For legumes, the situation is completely different: legume bruchids (there are as many different bruchid species as there are legume species) enter green pods well before harvest, and by harvest they have completed their development cycle inside the seeds and have begun to emerge from physiological maturity. But at the harvest stage, part of the population is still present in the dry seeds, and emergence continues if nothing is done to rapidly disinsect infested batches. In this case, the percentage of "bruised seeds" will continue to rise during storage, right up to the end of winter (figure 10). Among field legumes, soybean and lupin seeds are not attacked by bruchids and have no particular need for disinsectisation at harvest time. However, with varietal improvement reducing levels of anti-nutritional factors, and global warming, it is possible that in a few years' time, certain species of bruchid will be able to develop on these "refractory species", which are insensitive to bruchid attacks having co-evolved on other legume species.
The bruchids that emerge from legume stocks at the end of winter return to the crops and lay their eggs as soon as flowers and the first pods appear in spring (figure 11).
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As bruchids are already present in seeds at harvest, infested batches intended for human consumption must be systematically "disinfested" at harvest.
To avoid treating all batches of legumes at harvest to eliminate any bruchids still present (not all harvest batches are infested with bruchids at harvest), sorting between infested and healthy batches can be facilitated by the use of acoustic detection probes (Tomasini and Fleurat-lessard, 2017), which enable rapid detection of active larvae. Without positive detection, batches are declared healthy and do not need to be disinsected by phosphine fumigation or carbon dioxide (CO₂) inerting.
