasmine (AJ) (Jasminum sambac and Jasminum azoricum) and peppermint (PP) Mentha arvensis and their nanoformulations against 2nd and 4th instar larvae of Culex pipiens, was evaluated after subjecting to different concentrations (62.5, 125, 250, 500, 1000, and 2000 ppm). Two forms of phase-different nanodelivery systems of layered double hydroxide LDH and oil/water nanoemulsions were formulated. The synthesized nanoemulsions showed particle sizes of 199 and 333 nm for AJ-NE and PP-NE, with a polydispersity index of 0.249 and 0.198, respectively. Chemical and physiochemical analysis of TEM, SEM, XRD, zeta potential, drug loading capacity, and drug release measurements were done to confirm the synthesis and loading efficiencies of essential oils' active ingredients. At high concentrations of AJ and PP nanoemulsions (2000 ppm), O/W nanoemulsions showed higher larval mortality than both LDH conjugates and crude oils. The mortality rate reached 100% for 2nd and 4th instar larvae. The relative toxicities revealed that PP nanoemulsion (MA-NE) was the most effective larvicide, followed by AJ nanoemulsion (AJ-NE). There was a significant increase in defensive enzymes, phenoloxidase, and α and β-esterase enzymes in the treated groups. After treatment of L4 with AJ, AJ-NE, PP, and PP-NE, the levels of phenoloxidase were 545.67, 731.00, 700.00, and 799.67 u/mg, respectively, compared with control 669.67 u/mg. The activity levels of α-esterase were 9.71, 10.32, 8.91, and 10.55 mg α-naphthol/min/mg protein, respectively. It could be concluded that the AJ-NE and PP-NE nanoformulations have promising larvicidal activity and could act as safe and effective alternatives to chemical insecticides.

Efficacy of D-Limonene Nanoemulsion Against Rhipicephalus annulatus and Rhipicephalus sanguineus Ticks

PURPOSE

Ticks infestation has a negative impact against human and animal health through blood sucking, transmission of blood-borne diseases and also caused economic losses.

METHODS

In the present study the adulticidal, ovicidal and larvicidal activity of D-limonene nanoemulsion (DLN) were evaluated against two tick species; Rhipicephalus annulatus and Rhipicephalus sanguineus. Nanoemulsion form of D-limonene was prepared, and its characteristics were evaluated using a UV spectrophotometer and zeta droplet size measurement. Acetylcholinesterase activity was determined.

RESULTS

The results revealed significant adulticidal effect with low LC50 and LC90 for D-limonene pure form (DL) against both adult tick spp. (R. annulatus and R. sanguineus) ((0.958 and 1.559%) and (2.26 and 3.51%), respectively). DLN LC50 and LC90 values were ((1.277 and 2.396) and (3.97 and 7.28), respectively) against R. annulatus and R. sanguineus, respectively. DL and DLN showed significant ovicidal effect against R. sanguineus at high concentrations (10 and 5%). In larval packet test, LC50 and LC90 values of DL were ((1.53 and 2.22%) and (6.81 and 12.07%), respectively) against R. annulatus and R. sanguineus, respectively, while LC50 and LC90 values of DLN were ((6.48 and 11.26%) and (7.82 and 13.59%), respectively) against R. annulatus and R. sanguineus, respectively. Significant acetylcholinesterase inhibition percentage was detected for both ticks spp. which treated by DL and DLN.

CONCLUSION

Pure DL is more effective than DLN form against R. annulatus and R. sanguineus.

Sustainable Pest Management Using Novel Nanoemulsions of Honeysuckle and Patchouli Essential Oils against the West Nile Virus Vector, Culex pipiens, under Laboratory and Field Conditions

Essential oils are natural plant products that are very interesting, as they are important sources of biologically active compounds. They comprise eco-friendly alternatives to mosquito vector management, particularly essential oil nanoemulsion. Therefore, the aim of this study is to evaluate the effectiveness of 16 selected essential oils (1500 ppm) in controlling mosquitoes by investigating their larvicidal effects against the larvae and adults of the West Nile virus vector Culex pipiens L. (Diptera: Culicidae); the best oils were turned into nanoemulsions and evaluated under laboratory and field conditions. The results show that honeysuckle (Lonicera caprifolium) and patchouli (Pogostemon cablin) essential oils were more effective in killing larvae than the other oils (100% mortality) at 24 h post-treatment. The nanoemulsions of honeysuckle (LC50 = 88.30 ppm) and patchouli (LC50 = 93.05 ppm) showed significantly higher larvicidal activity compared with bulk honeysuckle (LC50 = 247.72 ppm) and patchouli (LC50 = 276.29 ppm) oils. L. caprifolium and P. cablin (100% mortality), followed by Narcissus tazetta (97.78%), Rosmarinus officinalis (95.56%), and Lavandula angustifolia (95.55%), were highly effective oils in killing female mosquitoes, and their relative efficacy at LT50 was 5.5, 5.3, 5.8, 4.1, and 3.2 times greater, respectively, than Aloe vera. The results of the field study show that the honeysuckle and patchouli oils and their nanoemulsions reduced densities to 89.4, 86.5, 98.6, and 97.0% at 24 h post-treatment, respectively, with persistence for eight days post-treatment in pools. Nano-honeysuckle (100% mortality) was more effective than honeysuckle oils (98.0%). Our results show that honeysuckle and patchouli oils exhibited promising larvicidal and adulticidal activity of C. pipiens.

Mosquito Larvicidal Activity and Cytotoxicity of the Extracts of Aromatic Plants from Malaysia

Despite ongoing control efforts, the mosquito population and diseases vectored by them continue to thrive worldwide, causing major health concerns. There has been growing interest in the use of botanicals as alternatives to insecticides due to their widespread insecticidal properties, biodegradability, and adaptability to ecological conditions. In this study, we investigated the larvicidal activity and cytotoxicity effects of solvent extracts from three aromatic plants-Curcuma longa (turmeric), Ocimum americanum (hoary basil), and Petroselinum crispum (parsley)-against Aedes albopictus. Subsequently, we examined the phytochemical composition of the extracts through gas chromatography-mass spectrometry (GC-MS) analysis. Results revealed that the hexane extracts of O. americanum and P. crispum exhibited the greatest larvicidal activity with the lowest median lethal concentration (LC₅₀) values (<30 µg/mL) at 24 h post-treatment, with the former found to be significantly less toxic towards African monkey kidney (Vero) cells. The GC-MS analysis of the said extract indicated the presence of different classes of metabolites, including phenylpropanoids, very long-chain alkanes, fatty acids and their derivatives, and terpenes, with the most abundant component being methyl eugenol (55.28%), most of which, have been documented for their larvicidal activities. These findings provide valuable insights into the potential use and development of bioinsecticides, particularly from O. americanum.

D-limonene nanoemulsion: lousicidal activity, stability, and effect on the cuticle of Columbicola columbae

The current study was conducted to investigate the efficacy and stability of D-limonene (DL) and its nanoemulsion (DLN) against pigeon feather lice (Columbicola columbae) and their mode of action. DL pure form and DLN were prepared and characterized freshly and after storage for 50 days. In vitro bioassay on live lice was conducted with different concentrations of DL, DLN, and deltamethrin (DM). The results revealed significant mortality rates in the DL-, DLN-, DM-treated groups when compared with the control (p < 0.05). The scanning electron micrographs of lice treated with DL and DLN revealed collapsed bodies with destruction in the cuticle of the mouthparts and damaged antennae. The 50 days stored DLN showed stability in their effectiveness when compared with the freshly prepared formulation. DL and DLN caused significant inhibition (p ≤ 0.05) in acetylcholinesterase activity (AchE). Malondialdehyde level (MDA) was significantly increased while glutathione was significantly decreased in DL- and DLN-treated lice. In conclusion, DL and DLN have significant lousicidal activities. DLN showed better stability than DL after storage for 50 days. In addition, the mode of action of DL may associate with its effect on the cuticle of the lice body, inhibition of AchE, and increasing oxidative stress in the treated lice.

Safety and Efficacy of Pure and a Nanosuspension of D-limonene for Controlling Pigeon Lice

This study investigated the safety and efficacy of two forms of D-limonene (DL) against Columbicola columbae (pigeon feather lice); pure and a nanoemulsion formulation (DLN). The cell cytotoxicity of the prepared forms of DL/DLN was investigated using skin cell lines. In vitro and ex vivo bioassays were applied on lice. The ex vivo bioassay was done on cut feathers containing lice eggs. The in vivo experiment was conducted on pigeons naturally infested by lice. The infested pigeons were treated with DL, DLN, or deltamethrin (D) as a positive control. Both forms of D-limonene were found to be safe when applied to the normal human skin fibroblast cell line, but DLN was toxic to skin cell carcinoma. The in vitro and ex vivo results of both DL and DLN forms were similar. All eggs treated with DL, DLN, and D failed to hatch (100%). The in vivo results showed complete elimination of lice 24 h post-treatment (PT), and biochemical analysis showed that the treated birds retained normal kidney and liver functions. Treated groups also showed improved productivity in the 4 months PT. In conclusion, DL and DLN are safe and effective in controlling feather lice infestation in pigeons and successful treatment encourages bird productivity.

Colupulone, colupone and novel deoxycohumulone geranyl analogues as larvicidal agents against Culex pipiens

BACKGROUND

As climate change proceeds, the management of the population of mosquitoes becomes more and more challenging. Insect adulticides and larvicides constitute significant control techniques, with the latter being considered the leading mosquito control method. However, the development of mosquito resistance development and the adverse side effects caused by the extensive use of synthetic insecticides have turned research towards the discovery of environmentally-friendly solutions. Plants and bacteria have historically proven to be a good source of insecticidally active compounds, which may possess novel modes of action to overcome current resistance mechanisms and could also possess favorable human and environmental safety profiles. A previous study demonstrated that the naturally occurring prenylated acyl phloroglucinol deoxycohumulone is a potent larvicidal agent against Culex pipiens. Herein the structural characteristics that improve it are explored by evaluating colupulone and novel geranylated analogues.

RESULTS

Colupulone, a prenylated acyl phloroglucinol isolated from Humulus lupulus, colupone, and novel geranylated acyl phloroglucinol congeners, were synthesized and evaluated against Cx. pipiens larva. Results indicated that selected derivatives exhibited superior potency than deoxycohumulone (LC₅₀ 43.7 mg L^-1 ). Thus, strong activity was observed for colupulone (LC₅₀ 19.7 mg L^-1 ), and some novel geranyl analogues of deoxycohumulone reaching at LC₅₀ 17.1 mg L^-1 , while colupone and similar compounds were almost inactive.

CONCLUSION

The results determined the relationship between the target activity and the chemical structure of the tested compounds, and they revealed significantly improved larvicidal candidates. These results highlight the potential of the acyl phloroglucinol chemistry for further development of mosquito larvicides. © 2022 Society of Chemical Industry.

Larvicidal Activity of Two Rutaceae Plant Essential Oils and Their Constituents Against Aedes albopictus (Diptera: Culicidae) in Multiple Formulations

Aedes albopictus (Skuse) is a vector of several arboviruses, such as dengue, chikungunya, West Nile, and Zika viruses. At present, the use of synthetic insecticides is the main vector control strategy. However, the widespread and long-term use of insecticides has aroused several problems, including insecticide resistance, environmental pollution, and non-target species effects, thereby encouraging researchers to search for new alternatives derived from natural products. In recent decades, essential oils (EOs) as natural alternatives to control mosquitoes have received increasing attention. In the initial larvicidal activity screen, two Rutaceae plants (Citrus aurantium and Citrus paradisi) EOs were selected and evaluated for killing Ae. albopictus larvae. The LC50 values of C. aurantium and C. paradisi EOs against Ae. albopictus were 91.7 and 100.9 ppm, respectively. The main components of C. aurantium EO include diethyl o-phthalate (37.32%), limonene (10.04%), and methyl dihydrojasmonate (6.48%). The main components of C. paradisi EO include limonene (60.51%), diethyl o-phthalate (11.75%), linalool (7.90%), and styralyl acetate (6.28%). Among these main components of the two EOs, limonene showed potent larvicidal activity, with the LC50 value of 39.7 ppm. The nanoemulsions of limonene were prepared and characterized. The duration of larvicidal activity was greater in the limonene nanoemulsions than when limonene was applied in solvent. This study demonstrates that EOs of plants in family Rutaceae are a potential resource to develop new larvicides, and nanoemulsification is an effective method for improving the physicochemical properties and efficacy of natural products as larvicides.

Larvicidal potential and residual activity effect of kinnow peel oil against Aedes aegypti L

BACKGROUND & OBJECTIVES

Transmission of dengue virus by Aedes aegypti mosquito is one of the major global health concerns. The present study was aimed to explore the larvicidal potential of oil extracted from kinnow peel waste to be used as an efficient, economic and safe agent against Ae. aegypti.

METHODS

Kinnow peel oil was extracted and its five concentrations at 40, 50, 60, 70 and 80 ppm were tested against 4^th instar larvae of Ae. aegypti. Larval mortality (%) and LC₅₀ and LC₉₀ values of toxicity were determined followed by evaluation of the residual activity effect of its leftover effective concentration on larval mortality, development and emergence. Effect of storage (2, 4 and 6 months) on larvicidal potential of kinnow peel oil was also determined.

RESULTS

Out of the tested concentrations, 70 ppm of kinnow peel oil was found to be the effective concentration against 4^th instar larvae of Ae. aegypti. LC₅₀ and LC₉₀ toxicity values were 47.26 and 61.56 ppm, respectively. No residual activity effect in terms of larval mortality was found, however a significant delay in development (L4 to adult) was observed after placing new larvae in the leftover effective oil concentration. No effect of storage on larvicidal potential of 2, 4 and 6 months old kinnow peel oil in comparison to freshly extracted oil was observed.

INTERPRETATION & CONCLUSION

Kinnow peel oil proved to have a good potential as a biolarvicide against Ae. aegypti and could be used as an effective and eco-friendly mosquito control agent in the future.

Using nanoemulsions of the essential oils of a selection of medicinal plants from Jazan, Saudi Arabia, as a green larvicidal against Culex pipiens

Researchers are increasingly looking to plants as sources of novel ingredients active against vector-borne diseases. Medicinal plant extracts and their metabolites are an attractive source for such products. This study investigated the insecticidal activity of five essential oils extracted from the most common medicinal herbs in Jazan province, Kingdom of Saudi Arabia. Extracted oils and nanoemulsions synthesized from those oils were characterized before application at different concentrations to laboratory-reared fourth-stage larvae of Culex pipens. Basil (Ocimum bascilicum) and cumin (Cuminum cyminum) essential oils showed moderate larvicidal effect with LC50 81.07 ug/mL and 96.29 ug/mL, respectively. That activity was improved in their nanoemulsion forms, as evidenced by a reduction in the LC50 to 65.19 ug/mL for basil and 64.50 ug/mL for cumin. Clove (Syzygium aromaticum), henna (Lawsonia inermis) and ginger (Zingiber officinalis) oils showed weaker insecticidal activity, with LC50 values of 394 ug/mL, 306 ug/mL, and 494 ug/mL, respectively. Moreover, the nanoemulsion forms of those essential oils did not show any improvement in their insecticidal activity. In conclusion, of the studied plants, the nanoemulsions of basil and cumin showed significant larvicidal activity.

Fabrication of Microfiber-Templated Microfluidic Chips with Microfibrous Channels for High Throughput and Continuous Production of Nanoscale Droplets

A polydimethylsiloxane (PDMS) microfluidic chip with well-interconnected microfibrous channels was fabricated by using an electrospun poly(ε-caprolactone) (PCL) microfibrous matrix and 3D-printed pattern as templates. The microfiber-templated microfluidic chip (MTMC) was used to produce nanoscale emulsions and spheres through multiple emulsification at many small micro-orifice junctions among microfibrous channels. The emulsion formation mechanisms in the MTMC were the cross-junction dripping or Y-junction splitting at the micro-orifice junctions. We demonstrated the high throughput and continuous production of water-in-oil emulsions and polyethylene glycol-diacrylate (PEG-DA) spheres with controlled size ranges from 2.84 μm to 83.6 nm and 1.03 μm to 45.7 nm, respectively. The average size of the water droplets was tuned by changing the micro-orifice diameter of the MTMC and the flow rate of the continuous phase. The MTMC theoretically produced 58 trillion PEG-DA nanospheres per hour without high shear force. In addition, we demonstrated the higher encapsulation efficiency of the PEG-DA microspheres in the MTMC than that of the microspheres fabricated by ultrasonication. The MTMC can be used as a powerful platform for the large-scale and continuous productions of emulsions and spheres.

Curcumin Derivatives as Potential Mosquito Larvicidal Agents against Two Mosquito Vectors, Culex pipiens and Aedes albopictus

Vector-borne diseases have appeared or re-emerged in many Southern Europe countries making the transmission of infectious diseases by mosquitoes (vectors) one of the greatest worldwide health threats. Larvicides have been used extensively for the control of Aedes (Stegomyia) albopictus (Skuse, 1895) (Diptera: Culicidae) and Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) mosquitoes in urban and semi-urban environments, causing the increasing resistance of mosquitoes to commercial insecticides. In this study, 27 curcuminoids and monocarbonyl curcumin derivatives were synthesised and evaluated as potential larvicidal agents against Cx. pipiens and Ae. albopictus. Most of the compounds were more effective against larvae of both mosquito species. Four of the tested compounds, curcumin, demethoxycurcumin, curcumin-BF2 complex and a monocarbonyl tetramethoxy curcumin derivative exhibited high activity against both species. In Cx. pipiens the recorded LC50 values were 6.0, 9.4, 5.0 and 32.5 ppm, respectively, whereas in Ae. albopictus they exhibited LC50 values of 9.2, 36.0, 5.5 and 23.6 ppm, respectively. No conclusive structure activity relationship was evident from the results and the variety of descriptors values generated in silico provided some insight to this end.

Isolation of Volatile Compounds with Repellent Properties against Aedes albopictus (Diptera: Culicidae) Using CPC Technology

The present work describes the use of Centrifugal Partition Chromatography (CPC) for the bio-guided isolation of repellent active volatile compounds from essential oils. Five essential oils (EOs) obtained from three Pinus and two Juniperus species were initially analyzed by gas chromatography–mass spectrometry (GC/MS) and evaluated for their repellent properties against Aedes albopictus. The essential oil from needles of P. pinea (PPI) presented the higher activity, showing 82.4% repellency at a dose of 0.2 μL/cm². The above EO, together with the EO from the fruits of J. oxycedrus subsp. deltoides (JOX), were further analyzed by CPC using the biphasic system n-Heptane/ACN/BuOH in ratio 1.6/1.6/0.2 (v/v/v). The analysis of PPI essential oil resulted in the recovery of (−)-limonene, guaiol and simple mixtures of (−)-limonene/β-pheladrene, while the fractionation of JOX EO led to the recovery of β-myrcene, germacrene-D, and mixtures of α-pinene/β-pinene (ratio 70/30) and α-pinene/germacrene D (ratio 65/45). All isolated compounds and recovered mixtures were tested for their repellent activity. From them, (−)-limonene, guaiol, germacrene-D as well the mixtures of (−)-limonene/β-pheladrene presented significant repellent activity (>97% repellency) against Ae. albopictus. The present methodology could be a valuable tool in the effort to develop potent mosquito repellents which are environmentally friendly.