Because most of the storage pests have aerobic respiration, accumulation of carbon
dioxide and depletion of oxygen caused by their metabolic activity are the most obvious
result of physiological processes involved in an active colony of insects, mites, and
microflora in stored grain (Sinha et al. 1986, Mills 1986). Other metabolic products
produced by microflora, such as antibiotics and mycotoxins, have been studied with
considerable interest during the last few decades. But there is yet another group of
inconspicuous metabolites, the volatile chemicals, which are regularly produced by most
pest organisms in stored-grain ecosystems. In pre-harvest, agro-ecosystems various plant
volatiles play a decisive role in the co-evolution of plants and insects, and volatile
secondary plant compounds act as semiochemicals having specific functions in insect
populations and host-plant selection (Metcalf 1987). Insect volatiles such as
pheromones, and allomones have also been used extensively for detecting and even
-3-controlling pest insects in field crops (Roelfs and Carde 1974)