George Koliopoulos

Coactivity of sulfide ingredients: a new perspective of the larvicidal activity of garlic essential oil against mosquitoes

BACKGROUND The activity of several garlic oil ingredients against Culex pipiens L. larvae was studied. In addition to diallyl sulfide (DS) and diallyl disulfide (DDS), the garlic oils used included one essential oil (EO) and two semi-synthetic garlic essential oils (SSGEO1 and SSGEO2), which resulted from the enrichment of EO with DS and DDS standards respectively. The oils were compared with respect to their toxicity. RESULTS The chemical composition of the tested oils was evaluated by means of gas chromatography-mass spectrometry. Experimental data from the tested samples revealed high toxicity. In detail, DDS (6.09 mg L(-1)) was the most active, followed by SSGEO2 (7.05 mg L(-1)) and EO (8.01 mg L(-1)), while SSGEO1 and DS were relatively inactive. CONCLUSION The addition of DDS to EO did not change the toxic effect of the essential oil, whereas the presence of DS in excess produced an enriched essential oil with low toxicity. Furthermore, the antagonistic effect of DS and DDS against the other components of EO was shown by the application of two equations obtained from the literature. Their larvicidal performances were correlated, for the first time, with their detailed chemical composition. Data analysis strongly indicated the toxicity of the other EO sulfur ingredients.

A Study on Distribution and Seasonal Abundance of Aedes albopictus (Diptera: Culicidae) Population in Athens, Greece

ABSTRACT In September 2008, Aedes (Stegomyia) albopictus (Skuse 1894), a mosquito of great medical importance, was reported for the first time in a district of Athens, Greece. The following year, its distribution and population abundance over time around its first detection site was investigated. A network of 50 ovitraps was established in a surrounding area of 25 km2 and monitored for 17 mo from 17 August 2009 through 31 December 2010. Weekly servicing of the ovitraps and subsequent laboratory treatment of the collected mosquito eggs, revealed that Ae. albopictus is the dominant container breeding Aedes species and is widespread in the entire study area. The seasonal monitoring showed that this mosquito is continuously active from mid spring until the end of December with a considerably high oviposition activity recorded during summer and fall. Moreover, comparison of its activity during late August and end of December, between the two consecutive surveillance years, indicated a significant increase of population abundance the second year. The current study suggests the necessity of setting up in the city of Athens an integrated surveillance program in a greater scale for Asian tiger mosquitos effective control.

Evaluation of naturally occurring curcuminoids and related compounds against mosquito larvae

The three curcuminoid components commonly isolated from Curcuma longa, curcumin (1), demethoxycurcumin (2), and bis-demethoxycurcumin (3) were separated and isolated from a commercially available turmeric extract product in high purity and sufficient amounts. Three more derivatives of curcumin, the di-O-demethylcurcumin (4), di-O-methylcurcumin (5) and the di-O-acetylcurcumin (6) were also synthesized and characterized. All six compounds were evaluated for their larvicidal effect against the mosquito Culex pipiens. Curcumin (1) exhibited highly potent larvicidal activity with LC(50) value of 19.07mgL(-1). Moreover, di-O-demethylcurcumin (4), was found to be equally active with LC(50) value of 12.42mgL(-1). Based on the LC(90) values of the two compounds, di-O-demethylcurcumin (4) was the most active of all, resulting in an LC(90) value of 29.40mgL(-1), almost half of the LC(90) value 61.63mgL(-1) found for compound 1. The rest of the compounds were inactive at concentrations even as high as 150mgL(-1) indicating a dependence of the larvicidal activity upon the substitution patent and the presence of aromatic hydroxyl and methoxy moieties. These results show for the first time the potential of this valuable natural product regarding its use as vector control agent.

Influence of the microencapsulated pheromone from aged infusion as an oviposition medium of the West Nile virus vector Culex pipiens.

The main tendency for the control of West Nile virus vectors, without the presence of disease, is to perform integrated programs minimizing chemicals by using environmentally friendly substances which act as oviposition attractants such as oviposition pheromones and infusions. This is the first time that an aged infusion is combined with aged pheromone (microencapsulated). Initially, three common plants in Greece were evaluated as a potential oviposition medium: Oxalis pes-carpae, Jasminum polyanthum, and Avena barbata. All revealed an excellent oviposition attractancy which was more than 80%. O. pes-carpae was used for further investigation and attractancy over time was also studied. Finally, the combination of the synthetic pheromone (6-acetoxy-5-hexadecanolide) with the O. pes-carpae infusion revealed a synergistic effect only for the first day. This project was a first detection for the potential use of microencapsulated synthetic pheromone with infusion and results are discussed.

Bioefficacy of acyclic monoterpenes and their saturated derivatives against the West Nile vector Culex pipiens

Twenty acyclic monoterpenes with different functional groups (acetoxy, hydroxyl, carbonyl and carboxyl) bearing a variable number of carbon double bonds were assayed as repellent and larvicidal agents against the West Nile vector Culex pipiens. Seven of them were derivatives that were synthesized through either hydrogenation or oxidation procedures. All repellent compounds were tested at the dose of 1mgcm(-2) and only neral and geranial were also tested at a 4-fold lower dose (0.25mgcm(-2)). Repellency results revealed that geranial, neral, nerol, citronellol, geranyl acetate and three more derivatives dihydrolinalool (3), dihydrocitronellol (5) and dihydrocitronellyl acetate (6) resulted in no landings. Based on the LC50 values the derivative dihydrocitronellyl acetate (6) was the most active of all, resulting in an LC50 value of 17.9mgL(-1). Linalyl acetate, citronellyl acetate, neryl acetate, geranyl acetate, dihydrocitronellol (5), dihydrocitronellal (7), citronellol, dihydrolinalyl acetate (2), citronellic acid and tetrahydrolinalyl acetate (1) were also toxic with LC50 values ranging from 23 to 45mgL(-1). Factors modulating toxicity have been identified, thus providing information on structural requirements for the selected acyclic monoterpenes. The acetoxy group enhanced toxicity, without being significantly affected by the unsaturation degree. Within esters, reduction of the vinyl group appears to decrease potency. Presence of a hydroxyl or carbonyl group resulted in increased activity but only in correlation to saturation degree. Branched alcohols proved ineffective compared to the corresponding linear isomers. Finally, as it concerns acids, data do not allow generalizations or correlations to be made.

Asymmetric Mating Interference between Two Related Mosquito Species: Aedes (Stegomyia) albopictus and Aedes (Stegomyia) cretinus

Aedes (Stegomyia) albopictus (Skuse) and Aedes (Stegomyia) cretinus Edwards are closely related mosquito species with common morphological features and bio-ecological similarities. Recent mosquito surveillance in Athens, Greece, showed that they are sympatric mosquito species, with Ae. Albopictus developing quite higher population densities than Ae. Cretinus. The potential of mating interference between these species was investigated by reciprocal and homologous mating experiments in cages under laboratory conditions. In non-choice interspecific crosses (groups of males and females) females of both species produced sterile eggs. Insemination rate was 58% for Ae. Cretinus females and only 1% for Ae. Albopictus females. Aedes albopictus males were sexually aggressive and inseminated Ae. Cretinus females (31%) in choice experiments, where males of one species had access to mate with females of both species. Whereas, interspecific mating of Ae. Albopictus females with Ae. Cretinus males in the co-occurrence of Ae. Cretinus females was weaker (4%). Aedes cretinus females from non-choice crossing with Ae. Albopictus or Ae. Cretinus males were paired individually with conspecific males. The percentage of fertile Ae. Cretinus females was 17.5% when had encaged before with Ae. Albopictus males, compared to 100% when Ae. Cretinus females were encaged with conspecific males only. Probable ecological consequences of asymmetric mating between these ecologically homologous species in nature are discussed.

Hyperforin and deoxycohumulone as a larvicidal agent against Culex pipiens (Diptera: Culicidae)

The larvicidal effect of hyperforin (1), a bioactive compound of Hypericum perforatum, and deoxycohumulone (2) (biosynthetic precursor of hyperforin) were evaluated against Culex pipiens (Diptera: Culicidae) for the first time. All the acetate analogues (3-6) of hyperforin (1) and deoxycohumulone (2) were also synthesized and bioassayed to provide information on structural requirements for the tested compounds. Larvicidal results revealed that hyperforin (1) and deoxycohumulone (2) exhibited potent activity with LC50 value of 26.72 and 51.03 mg L(-1), respectively. The monoacetyl-deoxycohumulone (4) displayed lower activity with LC50 value of 135.92 mg L(-1), while all other acetate analogues were inactive at concentrations even as high as 150 mg L(-1), indicating that the free hydroxyl groups are essential for the larvicidal activity. The mortality values were increased, more than 80%, when 10 mg L(-1) piperonyl butoxide were added in hyperforin (1) or deoxycohumulone (2) bioassays. Finally, sub-lethal survival analysis is conducted for three doses of hyperforin (1) and deoxycohumulone (2) and results are discussed.

Imported Chikungunya fever case in Greece in June 2014 and public health response.

We report about the first imported case of Chikungunya fever in Greece in a Greek traveler returning from the Dominican Republic and the associated public health response. We investigated the case and performed focused epidemiological and entomological investigation in all areas the patient visited during the infectious period, to identify the targeted interventions needed. Entomological investigation revealed the occurrence of the competent vector Aedes albopictus (Diptera: Culicidae) in the environment surrounding the hospital where the patient was admitted and in her workplace. All captured mosquitoes tested negative for Chikungunya virus. We further conducted clinical and laboratory examination of the patient’s co-travelers, gave advice on appropriate personal preventive measures against mosquito bites to the patient and co-travelers and on vector control, and raised awareness among health professionals throughout Greece. The risk of introduction and local transmission of Chikungunya and other arboviruses in Greece and other European countries is present, as the competent vector exists in many parts of Europe. Public health professionals, travel medicine specialists and clinicians should maintain awareness regarding this possibility of importation of arbovirus cases in order to provide the appropriate advice, seek the prompt diagnosis, and implement appropriate interventions. Mobilization of various stakeholders will lead to enhanced epidemiological and entomological surveillance that will allow for improved risk assessment in each area.