Zur Wirkung hoher Temperaturen auf vorratsschädliche Insekten | Efficacy of high temperatures against stored product insects

Storage structures and buildings for food processing such as flour mills or bakeries can be disinfested by heat. This is done in Germany either by the use of ex-proof electric heaters or fossil-fuel burners, in which case heated air is fan-forced from outside into the structure through flexible ducts. Data presented here are from laboratory studies and practical heat treatments from 2001-2006 and summarize the relative sensitivity of immature and adult Mediterranean flour moths Ephestia kuehniella (Lepidoptera, Pyralidae), tobacco beetles Lasioderma serricorne (Coleoptera, Anobiidae), lesser grain borers Rhizopertha dominica (Col., Bostrychidae), granary weevils Sitophilus granarius and maize weevils S. zeamais (Col., Curculionidae), flat grain beetles Cryptolestes pusillus (Col., Cucujidae) and rustred flour beetles Tribolium castaneum (Col., Tenebrionidae). While the moth larvae proved rather sensitive towards high temperatures, the larvae and pupal stages of lesser grain borer and tobacco beetle where quite tolerant with 370 min required in lab studies for complete control at 50°C for both species. At 55°C complete control was achieved in up to 45 min. Experiences from practical treatments showed that it is difficult to achieve uniform temperatures at all locations in a large flour mill. In a number of cases, lethal temperatures could not be reached close to the outside walls in areas with faulty insulation, in narrow corners in the cellar or roof construction, and in insulating materials such as bag stacks of flour, packaging material, tightly packed electric cables, larger amounts of grain, malt, dust or garbage. All materials should be removed prior to treatment and difficult zones should be intensely heated, treated with diatomaceous earth or other contact insecticides in order to secure a complete disinfestation.