The population dynamics ofCryptolestes ferrugineus(Stephens) (Col., Cucujidae) in flour and on Manitoba wheat

Abstract

SummaryIf adults ofCryptolestes ferrugineus(Steph.), of which the females have already been fertilised, are cultured on flour at low densities, the rate of oviposition is independent of the density of adults and juvenile mortality is negligible. At high densities there is a heavy mortality amongst eggs and young larvae, and there is evidence that, providing no great degree of conditioning of the medium has occurred, an equilibrium is reached with the number of eggspluslarvae present at any time being independent of the density of adults. Cannibalism is undoubtedly a major cause of the juvenile mortality under these conditions. Where crowding of adults is so great that conditioning of the medium becomes important, the number of eggs plus larvae present at a given time after the cultures have been set up decreases with increasing density of adults, there being some indication of an inverse linear relation.Cultures ofC. ferrugineuson a mixture at 70 per cent. R.H. of sound grain and grain already slightly damaged byCrypiolestesare capable of initiating dense infestations in the laboratory, at least at moderate and high temperatures. Under optimal conditions the infestations develop within 15 days. Values deduced for the pre-adult period at various temperatures were similar to those obtained by Rilett (1949). At 17°C., development was extremely slow but the low temperature did not increase mortality. Cannibalism and competition by adults and fully developed larvae appear to play an important part in limiting the production and survival of the juvenile stages.Sound grain at 70 per cent. R.H. is unsuitable as a medium for culturingCryptolestesin the laboratory but it becomes suitable after relatively small additions of flour and damaged grains. At 33°C. at least, a point is suddenly reached where an infestation is initiated, the critical feature being increased survival of larvae rather than an increase in the number of eggs laid. An increase in humidity has a similar effect to adding food.Estimates of the production of CO2at various temperatures gave values higher than previously reported. From 21 to 33°C. the rate of increase of the respiration rate and the increase in the speed of development are proportional to rise in temperature. This is in accord with other indications thatC. ferrugineushas a high optimum temperature.