US Bee Diseases Report - 2010

There were some interesting graphs in the latest edition of the Devon BKA magazine this month. It covered samples and measurements taken in 13 US states by the USDA and interestingly, despite the large number of hives transported there every year California had the lowest levels of varroa infestation - in terms of numbers of mites in hives. Despite these low levels (less than half the mean) it had almost exactly the same incidence of DVW as all the other states with the exception of Hawaii. The low levels for Hawaii was thought to be due to the fact that varroa arrived in Hawaii relatively recently.

California did stand out as having by a significant margin the highest levels for KBV and IAPV - in both case more than twice the levels in the second rated state.

A total of 2700 colonies were sampled and interestingly not a single case of Nosema apis was detected with Nosema ceranae being detected in 51% of the sample although the "load" in terms of millions of spores per bee was lower in 12 states with the exception of Washington State where it was 3.5 with the mean being 0.454 with only 2 other states being above the mean, but both below 1.00.

Other interesting snippets are the high levels of Nosema in the Spring - indicating a possible link with faeces from overwintered bees. Another is the graph showing the number of varroa mites per 100 bees by month. Whilst most people would agree the total number of mites in a colony is greatest in the summer the graph shows that the number of mites per 100 bees is greatest in the winter. This is a little counter-intuitive (at least to me) but I guess what it means is the number of bees in the colony shrinks proportionally more than the number of mites so the ratio gets worse - from the bees' perspective. But note that the graph goes up again in 2011 for some reason - poor varroa control/resistance?

A link to the original document can be found here: http://www.aphis.usda.gov/plant_hea...downloads/2010-2011-Limited_Survey_Report.pdf

The home page has other links (although a bit dated): http://www.aphis.usda.gov/plant_health/plant_pest_info/honey_bees/

I see this has generated a lot of interest! I must put it forward for the "Dead Cat Bounce Award 2011" which is reserved for threads which get zero response. Are there any other nominations?

Just loads to read. All very good stuff so keep it coming but as soon as I was on the web site there were other reports also to read also!

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That is interesting to read and compare for example to the top writers of Beemaster. They tell that they need not to handle their hives because hives take care themselves. Then on state level professionals say that mite is a problem.

Then when we read the queen sellers how some strains of bees are "varroa tolerant". Again odd results.

The economic treshold is low compared to "dead out" numbers. The honey yields start to decline with much less numbers than "critical level".
When a mite violates a worker, It does not live long and it does not forage surplus.

Hi Rooftops,

Bit of a heavy read!

Some idle thoughts.

a) Lot of Israeli Acute Paralysis virus in California - perhaps it is involved with CCD?

b) Trepanosomes forsooth? Do bees get sleeping sickness?

c) Low incidence of varroa in Califonia - one wonders whether that relates to the amount of insecticides being lashed about? Mind you Florida has more than most, so maybe I am just being cynical.

chrismcd said:

c) Low incidence of varroa in Califonia - one wonders whether that relates to the amount of insecticides being lashed about? Mind you Florida has more than most, so maybe I am just being cynical.

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Environmental Factors may have an effect on the varroa growth rate.

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South Usa has no brood brake in hives. That makes varroa treating laborous. Texas is at the level of North Africa.

My friend a professional beekeeper visited in Florida 2 years ago. He went to local professional beekeeper. That told that he does not treat varroa. The whole business goes around plant pollination like with almond. It seems that hives take care themselves enough.

The environmental factor is very interesting. As I understand it high temperatures have an adverse effect on varroa.

Heat treatment was trialled a few years ago as a possible method for killing mites on the basis the mites died before the bees if the colony was artificially warmed but the method was too difficult to use in the field as I recall, so never took off. But the paper suggest the temperatures do not have to be taken so high for there simply to be an adverse effect on the mites.

Au contraire - it was very interesting

RoofTops said:

The environmental factor is very interesting. As I understand it high temperatures have an adverse effect on varroa.

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Hi Rooftops

Thanks again for an interesting link.

With the bees skill at temperature regulation I would suspect that cooking off the varroa would not be easy. AFAIK varroa originated in Indonesia, so presumably likes it reasonably hot.

I would like to believe that the last few cold winters we had in Yorkshire did not suit them at all, but that may be wishful thinking.

chrismcd said:

Hi Rooftops
AFAIK varroa originated in Indonesia, so presumably likes it reasonably hot.

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yes, that heat explanation is miserable. It is like in New Zeaand or in South Africa. When there is no brood brake and mites are under cappings, environment is difficult.