APIS Volume 3, Number 5, May 1985
In this issue
- Experimentation, Tracheal Mites and Selection
TRACHEAL MITES--TO EXPERIMENT OR NOT TO EXPERIMENT
[Editor's note 5/11/1997--this presaged the arrival of the Varroa mite; much of the information is relevant for both tracheal and Varroa. Tracheal mites have all but disappeared in Mexico; one possible reason is that treatment was never used and only the resistant strains survived. The arrival of the African bee also introduces more variables in that country.]
Beekeepers have always been experimenters. And there's little doubt this kind of study has advanced the craft considerably over the centuries. The tradition continues as the current confusing situation over tracheal mites persists. I have heard that a number of beekeepers are experimentally treating colonies with a wide range of chemicals in order to "control" mite infestations. The reasons why experienced bee researchers and others blanch at the thought are legion. They range from a wish to obtain for themselves highly infested colonies, not all that common, for study that have not been tampered with, to fear for the experimenting beekeeper's safety.
Many persons are understandibly frustrated by the apparent lack of research going on to control tracheal mites. That's particularly true for those in already infested areas (now officially all of Florida) as opposed to others who stubbornly assert that no mites exist in their states or operations. Beyond the politics of the situation, however, lies the real world of making the kind of research decisions needed that lead to effective solutions.
Dr. Elbert Jaycox has recently written an article in his beekeeping newsletter that points out some of the major kinds of decisions that must be made as research begins on chemical compounds for possible use either in quarantine or field treatments of infested bees. First and foremost, Dr. Jaycox says, relates to the type of material to use--fumigant or systemic. Fumigants must be able to disperse widely within a colony and penetrate the breathing tubes of all the bees in a colony to kill mites. Systemics are chemical compounds fed to bees that must be eaten, absorbed by the bees and then kill mites that feed on the bees blood (haemolymph). To be useful, he continues, both fumigant and systemics must kill the mites without killing many bees and not leave toxic residues which contaminate honey or wax.
Historically, Dr. Jaycox says, fumigants have been relied on for tracheal mite control. In at least one case, they have killed infested bees, weakening a colony. Many materials have killed all the mites in lightly infested colonies, but have rarely been effective when bees are heavily infested. The reasons include: (1) the fumigant doesn't reach all bees; (2) when it does reach all bees, it doesn't reach all the mites. Their may be as many as eighty adult mites, thirty-one larvae and eight eggs in a single bee. These can plug the breathing tubes (tracheae) so the fumigant will not enter. In addition, mites may be located deep inside an individual bee. They have been found in the smaller branches of the trachea and in air sacs in the head. According to Dr. Jaycox, therefore, "Probably because of these problems, Dr. Wolfgang Ritter and his associates in Germany found that colonies treated eight time at 4- to 7-day intervals with Folbex VA (bromopropylate) still contained bees infested with live mites."
Additional problems posed by fumigants, according to Dr. Jaycox, include differing resistance of mite eggs, larvae and adults. Because eggs are so difficult to kill, two fumigant treatments, timed to allow eggs to hatch, have better chances at control than one. In order to kill all mites in package bees, for example, Dr. Jaycox says they will probably have to be stored four to seven days and treated twice with effective miticides. This added expenses for the producer must also be passed on to the consumer.
Systemic treatments for mites allow for closer control of dosage than using fumigants, Dr. Jaycox says, and they also reduce possibility of contamination of hive bodies, frames, and wax. At the same time however, chances of leaving residues in honey increase, because nectar is processed by materials added by individual bees themselves. Not giving enough chemical to bees can also result in creating resistant strains or mites, according to Dr. Jaycox, which has already been observed with the use of phenothiazine in Japan.
If one carefully examines the above, it can be inferred that quality effective research on tracheal mites is no easy task. A great number of questions need to be answered. In infested bees, are the mites killed and not the bees? How many? All? How can it be shown they are actually dead? Remember, to evaluate a study requires infested bees be laboriously dissected and examined under a microscope by trained persons. In addition, any experiment that appears to work, must be repeatable to ensure reliability. Given that specific bees are destroyed to determine if materials are killing mites, it must be proven that repeat experiments are not somehow effected by bees removed during earlier trials.
Finally, no experiment is worth much without a control, an untreated colony in the exact same state genetically, qualitatively (same stores, amount of brood) and infested to the same degree as the colony being treated. This provides the basis for comparison to show a material's effectiveness. In bee research, developing effective control colonies is often the most difficult part of an experiment. This is because to be shown to be generally effective, experiments must usually be conducted on a large scale involving a great number of both infested and control colonies.
Does all this mean that experimentation with tracheal mites is something best left to the "experts. Not necessarily. Without resorting to chemicals, the beekeeper has at his/her disposal all the material needed to effectively and safely experiment with controlling mites--the honey bee's variable genetic complement. Selecting colonies that appear to be resistant and then propagating queens from them is an age-old scheme that has been shown to be effective in controlling American foulbrood, swarming, and pollen collecting.
Dr. Jaycox indicates that having bees resistant to mites would reduce losses and need for treating with chemicals. For example he mentions F.W. Calvert in England who has claimed that bees of the Buckfast strain could eliminate a mite infestation within twelve months and would prevent reinfestation. Unfortunatley, Dr. Leslie Bailey of Rothamsted Experimental Station was unable to confirm this resistance in Buckfast bees. A Beowulf Cooper, also of England, Dr. Jaycox says, reported he continually selected breeder queens from colonies resistant to mites and killed all infested colonies but one every winter. He used that one to infest the rest of the colonies in the spring as a continual selection process for resistance.
Selecting for resistance is not an "exact" science. Rather, it is more of an estimate of the state of a colony because the specific genetic links that might cause resistance are not known. All the beekeeper can go on is whether a colony seems to be somehow better off than others in a specific setting under specific conditions. Brother Adam at Buckfast Abbey, for example, appears to select his mite- resistant colonies on the basis of whether or not they overwinter. This is over simplistic to be sure because many things besides mites will affect overwintering capability, but given so little knowledge of the specifics of mite resistance, it is elegantly simple and apparently effective.
Selecting for genetic resistance is a far more forgiving and natural (some might even call it "organic") way to experiment without having to resort to potentially environmentally harmful chemicals and their possible complications. Dr. G.P. Georghiou, known worldwide for expertise in the area of insect resistance to pesticides and now retired from the University of California, has said that neither use of chemical toxicants nor development of resistance to chemicals by pest insects is recent. Life forms possess natural defense mechanisms to repel attacking organisms, developed over million of years of evolution. This is not only true for insect pests, but also for weeds and plant diseases, where chemicals have been developed for control. Some 447 insect species, 100 plant pathogens, 48 weeds and two species of nematodes are now resistant to chemical pesticides.
In a recent series of articles in Agrichemical Age, A.D. LaFarge looked at pesticide resistance that has been building up in insects ever since D.D.T. was developed. She dubbed this the "Evolutionary Squeeze." A dramatic example of resistance is found in the Colorado potato beetle, which has, "weathered the onslaught of arsenicals, chlorinated hydrocarbons, organophosphorous compounds, carbamates and pyrethroids."
Chemical manufacturers are also feeling the squeeze, according to Ms. LaFarge, who says that rate of introduction of new pesticides declined to almost nil between 1970 and 1980, while costs to develop a new chemical have risen from $1.2 million in 1956 to $30 million in 1984. For insect pest species, therefore, the most pressing future question is how to control pest populations as more and more become resistant to pesticides. The beekeeper would do well to look closely at the corrollary; that the perceived "problem" for pest species may be the best potential "answer" for maladies that affect honey bees. Indeed, it appears the beekeeper who continually experimentally selects stock for resistance to mites, chalkbrood, and European foulbrood will be way ahead of even the "experts" in knowledge and experience, if and when Varroa mites or Africanized honey bees arrive in this country.
Sincerely,
Malcolm T. Sanford
Bldg 970, Box 110620
University of Florida
Gainesville, FL 32611-0620
Phone (352) 392-1801, Ext. 143 FAX: (352)-392-0190
http://www.ifas.ufl.edu/~entweb/apis/apis.htm
INTERNET Address: MTS@GNV.IFAS.UFL.EDU
©1985 M.T. Sanford "All Rights Reserved
