Comparative effects of hypoxia, hypercapnia, and hypoxia/hypercapnia on the mortality and survival of Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae)

Abstract

The bean beetle Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae: Bruchinae) is one of the most damaging insects of Phaseolus bean worldwide, particularly in Africa. This study aimed to determine the effect of modified atmospheres (MAs) with CO2, N2 and its combination on the mortality and survival of all developmental stages of A. obtectus. All stages were exposed to three gas mixtures [99% N2 in air (hypoxia), 20% CO2 in air (hypercapnia), and 14% CO2 + 85% N2 + 1% O2 (combination)] at different exposure periods that lasted for 3 h or its duplicates until 100% mortality. The results revealed that the three gas mixtures had significant effects on the mortality of A. obtectus stages, which increased gradually with increasing exposure periods. Hypercapnia and hypoxia/hypercapnia effects were more severe on adult A. obtectus, which led to 100% mortality after 3 days of exposure for both treatments. No hatchability was recorded for both hypercapnia and hypoxia after 7 days of exposure, but hypoxia/hypercapnia led to 100% mortality after 5 days of exposure only. Also, the hypoxia/hypercapnia mixture was more effective on both larvae and pupae than hypoxia or hypercapnia alone. Hypoxia was also more effective on both larvae and pupae than hypercapnia. According to the LT50 and LT95 values, all stages of A. obtectus were more susceptible to hypoxia/hypercapnia than hypercapnia or hypoxia separately. Moreover, the sensitivity of all stages of A. obtectus to hypoxia/hypercapnia could be arranged as adult > egg = larva > pupa. The results showed that all gas mixtures led to fewer eggs per female, decreased of hatchability percentages, and less adult emergence percentages compared to the untreated control. Therefore, this study provides a greater understanding of hypercapnia, hypoxia, or hypoxia/hypercapnia in A. obtectus and shows the advantages of the hypoxia and hypercapnia combination in modified atmosphere treatments.