University of California
Beekeeping in San Diego County

Pathogens and Pests


Brood diseases

American Foulbrood (AFB)

American foulbrood is a highly contagious bacterial disease which can kill entire colonies of bees. It is caused by Paenibacillus larvae ssp. larvae, a pathogen that infects the mid-gut of honey bee larvae (Sammataro and Avitabile, 2011). While healthy capped broods have a tight pattern of sealed and open cells, the brood pattern of colonies affected by AFB appears patchy and irregular. Cell cappings may look dark, greasy, and sometimes sunken and perforated (Sammataro and Avitabile, 2011). Bee infected larvae change gradually in color, from white to chocolate brown, and as they decay they produce a distinctive foul rotten odor (Eckert, 1954).

AFB disease can be diagnosed by inserting a match or a toothpick through the wax capping, stirring it around, and withdrawing it carefully. Dead larvae infected by AFB are sticky and will “rope out” (Flottum, 2010; Sammataro and Avitabile, 2011).  For positive identification, brood samples can also be sent to a specialized lab (e.g., USDA-ARS Bee Research Lab) or use a Diagnostic Test Kit:

European Foulbrood (EFB)

European Foulbrood is a bacterial disease mainly caused by Melissococcus plutonius, which affects all casts of the honey bee. However, other types of bacteria may also be involved (Sammataro and Avitabile, 2011). Similar to infections by American Foulbrood, the brood pattern in EFB affected colonies can be patchy and irregular, since only some of the infected cells are sealed. Bee infected larvae turn yellow, then brown and black, and eventually die. However, decaying larvae infected by EFB are not as gluey or ropy as those infected by AFB. Therefore, the dried scales left from dead bodies are easily removed from the cells (Eckert, 1954). To diagnose EFB, brood samples can be sent to a lab or you can test for EFB using a Diagnostic Test Kit:


Fungal disease caused by Ascosphaera apis that affects honey bee larvae. This disease is diagnosed by the hard and chalky mummified larvae either in the brood frames, on the bottom boards or at the entrance of the hive (Flottum, 2014; Rose, 2010).


Fungal disease that affects larvae and pupae. It causes the mummification of brood. Mummies with stonebrood disease are hard and solid, not chalky and spongy, as those with the chalkbrood disease (Blackiston, 2015)


Viral disease. Infected larvae turn from white to yellow and eventually to dark brown. Older larvae develop dark head regions which are bent towards the center of the cell (Sammataro and Avitabile, 2011). They can easily be removed from the cells, since they appear to be in a sac filled of water, which gave the name “sacbrood” to the disease (Blackiston, 2015).

There are several other types of viruses that cause deformation on wings [(Deformed wing virus (DWV)]; black queen larvae and black cell walls (Black queen cell virus (BQCV); and bee paralysis [Acute bee paralysis virus (CBPV), chronic bee paralysis virus (CBPV); Israel acute paralysis virus (IAPV)]. There is also the Kashmir virus which attacks all stages of bees and brood but apparently does not cause clear symptoms (Sammataro and Avitabile 2011).

Adult diseases


Nosema is the most common of adult bee diseases (Sammataro and Avitabile, 2011). It can be caused by two different species of fungus, Nosema apis and N. ceranae. Both fungi infect the stomach of adult bees (Sammataro and Avitabile, 2011). The disease weakens the bees and can cause defecation inside the hive and at the hive entrance. For diagnosis and treatment see Mussen (2011).


Parasites and Pests

Varroa mite

The Varroa mite (Varroa destructor) is considered one of the most detrimental pests in the world for honey bee health, honey production and pollination services (USDA 2013; Rose, 2010; Honey Bee Coalition, 2016). Varroa mites are parasites that feed on the hemolymph of immature and adult honey bees. They weaken the bees and are vectors to diseases that can eliminate entire colonies (Ellis and Nalen, 2013).

Methods for detection, integrated pest management and control of varroa mites can be found at Rose, (2010), Sammataro and Avitabile (2011); Frazier et al., (2015); Honey Bee Coalition (2016).

Tracheal mites

Tracheal mites (Acarapis woodi ) are microscopic mites that pierce the breathing tubes of honey bee workers, queens or drones, to feed on the bee’s hemolymph. Female mites are .004 - .007 inches long and the male mites 0.003 – 0.005 inches long. Symptoms of high infestation are bees crawling on the ground near the hive, unable to fly and with wings at unusual angles (Rudloff, 2016).

Wax moth

The wax moth (Galleria mellonella) is a greyish brown moth with a 3 cm wingspan. The adult females penetrate the hive and lay eggs directly on the comb. The wax moth larvae feed on the wax and pollen, as well as on the host’s brood. The number of wax moths in a hive is usually kept under control in healthy bee colonies, but populations may explode in abandoned hives or stored frames.

Small hive beetles

Small hive beetle (Aethina tumida) larvae are worm-like organisms that eat the wax comb, as well as the stored honey and pollen. When they grow, the larvae leave the hive and burrow into the soil, passing through the pupal stage underground. Flying adults emerge to locate new hives (Ellis and Ellis, 2013).

Other pests

There are other pests that frequently invade the bee hives, including ants, skunks, and mice. Ants steal honey and destroy the brood; skunks scratch the hive entrance during the night and can eat the bees; mice invade the hives when the entrance of the hive is large and can destroy the comb (Eckert, 1954).

This site provides education and outreach to the public and beekeepers to protect public safety within San Diego County in response to the the new apiary ordinance. The site has been developed by the University of California Cooperative Extension - Farm and Home Advisers Office in San Diego County with support from the San Diego County - Agriculture, Weights, and Measures Office.

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