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■Bio-mathematics, Statistics and Nano-Technologies: Mosquito Control Strategies

protection rate of 91% at a concentration of 0.05% topical treatment. Thyme essential oil

significantly extended the duration of protection [35].

11.3.7

Neem oil

The Neem tree (Azadirachta indica) is a tropical evergreen tree native to India and

is also found in other southeast countries. A study evaluated repellent action of neem oil

against different mosquito species. 2% neem oil mixed in coconut oil provided 96 - 100%

protection from Anophelines, 85% from Aedes, 37.5% from Armigeres whereas it showed

wide range of efficacy from 61% to 94% against Culex spp. Therefore, neem oil can be

applied as a personal protection measure against mosquito bites [36]. The 20% Neem oil

in a field trial conducted by Amer et al. with mean percentage repellency 71%, had a

complete protection time for 3 h against An. arabiensis [32].

11.3.8

Rosemary oil

Rosemary is an evergreen aromatic shrub with a Mediterranean origin, which belongs

to Lamiaceae (Labiatae) family. Rosemary essential oil is obtained by steam distillation of

the flowering tops of the plant. It is widely used as culinary herb. However, rosemary oil

has been shown to be an effective repellent. The 20% oil solution of rosemary had a good

effectiveness in preventing Anopheles mosquitos, enabling 100% protection against An.

stephensi for 8 h [32]. Govindarajan et al. reported that rosemary at 1, 2.5 and 5mg/cm²

concentrations completely repels An. subpictus for 1, 1, and 1.5 h, respectively [37].

11.4

IMPROVING THE REPELLENT EFFICIENCY OF ESSENTIAL OILS

In order for the application of plant-based mosquito repellents to be a suitable alterna-

tive to chemicals, it is necessary to develop methods that will increase their effectiveness

and extend their protection time. Many methods have been described for the improvement

of repellent efficiency of essential oils. Synergistic interaction is the most used method

which is obtained by combination of several essential oils from different plants. A mixture

of active components present in various essential oils was found to efficiently enhance the

repellent effect, comparable to the effect of the sum of the individual components [38, 39].

Microencapsulation technique is one of the latest technologies used in the development

of plant- based repellent products. This technique encapsulates or entraps the plant’s active

ingredient within the shell or wall materials using a natural or synthetic polymer to form

microcapsules. Microencapsulation results in an increase in repellency duration via con-

trolled release of the essential oils [40].

An increase in repellent efficiency was also reported when fixative agents including

vanillin, liquid paraffin and salicyluric acid were used. The most widely used fixative agent

is vanillin and the duration of repellency is notably enhanced when vanillin is mixed with

the essential oils. In addition, microencapsulation or nanoemulsification combined with

vanillin treatment improve the effects and protection time of natural repellents [40, 41].