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Introduction

Throughout the history of apiculture in North America, beekeepers have had to deal with numerous hive parasites and diseases. Being heavily bred and domesticated, the European honeybee, Apis mellifera, is often vulnerable to pests and parasites. One such introduced pest that has recently posed a considerable threat to U.S. bee keeping is the small hive beetle, Aethina tumida (Figures 1-4). This parasitic cohabiter of honeybee hives can have a serious, and often fatal, effect on the hives it occupies. Since it was first detected in Florida in 1998 (Elzen et al., 1999), the small hive beetle has spread to hives in other states and drawn the attention of beekeepers and researchers alike.

Discussion

Morphology

The coleopteran family Nitidulidae contains approximately 2,800 described species in 172 genera worldwide. Nitidulid species show a wide variety of habits, feeding on rotting fruit, fungus, and parasitizing the nests of social Hymenoptera (Habeck, 2002). Many species in the family Nitidulidae are associated with fermentation, including the small hive beetle (Sanford, 2002). Nitidulids can be distinguished from other similar beetles (those with five tarsal segments) by their transverse procoxal cavities, grooved metacoxae, dilated tarsal segments, small forth tarsi, and three-segmented antennal club. All nitidulid beetles have eleven-segmented antennae inserted between the eyes and the base of the mandibles. Their antennae end in a characteristic club (Figure 5) which is variable in form, but always comprised of three segments (Habeck, 2002).

A. tumida beetles have a wide size range depending on both larval nutrition and the gender of the beetle. In general, male beetles (length: 5.12 +/- 0.07 mm; breadth: 3.21 +/- 0.04 mm) are smaller than their female counterparts (length: 5.27 +/-0.06 mm; breadth 3.25 +/-0.04 mm) (Neumann et al., 2001). Adult beetles range in color from yellowish brown to black, depending on their age. Adult A. tumida are covered in fine hairs, which make them difficult for beekeepers to pick up by hand (Sanford, 2002).

Figure 2: Aethina tumida adult, dorsal view.

Figure 3: Aethina tumida adult, lateral view.

Figure 4: Aethina tumida adult, ventral view.

Figure 5: Aethina tumida antenna.
(Photos: S. A. Stephens)

Development

As with all beetles, A. tumida undergoes holometabolous development with egg, larva, pupa, and adult stages (Figure 6). Eggs of the small hive beetle are 1.4 mm long, 0.26 mm wide and similar in appearance to honey bee eggs. Female beetles deposit their pearly-white eggs in irregular masses throughout the hive, but seem to prefer cavities and crevices such as those created by gaps between the hive frame and combs. The number of eggs a female beetle can lay at one time has not been determined yet, but it has been shown that only two or three beetles can lead to a heavy infestation. The incubation period varies from one to six days, with the majority of eggs hatching between two and four days (Sanford, 2002).

After the short incubation period, larval beetles (Figure 7) emerge from the eggs via a longitudinal slit. These newly-emerged larvae have large heads and protuberances along their bodies that are believed to protect them from drowning in honey. Larvae generally take ten to fourteen days to grow to pre-pupal size. Slower developing larvae are smaller and pupate into smaller adults (Sanford, 2002). Pre-pupal larvae enter a wandering phase, during which they venture outside of the hive to find suitable soil for pupation (Neumann et al., 2001). Pettis and Shimanuki observed that the majority of beetles pupate in soil at 1-10cm depth and within 30 cm of the hive entrance, with no beetles found at 180cm from the hive (Pettis and Shimanuki, 2000). Larval beetles excavate a smooth-walled earthen cell in the soil in which they pupate. Metamorphosis in the soil takes approximately seventeen days, after which the adult beetles may disperse over a large distance to infest other hives (Neumann et al., 2001). Newly emerged adult beetles are more active, readily take flight, and orient toward the light. After the first day or two as adults, beetles become less active and prefer less luminated areas within the hive (Sanford, 2002).

Figure 7: Aethina tumida larva. (Photo: S. A. Stephens)

Hive Parasitism

Adult and larval small hive beetles feed on honey, pollen, and brood in honey bee nests (Neumann et al., 2001). Laboratory tests have shown that A. tumida prefers honey bee eggs as a food source, even in the presence of excessive honey and pollen (Elzen et al., 2001). Experiments conducted by Eischen et al. (1999) suggest that, when deprived of hive products and brood, small hive beetles will feed on selected fruits and will often complete larval development on these alternative food sources. Recent experiments on longevity and reproductive success have supported these findings and led researcher to believe that small hive beetles are actually facultative parasites (Ellis et al., 2002). Small hive beetles do their damage in several ways: by burrowing into cells (Elzen et al., 1999), by consuming bee brood, and by defecating in the honey (Elzen et al., 2001). The most economically significant of these behaviors is the defecation by beetles in the hive’s honey stores (Elzen et al., 1999). Defecation in the honey promotes fermentation and renders the honey commercially unusable. Fermenting honey will often drip from cells opened by the beetles and produce a slimy film over the contents of the hive (Elzen et al., 1999). It has also been shown that once the number of beetles in the hive reaches a certain point bees will cease brood-rearing altogether (Sanford, 2002). In European honey bee hives, A. tumida infestations can consist of as many as 1,000 adults and several hundred larvae per hive (Elzen et al., 1999).

Until 1998, A. tumida had never been recorded in the Western Hemisphere (Elzen et al., 1999). It is believed that A. tumida was first introduced in North America in coastal sections of South Carolina and Georgia. Mitochondrial DNA sequencing of U.S. and African small hive beetles strongly suggests that the African and North American populations represent the same species, but has not allowed researchers to determine if the North American population is the result of one or multiple introductions (Evans et al., 2000). There is some evidence that the earliest North American record of the small hive beetle was in South Carolina in November of 1996 (Mostafa and Williams, 2002). However, the first confirmed detection was in Floridian honey bee hives in June of 1998, as identified by the Florida Department of Agriculture and Consumer Services (Sanford, 2002). Since this time, the small hive beetle has extended its North American range to 29 states (Figure 8 ) including Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Louisiana, Maine, Massachusetts, Maryland, Michigan, Minnesota, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, and Wisconsin (Mostafa and Williams, 2002). The main modes of transportation of A. tumida are believed to be the movement of hives by migratory beekeepers, the distribution of packaged bees, and possibly the distribution on alternative hosts (Delaplane, 1998). Entomologist have yet to establish whether the beetle is capable of persisting in more temperate regions of the country and, therefore, are uncertain as to how far its range will eventually spread (Sanford, 2002).

In contrast to the devastation it has caused in European honey bee hives, the small hive beetle is not considered a serious pest to bees in its endemic range of Subsaharan Africa (Elzen et al., 1999). In Africa, the beetle is rarely seen inundating a hive (Elzen et al., 2001) and primarily attacks damaged or weakened hives (Elzen et al. 1999). One survey found that only 7% of South African beekeepers listed A. tumida as a serious pest. Several possible reasons have been given for the difference between pest severity in Africa and the United States: 1) differences in African vs. European honey bee races; 2) differences in beekeeping practices, namely that African beekeepers tend to minimize the amount of honey stored in hives, compared with U.S. beekeepers; 3) A. tumida introduced into the United States may have escaped parasites, predators, and pathogens that limit African populations (Evans et al., 2000). However, in an attempt to find safe and effective ways of controlling A. tumida, researchers have searched for parasites and predators of the small hive beetle within its native range. So far, no such control organisms have been found (Elzen et al., 2001).

In recent years, much research attention has been focused on the behavioral differences between European honey bees and African subspecies of Apis mellifera. These differences have also been a large part of the focus of small hive beetle research. European honey bees have long been bred for increased docility, making them significantly less aggressive than their African relatives. It is believed that these differences in bee behavior account for the contrast in pest severity between Africa and the Western Hemisphere. In the New World, European honey bees show far less aggressive and investigative behavior towards adult small hive beetles (Neumann, 2001). South African beekeepers report observing their African honey bees continuously harassing adult beetles and removing larvae from the hive (Elzen et al. 2001). In a particularly interesting study, researchers found that African Cape honey bees, Apis mellifera capensis, use social encapsulation to defend their colonies against small hive beetles. Cape bee workers will use propolis (tree resin collected by the bees) to seal adult beetles into confinement areas. The entrapped beetles are prevented from engaging in mating and egg laying and prevented from doing further feeding damage to the hive. By postponing a more widespread infestation of the beetles, Cape bees protect their colonies from significant damage until it is time for the colony to abscond. In contrast to this, European honey bees are thought not encapsulate small hive beetles and are less likely to be triggered to abscond by the presence of hive parasites (Neumann, 2001). However, a series of recent experiments have demonstrated that at least some European honey bees are showing encapsulation behaviors when confronted with the small hive beetle (Ellis, 2003). These results could be the first signs that European honey bees have retained some behavioral defenses against A. tumida.

Control of the Small Hive Beetle

Proper management of bee colonies is the first line of defense against any hive disease or parasite. Sanitary conditions in the areas surrounding the hive or bee yard should be maintained by removal of extracted honey and beeswax from the vicinity. This avoids attracting beetles to the area with the scents of hive products. The stacking of supers containing beetle larvae onto healthy colonies is one way beetle infestations are spread from one colony to another and should be avoided. Common practices of stacking weak or empty colonies on stronger ones may have to be curtailed. Soil conditions around the hive can be very crucial to the success of pupating beetles. Therefore, one proposed method of control is to maintain the soil at either excessive humidity or constant dryness. Sandy soils may also prove unsuitable for developing beetles. Placing larval traps around the hive is also recommended to prevent beetle pupation (Sanford, 2002). Use of a modified hive entrance constructed from PVC pipe has also been shown to help control small hive beetles, but does have some adverse effects on the number of brood and on hive temperature (Ellis et al., 2002). Furthermore, stationary colonies have been shown to be more prone to infestation. Frequent movement of colonies may be advised to defend against the small hive beetle by breaking its life cycle. Overall, constant monitoring and careful observation of hive conditions is a beekeeper’s best defense against infestation by the small hive beetle (Sanford, 2002).

If an infestation of A. tumida (Figure 3) is suspected or detected within a beekeeper’s hives further measures can be taken to prevent the loss of colonies. Several chemicals have been authorized by the Environmental Protection Agency (EPA) for use in treating small hive beetle infestations. Chemical treatment of the beetles can take one of two approaches: treatment within the colony or treatment of developing pupae in the soil (Sanford, 2002). Strips impregnated with the organophosphate coumaphos placed under cardboard stapled to the bottom board of the hive have been demonstrated to provide good control of the small hive beetle within the hive (Elzen et al., 1999). The product ‘Check Mite +’ has been registered under an emergency-use label for use as an inside-hive treatment for beetle control (Hood, 2000). An emsulsifiable concentrate of 40% permethrin applied to the soil surrounding the hive has also been used for the treatment of the small hive beetle (Sanford, 2002). The soil treatment product Gard Star has similarly been approved for use by U.S. beekeepers to control beetles as they enter the soil to pupate (Hood, 2000). Household products, namely bleach, have recently been shown to be effective for controlling beetle larvae and for use in salvaging infested combs (Park et al., 2002). The fact that the small hive beetle has overlapping generations poses an additional problem to effective treatment (Sanford, 2002). For this reason, simultaneous treatment of both the hive and surrounding soil may be recommended.

Conclusion

North American beekeepers have long had to deal with introduced hive pests threatening their livelihoods. The recent introduction of the small hive beetle into the Western Hemisphere has lead to much concern among professional and hobby beekeepers alike. At this time, it is uncertain how far the pest will spread or what its overall impact on North American beekeeping will be. However, with careful monitoring of hives and proper treatment of infestations, there is hope for keeping the small hive beetle suppressed and slowing its spread to other states. As with all hive pests, the small hive beetle poses a challenge for beekeepers to intelligently manage their colonies and for researchers to apply and enhance their knowledge of apicultural systems.

Small Hive Beetle Links

Virgina Tech Entomology Department

University of Florida Deparment of Entomology and Nematology

University of Florida Cooperative Extension

Florida Department of Agriculture and Consumer Services

USDA: Beltsville Agricultural Research Center

University of Delaware

Literature Cited

Delaplane, K. S. 1998. The small hive beetle, Aethina tumida, in the Southeast. American Bee Journal, 138(12): 884-885.

Eischen, F. A., D. Westrvelt, and C. Randall. 1999. Does the small hive beetle have alternative food sources? American Bee Journal, 139(2): 125.

Ellis, J. D. Jr. 2003. Incarceration of small hive beetles: European bees are keeping beetles at bay, too. Bee Culture, February 2003.

Ellis, J. D. Jr., K. S. Delaplane, R. Hepburn, and P. J Elzen. 2002. Controlling small hive beetles (Aethina tumida Murray) in honey bee (Apis mellifera) colonies using a modified hive entrance. American Bee Journal, 142(4): 288-290.

Ellis, J. D. Jr., P. Neumann, R. Hepburn, and P. J. Elzen. 2002. Longevity and reproductive success of Aethina tumida (Coleoptera: Nitidulidae) fed different natural diets. Journal of Economic Entomology, 95(5): 902-907.

Elzen, P. J., J. R. Baxter, P. Neumann, A. Solbrig, C. Pirk, H.R. Hepburn, D. Westervelt, and C. Randall. 2001. Behavior of African and European subspecies of Apis mellifera toward the small hive beetle, Aethina tumida. Journal of Apicultural Research, 40(1): 40-41.

Elzen, P. J., J. R. Baxter, D. Westervelt, C. Randall, K.S. Delaplane, L. Cutts, and W. T. Wilson. 1999. Field control and biology studies of a new pest species, Aethina tumida Murray (Coleoptera, Nitidulidae), attacking European honey bees in the Western Hemisphere. Apidologie, 30: 361-366.

Evans, J. D., J. S. Pettis, and H. Shimanuki. 2000. Mitochondrial DNA relationships in an emergent pest of honey bees: Aethina tumida (Coleoptera: Nitidulidae) from the United States and Africa. Annals of the Entomological Society of America, 93(3): 415-420.

Habeck, D. H. 2002. Nitidulidae. In: American Beetles, Volume 2, pp. 311-315. Edited by R. H. Arnett Jr., M. C. Thomas, P. E. Skelley, and J. H. Frank. CRC Press, Boca Raton.

Hood, W. M. 2000. Overview of the small hive beetle, Aethina tumida, in North America. Bee World, 81(3): 129-137.

Mostafa, A. M. and R. N. Williams. 2002. New record of the small hive beetle in Egypt and notes on its distribution and control. Bee World, 83(3): 99-108.

Neumann, P., C. W. W. Pirk, R. Hepburn, A. J. Solbrig, F. L. W. Ratnieks, and P. J. Elzen, and J. R. Baxter. 2001. Social encapsulation of beetle parasites by Cape honeybee colonies (Apis mellifera capensis Esch.). Naturwissenschaften, 88: 214-216.

Park, A.L., J. S Pettis, and D. M. Caron. 2002. Use of household products in the control of small hive beetle larvae and salvage of treated combs. American Bee Journal,142(6): 439-442.

Pettis, J. S. and H. Shimanuki. 2000. Observations on the small hive beetle, Aethina tumida Murray, in the United States. American Bee Journal, 140(2): 152-155.

Sanford, Malcolm T. 2002. University of Florida Department of Entomology and Nematology: Featured Creatures. http://creatures.ifas.ufl.edu/misc/bees/small_hive_beetle.htm.

Additional Sources Available on the Small Hive Beetle

Ambrose, J. T., M. S. Stanghellini, and D. I. Hopkins. 2000. A scientific note on the threat of small hive beetles (Aethina tumida Murray) to bumble bee (Bombus sp.) colonies in the United States. Apidologie, 31: 457-458.

Baxter, JR., P. J. Elzen, D. Westervelt, D. Causey, C. Randall, F. A. Eischen, and W. T. Wilson. 1999. Control of the small hive beetle, Aethina tumida in package bees. American Bee Journal, 139(10): 792-793.

Eischen, F. A. 1999. Beetle watching. American Bee Journal, 139(6): 452-453.

Eischen, F. A., D. Westervelt, and J. Baxter. 1999. Small hive beetles in the honey house! American Bee Journal, 139(12): 934-935.

Ellis, J. D. Jr. 2002. Food for thought: How diet affects small hive beetles. American Bee Journal, 142(7): 515-517.

Ellis, J. D. Jr., K. S. Delaplane, and W. M. Hood. 2002. Small hive beetle (Aethina tumida Murray) weight, gross biometry, and sex production at three locations in the Southeastern United States. American Bee Journal, 142(7): 520-522.

Elzen, J. D. Jr., J. R. Baxter, D. Westervelt, C. Randall, L. Cutts, W. T. Wilson, F. A. Eischen, K. S. Delaplane, and D. I. Hopkins. 1999. Status of the small hive beetle in the U.S.: Now in four states, what’s next? Bee Culture, January, 1999.

Elzen, P. J., J. R. Baxter, D. Westervelt, C. Randall, and W. T. Wilson. 2000. A scientific note on observations of the small hive beetle Aethina tumida Murray (Coleoptera, Nitidulidae), in Florida, USA. Apidologie, 31: 593-594.

Hopkins, D. I., C. A. Nalepa, G. D. Hackney, and K. A. Kidd. 1999. Studies of the small hive beetle Aethina tumida in North Carolina. American Bee Journal, 139(7): 536.

Neumann, P., C. W. W. Pirk, R. Hepburn, P. J. Elzen, and J. R. Baxter. 2001. Laboratory rearing of small hive beetles Aethina tumida (Coleoptera, Nitidulidae). Journal of Apicultural Research, 40(3-4): 111-112.

Stanghellini, M. S., J. T. Ambrose, and D. I. Hopkins. 2000. Bumble bee colonies as potential alternative hosts for the small hive beetle (Aethina tumida Murray). American Bee Journal, 140(1): 71-75.

Taber, S. 1999. The small hive beetle, as described by A. E. Lundie in 1940. American Bee Journal, 139(6): 450-451.

Taber, S. 1999. The South Carolina small hive beetle experiment. American Bee Journal, 139(7): 534-535.

Taber, S. and M. Hood. 2000. Report on the South Carolina hive beetle experiment. American Bee Journal, 140(7): 548-549.

Wenning, C. J. 2001. Spread and threat of the small hive beetle. American Bee Journal, 149(9): 640-643.

©2003 Stephanie A Stephens