## 5 The Biological Properties of Camphor
### Insecicidal Activity  
Certain currently used synthetic pesticides threaten the integrity of the earth's ozone layer and other environmental buffers, therefore alternatives to these commercial chemicals are urgently needed [62]. Essential oils are considered good candidates because of their low toxicity to mammals, high volatility, ready availability in tropical countries and economical viability [63, 64]. Monoterpenoids believed to aid plants in chemical defence against phytophagous insects are capable of toxic interference with the biochemical and physiological functions of herbivorous insects [65, 66]. Numerous studies have indicated that camphor has insect repellent activity against stored-product pests. Using contact toxicity, grain treatment and repellency assays, the essential oil of camphor basil (_Ocimum kilimandscharicum_) and its major component, camphor, were investigated against four beetles. The doses of 100 mg/filter paper and 100 \(\upmu\)g/insect induced over 93% and 100% mortalities in _Stiophilus granarius_, _S. zeamais_ and _Prostephanus truncatus_, but only 70% and 100% mortality in _Tribolium castaneum_ after 24 h exposure. Development of eggs and immature stages within grain kernels, as well as progeny emergence, was completely inhibited in camphor-treated grain [67]. [PERSON] and [PERSON] [68] revealed the insecticidal activity of camphor basil (_O. kilimandscharicum_) against _Rhyzopertha dominica_ and _S. zeamais_ was due to camphor and the combined effects of different components, but camphor had no effect on the rice weevil (_Stiophilus oryzae_) with an LC\({}_{50}\) of greater than100 \(\upmu\)L/L. Another report indicated that camphor, as a pure compound, showed contact and fumigant activity against _S. oryzae_ and _Rhyzopertha dominica_, but had no effect on _Tribolium castaneum_ after 24 hours exposure at a dose of 0.1 \(\upmu\)L/720 mL volume [69]. [PERSON] _et al_. [70] found camphor exhibited the highest mortality (78.5%) just after 24 h at the highest tested dose (10.0 \(\upmu\)L/adult) for contact toxicity; for fumigant toxicity, camphor at its highest dose (120 \(\upmu\)L/350 mL vol.) caused 93.5% mortality. These results were in agreement with an earlier report by [PERSON] and [PERSON] [71], who observed that camphor, as the major isolate from essential oils of Chinese cinnamon (_Cinnamomum cassia_), Chinese star anise (_Illicium verum_) and camphor laurel (_Cinnamomum camphora_), showed contact efficacy against the lesser grain borer (_Rhyzopertha dominica_) and the maize weevil (_Stiophilus zeamais_). Insect repellent activity, rather than insecticidal activity, against the confused flour beetle (_Tribolium castaneum_) was noted. Exposure of the newly-laid eggs of the pulse beetle (_Callosobruchus chinensis_) to concentrations of 0, 12, 24, 48, and 96 ppm of camphor crystals in air-tight containers for one and four weeks resulted in 65.0% to zero (0%) hatching. Postembryonic development was affected when the newly-hatched larvae penetrated into the cowpea seeds; very few adults emerged from the infested seeds exposed to camphor [72]. Camphor was the most effective of the tested monoterpenoids to prevent the multi-coloured Asian lady beetle, _Harmonia axyridis_ (Pallas), from overwintering in buildings as determined by the olfactometer bioassay [73]. It also exhibited fumigation toxicity against false powder post beetle (_Dinoderus bifloveatus_) after 48 hours exposure [74]. Several monoterpenes (e.g., 1,8-cineole, citronellol, \(\alpha\) and \(\beta\)-pinene, linalool, isopinocamphone, camphor) tested against cattle-tick (_Booophilus micropylus_) larvae and camphor, in a 60 min-period, was lethal to 100% of the larvae [75]. _Blattella germanica_ (German cockroach) is one of the most important pests of the indoor environment, a major source of allergens and a potential carrier of faecal pathogens [76]. Using the filter-paper contact toxicity bioassay, both (1_R_)-(+)-camphor and (1_S_)-(-)-camphor were toxic against female \(B\).