Last week’s blog was about identifying any potential issues
in brood and attempting to diagnose the underlying pathology. The next step
towards prevention and treatment is an understanding of the spread of each pest
or disease. For successful prevention or suppression, it is important to know
the aspects of the life cycles of pests and diseases and be able to apply the
best integrated pest management (IPM) practices. This week will discuss how
these pests and diseases spread in honey bee colonies to set the groundwork
for a discussion of management practices.
It Takes a Village to Raise Brood - Part 2
American Foulbrood (AFB)
The usual route of contamination is that bee larvae consume
bacterial spores in contaminated food. The bees are most susceptible when less
than 24 hours old, but after 48 hours they become resistant to infection. The
bacteria multiply in the midgut of larvae and burst into the haemocoel killing
the developing bee. AFB is usually spread through housecleaning practices of the
honey bees; bees contaminate their mouth parts and digestive tracts and pass
the bacteria along to larva by cleaning cells or feeding. AFB spores can
live in larval food, soil, or beekeeping equipment for decades, so honey bees
and hives must be destroyed when there is an AFB infection.
European Foulbrood (EFB)
The usual route of contamination, similar to AFB, is that
the bee larvae consume bacteria in contaminated food. The bees are most
susceptible when less than 24 hours old, but after 72 hours they become
resistant to infection. The bacteria multiply in the midgut of larvae and
compete for food. EFB is also usually spread through housecleaning practices by
honey bees. Typically, symptoms of EFB do not show when there is an abundant supply
of food, but bacteria remain in the colony, within equipment and adult bees.
Chalkbrood
This infects bee larvae and pupae by ingestion of fungal
spores in contaminated food as well. The range of susceptibility for the Larvae
is from 1 - 5.5 days old but they are
most at risk at 3-4 days. Larvae become mummified in 2-3 days after infection,
and the fungal mycelium completely replaces the bee. Spores can reside in hives
without showing any symptoms but grow under certain conditions, such as high
moisture or low temperatures. Spores are spread by nurse bees from stored
pollen or housekeeping activities.
Varroa mites
These ectoparasites enter the cells just prior to capping
and feed on larvae and, subsequently adult bees. Their reproductive cycle is
carried out in brood cells. The female mites detach from bees when ready to
reproduce and enter brood cells. When brood is abundant, up to 80% of varroa
mites can be found in brood cells. The varroa mites are immersed in the bee’s
food, but soon start to feed on the larvae and lay eggs. One male and multiple
female mites are laid, and they reproduce inside the cell, before the bee
emerges. A maximum of 3 mites can be produced in a worker bee cell and 5 mites
for a drone cell. The female mites then attach to an adult bee to feed until
reproduction.
A better understanding of how pests and diseases spread in a
honey bee colony can help in applying the most effective management practices. Next
week’s blog will briefly discuss prevention and treatment with a focus on
Integrated Pest Management.
Written by John
MacDonald, ATTTA Seasonal Apiculturist johnmacdonald@perennia.ca
Connecting with ATTTA
Specialists
If you’d like to
connect with ATTTA specialists or learn more about our program, you can:
visit our website at https://www.perennia.ca/portfolio-items/honey-bees/
Email abyers@perennia.ca
References
Pernal, S.F. and Clay, H. (eds). 2013. Honey bee diseases
and pests 3rd Edition. Canadian Association Professional
Apiculturists, Beaverlodge, AB, Canada.