| Effect of "New" vs. "Old" Wax Brood Combs on Honey Bee Tracheal Mite Populations In North Dakota(1) |
| by ERIC ERICKSON(2),
ANITA ATMOWIDJOJO(2), ALAN KING(3), and JOANNE KING(3) Revised Manuscript received for publication June 1, 1998 ABSTRACT The honey bee tracheal mite (HBTM), Acarapis woodi, is a parasite that infests the tracheae of adult bees. This colony level study was undertaken to determine whether the relative age of brood combs in the hive affects the incidence/population dynamics of HBTM in commercially managed honey bee colonies. Mean HBTM infestations remained low throughout this study, averaging 4.8 percent over all treatments/dates. Even so, there was a significantly higher (P < 0.001) mean level of HBTM infestation for colonies on new comb versus those on old comb. Levels of unilateral and bilateral tracheal infestations were also significantly different. Similarly, colonies on new comb were three to four times more likely to be infested with HBTM than those on old comb. These results support the view that there is a within-the-hive environmental component to tracheal mite resistance in honey bees. An environmental component external to the hive (e.g. environmental differences between the two apiaries) is contra-indicated. INTRODUCTION Honey bee tracheal mites (HBTM), Acarapis woodi (Rennie), parasitize adult honey bees (Apis mellifera L.) by feeding and reproducing in the tracheae of their host, causing respiratory distress, loss of hemolymph, and possible secondary infection(s). Infestation levels above 30 percent (of the bees within a colony) contribute to a loss in colony vigor and productivity, and are likely to lead to the demise of the colony over winter (Henderson and Morse, 1990; Shimanuki et al., 1992). Several studies have shown that HBTM resistant strains of honey bees can be developed (see Loper et. al., 1992; Danka and Villa, 1996). Erickson et. al., (1996) demonstrated that low-level chronic infestations of HBTM may persist in honey bee colonies without apparent impact on colony vigor or productivity. The precise mechanism(s) responsible for the observed suppression of HBTM populations remains unknown, however, Danka and Villa (unpub.) have shown that grooming can play a role along with colony environment. In the course of our earlier study (Erickson et. al., 1996) we began to suspect that there might be differences in the level of HBTM infestations in colonies using new vs older brood combs. This pilot study was undertaken to determine if the age of brood comb might affect the incidence/dynamics of HBTM populations in commercially managed colonies. 1/Mention of a trade name or proprietary product does not constitute its endorsement by the U.S. Department of Agriculture. Agricultural Research Service. 2/U. S. Department of Agriculture, Agricultural Research Service, Carl Hayden Bee Research Center, 2000 East Allen Road, Tucson, AZ 85719- 1596. 3/Marion, ND 58466. METHODS AND MATERIALS This study was undertaken in the fall of 1994 near Marion in southeastern North Dakota. Test colonies were overwintered at each of two apiary sites in virtually identical settings within 3.2 km (2 miles) of each other. However, during summer, the colonies were moved 1 to 3 times annually to maximize honey production, then returned to the winter apiary. Each winter apiary contained 80-88 established colonies in standard 24.5 cm (9.625 in) deep Langstroth hives on pallets. All colonies placed in one apiary were in hives having only 'old' brood combs, e.g. combs more than 15 years old (for the purposes of this study we refer to these combs as "old", recognizing, of course, that the combs in some commercially managed colonies can be much older). All hives in the second apiary contained only 'new' brood comb, drawn from foundation installed between 1991 and 1993. Due to the seasonal movement of all colonies among summer apiary sites, colonies placed in the two study locations in the fall were not necessarily the same colonies that had been taken from there in the spring; however, each fall only old comb or new comb colonies were returned to the respective apiary study sites for wintering. All colonies were managed in an identical manner following the normal management practices of the commercial beekeepers (A.& J. King) (Erickson et. al., 1996). These practices include maintaining one brood chamber below a queen excluder, requeening queenless colonies using daughter queens reared from superior stock selected by the beekeepers, supering, and honey removal. In the fall, in preparation for the extended winters characteristic of the area, all honey above the queen excluder in each colony was removed. The colonies were reduced to one brood chamber, weighed, and fed an amount of undiluted high fructose corn syrup (HFCS) equal to the difference between actual hive gross weight and a target gross weight of ~38 kg (85 lbs). The colonies were placed, wall to wall, on pallets in two tiers of four per pallet. These eight colony packs were covered with black plastic corrugated cartons. One ply of Reflectix® insulation (foil covered bubble pack) was placed on top. Each colony was provided with an upper entrance. Colonies were packcd for winter in late October-early November, then unpacked in late March-early April when they were fed diluted HFCS as needed. Populous winter survivors were split to offset winter losses. Tracheal Mite Analyses Approximately one-hundred adult bees were removed from the brood nests of 25 randomly selected colonies (20 colonies were sampled in the spring of 1995) in each treatment group beginning in 10/94 and continuing, both spring and fall until 4/96. All samples were taken at the winter apiaries just before the colonies were packed in the fall and just after they were unpacked in the spring, but before they were split. Colonies sampled were selected at random on each sampling date. The samples were immediately frozen and sent to the Carl Hayden Bee Research Center, Tucson, AZ where they were thawed and dissected. For analysis, thirty bees were removed at random from each sample to determine the level of HBTM infestation for each colony/treatment/date. HBTM infestations were estimated using the procedures of Delfinado-Baker (1984): Prothoracic collars were removed from each of the 30 bees, clarified for 24-36 h in five percent potassium hydroxide at 39º C, and examined at 100 x magnification with a stereo-microscope. Percent infestation was calculated from the mean number of infested bees among samples for each treatment. Differences between comb types were determined at the 0.05 level via randomized complete block Analysis of Variance (SAS, 1995) with sampling dates as blocks. RESULTS AND DiSCUSSION As in our earlier study (Erickson et. al., 1996), mean HBTM infestations remained low throughout this study, averaging 4.8 percent (range = 0-40%) over all treatments/dates. Even so, there were significant differences in levels of HBTM infestation between treatments for each sampling date. The over-all mean percent infestation was significantly higher (P < 0.001) for colonies on new comb versus those on old comb (5.2 vs 1.2%, respectively). Levels of unilateral and bilateral tracheal infestations were also significantly (p < 0.05) different (1.3 vs 0.3, and 0.2 vs 0.01 for new and old comb hives, respectively). Similarly, colonies on new comb were three to four times more likely to be infested with HBTM than those on old comb as is evident in the following table.
These unexpected results are difficult to explain. Nelson and Gochnauer (1982) and Koenig et. al., (1986) found that chalkbrood infestations were several times greater in hives with old comb versus those with in new comb. They presumed that this was due to old comb serving as a reservoir for the disease organism. We know of no other similar studies of parasites/diseases relative to new vs old brood comb. It is well known that old comb harbors accumulations of pesticide residues, infectious agents and other elements detrimental to the health of the honey bee colony. It would be unwise to interpret our results as a suggestion that colonies on old comb are somehow healthier (note: these colonies were already highly resistant to HBTM). However, these results do lend credence to the view that there is a within-the-hive environmental component to tracheal mite resistance in honey bees. An environmental component external to the hive (e.g. environmental differences between the two apiaries) is contra-indicated since: 1) all colonies were moved at random one to three times each year; 2) colonies to be returned to the two wintering apiaries were chosen at random, and, 3) fall sampling was accomplished soon after the colonies were returned to the wintering site. Additional studies in other localities are needcd to substantiate these results and to expose the mechanism(s) behind this aspect of tracheal mite biology. Hopefully, these results will contribute to future understanding of the mechanisms responsible for HBTM resistance in honey bees. References Danka, R. G., and J. D. Villa. 1996. Influence of resistant honey bee hosts on the life history of the parasite Acarapis woodi, Exper. & Appl. Acarology 20:313-322. Definando-Baker, M. 1984. Acarapis woodi in the United States. Amer. Bee J. 124 (11): 805-806. Erickson, E. H., A. King, J. King. 1996. Natural suppression of honey bee tracheal mites in North Dakota: A five year study. Amer. Bee J. 136(5):365-367. Koenig, J. P., G. M. Boush, and E. H. Erickson, Jr. 1986. Effect of type of brood comb on chalk brood disease in honey bee colonies. J. Apic. Res. 25 (1):58-62 Loper, G. M., G. D. Waller, D. Steffens, and R. M. Roselle. 1992. Selection and controlled natural mating: A solution to the honey bee tracheal mite problem. Amer. Bee J. 132(9):603-606 Nelson, D. L., T. A. Gochnauer. 1982. Field and laboratory studies on chalkbrood disease of honey bees. Amer. Bee J. 122(1):29-34. Sas Institute Inc., 1995. SAS/STAT user's guide; statistics, Version 6, third ed. SAS Institute, Inc. Cary, North Carolina. Shamanuki, H., D. A. Knox, B. Furgala, D. M. Caron, and J. L. Williams. Diseases and pests of honey bees. IN: The hive and the honey bee. J. M. Graham (ed.). p. 1083-1151. |