Effect of grain on apparent respiration of adult stored-product Coleoptera in an air-tight system : Implications for fumigant testing

Observed rates of carbon dioxide production and oxygen consumption by adult Sitophilus oryzae on wheat in a 2.5 L sealed system for a 24 h period were about four times greater than the sum of the rates of insects alone and wheat alone while apparent RQ values for adults on grain were in the range 0.5 to 1.0. It was found that change in apparent RQ was not due to sorption of carbon dioxide by the wheat but due to changes in insect physiology. Studies of adult Tribolium castaneum, Rhyzopertha dominica, S. oryzae and Sitophilus zeamais without food, in a 40 mL sealed system, showed a progressive change in apparent RQ from 1.0 to 0.5 in 5 h and as carbon dioxide rose to exceed 1%. These results indicate that caution is needed when interpreting fumigant dosage/response data obtained in sealed systems where carbon dioxide concentrations exceed about 1% and changes in respiratory physiology start to occur.