The main factors influencing the effectiveness of inerting with carbon dioxide (CO₂), or possibly with dinitrogen (N₂), are (in decreasing order of importance):
- grain temperature
- gas concentration (CO₂) on injection into the charged container
- inerting maintenance time
- the species of insect to be eradicated.
The influence of each of these factors on inert gas efficiency has been studied by numerous R&D teams in all developed countries producing cereals, oilseeds and pulses (Australia, USA, Canada, Israel, Germany, UK, Italy, Spain, Portugal and France). Today, we have robust scales guaranteeing the efficacy of disinsectisation using the two most commonly used inert gases (CO₂ and N₂) for the disinsectisation of 'organic' seeds, legumes and field cereals under AB or quality label schemes.
To help you understand the best practices for effective disinsectisation using CO₂, the effect of each of the four factors determining disinsectisation efficiency is shown in the following graphs.
An abacus is available to help users determine the minimum duration for maintaining a certain CO₂ concentration, resulting in insect mortality at all stages of development. The nymph is the most resistant stage, particularly when the CO₂ concentration is around 50% (around 10% oxygen remains). This tolerance to anoxia is linked to the insect's very low respiration rate at this stage of metamorphosis.
Conditions for optimum CO₂ inerting efficiency
The inherent insecticidal effect of CO₂ only manifests itself in the presence of a certain level of residual oxygen: exposing wheat grains infested by the hidden forms of the weevil, Sitophilus oryzae, to an atmosphere of pure CO₂ (100% CO₂) gives poorer disinsectisation results than an atmosphere of 50% CO₂, combined with 4, 10 or 20% oxygen (diazote excipient).
