Diseases of bees / Ministry of Agriculture and Fisheries.

Date:
1948
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of bees / Ministry of Agriculture and Fisheries. Source: Wellcome Collection.

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    Cause. This disease is the result of a bacterial infection of the young larvae which causes their death when they are about four days old. The bacteria present in the dead larvae show a variety of form, and the picture presented under the microscope, as well as the symptoms seen in the comb, may vary between one larva and another, or between one case of disease and another. The characteristics of the disease are therefore not so uniform and regular as those of American Foul Brood. Though the death of the larvae is caused by bacterial action, recent research work in Switzerland, where the disease is very prevalent, indicates that the organism which is responsible may be found in apparently quite healthy colonies, and that some other factor, the nature of which remains to be discovered, may determine the actual onset of a state of disease in the brood. Symptoms. Shortly before death the infected larva becomes restless and wanders about inside its cell instead of remaining in the normal coiled position characteristic of a healthy larva of the same age. Consequently, when it dies, about four days after hatching from the egg, it is found in an unnatural attitude—across the mouth of the cell, twisted spirally around the walls, or stretched out lengthwise from the mouth to the base (see Fig. 7). The plump, pearly-white appearance is lost; the larva collapses as though it had been melted, it turns yellowish-brown and eventually dries up to form a loosely attached, brown scale. In the scale the tracheae of the larva can sometimes be seen as a network of glistening threads. The consistency of the recently dead larva varies: it may be sticky or porridge-like, but not ropy. The smell of the larval remains also varies, both in intensity and in quality: it may be exceedingly foul or merely sour, depending upon the type of bacterium which has become established after the initial infection. The disease is essentially one of the unsealed brood but some of the infected larvae may survive until their cells are sealed, in which case there may be a few sunken or perforated cappings to be seen. Spread. Within the hive the disease may spread to such an extent that there is a Serious reduction in the number of workers emerging from the combs, followed by the decline and death of the colony. In other cases, after an appearance of the disease in the spring or early summer, the symptoms may gradually disappear during the course of the season, until no visible signs are left by the autumn. A reappearance is, however, likely in the following spring, and in the meantime the disease may have spread to other colonies in the apiary, either in an active, visible form, or in a dormant form which may become active at a later date. In general, the factors already considered in connexion with the spread of American Foul Brood apply also to the spread of European Foul Brood. Two points of difference should, however, be mentioned. First, the scales of ‘European Foul Brood are easily removed by the bee and therefore do not persist as visible evidence of the disease, though the combs may nevertheless be capable of carrying it. Secondly, some larvae with a mild infection of European Foul Brood may pupate and develop into workers whose bodies are already contaminated with bacteria from the cell in which they were reared; so it is likely that the drifting of young bees from one hive into another may account for the rapidity of spread which often occurs in apiaries where the disease has made its appearance.