Quantitative Studies on Tyroglyphid Mite Populations

Abstract

The quantitative study of the physical ecology and essential requirements of Tyroglyphid mites appears to have received relatively little attention, although they are serious pests of stored flour and other cereal products. This may be due to the practical problems inevitably associated with routine population studies of small animals under controlled conditions, particularly when on a quantitative basis.The necessity to separate the populations from the food material on which they subsist is one such problem, and, as Solomon (1945) has pointed out, this is a prerequisite to the accurate determination of population densities of flour mites. The published methods of separation, suitable for the treatment of flour, suffer from certain disadvantages which render them unsuitable for the present purpose, as will be indicated later.In quantitative experiments in which the weight of the medium supporting the population is involved, especially those conducted at several humidity levels, variation of the moisture content is a complication. Further problems are connected with the sampling of cultures in which the population is unevenly distributed.The present work is concerned with the solution of these problems and the design of a quantitative technique. This technique has been applied successfully to the study of Tyroglyphid populations at the egg stage and the results of experiments using Thyreophagus entomophagus (Lab.) are reported. The Preparation of Infested Flour for Examination.The existing methods of treating infested flour have been adequately reviewed by Solomon (1945) and therefore will be referred to only briefly. Berlese funnel techniques depending on the controlled application of heat to the infested flour and collection of the mites which migrate from the untenable conditions imposed on them, have been described by Chernuishev (1938) and Petrova (1940). The latter worker claimed the recovery of from 85 to 92 per cent, of the living mites present within 25 minutes. These techniques tend to be time-consuming and since only the mobile stages of the population are separated, they provide no direct information on oviposition.Methods which depend on floating the mites (density about 1-0) from the flour (density about 1-4) using a liquid of intermediate density have also been described. Shchastny (1939) used a 1:1 brine/glycerol mixture for this purpose, after first treating the flour with ethanol; separation of the mites was hastened by centrifuging. Solomon (1945) employed dichlorethylene with which the flour was agitated in a long-necked flask; the mites were raised almost to the top of the neck by the addition of further fluid and removed on small pieces of filter paper.These methods are open to the objection that a proportion of the mites may remain entangled with the flour and no experimental work to test their efficiency has been reported. In the writer's experience, hatched eggs cannot be separated by these methods, which were therefore abandoned as inherently unsuitable for the present purpose.