Taking the tropics home: Controlled Atmospheres for the control of tobacco beetles in large-scale testing

For years phosphine fumigation has been used for pest control in tobacco. Problems arose with the development of resistant insect strains. Moreover, toxic fumigants are potentially hazardous to man. This is why a consortium of interested tobacco companies, the CORESTA subgroup Pest and Sanitation Management in Stored Tobacco, decided for a large-scale testing of controlled atmospheres (CAs) at practical conditions. In most tobacco producing countries warm product temperatures favour the efficacy of hypoxic atmospheres and allow for sufficiently short treatment times. To obtain similar treatment times in Central Europe it was decided to heat the incoming tobacco prior to CA application. Samples of all stages of tobacco beetles were added to tobacco bales in order to monitor the efficacy of the treatment. Data loggers for temperature and r.h. were added to the samples to record physical conditions during transportation and treatment. Untreated control samples accompanied the experimental samples. One of the treatment chambers was a gastight cube measuring 10m in each direction. Practical treatments proved difficulties to reach uniform high temperatures in such a chamber. In some cases cold winter temperatures on the outside of the chamber led to massive condensation of water from tobacco leaves. Eggs, various larval stages, pupae, and adult beetles could be controlled with a hypoxic CA containing some 0.5% oxygen at temperatures of 28°C and within 9 days of exposure time. Few survivors were recorded, when a similar CA was tested at 38°C and 2.5 days exposure time.