What you can do to prevent or limit their damage
Author: Jon Zawislak, Department of Entolomogy and Plant Pathology, Mississippi State University
The small hive beetle Aethina tumida (SHB) is an invasive pest of bee hives, originally from sub-Saharan Africa. These beetles inhabit almost all honey bee colonies in their native range, but they do little damage there and are rarely considered a serious hive pest.
It is unknown how this pest found its way into the U.S., but was first discovered to be damaging honey bee colonies in Florida in the late 1990s. It has since spread to more than 30 states, being particularly prevalent in the southeast. The beetles have likely been transported with package bees and by migratory beekeepers, but the adult beetles are strong fliers and are capable of traveling several miles at a time on their own.
In the United States these beetles are usually considered to be a secondary or opportunistic pest, only causing excessive damage after bee colonies have already become stressed or weakened by other factors. Infestations of beetles can put significant stress on bee colonies, which can be compounded by the stress of varroa mites and other conditions. If large populations of beetles are allowed to build up, even strong colonies can be overwhelmed in a short time.
Honey bee colonies appear able to contend with fairly large populations of adult beetles with little effect. However, high beetle populations are able to lay enormous numbers of eggs. These eggs develop quickly and result in rapid destruction of unprotected combs in a short time. There is no established threshold number for small hive beetles, as their ability to devastate a bee colony is related to many factors of colony strength and overall health. By maintaining strong bee colonies, and keeping adult beetle populations low, beekeepers can suppress the beetles’ reproductive potential.
Fig. 1. SHB adults are often observed in the hive with their head and antennae tucked down beneath the thorax. They are oblong in shape, around 6 mm long, and with variable coloration that ranges from tan to reddish-brown, dark brown or black.
Fig. 2. SHB larvae will grow to about 1/2" in length. They possess 3 pairs of well-developed legs, and have rows of short spines projecting from their bodies.
Adult SHB are 5-7 mm (1/4”) in length, oblong or oval in shape, tan to reddish brown, dark brown or black in color, and covered in fine hairs, but their size and appearance can be highly variable within a population. The adults are usually observed in the hive with their heads tucked down beneath the thorax, so that antennae and legs are often not apparent (Fig. 1). The larvae are elongated, cream-colored to slightly golden grubs, growing to 10-12 mm (1/2”). They may be mistaken for young larvae of the greater wax moth (Galleria mellonella). The two types of larvae can be differentiated by their appearance. Beetle larvae (Fig. 2) have three pairs of well-developed legs near the anterior end, while wax moth larvae have three pairs of legs near the anterior and four pairs of less-developed prolegs toward the posterior. SHB larvae also have numerous dorsal spines, which wax moth larvae are lacking. Both pests can be found simultaneously in the same hive, however.
Honey bees are not able to efficiently remove adult beetles from the hive, and their hard shells resist stinging. Rather, the bees are observed to pursue adult beetles across the combs. Beetles will seek cracks and crevices in which to escape from the bees, who in turn will imprison the beetles in these cracks, preventing them from escaping. The beetles have developed the ability to stimulate the mouth parts of worker bees with their antennae, similar to drones begging for food, and are able to trick their guards into feeding them. This behavior allows the beetles to survive in confinement for extended periods. Opening hives for inspections may free the beetles from their confinement.
Sometimes the SHB population becomes too large for the worker bees to protect against, and the beetle population can increase rapidly. This may happen due to weakening colony health or declining bee population, or due to beekeeper action. When swarming occurs, the number of bees available to patrol the interior of the hive is reduced, which may allow the beetle population to surge. When colonies are split, or nucs are created, the number of bees in the new colonies may be insufficient to protect against the beetle population. Mating nucs used in queen rearing may be particularly susceptible to SHB. Over-supering hives provides the beetles with excessive space in which to move and hide and provides additional oviposition sites, while increasing the area that the worker bees must patrol.
The use of grease patties for tracheal mite control, or the addition of protein supplement patties for spring build-up, may increase SHB infestations. Both adult and larval beetles are attracted to these patties as a food source. If patties are found to be infested with larvae, they should be removed immediately, and disposed of by wrapping them in several layers of plastic bags to prevent SHB from escaping.
The adult female beetles will lay egg masses in cracks and crevices around the hive, or directly on pollen and brood combs. Beetles may puncture the capping or wall of a brood cell and deposit eggs inside of it. A single female beetle can produce over 1000 eggs in her lifetime. Beetle eggs are similar in shape to those of honey bees, but approximately 2/3 the size. Eggs generally hatch in 2-4 days, and the larvae immediately begin to feed on pollen, honey, and bee brood. In 7-10 days, beetles complete their larval development and will exit the hive to pupate in the soil. The majority of larvae remain within about 180 cm (6’) of the hive they exit, but can crawl much longer distances if needed. Larvae will burrow up to 10 cm (4”) into the soil, where they remain 3-6 weeks to complete pupation. Within 1-2 days of emerging from the soil, adult beetles will seek out a host bee colony, which they locate by odors (Fig. 3).
The adults are strong fliers, and can disperse to other beehives easily. Beetles are also thought to travel with honey bee swarms. Individual beetles can live up to 6 months or more, and several overlapping generations of beetles can mature within in a colony in a single season. Beetle reproduction ceases during the winter, when adult beetles are able to overwinter within the bee cluster.
|Fig. 3. Life Cycle of the Small Hive Beetle.|
Economic damage from SHB occurs when the bee population is insufficient to protect the honey combs from the scavenging beetle larvae. When adult beetles first invade a colony, they may go unnoticed until their populations increase through reproduction or immigration. Both adult and larval beetles will prey upon honey bee eggs and brood.
When large numbers of beetle eggs hatch in weak colonies, the combs of honey can become “wormy” and take on a glistening, slimy appearance (Fig. 4). Unlike wax moths, these beetle larvae do not necessarily damage the combs themselves, and do not produce extensive webbing. Ruined honey can be washed from the combs, which may then be frozen for 24 hours to kill any beetles or eggs on them, and placed back onto a strong hive to be cleaned and repaired by the bees.
When large numbers of adult beetles defecate in the honey, they introduce yeasts, causing the honey to ferment and run out of the cells. In this case, the queen bee may cease laying, and the entire colony may abscond. Weak colonies are particularly vulnerable to attack, but even strong colonies can be overwhelmed by large populations of beetles. Nucleus colonies used for queen production or colony splits can be especially vulnerable to beetle attacks.
Beetles can create sudden problems if bee escapes are used prior to harvesting, and supers of honey are left virtually undefended by bees. If honey is removed from the hive, but not immediately extracted, beetles can invade the honey house and quickly ruin a large portion of a honey harvest. Wet cappings from recently extracted honey are also extremely attractive and vulnerable to beetle infestation. Honey contaminated by small hive beetles will be rejected by bees, is entirely unfit for human consumption, and should never be bottled or mixed with other honey for packing.
Fig. 4. Honeycombs infested with SHB larvae take on a glistening or "slimey" appearance. Honey contaminated by beetle larvae is unfit for consumption by either bees or humans.
Beetles are easily detected by visual inspection of colonies. When a hive is opened, adult beetles may be observed running across the underside of the outer cover, on either side of the inner cover, and on the top bars of frames. Also, beetles may be seen running across the surfaces of combs (Fig. 5). To detect beetles in the top hive body, open the hive and place the outer cover on the ground in a sunny spot, and place the top hive body into the cover (Fig. 6). Conduct normal colony inspection activities on the rest of the hive. If present in the top super, adult beetles will retreat from the sunlight, and after about 10 minutes you may lift the hive body and look for beetles in the cover. Beetles in the lower hive body will similarly retreat to the bottom board as the colony is disturbed.
Strips of corrugated cardboard, with the paper removed from one side, or pieces of corrugated plastic (obtained as scraps from a sign shop) can be placed on the bottom board at the rear of the hive. Adult beetles, fleeing from bees, may seek shelter in the small spaces of the corrugations, and can be easily seen. Bees may chew up and remove cardboard strips left in a hive for extended periods.
Varroa sticky boards are usually ineffective in detecting small hive beetles. Adult beetles prefer dark conditions, and will migrate toward the tops of hives that have screen bottoms, and may be more easily detected by placing corrugated strips on the top bars of the upper super or above the inner cover
Small hive beetle larvae are often found clustered together in corners of a hive or on frames. This behavior also differentiates them from wax moth larvae, which are found scattered throughout a hive. Older beetle larvae orient toward light sources, and in the honey house, a single fluorescent light near the floor may attract beetle larvae, which exit the hives when seeking a place to pupate. These larvae can be swept up and drowned in soapy water.
Surfaces of combs that appear slimy, or fermented honey bubbling from the combs, are positive signs of beetle activity. Fermented honey has an odor described as decaying oranges.
If you suspect the presence of hive beetles, you may contact your state apiary inspector to arrange a visit, or you may bring a specimen in alcohol to your local Cooperative Extension office for positive identification.
Fig. 5. Adult beetles may be seen running across the combs, often pursued by honey bees.
Fig. 6. To detect SHB in the top super of a hive, place it on the hive lid in a sunny spot for abotu 10 minutes. The bright light will drive the beetles down to the bottom. If present, adult beetles should be visible on the lid when the super is lifted.
Prevention is the most effective tactic of small hive beetle control. Chemical controls are available, but are of limited use. Good beekeeping management practices in the bee yard and in the honey house are sufficient to contain hive beetle problems in most cases. A combination of cultural and mechanical controls will usually help to maintain beetle infestations within a manageable range.
Keep bee colonies healthy and strong. Reduce stresses from diseases, mite parasitism, and other factors. Maintain and propagate bee stocks with hygienic traits that are better able to detect and remove pests and diseased brood. Eliminate, requeen, or strengthen weak colonies.
Use caution when combining colonies or exchanging combs and hive bodies, because beetles and their eggs can be introduced into other colonies, which can be overwhelmed. Making splits from heavily infested hives can cause a serious outbreak if insufficient numbers of bees remain to protect the hive. Avoid over-supering hives, which increases the area that the bees must patrol.
Maintain a clean apiary and honey house to reduce attraction to beetles. Avoid tossing burr comb onto the ground around hives, which may attract pests. Adult beetles tend to prefer shady locations. If possible, place hives where they receive direct sunlight at least part of the day. Keep hives and frames in good condition. Warped, cracked and rotten hive bodies provide beetles with many places to hide, and make them more difficult to detect by bees or beekeepers. When debris is left to accumulate on a bottom board, beetle larvae can complete pupation inside the hive. Regular cleaning or use of screen bottom boards can prevent this build-up of debris.
Honey that is removed from a colony should be extracted within 1-2 days. Wax cappings are an attractive food for beetles, and should be processed quickly or stored in sealed containers. Honey supers can be removed from weak colonies to lessen the territory of combs that the bees must patrol. If not ready for extraction, these supers can be placed on strong colonies, in a manner similar to protecting them from wax moth infestations. However, if small hive beetles or their eggs are present on the combs, the addition of these beetles can be sufficient to cause the strong colony to collapse. Honey supers can be frozen at -12°C (10°F) for 24 hours to kill all stages of beetles before transferring supers to a strong colony. Store empty supers under conditions of good air circulation and less than 50% humidity.
Pollen traps should not be left on heavily infested hives for extended periods. The unprotected pollen can serve as a substantial protein source for beetles, as well as a protected breeding site.
Utilize mechanical traps in the hive to reduce the number of adult beetles that can produce eggs, while also reducing the need for pesticides.
Mechanical Traps for eliminating Small Hive Beetles
The West Trap is placed on the bottom board, and requires a wooden shim to maintain proper space beneath the frames. It contains a shallow pool of oil, and is covered by a slatted screen that excludes bees. Adult beetles enter the trap from above, to escape from bees, and fall into the oil and drown. Hives must be kept extremely level for these traps to be effective. These traps preclude the use of screen bottom boards for ventilation.
The Hood Trap attaches to a standard bee hive frame. It has a compartment filled with apple cider vinegar as an attractant, and compartments filled with mineral oil, which drown the beetles as they enter. A potential drawback of this design is the empty space around the trap, which bees will often fill with drone comb, increasing a problem with varroa if left unattended. This area of drone comb, however, can be regularly removed and disposed of when about 50% of the drone cells are capped, which can effectively trap and remove a portion of reproducing varroa mites before they can emerge.
The Freeman Beetle Trap is similar to the West Trap in function. It replaces the bottom board with a 3 mm (1/8”) screen mesh, as used for varroa control. An oil-filled tray is inserted into a compartment below the screen. Adult beetles enter the trap to escape from bees, and fall into the oil and drown. Wandering beetle larvae may also fall into the trap as they attempt to exit the hive to pupate. These traps can passively eliminate some varroa mites as well. Hives must be kept level for these traps to work.
A variety of beetle traps, such as AJ’s Beetle Eater and Beetle Jail Jr., consist of shallow oil-filled troughs with slotted lids. These traps are suspended between frames of brood or honey. Adult beetles enter the traps to hide from bees, and are drowned in the oil. These types of traps are inexpensive and easy to use, but may need to be emptied and refilled regularly. Over time the bees may tend to propolize over some of the openings. Some manufacturers suggests placing a small sheet of vinyl across the top of the trap to prevent propolizing, but this may provide the beetles with sufficient cover without entering the trap. Similar in design and function, Cutt’s Beetle Blasters are disposable, and can be discarded when full of beetles.
Beetlejail traps are designed to prevent hive beetles from invading a bee hive, by trapping them as they seek to enter, and drowning them in oil.
Sonny-Mel traps are homemade, consisting of a small plastic sandwich box, with 3mm (1/8”) holes. The bottom of the trap contains a shallow layer or layer of mineral oil, and a smaller container (usually a small plastic jar lid or bottle cap) of liquid bait. To make a bait, combine 1 cup water, 1/2 cup apple cider vinegar, 1/4 cup sugar, and the peel of 1 ripe banana (chopped in small pieces); allow to ferment for 1-2 days. These traps are placed on the top bars of the upper super, and require the addition of a wooden frame to provide space for the trap.
This summary is provided as a convenience for the reader. The mention of any brand name or commercial product does not constitute or imply any endorsement, nor discrimination against similar products not mentioned.
The pupal stage is a vulnerable time in the beetle life cycle. Slightly moist, loose, sandy soil is optimal for their development. Locating colonies on hard clay or rocky soil, rather than light sandy soil, can reduce the number of beetle larvae that successfully pupate. If numerous larvae are discovered in the hive, the soil around the colony can be treated with a permethrin drench to prevent the larvae from pupating, killing them in the soil. Use with caution, as permethrin is highly toxic to bees!
Prepare the site by removing fresh water sources and feeding stations. Mow vegetation around the hives to be treated, to allow the solution to directly contact the soil. Mix 5 ml (1 teaspoon) GardStar® 40% EC into 1 gallon of water (enough to treat 6 hives). To avoid contaminating the bee hive surface with pesticide drift, do not use a sprayer. Apply the solution using a sprinkler can. Thoroughly drench the area in front of the hive (and beneath it, if screen bottom boards are used), wetting an area 18-24 inches around the hive, ensuring that wandering beetle larvae will contact treated soil.
Application should be made late in the evening when few bees are flying. Do not contact any surface of the bee hive or landing board with insecticide. USDA testing indicates that permethrin binds to the soil and remains active for 30-90 days, depending on soil type, pH, and moisture content. Reapply as needed.
Permethrin is corrosive and can cause irreversible eye damage. Avoid contact with eyes, and wear proper eye protection during application. Read and follow all label instructions for the legal and appropriate use of any pesticide.
Studies have indicated that soil-dwelling entomopathogenic nematodes have potential to provide some control of pupating SHB. Some species of these nematodes are commercially available from biological suppliers for use in the soil under and around bee hives. It is not yet evident whether these nematodes are effective in all soil types, or if they can persist through drought or overwintering conditions in all areas, however, they may be useful as part of an overall integrated pest management plan.
Because of insufficient scientific evidence on the efficacy of this control method, specific recommendations for the use of nematodes cannot be made at this time.
The chemical coumaphos (sold as Checkmite+ for varroa control) is the only pesticide registered for in-hive treatment of small hive beetles. Consult your local Cooperative Extension office or Department of Agriculture for specific recommendations in your state.
These instructions are a presented as a general guideline. Users are responsible for reading and following all label instructions for the legal and appropriate use of any pesticide.
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