Insect repellents mediate species-specific olfactory behaviours in mosquitoes.

BACKGROUND: The species-specific mode of action for DEET and many other mosquito repellents is often unclear. Confusion may arise for many reasons. First, the response of a single mosquito species is often used to represent all mosquito species. Second, behavioural studies usually test the effect of repellents on mosquito attraction towards human odorants, rather than their direct repulsive effect on mosquitoes. Third, the mosquito sensory neuron responses towards repellents are often not directly examined. METHODS: A close proximity response assay was used to test the direct repulsive effect of six mosquito repellents on Anopheles coluzzii, Aedes aegypti and Culex quinquefasciatus mosquitoes. Additionally, the behavioural assay and calcium imaging recordings of antennae were used to test the response of An. coluzzii mosquitoes towards two human odorants (1-octen-3-ol and benzaldehyde) at different concentrations, and mixtures of the repellents lemongrass oil and p-menthane-3,8-diol (PMD) with DEET. RESULTS: Anopheles coluzzii mosquitoes were repelled by lemongrass oil and PMD, while Ae. aegypti and Cx. quinquefasciatus mosquitoes were repelled by lemongrass oil, PMD, eugenol, and DEET. In addition, high concentrations of 1-octen-3-ol and benzaldehyde were repellent, and activated more olfactory receptor neurons on the An. coluzzii antennae than lower concentrations. Finally, changes in olfactory responses to repellent mixtures reflected changes in repulsive behaviours. CONCLUSIONS: The findings described here suggest that different species of mosquitoes have different behavioural responses to repellents. The data further suggest that high-odour concentrations may recruit repellent-sensing neurons, or generally excite many olfactory neurons, yielding repellent behavioural responses. Finally, DEET can decrease the neuronal and behavioural response of An. coluzzii mosquitoes towards PMD but not towards lemongrass oil. Overall, these studies can help inform mosquito repellent choice by species, guide decisions on effective repellent blends, and could ultimately identify the olfactory neurons and receptors in mosquitoes that mediate repellency.

Bacteria: A novel source for potent mosquito feeding-deterrents.

Antibiotic and insecticidal bioactivities of the extracellular secondary metabolites produced by entomopathogenic bacteria belonging to genus Xenorhabdus have been identified; however, their novel applications such as mosquito feeding-deterrence have not been reported. Here, we show that a mixture of compounds isolated from Xenorhabdus budapestensis in vitro cultures exhibits potent feeding-deterrent activity against three deadly mosquito vectors: Aedes aegypti, Anopheles gambiae, and Culex pipiens. We demonstrate that the deterrent active fraction isolated from replicate bacterial cultures is highly enriched in two compounds consistent with the previously described fabclavines, strongly suggesting that these are the molecular species responsible for feeding-deterrence. The mosquito feeding-deterrent activity in the putative fabclavine-rich fraction is comparable to or better than that of N,N-diethyl-3-methylbenzamide (also known as DEET) or picaridin in side-by-side assays. These findings lay the groundwork for research into biologically derived, peptide-based, low-molecular weight compounds isolated from bacteria for exploitation as mosquito repellents and feeding-deterrents.

Behavioral responses of gravid Culex quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus mosquitoes to aquatic macrophyte volatiles.

Mosquitoes use many cues to assess whether a habitat is conducive for reproduction, possibly including the presence of stimuli from aquatic macrophytes. The effect of water infusions of water hyacinth (Eichhornia crassipes), water lettuce (Pista stratioles), parrotfeather (Myriophyllum aquaticum), and water pennywort (Hydrocotyle umbellata) on mosquito oviposition and attraction was investigated. Gravid Culex quinquefasciatus deposited significantly more egg rafts in water hyacinth, water lettuce, or Bermuda hay (positive control) infusions compared to water, while water pennywort and parrotfeather infusions did not differ from water. In-flight attraction responses of Cx. quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus were evaluated. The strongest attraction of gravid Cx. quinquefasciatus and Ae. aegypti occurred in the presence of volatiles from infusions of water hyacinth and water lettuce, which were equal in attractiveness to hay infusion. Water pennywort and parrotfeather infusions were not attractive. Gravid An. quadrimaculatus were not attracted to aquatic plant volatiles. The results suggest that water hyacinth and water lettuce emit volatile chemicals that attract two of three mosquito species tested and stimulate oviposition by Cx. quinquefasciatus, demonstrating that the level of attraction of aquatic plant volatiles varies among species in ways that may have relevance to bait-based detection and control methods.

Baccharis dracunculifolia (Asteraceae) essential oil toxicity to Culex quinquefasciatus (Culicidae).

The control of mosquitoes by means of chemical insecticides has been a problem, mainly due to the possibility of resistance developed by insects to xenobiotics. For this reason, demand for botanical insecticides has increased. In this sense, the present work aims to verify the susceptibility and morphological and biochemical alterations of Culex quinquefasciatus larvae after exposure to essential oil (EO) of leaves of Baccharis dracunculifolia. To observe the larvicidal action, larvae were exposed to EO at concentrations of 25, 50, 100, and 200 mg/L, until their emergence to adults. The control group was exposed to deionized water and dimethyl sulfoxide. Morphological analyses were also carried out using hematoxylin and eosin, mercury bromophenol blue, Nile blue, and periodic acid Schiff. Biochemical analyses of total glucose, triacylglyceride (TAG), protein, and acetylcholinesterase levels were performed. The phytochemical analysis of the EO showed (E)-nerolidol as the major compound (30.62%). Larvae susceptibility results showed a LC50 of 34.45 mg/L for EO. Morphological analysis showed that there were histological changes in midgut. For biochemical analyses, the glucose level in the larvae exposed to EO for 24 h decreased significantly, unlike the TAG levels, which increased. The total protein level of the larvae also increased after exposure for 24 h, and acetylcholinesterase levels decreased significantly. Taking all our data into account, we can conclude that EO causes destabilization in larva, leading to histological changes, metabolic deregulation and, consequently, their death.

Natural Product-Based Pesticide Discovery: Design, Synthesis and Bioactivity Studies of N-Amino-Maleimide Derivatives.

Natural products are an important source of pesticide discovery. A series of N-amino-maleimide derivatives containing hydrazone group were designed and synthesized based on the structure of linderone and methyllinderone which were isolated from Lindera erythrocarpa Makino. According to the bioassay results, compounds 2 and 3 showed 60% inhibition against mosquito (Culex pipiens pallens) at 0.25 µg·mL−1. Furthermore, the results of antifungal tests indicated that most compounds exhibited much better antifungal activities against fourteen phytopathogenic fungi than linderone and methyllinderone and some compounds exhibited better antifungal activities than commercial fungicides (carbendazim and chlorothalonil) at 50 µg·mL−1. In particular, compound 12 exhibited broad-spectrum fungicidal activity (>50% inhibitory activities against 11 phytopathogenic fungi) and compounds 12 and 14 displayed 60.6% and 47.9% inhibitory activity against Rhizoctonia cerealis at 12.5 µg·mL−1 respectively. Furthermore, compound 17 was synthesized, which lacks N-substituent at maleimide and its poor antifungal activity against Sclerotinia sclerotiorum and Rhizoctonia cerealis at 50 µg·mL−1 showed that the backbone structure of N-amino-maleimide derivatives containing hydrazone group was important to the antifungal activity.

The effect of dietary antioxidant supplementation in a vertebrate host on the infection dynamics and transmission of avian malaria to the vector.

Host susceptibility to parasites is likely to be influenced by intrinsic factors, such as host oxidative status determined by the balance between pro-oxidant production and antioxidant defences. As a result, host oxidative status acts as an environmental factor for parasites and may constrain parasite development. We evaluated the role of host oxidative status on infection dynamics of an avian malarial parasite by providing canaries (Serinus canaria) with an antioxidant supplementation composed of vitamin E (a lipophilic antioxidant) and olive oil, a source of monounsaturated fatty acids. Another group received a standard, non-supplemented food. Half of the birds in each group where then infected with the haemosporidian parasite, Plasmodium relictum. We monitored the parasitaemia, haematocrit level, and red cell membrane resistance, as well as the transmission success of the parasite to its mosquito vector, Culex pipiens. During the acute phase, the negative effect of the infection was more severe in the supplemented group, as shown by a lower haematocrit level. Parasitaemia was lower in the supplemented group during the chronic phase only. Mosquitoes fed on supplemented hosts were more often infected than mosquitoes fed on the control group. These results suggest that dietary antioxidant supplementation conferred protection against Plasmodium in the long term, at the expense of a short-term negative effect. Malaria parasites may take advantage of antioxidants, as shown by the increased transmission rate in the supplemented group. Overall, our results suggest an important role of oxidative status in infection outcome and parasite transmission.

"Singing in the Tube"--audiovisual assay of plant oil repellent activity against mosquitoes (Culex pipiens).

Plant essential oils have been suggested as a promising alternative to the established mosquito repellent DEET (N,N-diethyl-meta-toluamide). Searching for an assay with generally available equipment, we designed a new audiovisual assay of repellent activity against mosquitoes "Singing in the Tube," testing single mosquitoes in Drosophila cultivation tubes. Statistics with regression analysis should compensate for limitations of simple hardware. The assay was established with female Culex pipiens mosquitoes in 60 experiments, 120-h audio recording, and 2580 estimations of the distance between mosquito sitting position and the chemical. Correlations between parameters of sitting position, flight activity pattern, and flight tone spectrum were analyzed. Regression analysis of psycho-acoustic data of audio files (dB[A]) used a squared and modified sinus function determining wing beat frequency WBF ± SD (357 ± 47 Hz). Application of logistic regression defined the repelling velocity constant. The repelling velocity constant showed a decreasing order of efficiency of plant essential oils: rosemary (Rosmarinus officinalis), eucalyptus (Eucalyptus globulus), lavender (Lavandula angustifolia), citronella (Cymbopogon nardus), tea tree (Melaleuca alternifolia), clove (Syzygium aromaticum), lemon (Citrus limon), patchouli (Pogostemon cablin), DEET, cedar wood (Cedrus atlantica). In conclusion, we suggest (1) disease vector control (e.g., impregnation of bed nets) by eight plant essential oils with repelling velocity superior to DEET, (2) simple mosquito repellency testing in Drosophila cultivation tubes, (3) automated approaches and room surveillance by generally available audio equipment (dB[A]: ISO standard 226), and (4) quantification of repellent activity by parameters of the audiovisual assay defined by correlation and regression analyses.

Efficacy of essential oil from Cananga odorata (Lamk.) Hook.f. & Thomson (Annonaceae) against three mosquito species Aedes aegypti (L.), Anopheles dirus (Peyton and Harrison), and Culex quinquefasciatus (Say).

The essential oil of Cananga odorata flowers was evaluated for oviposition-deterrent, ovicidal, insecticidal, and repellent activities toward three mosquito species: Aedes aegypti, Anopheles dirus, and Culex quinquefasciatus. Oviposition deterrence of the oil was evaluated on gravid females using oviposition deterrence bioassay. The results showed that 10 % Ca. odorata exhibited high percent effective repellency against oviposition at 99.4 % to Ae. aegypti, 97.1 % to An. dirus, and 100 % to Cx. quinquefasciatus. Ca. odorata oil was tested for ovicidal activity. Regression equations revealed that the ovicidal rates were positively correlated with the concentrations of the essential oil. As the concentration of essential oil increased from 1, 5, and up to 10 % concentration, the ovicidal rate increased accordingly. Larvicidal activity of the oils was used on immature stages (third and fourth instar lavae and pupae). The maximum larval mortality was found with 10 % Ca. odorata against immature stages, and there were LC50 values ranged from 10.4 to 10.5 % (for Ae. aegypti), <1 % (for An. dirus), and <1 % (for Cx. quinquefasciatus). Adulticidal properties were evaluated with unfed females. Ten percent Ca. odorata oil had high knockdown rates against the three mosquito species at 96 % (for Ae. aegypti), 98.4 % (for An. dirus), and 100 % (for Cx. quinquefasciatus), with EC50 values of 6.2, 4.7, and 5.4 %, respectively. It gave moderate mortality rates after 24 and 48 h of exposure. Ca. odorata oil was assessed for repellency to females by using the modified K&D module. Ten percent Ca. odorata oil gave the strongest value against Ae. aegypti, An. dirus, and Cx. quinquefasciatus, with percentage repellency of 66, 92, and 90 %, respectively. This study demonstrates the potential for the essential oil of Ca. odorata essential oil to be used as a botanical insecticide against three mosquito species.

Larvicidal, oviposition, and ovicidal effects of Artemisia annua (Asterales: Asteraceae) against Aedes aegypti, Anopheles sinensis, and Culex quinquefasciatus (Diptera: Culicidae).

This study focuses on the larvicidal, oviposition, and ovicidal effects of a crude extract of Artemisia annua against Aedes aegypti, Anopheles sinensis, and Culex quinquefasciatus. Dried cells of Artemisia annua from cell suspension cultures were extracted using hexane. The extract showed moderate larvicidal effects against mosquitoes. At 24-h post treatment, the LC50 values for Anopheles sinensis, Aedes aegypti, and Culex quinquefasciatus were recorded as 244.55, 276.14, and 374.99 ppm, respectively. The percentage mortality of larvae was directly proportional to the tested concentration. Anopheles sinensis was found to be the most susceptible species, whereas Culex quinquefasciatus was the most tolerant to the Artemisia annua extract. The results indicated that the Artemisia annua extract showed concentration-dependent oviposition deterrent activity and had a strong deterrent effect. At 500 ppm, the percentage effective repellency was more than 85% compared with the control group for all the species, with oviposition activity index values of -0.94, -0.95, and -0.78 for Aedes aegypti, Anopheles sinensis, and Culex quinquefasciatus, respectively. In the ovicidal assay, the percentage hatchability of eggs after treatment with 500 ppm of Artemisia annua extract was significantly lower than the control, with values of 48.84 ± 4.08, 38.42 ± 3.67, and 79.35 ± 2.09% for Aedes aegypti, Anopheles sinensis, and Culex quinquefasciatus, respectively. Artemisia annua was found to be more effective against Aedes aegypti and Anopheles sinensis compared with Culex quinquefasciatus. This study indicated that crude extract of A. annua could be a potential alternative for use in vector management programs.

Evaluation of commercial products for personal protection against mosquitoes.

Human landing catch studies were conducted in a semi-field setting to determine the efficacy of seven commercial products used for personal protection against mosquitoes. Experiments were conducted in two empty, insecticide free, mesh-enclosed greenhouses, in Israel, with either 1500 Aedes albopictus or 1500 Culex pipiens released on consecutive study nights. The products tested in this study were the OFF!(®) Clip-On™ Mosquito Repellent (Metofluthrin 31.2%) and the Terminix(®) ALLCLEAR(®) Sidekick Mosquito Repeller (Cinnamon oil 10.5%; Eugenol 13%; Geranium oil 21%; Peppermint 5.3%; Lemongrass oil 2.6%), which are personal diffusers; Super Band™ Wristband (22% Citronella oil) and the PIC(®) Citronella Plus Wristband (Geraniol 15%; Lemongrass oil 5%, Citronella oil 1%); the Sonic Insect Repeller Keychain; the Mosquito Guard Patch (Oil of Lemon Eucalyptus 80mg), an adhesive-backed sticker for use on textiles; and the Mosquito Patch (vitamin B1 300mg), a transdermal patch. It was determined that the sticker, transdermal patch, wristbands and sonic device did not provide significant protection to volunteers compared with the mosquito attack rate on control volunteers who were not wearing a repellent device. The personal diffusers: - OFF!(®) Clip-On™ and Terminix(®) ALLCLEAR(®) Sidekick - provided superior protection compared with all other devices in this study. These diffusers reduced biting on the arms of volunteers by 96.28% and 95.26% respectively, for Ae. albopictus, and by 94.94% and 92.15% respectively, for Cx. pipiens. In a second trial conducted to compare these devices directly, biting was reduced by the OFF!(®) Clip-On™ and the Terminix(®) ALLCLEAR(®) by 87.55% and 92.83%, respectively, for Ae. albopictus, and by 97.22% and 94.14%, respectively, for Cx. pipiens. There was no significant difference between the performances of the two diffusers for each species.

Larvicidal and pupicidal activity of extracts and fractionates of Eichhornia crassipes (Mart.) Solms against the filarial vector Culex quinquefasciatus Say.

Petroleum ether, acetone, ethyl acetate, aqueous extract, methanol and ethanol fractionate of Eichhornia crassipes (Mart.) Solms was tested for their larvicidal efficacy against the different instars (I, II, III and IV) and pupae of Culex quinquefasciatus Say. The larval mortality was observed after 24 h of the treatment. The extracts showed a dose-dependent toxicity to larvae. The toxicity of the extracts decreased with increase in larval stage. Ethanol fractionate of E. crassipes showed the highest larvicidal and pupicidal activity against C. quinquefasciatus compared to other solvent extracts and fractionates with LC(50) 71.43, 94.68,120.42, 152.15 and 173.35 ppm for I, II, III, IV and pupae, respectively. Presence of metabolites like flavonoids, alkaloids, anthroquinones and anthocyanins in the tested extracts might be the reason for the larvicidal and pupicidal activity of the plant extracts and fractionates of waterhyacinth. Mosquito-repellent activity was not exhibited by these extracts at the tested concentrations. The results demonstrated the potential of the aquatic plant E. crassipes in the successful control of the filarial vector C. quinquefasciatus.

Effect of Ageratum houstonianum Mill. (Asteraceae) leaf extracts on the oviposition activity of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae).

Plant extracts have been studied extensively for their insecticidal activity against immature stages and adult mosquitoes. They have also been reported to influence the habitat preference of ovipositing mosquitoes. Ageratum houstonianum, a medicinal plant belonging to the family Asteraceae, has been reported to possess insecticidal activity, and in the present study, the ovipositional attractant/deterrent activity was studied. The effect of Ageratum houstonianum crude leaf extracts on the oviposition of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus was studied at 0.1 % concentration in laboratory. Among hexane, ethyl acetate and methanol crude leaf extracts, methanol showed an effective deterrent activity against all the three vector species with an oviposition active index of -0.8, -0.8 and -0.9, respectively. Field trials carried out to study the effect of 0.1 % methanol extract on oviposition of Aedes species indicated effective deterrence ranging from 79.0 to 100.0 % in indoor and 74.6 to 100.0 % in outdoor ovitraps. The potential oviposition deterrent property of Ageratum houstonianum crude leaf extracts observed in both laboratory and field studies indicates the presence of phytocompounds that act as effective contact deterrent. Further, isolation, identification and preparation of suitable formulation of the effective phytocompounds of Ageratum houstonianum that act as a contact deterrent are required.

Larvicidal efficacy of botanical extracts against two important vector mosquitoes.

OBJECTIVE: To determine the larvicidal efficacy of different solvent leaf extract of Ervatamia coronaria and Caesalpinia pulcherrima against Anopheles subpictus and Culex tritaeniorhynchus. MATERIALS AND METHODS: Twenty five early third instar larvae of Anopheles subpictus and Culex tritaeniorhynchus were exposed to various concentrations and were assayed in the laboratory. The larval mortality was observed after 24 h of treatment. RESULTS: Among three solvent extracts tested the maximum efficacy was observed in the methanol extract. The LC50 (LC90) values of Ervatamia coronaria and Caesalpinia pulcherrima against early third instar of Anopheles subpictus were 86.47 (159.59) and 113.26 (207.73) ppm and Culex tritaeniorhynchus were 131.53 (245.37) and 165.28 (299.45) ppm, respectively. No mortality was observed in controls. CONCLUSIONS: From the results it can be concluded the crude extract of Ervatamia coronaria and Caesalpinia pulcherrima were excellent potential for controlling Anopheles subpictus and Culex tritaeniorhynchus mosquito larvae.

Larvicidal activity of extracts from Artemisia species against Culex pipiens L. mosquito: comparing endemic versus ubiquist species for effectiveness.

The larvicidal activity of ethanolic leaf extracts from two Artemisia species, Artemisia campestris var. glutinosa and A. molinieri, on mosquito Culex pipiens Linnaeus (Diptera, Culicidae) larvae was investigated. Since A. molinieri is a rare and protected species confined to temporary ponds of Southern France, its toxic activity may help to value this species and to finance its conservation. A. molinieri extracts showed a higher larvicidal activity (from 50 ppm (K=9.488, DDL=4, P<0.001)) than those from A. campestris var glutinosa (from 500 ppm (K=9.488, DDL=4, P<0.01)) after 48 h of exposure. Calculated lethal concentrations, after 48 h of exposure, (LC(50)) were low, 9091 and 9898 ppm for A. molinieri and A. campestris var. glutinosa extracts, respectively, but using a non-pollutant solvent (ethanol). However, A. molinieri may be valued as an environmentally friendly biocide and developing its culture may be of interest for both pesticide activity and conservation purpose.

Repellent properties of Cardiospermum halicacabum Linn. (Family: Sapindaceae) plant leaf extracts against three important vector mosquitoes.

OBJECTIVE: To determine repellent activity of hexane, ethyl acetate, benzene, chloroform and methanol extract of Cardiospermum halicacabum (C. halicacabum) against Culex quinquefasciatus (Cx. quinquefasciatus), Aedes aegypti (Ae. aegypti) and Anopheles stephensi (An. stephensi). METHODS: Evaluation was carried out in a net cage (45 cm×30 cm×25 cm) containing 100 blood starved female mosquitoes of three mosquito species and were assayed in the laboratory condition by using the protocol of WHO 2005; The plant leaf crude extracts of C. halicacabum was applied at 1.0, 2.5, and 5.0 mg/cm(2) separately in the exposed area of the fore arm. Only ethanol served as control. RESULTS: In this observation, the plant crude extracts gave protection against mosquito bites without any allergic reaction to the test person, and also, the repellent activity was dependent on the strength of the plant extracts. The tested plant crude extracts had exerted promising repellent against all the three mosquitoes. CONCLUSIONS: From the results it can be concluded the crude extract of C. halicacabum was potential for controlling Cx. quinquefasciatus, Ae. aegypti and An. stephensi mosquitoes.

Toxicological studies for some agricultural waste extracts on mosquito larvae and experimental animals.

OBJECTIVE: To evaluate some agricultural waste extracts as insecticide and their effects on enzyme activities in liver and kidney of male mice. METHODS: The insecticidal activity of five tested compounds (one crude extract and 4 waste compounds) was bioassay against the 3rd instars of the Culex pipiens (Cx. pipiens) larvae in the laboratory. The LC50 values of eucalyptol, apricot kernel, Rice bran, corn, black liquor and white liquor are 91.45, 1 166.1, 1 203.3, 21 449.65, 4 025.78 and 6 343.18 ppm, respectively. Selection of the compounds for the subsequent studies was not only dependent on LC50 values but also on the persistence of these wastes products on large scale. RESULTS: White and black liquor did not produce any gross effect at 200 mg/Kg body weight. No apparent toxic symptoms were observed in tested animals during the whole period of the experiment which run out for 14 days. No statistically significance was observed in the enzyme cholinesterase activity, the activities of liver enzymes and kidney function in treated mice with black and white liquors. While, no and slight inhibition was observed after the 2 weeks of treatment period with deltamethrin and fenitrothion reached to about 24% in plasma cholinesterase enzyme activity. Significantly increase in the activities of liver enzymes and kidney function in treated mice with deltamethrin and fenitrothion. CONCLUSIONS: Black liquor can be used efficiently to control Cx. pipiens larvae under laboratory condition. Environmental problem caused by rice straw can be solved by converting the waste material to beneficial natural selective insecticide.

Larvicidal, adult emergence inhibition and oviposition deterrent effects of foliage extract from Ricinus communis L. against Anopheles arabiensis and Culex quinquefasciatus in Sudan.

Malaria and filariases are prevalent in Sudan and their control depends largely on preventive measures against mosquito vectors. The present work aimed to investigate the larvicidal, adults emergence inhibition and oviposition deterrent effects of aqueous extracts from leaves of Ricinus communis L. against the mosquitoes, Anopheles arabiensis and Culex quinquefasciatus as a biological control means. The larval mortality was observed after 24 hours. The LC50 values calculated were 403.65, 445.66 and 498.88 ppm against 2nd, 3rd and 4th instar larvae of An. arabiensis and 1091.44, 1364.58 and 1445.44 ppm against 2nd, 3rd and 4th larval instars of Cx. quinquefasciatus. 50% of adult emergence inhibition (EI50) were 374.97 and 1180.32 ppm against 3rd instar larvae of An. arabiensis and Cx. quinquefasciatus. The extract showed oviposition deterrent effect against both species. Results reveal that the crude extract of R. communis possesses remarkable larvicidal, adult emergence inhibition and oviposition deterrent properties against both the tested species and can be used as biological control means.

High quality bergamot oil from Greece: Chemical analysis using chiral gas chromatography and larvicidal activity against the West Nile virus vector.

Tauhe essential oils contained in the rind of the fruit and the leaves of bergamot from Greece (Citrus aurantium subsp. bergamia) were studied. The bergamot trees in question were cultivated on Kefalonia Island. The plant material (leaves and fruits in different stages of maturity) was collected between December and March for a two year period. The rind of the fruit was separated manually and the essential oil was obtained either by cold pressing or by hydrodistillation. The maximum yield calculated on a wet weight of fresh rinds basis was 1.8%. The essential oils were first analyzed by GC-MS with a DB-5 column and then with a beta-Dex enantiomeric column. The main constituent of the cold pressed essential oil of the rind was (-)-linalyl acetate with optical purity >99.9%. Other important constituents were (-)-linalool, (+)-limonene and gamma-terpinene. The best value of linalool/linalyl acetate ratio was 0.38 and the maximum sum of linalool+linalyl acetate was found to be 55.8%. The larvacidal activities of the obtained essential oils and the compounds (+/-)-linalyl acetate, (+/-)-linalool and (-)-linalool were evaluated against larvae of the mosquito species Culex pipiens (Diptera: Culicidae), the West Nile virus vector, under laboratory conditions. The cold pressed essential oil showed an LC(50) value of 58 mg/L, while the LC(50) value of the corresponding essential oil obtained by hydrostillation was 106 mg/L. The essential oil of the leaves presented similar larvicidal toxicity with the cold pressed oil of the rind (LC(50)=68 mg/L).

Larvicidal activity of bis(2-ethylhexyl) benzene-1,2-dicarboxylate from Sterculia guttata seeds against two mosquito species.

The larvicidal activities of various fractions of the hexane extract of the seeds of Sterculia guttata against larvae of Aedes aegypti and Culex quinquefasciatus were determined. Bis(2-ethylhexyl) benzene-1,2-dicarboxylate (1) was identified as one of the active principles, displaying chronic toxicity against both types of larvae, with LD50 values of 79 and 64 ppm, respectively.

Repellent activity of five essential oils against Culex pipiens.

Essential oils extracted from the seeds of anise (Pimpinella anisum), dried fruits of eucalyptus (Eucalyptus camaldulensis), dried foliage of mint (Mentha piperita) and basil (Ocimum basilicum) and fresh foliage of laurel (Laurus nobilis) were tested for their repellency against the adult females of Culex pipiens. All essential oils showed repellency in varying degrees, eucalyptus, basil and anise being the most active.