Aethina tumida

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Authors: Ellis, A.M., Ellis, J.D., and A.C. Hodges, University of Florida

5193005
Taxonomy
Kingdom: Animalia
Phylum: Arthropoda
Class: Hexapoda (including Insecta)
Order: Coleoptera
Family: Nitidulidae
Genus: Aethina
Species: A. tumida
Scientific Name
Aethina tumida
Murray, 1867
Common Names

small hive beetle


Contents

Introduction

The small hive beetle, Aethina tumida Murray - SHB, is native to sub-Saharan Africa where it is an occasional pest in honey bee (Apis mellifera) colonies. SHB was confirmed in the Southeastern US in 1998 in a commercial apiary in FL but previously unidentified specimens indicate its presence in the US since at least 1996. SHB was initially problematic in areas near ports such as Charleston, SC and Savannah, GA as well as parts of FL. However, it has spread through the entire eastern half of the US and is now reported in Texas and California.

Description

Newly emerged SHB are light brown in color, becoming progressively darker (almost black) as their exoskeleton hardens. These color changes may occur in the pupal cell before the adult emerges. Adult female (5.7 ± 0.02 mm) SHB are generally longer than males (5.5 ± 0.01 mm) but both are nearly identical in width (~ 3.2 mm). Adult females (14.2 ± 0.2 mg) are also heavier than males (12.3 ± 0.2 mg) and occur in greater proportions of the population. Despite average general biometry, naturally occurring SHB can vary greatly in size, possibly depending on diet, climate, etc.

SHB eggs are 1.4 × 0.26 mm (l × w) pearly white in appearance. Newly emerged SHB larvae have relatively large heads and numerous protuberances covering their bodies. Larval growth rate varies depending on diet but the majority mature in 10-14 days. Upon full maturation, larvae will have reached a length and width of 9.5 mm and 1.6 mm respectively. Early-stage pupae of SHB are pearly white, having characteristic projections on the thorax and abdomen. Later-stage pupae darken as their exoskeleton develops and hardens.

Life Cycle

SHB biology is generally understood. Upon emerging from the ground, adult SHB search for honey bee colonies, probably locating a host colony by a suite of olfactory cues. Studies have shown that odors from adult bees and various hive products (honey, pollen) are very attractive to flying SHB. SHB fly before or just after dusk. Upon entering the host colony, the adults seek cracks and crevices where they hide from bee aggression. Remarkably, honey bees station guards around the cracks where SHB hide. The ‘prison’ guards keep the SHB confined to the cracks and out of the brood combs where there is an ample supply of honey, pollen, and brood on which SHB reproduce. SHB appear to be sexually mature about 1 week after emerging from the soil. It is not known if they mate multiple times. If allowed to reproduce, female SHB will oviposit directly onto food sources such as pollen or brood combs. The long, flexible ovipositors are well adapted for laying eggs in tiny, concealed places. Female SHB may deposit irregular masses of eggs in crevices or cavities away from the bees’ reach. A female SHB may lay 1,000 eggs in her lifetime although recent data suggest that the number might be upwards of 2,000. The majority of these eggs hatch within three days; however, some eggs are still viable and hatch after 5 days. Humidity appears to be a crucial factor influencing hatch rates, as SHB eggs are prone to desiccation if exposed to circulating air and relative humidity below 50%.

Newly hatched larvae immediately begin feeding on whatever food source is available, including honey, pollen, and bee brood, although they have demonstrated a preference for bee brood. Maturation time for larvae is generally 10-14 days, although some may feed longer than a month. Once the larvae finish feeding, a ‘wandering’ phase is initiated where larvae leave the food source and migrate out of the colony to find suitable soil in which to pupate. Larvae in this stage are remarkably resilient to climatic conditions and may even wander great distances to find suitable soil.

Most larvae pupate within 90 cm of the hive, but some may migrate much further from the hive in an effort to find ideal soil,. Nearly 80% of the larvae burrow into the soil less than 10 cm from the soil surface but not generally more than 20 cm. Once larvae cease burrowing, they construct a smooth-walled, earthen cell in which they pupate. The pupation period can vary greatly depending on factors such as soil temperature, etc. However, the majority of adults emerge after being in the soil 3-4 weeks. Upon adult emergence, the entire life cycle begins again. The turnover rate from egg to adult can be as little as 4-6 weeks; consequently, there may be as many as 6 generations in a 12-month period under moderate US climatic conditions.

Damage

Most major damage associated with SHB has occurred in South Carolina, Georgia, and Florida, with Florida experiencing the most damage. In 1998, Florida beekeepers reported an estimated $3 million loss due to damage caused by SHB. Most other states where SHB occur report only isolated incidences of apiary-wide damage.

In its native range, SHB regularly occurs in honey bee colonies but it does not cause damage in strong, healthy ones. In the US though, SHB damage in European races of colonies follows the characteristic 1) adult invasion into colonies, 2) population build-up of SHB, 3) reproduction of SHB, 4) significant damage to brood, pollen, and honey stores by feeding SHB larvae, 5) mass exodus of larvae from the colony, 6) pupation in the soil, and 7) emergence as adults and subsequent re-infestation of colonies. There is a fermentation of hive products (particularly honey) associated with feeding larvae. This likely occurs due to specific yeasts associated with SHB. Honey damaged by SHB is rendered foul and unfit for human consumption. Colonies heavily infested with adult SHB may abscond (entirely leave the nest) although the number of adults needed to elicit this behavior often must be high (>1000 SHB adults/colony).

SHB damage to living colonies is not the only loss experienced by beekeepers. Adult and larval SHB can be a significant problem in unextracted and unprotected honey crops stored in the honey house. As a result, beekeepers realize the necessity of extracting honey quickly and moving the equipment out of honey houses to discourage ensuing build-up of SHB larvae. Further, stored, unprotected supers containing honey or supers containing pollen residues are prime targets for SHB reproduction and subsequent damage. Despite the considerable damage that SHB may cause in bee colonies in the US, they are increasingly considered a secondary pest of bee colonies, much like the greater (Galleria mellonella L.) and lesser (Achroia grisella Fabricius) wax moths. Colonies hosting other bee diseases/pests are more likely to suffer SHB damage than are healthy colonies. It appears that SHB rarely kill a colony. They usually ‘finish the job’ started by another colony malady, whether disease/pathogen or management-related.

Control/Management

Since the introduction of SHB into the United States, various in-hive chemical controls have not been embraced by many beekeepers and seem only effective for short term reduction of beetle populations in severe infestations. Soil treatments with insecticides are only effective in the small, inadequate area of the ground to which they are applied. Attention has focused on cultural, biological, and genetic controls. Cultural/mechanical controls result from a change in practice with the intention of limiting, but not eradicating, a pest. Practices such as removing honey, bits of comb and wax cappings from around the honey house or extracting area will minimize foodstuffs to which SHB may be attracted. It is also important to extract honey from supers soon after removal from the hive to reduce the damage that SHB adults and larvae do to standing, unprotected crops. Reducing the relative humidity to 50% in honey houses and other places where honey is stored inhibits SHB eggs from hatching. In the apiary, one should eliminate, requeen, or strengthen weak colonies to reduce colony stress and to make the colony better able to deal with SHB. One should avoid other conditions that might lead to colony stress such as brood diseases, mite problems, wax moth activity, failing queens, excessive swarming and over-supering. Two effective in-hive trapping devices have been developed for SHB control. One is the Hood beetle trap which fits in a standard hive frame. It can be filled with apple cider vinegar to attract and drown adult SHB. Another is the West beetle trap, which is designed to rest on the bottom board of a colony. It is covered with a lid containing small holes through which SHB can pass, but which bees cannot follow. The idea is that SHB run from bee aggression, through the holes in the lid of the trap, and into a tray filled with vegetable oil. The SHB then become coated with oil and presumably suffocate.

Other control measures are in various stages of development. A symbiotic yeast associated with SHB has been discovered which, when mixed with pollen, attracts other SHB to weakened colonies. Researchers are taking advantage of this relationship and are developing traps using the yeast mixed with pollen as bait for adult SHB. Two species of soil-dwelling nematodes have demonstrated activity against pupating SHB. Also, researchers have shown that some honey bee colonies are able to detect and remove brood that has been oviposited on by SHB. This behavior, called hygienic behavior, can be selected for in breeding programs and can help reduce SHB problems.

At present, the best general recommendations are to observe sanitary practices in the apiary, honey house, and equipment storage areas, while maintaining strong, active colonies.

SHB has continued to spread across the US but most SHB-associated damage has been confined to the southeastern US, possibly due to climatic conditions. If you suspect Aethina tumida, contact your local cooperative extension agent or local NPDN diagnostic lab.

Selected References

  • Ellis, JD (2005) Reviewing the confinement of small hive beetles (Aethina tumida) by western honey bees (Apis mellifera). Bee World, 86(3): 56-62.
  • Ellis, JD, Hepburn, HR (2006) An ecological digest of the small hive beetle (Aethina tumida), a symbiont in honey bee colonies (Apis mellifera). Insectes Sociaux, 53(1): 8-19.
  • Hood, WM 2004. The small hive beetle, Aethina tumida: A review. Bee World, 85(3): 51-59.

Acknowledgements

We thank Jerry Hayes, Florida Department of Agriculture & Consumer Services, Division of Plant Industry and Steve Bambara, Department of Entomology, North Carolina State University for their editorial review.

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