Title : Ecology and sensitivity of Aedes albopictus and Aedes aegypti to the essential oils of Ageratum conyzoïdes and Chromolaena odorata
Abstract:
A good knowledge of the ecology of Aedes as well as their bionomics is a prerequisite to better plan control interventions. The present study aims at determining the ecology and the aggressiveness of Aedes aegypti and Aedes albopictus in some rural and urban areas of Douala, Kribi and Ayos in order to propose an alternative method of vector control based on formulations on essential oils from Ageratum conyzoides and Chromolaena odorata plants. The larvae were collected using the Dipping method and reared using the Desfontaine method. The essential oils from the fresh leaves of Ageratum conyzoides and Chromolaena odorata were extracted by steam distillation using Clevenger-type equipment. The chemical composition of the essential oils was determined by GC-MS. Insecticide tests were also carried out according to the WHO protocol on the larvae of Ae. albopictus collected from breeding sites.
A total of 533 breeding sites were identified, including 61.7% in urban areas and 38.3% in peri-urban areas. Of these breeding sites, 98.3% were artificial and mainly represented by worn tires. The most productive sources were used tires in both urban (n= 13,371; 53.2%) and peri-urban (n= 5,982; 42.94%) areas. In urban areas, Ae. albopictus (52.35%) and Ae. aegypti (46.86%) were mainly found in used tires while in peri-urban areas, Ae. albopictus (45.01%) was mainly found in scrap tires, and Ae. aegypti (38.65%) in the holes of concrete blocks. Ae.albopictus and Ae. aegypti lived in sympatry in 332 breeding sites, including 228 in urban areas and 104 in peri-urban areas. The results on the chemical composition of essential oils reveal that Precocene I (54.4%) and Andro encecalinol (24.69%) were the major compounds of fresh leaves of A. conyzoides while Geijerene (20.02%) and trans-Muurola-4(14),5-diene (19.15%) were the main compounds of fresh leaves of C. odorata. Essential oil from the fresh leaves of A. conyzoides was the most effective with 100% mortality of mature larvae obtained after 10 hours of exposure to a 75ppm concentration. This study demonstrates the ecological plasticity of Ae. albopictus and Ae. aegypti in the cities of Ayos, Douala and Kribi. The sensitivity of Ae. albopictus larvae to the essential oil of A. conyzoides and their resistance to that of C. odorata, suggests that the combination of existing vector control methods associated with the essential oil of A.conyzoides could significantly reduce the density of Ae. Albopictus in an elimination context.
Key words: Ae. albopictus, Ae. aegypti, ecology, agressiveness cycle, A. conyzoïdes, C. odorata, essential oil, Douala, kribi, Ayos, Urban area, Sub-urban area
