Diseases of Bees.—It is quite natural that bees living in colonies should be subject to diseases, and only since the introduction of movable-comb hives has it been possible to learn something about these ailments. The most serious disease with which the bee-keeper has to contend is that commonly known as “bee-pest” or “foul brood,” so called because of the young brood dying and rotting in the cells. This disease has been known from the earliest ages, and is probably the same as that designated by Pliny as blapsigonia (Natural History, bk. xi. ch. xx.). Coming to later times, Della Rocca minutely describes a disease to which bees were subject in the island of Syra, between the years 1777 and 1780, and through which nearly every colony in the island perished. From the description given it was undoubtedly foul brood, and the bee-keepers of the island became convinced, after bitter experience, that it was extremely contagious. Schirach also mentioned and described the disease in 1769, and was the first to give it the name of “foul brood.” Still later, in 1874, Dr Cohn, after the most exhaustive experiments and bacteriological research, realized that the disease was caused by a bacillus, and—nine years later—the name Bacillus alvei was given to it by Cheyne and Cheshire, whose views were in agreement with those of Dr Cohn.
The illustration (fig. 27) shows a portion of comb affected with foul brood in its worst form. The sealed cells are dark-coloured and sunken, pierced with irregular holes, and the larvae in all stages from the crescent-shaped healthy condition to that in which the dead larvae are seen lying at the bottom of the cells, flaccid and shapeless. The remains then change to buff colour, afterwards turning brown, when decomposition sets in, and as the bacilli present in the dead larvae increase and the nutrient matter is consumed, the mass in some cases becomes sticky and ropy in character, making its removal impossible by the bees. In course of time it dries up, leaving nothing but a brown scale adhering to the bottom or side of the cell. In the worst cases the larvae even die after the cells are sealed over; a strong characteristic and offensive odour being developed in some phases of the disease, noticeable at times some distance away from the hive.
| Fig. 27.—Foul Brood (Bacillus alvei). |
| (From Cheshire’s Bees and Bee-keeping, Scientific and Practical.) |
Two forms of foul brood have been long known, one foul smelling, the other odourless; and investigations made during 1906 and 1907 showed that the etiology of the disease is not by any means simple, but that it is produced by different microbes, two others in addition to Bacillus alvei playing an important part. These are Bacillus brandenburgiensis, Maassen (syn. B. burri, Burri: B. larvae, white), and Streptococcus apis, Maassen (syn. B. Guntheri, Burri). The first two are found in both forms of foul brood, whereas the last is only present with B. alvei in the strong-smelling form of the disease, in which the larvae are attacked prior to the cells being sealed over.
The brood of bees, when healthy, lies in the combs in compact masses, the larvae being plump and of a pearly whiteness, and when quite young curled up on their sides at the base of the cells. When attacked by the disease, the larva moves uneasily, stretches itself out lengthwise in the cell, and finally becomes loose and flabby, an appearance which plainly indicates death.
When the disease attacks the larvae before they are sealed over Bacillus alvei is present, usually associated with Streptococcus apis, which latter imparts a sour smell to the dead brood. In cases where the disease is odourless the larvae are attacked after the cells are sealed over, and just before they change to pupae, when they become slimy, sputum-like masses, difficult to remove from the cells. Under these conditions Bacillus brandenburgiensis is found, although Bacillus alvei may also be present. The two bacilli are antagonistic, each striving for supremacy, first one then the other predominating. Various other microbes are also present in large numbers, but are not believed to be pathogenic or disease-producing in character.
It is, therefore, seen that at least three different microbes play an important part in the same disease. The danger of contagion lies in the wonderful vitality of the spores, and their great resistance to heat and cold. Dr Maassen records a case where he had no difficulty in obtaining cultures from spores removed from combs after being kept dry for twenty years. It should be borne in mind that the disease is much easier to cure in the earlier stages while the bacilli are still rod-shaped than when the rods have turned to spores.
Since the bacterial origin of foul brood has been established, the efforts of some bacteriologists have been employed in finding a simple remedy by means of which the disease may be checked in its earliest stages, and in this an appreciable amount of success has been attained. Nor has foul brood in its more advanced forms been neglected, all directions for treatment being found in text-books written by distinguished writers on apiculture in the United Kingdom, America and throughout the European continent.
The only other disease to which reference need be made here is dysentery, which sometimes breaks out after the long confinement bees are compelled to undergo during severe winters. This trouble may be guarded against by feeding the bees in the early autumn with good food made from cane sugar, and housing them in well-ventilated hives kept warm and dry by suitable coverings. When bees are wintered on thin, watery food not sealed over, and are unable for months to take cleansing flights, they become weak and involuntarily discharge their excrement over the combs and hive, a state of things never seen in a healthy colony under normal conditions. The stocks of bee-keepers who attend to the instructions given in text-books are rarely visited by this disease.
The above embraces all that is necessary to be said in relation to diseases, though bees have been subject to other ailments such as paralysis, constipation, &c.