Mortality of eggs of the cowpea bruchid, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in carbon dioxide under high pressure

Abstract

The aim of this study was to provide empirical data on the effect of ambient carbon dioxide (CO2) under high pressure on the mortality of Callosobruchus maculatus (F.) eggs at different ages. The mortality of the eggs was assessed in combinations of four CO2 pressures (15, 20, 25, and 30 bar) and five egg-age groups (one, two, three, four and five days old) with 5, 10, 15, and 20 min exposure periods. The investigations were carried out in an automated pilot plant (volume: 1.1 l) at 25°C and 70% r.h. After each exposure period the gas pressure was decreased to atmospheric level in one second. One-day-old eggs were found to be the most tolerant, requiring 30 bar and 20 min exposure for complete extermination. On the other hand, five-day-old eggs were the least tolerant, requiring only 20 bar and 10 min. The tolerance of the eggs declined with age and the mortality was influenced by the pressure level and the exposure period. To achieve 100% mortality, increasing pressure was more effective than increasing exposure time. Decisions regarding pressure and exposure time of CO2 should be made case by case, because the effect of CO2 appears to vary depending on the age of the egg.