The effect of oxygen and carbon dioxide gradients on the vertical dispersion of grain insects in wheat

Abstract

A study was made on the dispersion of 0–14 day old adult Oryzaephilus surinamensis (L.), Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at 25°C in vertical columns of wheat (m.c. 12.1%) 100 cm tall. When the columns contained ordinary air, O. surinamensis dispersed from top to bottom within 24 hr whereas S. oryzae and R. dominica penetrated to a depth of only 50 cm in 72 hr. When controlled gas gradients were imposed on the columns from the bottom, the concentration of O 2 in one series of experiments ranged from 0.9% at the bottom to 18.5% at the top whilst in another series that of CO 2 ranged from 70.5% to 3.3%. In both gas gradients the downward dispersion of O. surinamensis was restricted but the distribution of the other two insect species was unaffected because they did not penetrate deep enough to encounter unfavorable concentrations.