Most organisms have natural enemies. The use of parasites/parasitoids, predators and diseases is a time-honored way to help control pest populations, be they insects, weeds, mammals or others. This is called “biological control.” For example, the ancient Chinese moved ant nests into orchards to protect their citrus trees. Perhaps the most famous example of biological control is purposeful introduction into California of the vedalia beetle from Australia in 1889 to control cottony cushion scale. The vedalia beetle literally saved the California citrus industry, and since that success, it has been exported to many other parts of the world, often with equally good results .
Because they have been relatively inexpensive and effective, the beekeeping industry has used pesticides to control many insects and mites that are associated with honey bees. As these chemicals have undergone more and more scrutiny, however, many have fallen by the wayside while others are also at risk of losing their label. As a consequence, biological control is becoming more important as a possible alternative and can be an important way to help beekeepers get off the “pesticide treadmill.”
The wax moth is a large problem in many areas, especially in hot climates in empty supers that are stored for any period. Traditionally, several chemicals have been used to fumigate empty supers. A few years back, a biological control was found for wax moth. This was a specific strain of bacteria called Bacillus thuringiensis that proved deadly to wax moth larvae. The formulated product called Certan® was effective against moth larvae when applied as a spray on combs, but because of little demand for the product at the time, it was discontinued. Other strains of B. thuringiensis, often just called Bt, are available for other lepidopteran pests, but are less effective on wax moths.
Another biological control against wax moth is a tiny parasitic wasp called Trichogramma. Franz Bollhalder has written an article published in Bee Biz (No. 11, Spring 2000, p. 14) no longer published, on this topic. According to Mr. Bollhalder, five batches of parasitic wasps (Trichogramma) were released at three-week intervals in 12 comb stores owned by Swiss beekeepers from the beginning of June to the end of August. Cardboard discs were used to deliver the wasps’ ready-to-hatch eggs. In seven of the comb stores, wax moths were controlled to the extent that no damage occurred in spite of massive infestation pressures found in most testing areas. Two important points for this to be successful include installing close-fitting doors on comb storage facilities and checking newly stored combs for wax moth infestation. Compelling reasons to use Trichogramma include its ease of application, lack of residue problems and no need for a label.
Mr. Bollhander concludes in his paper: “Six releases @ 450 to 500 Trichogramma from mid-May (calendar week 21) in 3-week intervals are sufficient for treating a comb store of maximum volume 0.8 cubic metres. The additional, sixth, release compared with the previous year extends the Trichogramma application by three weeks. This is necessary for successful use in warmer areas, where the wax moth season lasts longer.” More information on acquiring and managing Trichogramma can be found on the World Wide Web.
A much tougher biological control problem is for tracheal and Varroa mites that have plagued beekeepers in the United States since the early 1980s. These critters are much more intimately associated with honey bees as they share the same nest. Tracheal mites live most of their lives inside the honey bees’ breathing tubes (tracheae), which greatly protects them. Some fumigants like those from menthol crystals and/or formic acid appear to work at least on a limited basis, but are dependent on ambient temperature for greatest effect. These materials are not strictly biological control, more effectively part of integrated pest management.
Because Varroa is found on the exterior of adult honey bees, it is more vulnerable than the tracheal mite . One line of research is being conduct at the Rothamsted bee research facility of the United Kingdom’s Institute of Arable Crops Research (IACR). Fungi are the most promising natural enemies of Varroa, according to some investigators. Several commercial fungal products have already been developed for specific pests in horticultural and agricultural systems, consisting of spore formulations that are applied directly to the target.
A specific fungus has been found that makes Varroa sick, according to A. Melathopoulos, B. Ruzicka and J. Gates in Canada. Their paper, “Can You Make Varroa Sick?” appears in HiveLights (November 2000, pp. 15-16), the official organ of the Canadian Honey Council. The authors investigated the effect of introducing spores of the mite-killing fungus, Hirsutella thompsoni into bee colonies . They compared the effectiveness of two formulations (spray and dust) with formic acid and Apistan®. According to the results, H. thompsoni shows considerable promise in preliminary experiments, but more needs to be done to develop a proper formulation and improved delivery method.
Besides fungi, information has recently appeared on Internet discussion lists that some beekeepers have observed lower Varroa populations in honey bee colonies with populations of pseudoscorpions. Although they also can prey on honey bees, the fact that these arthropods feast on mites, among other creatures found in a hive, suggests they might be a viable biological control option. D. Caron and K. Ross in the second edition of Honey Bee Pests, Predators, and Diseases (Cornell University Press, 1990), edited by R. Morse and R. Nowogrodski indicate these arthropods have been detected in beehives from Brazil to India. In that publication, the authors conclude: “In general, the question of whether the benefits of pseudoscorpions to honey bees are outweighed by the harm they cause is unresolved.” Thus, it appears that not enough is known about pseudoscorpions at this time to consider them as a viable biological control option. In addition, there may be great risk to bee colonies if these creatures are inappropriately transferred from one habitat to another. This has been called the “Nemesis Effect,” and must be taken seriously when considering the introduction of any species for biological control or other reasons.
The current situation with reference to American foulbrood and its resistance to one legal control, Terramycin®, is troubling. However, there is research being done, which might result in a biological control of this important honey bee disease. It is based on an old biological principal, competition, and parallels another story related here that discuses fungal control on plants facilitated by honey bees.
A paper found on the World Wide Web by Dr. Brian Dancer and colleagues states, “Arising from the comparative studies on Paenibacillus larvae subspp. larvae and Paenibacillus larvae subspp. pulvifaciens we discovered that like subsp. larvae, subsp. pulvifaciens produces active antibiotics as it sporulates which are active against a wide range of bacteria. Among the latter are M. plutonius which causes European foulbrood in honey bees. As is common in bacteria, the antibiotic(s) are not inhibitory to their producers nor to the other subspecies, subspp. larvae. However, during growth pulvifaciens produces a bacteriocin which is toxic for subsp. larvae, causing it to lyse. These observations have been patented and are the basis of ongoing investigations to determine whether spores of subsp. pulvifaciens can be applied to hives to prevent or treat both bacterial diseases of honey bees. The strains of subsp. pulvifaciens are unmodified and derive from hive material; as such they would make a welcome alternative to applied purified antibiotic and could help to reinforce the healthful image of honey and other bee products.”
A more recent effort concerns the use of “phages.” This is a short hand for bacteriophages, which are viruses that attack bacteria. In spite of all the efforts listed above, biological control for many maladies of Apis mellifera remains only a dream at the moment.