Preliminary observations on the use of low temperatures in the cultural heritage protection

Each insect species has different temperature optima: the more this parameter deviates from these values the more the insect suffers negative consequences, up to the death. Temperature can be easily editable. Therefore, the application of low temperatures may represent a physical method for the protection of valuable cultural objects, alternative, for example, to chemical ones. In this paper we report laboratory tests results, carried out on Trogoderma inclusum LeConte (Coleoptera: Dermestidae), a species harmful to leather items such as bindings of books and mummies, in order to reach its control by applying low temperatures. The tests were conducted using specimens obtained from laboratorybreeding blocks maintained at 27 ± 2°C and 75 ± 5% R.H., in a temperaturecontrolled room of the Institute of Entomology and Plant Pathology, Piacenza. The aim of the tests was to determine the time necessary to obtain the total mortality of the different instars of development at temperatures of -10°C and -20°C. The insects, in the various instars of development of egg, larva, pupa and adult, were treated with low temperatures in two different ways: - inserting the Petri dishes containing the insects directly in the freezer without any protection, in order to obtain an immediate lowering of the temperature, and - inserting the Petri dish in a niche carved in an old book so that the lowering of the temperature is gradual. In some cases the insects were kept at +4°C for a time before the test to determine whether exposure to low temperature before treatment could induce a resistance to it. The results show that the method can be validly applied for cultural heritage objects protection, attacked by the species concerned.