Green chemistry includes compounds that are isolated from botanical sources.Botanically based insect repellents are available on the market,but they utilize monoterpenes as their active ingredients;some are quite repellent,especially as spatial repellents,but their time of protection is typically around two hours.Sesquiterpenes are 15-carbon compounds from plant essential oils that are 50％ heavier in their molecular weights than monoterpenes.Some Sesquiterpenes have excellent mosquito repellency,including protection for 6-8 hours.Their innate repellency is as good as commercial synthetic repellents,and their residual activity matches that of the commercial repellents much better than the monoterpenes.