Mosquitocidal activity of some volatile oils against Aedes caspius mosquitoes.

Vector borne diseases are a major source of illness and death worldwide. Mosquitoes are one of the most important vectors that alone transmit diseases to more than 700 million people per annum1. For instances, malaria alone kills 3 million each year, including 1 child every 30 sec2, is transmitted by Anopheles gambiae and Aedes caspius is the vector of Tahyna (TAH) virus in the Mediterranean region, a potential reservoir of “Rift Valley Fever Virus” (RVF) during interepizootic periods, harbor some microsporidia and the West Nile virus (WNV), and the bacterium Francisella tularensis, the causative agent of tularemia could be detected in natural populations3. Control of such diseases is becoming increasingly difficult because of increasing resistance in mosquitoes to synthetic insecticides4. An alternative and recent approach for mosquito control is the use of natural products of plant origin, botanical derivatives. Beside their toxicity to pests, these botanical insecticides are readily biodegradable and usually lack toxicity to higher animals5 that means they are eco-friendly. Pyrethrum and neem are well-established commercial pesticides based on plant essential oils and have recently entered the market place. A huge number of botanical derivatives exhibited mosquitocidal activity6,7. They act as ovicides, larvicides, pupicides, adulticides, repellents, oviposition deterrents beside their insect growth regulating activity. Cinnamon (Cinnamomum cassia), Sabina (Sabina vulgaris), White camphor (Cinnamomum glanduliferum), and Wintergreen (Liex chinensis) oils exhibited larvicidal activity against the dengue vector Aedes aegypti larvae8. Furthermore, Cinnamon oils exhibited antimicrobial activity9, antimycotic activity10, insecticidal activity against the oak nut weevil Mechoris ursulus11 and mosquito repellent activity against the dengue vector Ae. aegypti12. Since there is no available information about utilizing these oils in Ae. caspius control, this study mainly compares between the mosquitocidal capacities of these oils and the mosquitocidal capacities of a couple of their mixtures against Ae. caspius. Field collected IV instar larvae of Ae. caspius were used in the present work. Volatile oils used in the present work are extracted from Cinnamon, Sabina, White camphor and Wintergreen and were supplied by Biopesticide Research Centre, Yangling, China. Larvae were exposed to one sublethal concentration 5 ppm, and selection of this dose was based on previous study against Ae. aegypti8 whereas LC50 of white camphor, cinnamon and wintergreen oils were 43.0, 58.4 and 81.3 mg/L respectively but Sabina was inactive (Table 1). Hence, the present study investigated the influence of a very low dose, 5 ppm (10th time lower than the most active oil), on the larval development until mosquito emergence compared to mixtures from different oils at the same dose. WHO methodology13 was adopted for evaluating the activity of the volatile oils against mosquitoes. The corresponding dose of 1 ml was added to 99 ml of distilled water. Lots of 25 newly moulted IV instar Ae. caspius larvae were used per cup. Control received 1 ml of ethanol only. Four replicates for each dose were conducted. For accurate determination of the mosquitocidal activity, the larval and pupal mortality as well as adult emergence were daily recorded up to emergence of the adults or death of the last larva or pupa. Due