The Traditional, Historical and Prehistoric Use of Ashes as an Insecticide, with an Experimental Study on the Insecticidal Efficacy of Washed Ash

Ashes and other inert dusts can be used as insecticides. Insect mortality results from desiccation, caused by damage to the protective epicuticular lipid layer by dust particles. Dusts are used in many societies in the protection of stored products. A brief survey is given of the traditional and historical use of ashes in stored products protection. Archaeological records from Egypt are connected with historical records dating back to the second millennium BC. The use of sorptive dusts against fleas and lice is discussed briefly. The possible use of ashes in pest control on house floors is described for the Early Iron Age farmstead 'House Q', Assendelver Polders, The Netherlands. Subsistence farmers in northern Cameroon use ashes to protect stored cowpeas, but they wash the ashes with water before use. The effect of washing on the insecticidal efficacy was investigated experimentally. Five insect species were used: four species of stored product beetles (Sitophilus granarius (Linnaeus), Cryptolestes jerrugineus (Stephens), Tribolium castaneum (Herbst) and larvae of Tenebrio molitor (Linnaeus) and a blow-fly species, Calliphora vomitoria (Linnaeus). For each of these species one sample was treated with ash from burnt cow dung and another sample was treated with similar ash, but boiled in water and dried. No food was supplied. The experiments showed that washed ash worked faster than unwashed ash. On average, washing shortened the mortality period of the beetles by 30% and the knock-down period by 45%. The background of the use of ashes in sacred purification rites is considered and connected with early ectoparasite control. The application of ashes and other dusts as insecticides throughout cultures and periods is of such importance that laborious ways of processing have evolved to increase their efficacy. In archaeology, therefore, ashes must not only be regarded as remains of burnt material, but also as an important; intentionally used product that can be recovered from a variety of contexts.