Determination of volatile compounds that elicit removal of diseased brood by hygienic honey bees.

View the project final report

• 2007 annual report
• 2008 annual report

Commodities

• Animals: bees

Practices

• Animal Production: Beekeeping

Honey bees are susceptible to a number of diseases and parasitic mites, which are commonly treated with antibiotics and pesticides by beekeepers. The widespread use of chemical treatments has resulted in the contamination of hive products and chemical resistance by pathogens and parasites. Bees bred for hygienic behavior reduce the pathogen load by removing diseased and parasitized brood from the hive. Previous research suggests that hygienic bees respond to olfactory cues coming from the abnormal brood.

This project investigated the chemical profiles of chalkbrood infected larvae and confirmed with field bioassays that hygienic behavior is a response to olfactory cues.

Introduction:

I investigated the chemical stimuli that individual honey bees detect in diseased larvae that initiate hygienic behavior. Hygienic behavior is defined as the detection and removal of diseased larvae from the nest (Rothenbuhler 1964). Hygienic behavior has been recognized as an important natural mechanism of disease resistance in honey bee colonies since the late 1930’s (Woodrow and Holst, 1942). One of the most important aspects of hygienic behavior is that individual bees must detect and respond to appropriate stimuli from the diseased larvae early in the progression of the infection, before the pathogen becomes infectious. In this way, the quick and efficient detection and removal of the diseased larvae by many bees prevent disease transmission throughout the colony.

Specifically, we investigated the hygienic response of bees to the fungal pathogen, Ascosphaera apis, which causes chalkbrood disease in larvae. Chalkbrood infection begins in the gut of a larva and slowly grows outward until it penetrates the cuticle before pupation begins. At this point, rapid growth and sporulation of the fungus occurs (Gilliam, 1997). If adult bees remove infected larvae after the fungus has penetrated the cuticle, spores are ingested by adult bees and fed back to healthy larvae in the bee food. The uninfected larvae ingest the spores and the infection perpetuates. Therefore, for hygienic behavior to be effective against chalkbrood, the adult bees must remove the infected larva before the fungus has penetrated the cuticle.

I tested two hypotheses:
1) hygienic behavior of honey bees can be elicited in field colonies by experimental application of appropriate olfactory stimuli; and
2) hygienic behavior is based on a threshold response in which colonies containing bees with the highest olfactory sensitivity to diseased brood initiate the hygienic response more quickly as compared to colonies containing bees with a lower olfactory sensitivity.

1. Determine differences between the volatile chemical composition of healthy honey bee larvae and those that are infected with the fungal disease chalkbrood.

2. Determine which compounds unique to chalkbrood infected larvae are detected by honey bees.

3. Develop a bioassay that involves introducing synthetic compounds of diseased brood into field colonies to directly test if hygienic behavior can be elicited by the compounds alone.