Diseases of Bees in New Zealand

New Zealand Journal of Agriculture, Volume 79, Issue 5, 15 November 1949, Page 483

Diseases of Bees in New Zealand

BEE diseases may be divided into two groups—those which affect bees in the larval or pupal stage, called brood diseases, and those affecting adult bees. Brood diseases include American foul-brood (the most serious of bee diseases in New Zealand) and sac brood, and diseases of adult bees include Nosema apis, Malpighamoeba mellifica prell, and Isle of Wight or acarine disease. They are the subject of this article -by T. Palmer- Jones, Research Officer, Department of Agriculture Animal Research Station, Wallaceville.

American foul-brood is a brood disease caused by a bacterium, Bacillus larvae, which attacks both worker and drone brood, usually in the pre-pupal stage. Thanks to the system of registration and inspection of hives in New Zealand, foul-brood is under control, but it is still the most serious of bee diseases. Only rarely is a laboratory test necessary—if brood has become dried up and the characteristic physical appearance, ropiness, and odour are not evident. Normally Apiary Instructors and experienced beekeepers can recognise the disease.

When conditions become unsuitable for bacterial growth, such as after the death and complete breakdown of the larva on which the bacterium feeds, it changes from the vegetative, or growing stage to the spore or dormant stage. These spores are resistant to changes in temperature and humidity and do not require food; they remain alive until they encounter a fresh host and so infect a new hive. When diseased brood reaches the stage of drying in which it becomes scale-like the spores are present in enormous numbers. The highly-resis-tant spores are the cause of the difficulty always experienced in attempting to eradicate American foul-brood by methods other than gassing the bees with a cyanide compound and burning them and the infected equipment. However, boiling for 30 minutes can be depended on to destroy the virulence of spores of B. larvae under any ordinary conditions. The disease is spread by robbing, transferring equipment, and exposure of honey containing spores. • Control Methods ; , . Resistant stocks: Bees less than normally liable . to infection with American foul-brood have been bred with success in the United States of America. However, the resistance of these colonies is not a true resistance, but depends on the greater speed and efficiency of these bees in removing diseased and dead larvae, so preventing Bacillus larvae from obtaining a hold on the colony.

Sulphathiazole has been found to help bees to combat the growing stage of B. larvae, but it has no effect on the spores. Hence, if a hive is treated, all the stored honey , which may contain spores must be removed before the medicated syrup is fed or reinfection may occur. A treated hive must be watched carefully, as the disease may recur. In New Zealand, which has a low incidence of infection, burning is safer and treatment with sulphathiazole is not encouraged. In some States of the U.S.A, infection is very widespread and burning of diseased hives would cause serious economic loss. The main points against the use of sulphathiazole may be summarised as follows:

In some cases queen bees have been adversely affected by the drug.

There is some risk that the drug may reach extracted honey. Though it would be unlikely to be present in amounts sufficient to make the honey unsuitable for human consumption, such honey could hardly be sold as a pure natural food. Amateur beekeepers are likely to experiment with the drug carelessly, so spreading foul-brood to the detriment of commercial apiarists. A strain of B. larvae resistant to sulphathiazole may appear. In the U.S.A, some apiarists are now forced to feed all their hives with the drug to keep down the disease, the spores of which have become distributed throughout their apiaries.

The British authorities have officially banned the use of sulphathiazole because of the risks involved. There appears no doubt that, if it were used in New Zealand in its present ' stage of development, the sulphathiazole treatment would lead to a spread of American foul-brood which would be disastrous for the beekeeping industry.

Diagnosis The method used for the diagnosis of B. larvae at the Animal Research Station, Wallaceville, is briefly as follows: ■

A water mount of suspected material is examined for spores. This is only a confirmatory test, as other types of spore may resemble B. larvae. The suspected material is boiled for 1J minutes in water, so killing less heat-resistant bacteria. The boiled material is used to inoculate special media. B. larvae will not grow on the ordinary laboratory media. . . If growth occurs, the organism is stained and examined for the typical gram positive rods of B. larvae. As a check the organism obtained is used to inoculate ordinary media. If the organism is B. larvae, it will not grow. B. larvae has the power of reducing nitrates to nitrites, and this test is applied for additional confirmation. Sac Brood A disease caused by a virus, sac brood affects only brood, causing it to die and assume a sac-like appearance. An outbreak in Canterbury was investigated by the author ,in 1941. Though it caused much loss of hive strength in some apiaries, the outbreak was. not a serious threat. Occasionally infected hives are reported in various parts of New Zealand, but the disease is now uncommon. No method of treatment is, known. Diagnosis depends on the sac-like appearance and absence of bacteria in the diseased brood. Nos ema apis A severe outbreak of Nosema apis, a disease of adult bees, was experienced in New Zealand in 1946-47, cases occurring throughout both islands. Nosema apis is a parasitic, sporeforming member of the protozoa microscopic, single-celled animals. The spores are more or less oval, about 2/10,000in. long and half as wide. Bacteria are roughly l/25,000in. in diameter. Life Cycle When Nosema spores reach the stomach of a bee they shed their

coats and liberate the parasites, which enter the cells lining the stomach. There they grow and multiply rapidly, and finally produce numerous spores, which pass through the bee and can infect a fresh host. These spores are thus the means Nosema has of perpetuating itself, as otherwise when the bee died Nosema would die also.

Field bees become weakened by the enormous number of parisites in their stomachs and are unable to return to the hives when out foraging. In badly-diseased hives all the adult bees may show some, degree of infection. Queens are attacked, but brood is immune. , The disease reaches its height in spring, though it may persist throughout the year. Symptoms - A loss in hive strength without apparent cause is usually the first sign of infection, other symptoms often being difficult to detect.' In very bad cases the bees may be seen crawling from the hives, being unable to fly, and there may be dysentery. Microscopic examination is. necessary for diagnosis of the disease. Bees, preferably living, should be sent to Wallaceville for diagnosis after consultation with the local Apiary Instructor.

Economic Importance Nosema has been reported in Australia, Brazil, Canada, England, Germany, Switzerland, and the U.S.A. It would be suprising if it were not present in New Zealand, as it was reported in Australia in 1910. It was probably introduced to New Zealand in the early days of beekeeping, as it must be one of the commonest and most widely-distributed of bee diseases. Nosema is a far less serious disease than American foul-brood. Strong colonies with a mild infection soon throw it off and recover, as was the case .at Wallaceville. A weak colony with a heavy infection may die out, and occasionally a group of hives, perhaps with lowered resistance, becomes a total loss, but usually the economic loss to the industry is small. If the

queen becomes infected with Nosema, the hive will decline rapidly and the bees may attempt supersedure. From past accounts of spring dwindling or reduction of hive strength in New Zealand there is little doubt that Nosema has been present for many years. > Control Methods Isolation of infected , colonies is not recommended. In the case of such a widespread outbreak as that which occurred in New Zealand in 1946-47 isolation and disinfection of individual hives would be impracticable. Where dysentery occurs, hive mats should be burnt to prevent risk of their transfer to uninfected hives. Badly-infected hives should not be moved to clean

apiaries. Contamination of drinking water and robbing of diseased hives probably cause the disease to spread. Requeening a hive in which the queen is infected or combining it with the queen and. bees of a nucleus hive is a step which is often successful. Treatment with drugs has not been found of use so far. One of the difficulties in assessing the value of drugs is that many hives recover naturally from Nosema, so control hivesthat is hives not fed the drug—must be used. Treated hives and the untreated controls should all have the same degree of infection if the drug is to be tested accurately. The danger of any drug used reaching extracted honey which may be sold to. the public and its possible adverse effect on the bees are important factors in such trials. In the U.S.A, gentian violet, emetine HCI, chinoformin, tryparsamide, chlorosan, and . sulphathiazole have been tested. None appeared to be effective. In Russia b. naphthol, xerophorm, picric acid, urotropin, phenol, collargol, salol, and gramicidin were tried. None was satisfactory. * Dr. Butler, at Rothamsted, England, is trying the effect of stovarsol, propamidine, and tryparsamide. Trials have not been completed. D. S. Robinson, Apiary Instructor, Department of Agriculture, Hastings, and the author have been carrying out trials of drugs against Nosema for several seasons. Drugs selected are known to be useful against organisms resembling Nosema. They are fed to hives in gradually-increasing doses, mixed in sugar syrup, so that tolerance of bees for them is first established. Finally, a group of hives is fed the drugs and samples from these and a control group are examined at intervals in the laboratory so that the course of the disease can be followed. Drugs already tested, with the weights fed in a single dose to a colony given in parentheses, are atebrin (3 grammes),

sulphapyridine (5 grammes), phenamidine (4 grammes), stilbamidine (.75 gramme), - and pentamidine (.25 gramme).. None of these drugs has shown any promise, but the work will continue. Malpighamoeba mellifica prell A _ disease affecting adult bees, Malpighamoeba mellifica prell is often associated with Nosema, but so far only one infected hive has been found in New Zealand (in August, 1948) , though hundreds of bees have been examined for it. It is caused by a microscopic. amoeba which destroys the cells in the malpighian tubules. It does not usually cause severe losses of bees and is regarded as of minor importance. Poisoning of Bees Though poisoning is not a disease, it is mentioned because it can cause heavy mortality among bees. Usually it is caused by arsenic contained in lead arsenate used as a fruit tree spray. A serious blow to the industry, involving the loss of hundreds of hives, recently resulted in the Hawkes Bay area through the careless use of this spray. Apart from loss of field bees, pollen may be contaminated and may poison the brood.

THE greatest care possible must be taken that nothing touches any electric power line. It is not necessary to know the difference between the various • types of electric linesall are dangerous and contact with any may cause fatality. It is important that farmers particularly should be aware of the danger because, as reports of accidents show, it is in connection with ,the movement of farm machinery that fatal, contacts with power lines occur all too frequently. Farmers should make certain that no farm implement whether stationary or when being moved can touch electric lines. Before moving . a 'stacker the ■ jib should be lowered, and 'similar action should be taken with the upward projecting part of any other implement before it is shifted;. ' When repairing buildings farmers should keep clear of all electric lines and they should not hesitate to ask a supply authority to make its lines dead ,if work is to be done near the point where lines are attached to buildings. Farmers should report anything unusual about electric lines or installations on the-farm, or even the lines on the road. When any part of the installation becomes faulty it should. be repaired by an electrician.

The lethal dose of arsenic for a bee is about .00005 milligram. One ounce of lead arsenate is sufficient to kill 120,000,000 bees

Diagnosis is carried out at Wallaceville, a large sample of bees (at least 500) being required. Isle of Wight or Acarine Disease Fortunately unknown in New Zealand, Australia, Canada, or America, Isle of Wight disease or acarine disease is one of the most deadly bee diseases known in Europe and England, where it causes great losses. It is caused by a small mite Acarapis wood!, which enters the tracheae of adult bees through the prothoracic spiracles and weakens its hosts by feeding on their juices.

Now that air transport is available there is danger that Isle of. Wight disease could enter New Zealand with imported queen bees. However, . the Apiaries Regulations 1948, made under the Apiaries Act 1927, give power to prohibit the importation of bees except under certain conditions. The Department of Agriculture would not grant permits to . import bees from any country or State where acarine disease of honey bees is known to exist, and any bees introduced without a permit may be 'seized and destroyed. In addition,, queen bees which arrive from such countries must first pass through Wallaceville laboratory, where their escort bees are examined for Isle of Wight disease before the queens are dispatched to the apiarist who ordered them. If all escort bees are free from the disease, the queen is transferred to a new cage and provided with fresh escort bees before she . leaves the laboratory. ’ This eliminates the risk of the disease being brought to New Zealand.

DANGER!