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STUDIES ON THE DERMESTID BEETLE TROGODERMA GRANARIUM EVERTS: ECOLOGY IN MALT STORES
Author(s) -
BURGES H. D.
Publication year - 1959
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1959.tb07278.x
Subject(s) - biology , trogoderma granarium , diapause , larva , population , ecology , zoology , pupa , insect , demography , sociology
Detailed studies on the environment in malt stores and its effect on the Khapra beetle are described. The observations are correlated with the conclusions from parallel laboratory work. Bulks of malt are stored at 26–69° C. and cooling near their centres is slow. After loading, the distribution of heat is controlled mainly by the position of the kiln, the size of the store and the development of Khapra infestations. Three zones of temperature may be recognized, too hot for Khapra (above 40° C.), favourable (30–40° C.) and too cool for rapid breeding (below 30° C.). Population growth may be progressively retarded by cooling, or heat from the kiln and insect‐heating may allow continuous breeding, although part of the malt may be heated above 40° C., causing migration of the larvae. Some migrants stop in a new favourable zone and others continue into the cool zone, often for a long way. The larva is the most prominent stage in most populations. Throughout population growth, low temperature and the accumulation of faecal pellets cause some larvae to enter diapause and hide either in crevices or on the walls just below the malt surface. After the malt is unloaded, huge numbers of larvae may be hidden and some may survive for more than 4 years. Reloading with new, hot malt stimulates some of the cryptic larvae to emerge, pupate and breed. More larvae emerge from the hottest positions than from elsewhere. The very sharp gradient of humidity in stores does not appear to influence larval behaviour. In contrast to unmalted cereals, malt is too dry to allow a significant upward translocation of moisture above a hot region. Control is very difficult. Current methods involve persistent attack on larvae in empty stores with methyl bromide and contact insecticides, combined with structural improvements. Control by cooling the malt before storage is promising.