Laboratory study on larval competition between two related mosquito species: Aedes (Stegomyia) albopictus and Aedes (Stegomyia) cretinus.

Aedes albopictus (Asian tiger mosquito) and Aedes cretinus are closely related mosquito species with similar morphological and bio-ecological characteristics. These species have been detected in specific areas of Athens, Greece, with Ae. albopictus developing significantly higher population densities than the native mosquito Ae. cretinus. In a laboratory factorial experimental design, we investigated the potential of interspecific and intraspecific competition between larvae of these species under various food and population density conditions. Duration of larval development, survival rate from the first larval instar until adulthood and the wing length of females were measured. When these two species developed on their own, larvae developed faster and the females were larger at high food provision, indicating intraspecific competition. When the two species developed in the same environment and food provision was low, Ae. albopictus outcompeted Ae. cretinus. In particular, the larval developmental time when these species competed with each other was 1.3 to 2.4 days shorter for Ae. albopictus and 0.9 to 1.4 days longer for Ae. cretinus, compared with single species development. Interspecific competition resulted to larger Ae. albopictus females at limited food availability and low density of individuals. Our findings indicate that Ae. albopictus is a superior competitor to Ae. cretinus, primarily at limited larval food resources, and this may account for the expansion of Ae. albopictus and the limited presence of Ae. cretinus in areas of Athens, Greece, where these related species co-exist.

Chemical composition and assessment of larvicidal and repellent capacity of 14 Lamiaceae essential oils against Aedes albopictus.

In the current laboratory study, 14 essential oils (EOs) derived from 12 Lamiaceae plant species and their major components were screened for their larvicidal and repellent properties against Aedes albopictus, an invasive mosquito species of great medical importance. The results of toxicity bioassays revealed that the EOs from Thymus vulgaris, Ocimum basilicum, Origanum dictamnus, Origanum majorana, and Origanum vulgare, as well as their major components (terpenes), namely thymol, carvacrol, p-cymene, and γ-terpinene exerted the highest larvicidal effect. Essential oils from Mellisa officinalis, Origanum dictamus, Mentha spicata (chem. piperitenone epoxide), Origanum majorana, and Satureja thymbra were the most potent repellents, with the last two assigned as the best ones. Among the terpenes tested, piperitenone epoxide, carvacrol, thymol, and piperitenone provided the highest level of protection against Ae. albopictus adults. Chemical analysis revealed the presence of a high number of terpenes in the EOs, while in most cases, the biological action of the tested EOs and their major components was in consistency. The most effective EOs and terpenes that were identified through the current laboratory bioassays could be used as alternative agents to control larvae and repel adults of Ae. albopictus.

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 [corrected] developing quite higher population densities than Ae. cretinus [corrected] . 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 [corrected] 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 [corrected] 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 [corrected] 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 [corrected] males, compared to 100% when Ae. cretinus [corrected] females were encaged with conspecific males only. Probable ecological consequences of asymmetric mating between these ecologically homologous species in nature are discussed.

Essential oil composition, adult repellency and larvicidal activity of eight Cupressaceae species from Greece against Aedes albopictus (Diptera: Culicidae).

The present study evaluated leaf essential oils from eight Cupresaceae species; Cupressus arizonica, Cupressus benthamii, Cupressus macrocarpa, Cupressus sempervirens, Cupressus torulosa, Chamaecyparis lawsoniana, Juniperus phoenicea, and Tetraclinis articulata for their larvicidal and repellent properties against Aedes albopictus, a mosquito of great ecological and medical importance. Based on the LC(50) values, C. benthamii essential oil was the most active (LC(50) = 37.5 mg/L) while the other tested Cupressaceae essential oils provided rather moderate toxicity against larvae (LC(50) = 47.9 to 70.6 mg/L). Under the used laboratory conditions, three of the essential oils (C. benthamii, C. lawsoniana, and C. macrocarpa) provided sufficient protection against mosquito adults, equivalent to the standard repellent "Deet" in the 0.2 mg/cm(2) dose, while C. macrocarpa assigned as the superior repellent oil in the 0.08 mg/cm(2) dose. Chemical analysis of the essential oils using gas chromatography and gas chromatography-mass spectrometry revealed the presence of 125 components.

Evaluation of bioefficacy of three Citrus essential oils against the dengue vector Aedes albopictus (Diptera: Culicidae) in correlation to their components enantiomeric distribution.

Laboratory experiments were conducted to study the bioefficacy against Ae. albopictus of three Citrus essential oils, derived from peels of Citrus sinensis, Citrus limon, and Citrus paradise and of their components. Chiral gas chromatography analysis revealed the dominant occurrence of R-(+)-limonene and (-)-ß-pinene in all three essential oils while in the case of lemon oil γ-terpinene, neral, and geranial detected also among other components. The tested Citrus essential oils were toxic against mosquito larvae with LC(50) values ranging from 25.03 to 37.03 mg l(-1). Among citrus essential oils components tested, γ-terpinene was the most toxic (LC(50) = 20.21 mg l(-1)) followed by both enantiomeric forms of limonene (LC(50) = 35.99 and 34.89 mg l(-1), for R-(+)-limonene and S-(-)-limonene, respectively). The delayed toxic effects after exposure of larvae to sublethal (LC(50)) doses were also investigated for citrus essential oils and their major component R-(+)-limonene, indicating a significant reduction of pupal survival. In repellent bioassays, lemon essential oil, S-(-)-limonene, citral (mixture of neral\geranial) and (+)-ß-pinene were the most effective compared with other citrus essential oils and components against adult mosquitoes. Repellent bioassays also revealed that limonenes and ß-pinenes showed an isomer dependence repellent activity. Finally, according to enantiomeric distribution of limonene and α- and ß-pinene, the repellency of lemon essential oil is possibly attributed to the presence of citral.

A study on distribution and seasonal abundance of Aedes albopictus (Diptera: Culicidae) population in Athens, Greece.

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 mosquito's effective control.