The degradation of the natural pyrethrins in crop storage.

Prolonged storage of harvested Tasmanian pyrethrum crop from Tanacetum cinerariaefolium has resulted in substantial losses of the pyrethrin esters due to the environmental conditions in the storage shed. The generation of heat, the presence of moisture and oxygen, and the microbial activity were identified as possible causes. A pyrethrum crop sample was divided up and stored in different conditions relating to these variables, and the pyrethrins content was monitored over time using a standard method. Temperature was determined to be a critical factor in the rate of the degradation of the natural pyrethrins. Moisture, oxygen, and microbial activity unexpectedly did not play a major role in the degradation. An initial rapid loss of the natural pyrethrins was observed before the pyrethrins content stabilized at a loss of around 65%. This suggests that the plant structure may provide chemical or physical protection to the pyrethrins. In all cases, the majority of the loss was attributed to the pyrethrin I and pyrethrin II esters.