| THE
SMALL HIVE BEETLE, AETHINA TUMIDA. |
| Science Bulletin 220 UNION OF SOUTH AFRICA DEPARTMENT OF AGRICULTURE AND FORESTRY (Entomological Series 3) 1940 A. E. LUNDIE, Ph.D., Research Apiculturist Division of Entomology, Pretoria INTRODUCTION It is surprising that the insect to be described in this paper, although it is so common and can be so troublesome to the beekeeper, has not been mentioned previously in our apicultural literature. The absence of any mention of this trouble by beekeepers contributing to our journals is but another reminder that South African apiculture is still in its very infancy. It is suggested that this insect, Aethina tumida, should be called "the small hive beetle" to distinguish it from another and much larger beetle, Hyplostoma fuligincus, which is also to be frequently found in bee hives in South Africa. Although the mature beetles are black, it may be well to avoid this adjective in any descriptive title to be given to the insect, because some beetles, on emerging from the ground, are a very light brown, and the period during which they turn from light brown to a dark brown and finally black is variable. However, the majority of these beetles after reaching maturity do not become active till a fairly high degree of pigmentation has set in. The writer first became acquainted with this small beetle in 1924, shortly after hiving his first swarm of bees in Pretoria. A nucleus from this swarm was set aside for increase, but a later visit showed that the bees had absconded, and that the combs had become a seething mass of "worms", which were easily recognized as beetle larvae. Various facts about this insect and its habits were gleaned from time to time in practical work in the apiary, but it was not till 1931 that the writer, due to curtailment of his itinerant work, had the opportunity of commencing a detailed study of the insect. After further interruption the study was resumed in January 1938 and this paper gives the results of the investigations to date. Our early entomologists received a few queries from beekeepers on an insect which was undoubtedly Aethina tumida, but in the absence of any detailed work on this insect it was suggested then that these beetles were probably not a pest, and that they were merely associated with the bees for the shelter and warmth which the hive and cluster afforded. The first South African record of the insect is by Mr. R. H. T. P. Harris, who submitted specimens for identification from Durban in 1920. Aethina tumida was first named and described by Andrew Murray in 1867 in the "Annals and Magazine of Natural History", London, from two specimens which were sent to him by the Rev. W. C. Thomson from Old Calabar on the West Coast of Africa, but no mention is made of the insect being associated with honey bees in any way. This reference indicates that Aethina tumida must be widely distributed over the African continent. The writer has failed to find any other reference to the insect in the entomological literature available to him. Aethina tumida belongs to the family Nitidulidae, about which W. S. Blatchley remarks that "The name Nitidula applied by Fabricius to the typical genus, is very inappropriate for the family, since it literally means shining or elegant, whereas the great majority of the species are clothed with a fine pubescence which does not permit of their to any great extent". This fine pubescence is present in Aethina tumida. The habits of this family were picturesquely described by Murray in the "Transactions of the Linnean Society", London, in 1864, as follows:-
In discussing the Trigona or stingless bees of Australia in his book "A Cluster of Bees", Tarlton Rayment mentions three beetles, Brachypeplus planus Er., Brachypeplus meyricki Blkb. and Tribolium myrmecophilum Lea and their association with these bees, but they are evidently not associated with honeybees in the same way as Aethina tumida, because he reports on the more abundant species B. planus, "Beetles placed on the combs of hive bees were immediately carried off by the workers". Honeybees cannot eject A. tumida beetles so easily. These beetles can invade strong colonies of honeybees as well as weak ones with equal impunity. These two references, both from Australia, are the only ones the writer has been able to find, which report an association of beetles and social bees which bears some similarity to the association of A. tumida with the honeybee in Africa. Although A. tumida is not a major pest, there are localities where, and seasons when, it assumes such importance that it becomes almost as serious as the compolitan wax moth, and its control requires an equal vigilance from the beekeeper. The absence of any reference to this beetle in our apicultural literature is probably due to the fact that most beekeepers who have been troubled by the larvae of this beetle have mistaken these larvae for wax moth larvae; and to add to their confusion combs are often infested simultaneously by the larvae of these two insects. The morphological differences between lepidopterons and coleopterous larvae are not generally known by laymen. Although the beetles may be found anywhere in the hive, their favourite rendeavous seems to be the rear portion of the bottom board, where they probably escape to some degree the attention of both the bees and the beekeeper. Here not only are the beetles out of the maelstrom of traffic to and from the hive, but probably they can also secure their food, with a minimum of interferance from the bees, from the pellets of pollen that fall from the cluster of bees above them. The beetles, however, may be seen, immediately the inner cover is removed from the hive, lurking in the cavity behind the metal rabbets or in cavities in any burr-comb the bees may have built between the top bars of the frames and the cover of the hive. When the frames of the hive are examined, these beetles may be seen running along the surface of the comb to disappear for a moment in a cell before emerging again to continue their scramble for a "safer" hiding place, perhaps in another cell nearby, where they may remain motionless and so escape the attention of the observer.One may also see a bee "close with" one of these beetles, curling its abdomen around the beetle in a vain endeavour to penetrate the hard chitinous armour of he intruding beetle, or the bee may be fortunate in getting a good hold of the beetle in this struggle and, taking flight, it "jettisons" the invading beetle at some distance from the hive. However, this does not appear to happen very frequently, for many beetles can live for long periods of time, even in strong colonies, with relative impunity. THE NATURE OF THE PEST. The small hive beetle is a scavenger, which may be likened to the cosmopolitan wax moth in many ways, but fortunately it is not nearly so destructive to the combs. Just as the wax moths begin their ravages in combs in storage, or in weak colonies, so does the small hive beetle become a nuisance to the beekeeper. Any factor which so reduces the ratio of the population of a colony of bees to its comb surface that the bees are no longer able to protect this comb surface adequately is a precursor to the ravages of both the wax moths and Aethina tumida. Such factors as incorrect supering of the hive, excessive swarming, long standing European foulbrood, pilfering of some of the honey of the hive by thieves, who may pour water over the bees or use excessive smoke in obtaining their spoils, may result in a heavy infestation of Aethina tumida larvae, before the beekeeper is able to improve the condition of the colony. The following are some of the principal occasions when a beekeeper may experience some trouble from this insect. Combs of honey that have to stand in the honey-house for a period before or after the extraction of the honey, are liable to become "wormy", especially those combs that contain a certain amount of pollen. Cappings which are invariably set aside at extracting time by the beekeeper to be worked at a later date are liable to become "wormy" before they are melted down into cakes of wax. Honey left over Porter bee-escapes for several days before its removal may develop the larvae repidly as a result of the additional warmth which this honey gets from the colony of bees below it. The larvae will pierce the cappings, side walls, and mid-rib of newly made or other relatively delicate comb, causing the honey to "weep" badly (Fig. 1 and Fig. 2), but old combs with several generations of cocoons can withstand heavy infestations well (Fig. 4) and can be used again in the hives after the gummy mixture of honey and larval excrement has been washed off with water under some pressure, such as that from a garden hose. There are two characteristic conditions of the larval infestation which depend upon the relative abundance of honey and pollen in the infested area of the comb. When this area contains a small amount of honey and the larvae are feeding on the pollen mainly, their faeces have a dry "shredded" appearance, and the larvae themselves are a bright, dry, clean white; but when the honey being worked by the larvae is more abundant, this at first becomes discoloured, due to the faeces which the larvae void in the honey; then it becomes thin and ferments with a very characteristic odour, somewhat like that from decaying oranges. This odour in a honey room is usually the first warning to a beekeeper of the presence of active larvae in his supers. As the fermentation progresses, frothy bubbles ooze out of the cells of the comb (Fig. 1) and the "honey" falls to the bottom board where, in the case of an old infestation, it may accumulate sufficiently to run out of the entrance of the hive to the ground, or collect to form a layer an inch or more thick should the entrance become blocked or the hive bottom slope be to the rear of the hive. In this case the larvae become so thoroughly covered by the fermenting honey that they present an unpleasant slimy appearance, and when they begin to migrate away from this mixture, they leave trails of it behind them, discolouring everything over which they crawl. With further fermentation and drying, the mixture of honey and larval excrement becomes sticky, and still later shrinks to a granular or somewhat spoungy mass, which can neither be scraped nor washed off easily from the bottom board. The full-grown larvae leaving the hive through any crevices large enough to give them egress on their way to the ground to pupate may carry a small proportion of this sticky mixture to the outside of the hive. Tracks of the mixture may be left in such quantities that in a heavy infestation even the outside of the hive may become quite badly discoloured [Fig. 5 and Fig. 6 (a)] by the hosts of migrating larvae on their exodus from the hive. A perusal of Fig. 6 (b) will give some idea of the number of larvae which can develop in a few honey combs. This illustration represents a few of the dead larvae collected from the concrete floor of a honey room, where an infestation of some of the honey combs had occurred. These larvae died shortly after reaching maturity, having failed to find a suitable place on the hard concrete surface in which they could pupate. Apiaries that have been established for a number of years are more likely to harbour a larger number of A. tumida beetles than recently established apiaries. Once a colony or a number of colonies in an apiary have retrogressed so far that these beetles have been able to breed in considerable numbers, other and normal colonies in the same apiary will harbour a greater number of these beetles, and there will be the danger that any supers from such an apiary will develop "wormy" combs rapidly, soon after they are left in storage in the honey-house. One of the riddles of beekeeping is the total absence of American foulbrood in South Africa. This disease is prevalent in the Mediterranean countries and seems to be present in Northern Africa; but just why should Southern Africa be free of this disease, when conditions seem so ideal for relaying it down the length or "backbone" of the African continent? Perhaps in the warm tropics the rapid work of scavengers, of which the wax moths and Aethina tumida must play an important role, accounts for the absence of this foulbrood in Southern Africa. DISTRIBUTION OF Aethina tumida. In an attempt to get some information on the distribution of Aethina tumida in South Africa, a questionnaire on this insect, accompanied by specimens of the beetle, was sent to forty-four beekeepers of long standing. Only eleven beekeepers of the thirty-one that responded to this questionnaire showed that they were familiar with the beetle or its larvae. Ten of these beekeepers live in the low-veld or warmer areas of the Transvaal, and in the coastal areas of Natal and the Cape Province. One beekeeper on the Transvaal high-veld, who at first reported that he had never seen the beetle before, sent in specimens from his apiary at a later date. Beekeepers of very long experience in the Western Province and the Cape Midlands were not familiar with the beetle. Perhaps the climate and the nature of the soil militate against a rapid development of the beetle in these areas. The presence of the beetle in Old Calabar, on the West Coast of Africa, suggests that A. tumida is widely distributed over the African continent, and in the absence of definite records it may be assumed that the beetle will be found in any of the tropical and subtropical regions of Africa. CONDITIONS UNDER WHICH THE LIFE HISTORY OF Aethina tumida WAS STUDIED. A knowledge of the inability of A. tumida to live long without regular supplies of fresh water and of the humidity requirements of the soil for the pupal period, gleaned from the 1931-32 study, enabled the writer to make more rapid progress in the 1938 study of this insect. At first the full-grown larvae obtained from a heavily-infested hive were placed on damp soil in three types of containers:-
There was a high mortality of the pupae in the small tins, due to the small volume of soil present and the free passage of air through the junction of the transparent material and the metal rims of the lids, which dried the soil rather rapidly. In spite of the larger volume of the glass jars and the use of paper covers to retard evaporation, the soil in these containers also dried out too rapidly. The larger tin boxes proved to be the most satisfactory and were used throughout the greater period of this study. The soil was sifted through a piece of perforated metal with holes 1/16 inch in diameter and remained moist long enough for several generations, without any addition of water. The degree of moisture which was maintained in these tins may be judged by the ease with which several specimens of the common earthworm (Lumbricus sp.) grew to a length of about three inches in the soil in some of these tins and were kept in this way with no further addition of moisture for several months. All the tins were kept on a table in an unheated room some 12x12x12 feet in extent and having a window (3x6 feet) on the north side of the building. The room was used as the writer's office. Its temperature would approximate that of any medium-sized honey-room used by beekeepers in extracting and storing their honey. The adult beetles were kept in the larger tins. They were removed daily to a clean tin containing fresh food and a clean piece of cotton wool soaked in water, except at the week-ends, when the beetles would be two days with one lot of food and water. The food supplied was a mixture of honey and pollen, thoroughly worked together to form a thick paste. The larvae were also fed on this mixture, but no water was supplied to them. The ease with which A. tumida can be bred in tins or petri dishes and the longevity of the insect, would make it a very suitable one to breed for general laboratory purposes or for museums exhibiting live insects. |