Efficacy of heat against the mediterranean flour moth Ephestia kuehniella and methods to test the efficacy of a treatment in a flour mill

The Mediterranean flour moth Ephestia kuehniella is a typical pest in German flour mills and was tested in laboratory experiments at 45 °C, 50 °C and 55 °C for the efficacy of heat. Eggs, pupal and young larval stages were found most tolerant surviving up to 60 min at 45 °C, up to 7 min at 50 °C and up to 5 min at 55 °C, respectively. Fitting a log trend through the data gave lethal exposure times of 660 min at 45 °C, 27 min at 50 °C and 7.2 min at 55 °C. Differences between the most tolerant and most sensitive developmental stages became smaller with increasing temperature. Results are compared with those of stored product beetles, such as the red flour beetle Tribolium castaneum, the granary weevil Sitophilus granarius and the lesser grain borer Rhizopertha dominica. Among the grain pests this latter species was by far the most heat tolerant. All developmental stages and adults of R. dominica were used as bio-indicator in a practical heat treatment in a flour mill. Insect survival was detected in most samples where temperature did not exceed 50 °C as recorded by data loggers. Infrared-thermography was found a helpful tool to detect areas of heat loss from outside and cold bridges that might allow the survival of insects from inside. These are the areas that should be heated first in order to drive out insects towards zones where they are more easily controlled later on. Insulating materials such as large amounts of grain, straw and husks, flour dust or packaging materials should be removed from buildings prior to treatment.