Influence de la teneur en oxygène sur la sensibilité de certains stades juvéniles de Sitophilus oryzae et S. granarius au dioxyde de carbone
1991
Fleurat-Lessard, F. | Torc'h, J.M.
SUMMARY: The influence of oxygen content at atmospheres enriched with carbon dioxide on the mortality of hidden stages of Sitophilus spp. in wheat grains Among grain insect pests, Sitophilus spp. are very tolerant of inert gases used in modified atmosphere. When there is a high concentration of carbon dioxide in the gas mixture, a low residual oxygen concentration enhances the speed of action of the modified atmosphere. This has been observed easily with some juvenile stages of S. oryzae (about 3rd instar larvae to late pupae). The authors have exposed these stages, hidden inside wheat grains, to atmospheres containing 50% CO₂ (fixed concentration level), associated with O₂ concentrations increasing from 4 to 20% (v/v), with N₂ as balance. When O₂ levels increase, the exposure time necessary to kill the insects is significantly shortened for S. oryzae. The time to kill 50% (LT₅₀) was respectively 3.4-2.2 and 1.7 days with O₂ concentration levels 4-10 and 20% in the gas mixture. For S. granarius the effect is insignificant, with LT 50 values in a narrow range between 2.4 and 2.25 days, at all concentrations of O₂ tested. The specificity of the reaction of some S. oryzae juvenile stages to atmospheres with a high CO₂ concentration artificially enriched with O₂ is demonstrated. This species showed a greater reactivity to the synergitic effect of O₂ in CO₂ enriched atmospheres than the granary weevil, S. granarius, which showed nearly none in trials carried out under the same conditions. The difficulties of determining the nature of the physiological injury to hidden stages of Sitophilus spp. are emphasized. Some hypotheses on the physiological mecanisms are proposed.
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