I'd choose 'never' over 'always'.

 

>I'd choose 'never' over 'always'.

Never is better

>The instructor told us that in South Texas we should always use a screened bottom board because of the heat.

"My bee inspector told me" If I have a nickel every time...

IMO a screened bottom board should never be left open. If it's cold the bees have to work harder to keep warm, if it's hot they have to worker hard to cool. The brood nest is 93 degrees; spring, summer, fall, winter, day or night. The humidity is also maintained by the bees. This additional work cost energy in the form of honey. Additional use of honey during winter or dearth could lead to starvation.

 

I am in north Arkansas and I use screened bottom boards year around on both colonies and nucs. You could try a mix, screen open or closed and see what affect the type bottom board has on your colonies. I see no evidence that shows open screens make it harder for the colony to cool the interior of the hive.

 

If you really want to use a screened bottom, build it so that there is an oil* tray beneath the screen. Enclose the tray so that the only access for insects is through the screen (plus a door/plug for tray maintenance access).

Bees use evaporative cooling to regulate hive temperature on hot days. Evaporative cooling can reduce air temperature to below the ambient air temperature. A large volume of air moving through an open screen bottom might increase "ventilation", but that won't help get the air below ambient temperature. Open screened bottoms reduce the effectiveness of bees' evaporative cooling efforts.


*An alternative for oil in the tray is diatomaceous earth.

 

*An alternative for oil in the tray is diatomaceous earth.

I've got the hives sitting over some stepping stones with the DE underneath.

 

With each answer you have to consider the source including what part of the country they live in. I live in N E Florida, screened bottom boards are all I use. During the cooler months I keep a West Beetle Trap in my hive. When the nights get in the low 40,s I will also put an entrance reducer in to help the bees regulate the temps. If the day is going to warm up comfortably for the bees, I take the entrance reducer out before I leave for work. This helps the bees regulate the temperature of the hive. During the hotter months ,the bees don't have any problem keeping the hive warm. The heat does it for them. If anything, the screened botttom board helps with some air flow. Small hive beetles will be chased by the bees into the tray filled with mineral oil and suffocate. However, a strong hive will keep the beetles corralled in a corner and the sbb is pulled out or it will get to hot inside the hive. A weak or new hive I may leave it in.

 

That is like helping the air conditioner by opening the front door all the windows.

 

:doh:

I have no doubt that most bees in most parts of the country can adapt to this. I have seen bee trees with volley ball size entrances that survive for years. The additional work load on the bees cost energy, additional duties that might be taking away from raising brood...

Bees are very adaptable; look at all the stress they are put through and still survive; pests, pesicides, loss of forage, mono crops, pathogens, migratory... the list goes on. Leaving the door open while the air conditioning is on is just another stresser.

 

I choose always over never.

 

When I see a colony of bees with the bees bearding outside I assume it is caused by one of two reasons, the volume of the hive is too small for the adult population or the interior of the hive is too hot and the adults have vacated to reduce the amount of heat generated by their bodies. There may be reasons for adults to be outside bearding that I have not considered, but I think a bee loafing outside is not a normal situation.

When I have opened the hives that have screened bottom boards with the screen closed by the insert, I would find very few adults on the frames tending brood, the majority were on the hive sides fanning to move the air out of the entrance. When the insert was removed the adults would move back into the hive and go on to the frames and fewer adults were on the sides fanning to move air. Bees fanning to move air or bees on brood frames tending brood, which is wasted energy?

Those that use screened bottoms, put the insert in on a hot day and watch the bees abandon the interior, remove it and see them return to the inside. Listen for any increase of fanning noise that would be caused by those bees returning to the inside to become fanners to cool the hive. I have no reason to believe they do so.

The beekeeping literature before screened bottoms all recommended to open the entrances during the hot weather, even lifting the supper above the bottom board by putting blocks of wood at the corners to increase the ventilation area to cool the hive. It appears the venturi effect doesn't actually benefit the brood area as much as some believe. If it did, we would be reducing the area to increase the air speed.

If anyone has the name of a controlled study, done on screened bottom boards, showing decreased cooling of the hive interior, please post it for our education. In the absence of a study anything we say is just an opinion we are stating, not hard evidence.

As with all things on the net, "Buyer Beware."

 

More info on thermoregulation and evaporative cooling by a bee colony is in this paper by Dr. David Tarpy:
https://www.cals.ncsu.edu/entomology/apiculture/pdfs/Mathis&Tarpy.2007 copy.pdf

... others ...
https://www.researchgate.net/profil...32_Temperature_control_in_honey_bee_colonies/links/0c96051ab76511f529000000.pdf

https://www.researchgate.net/profil...s_mellifera_L._Races_in_Central_Saudi_Arabia/links/54853cd00cf283750c370f33.pdf


Ask yourself how "ventilation" can possibly reduce air temperature within a hive to below outside air temperature. When its 105 degrees F outside, evaporative cooling (water misting) is the only strategy AFAIK that can reduce the inside temperature below that 105 degree ambient outside temperature. To make evaporative cooling work efficiently, bees need to be able to regulate airflow. An open screened bottom makes that regulation more difficult for the bees.

.

 

Here is one (focused on varroa growth in regard to temp changes, thus not totally temp. related): http://www.ncbi.nlm.nih.gov/pubmed/14977099

I did not read the whole article, but this one suggests that "the anti-varroa bottom board must never be used with its bottom hole opened as this leads to a lowering of cluster temperature resulting in ideal conditions for varroa development."

Further explaining that "the results of this trial during the first season were contradictory. They suggested that the fact of using an open screened bottom board created favorable conditions for varroa development thus canceling the advantages of its use."
__

"Nevertheless, the negative impact of the use of open anti-varroa bottom boards was not universal since in 2000, the AV sub groups of two locations (MAI and JOY) demonstrated positive results despite opened bottoms."

__

"However these exceptions can be logically explained. For location MAI in 2000 as well as YBO in 2001, the manner of placing the hives on the ground and the terrain conditions limited the air circulation under the open bottom boards and therefore limited the cooling effect on the hive. Furthermore the colonies in the MAI group in 2000 were maintained in a crowded two super condition for the production of queen cells. No doubt, this condition contributed to higher brood chamber temperatures. The third location (JOY) was situated in a well sheltered clearing fully exposed to the sun. It is possible that for these locations and in these circumstances, the open bottom boards did not cause a lowering of temperature of the brood chamber."


One here is another (about the small hive beetle): http://www.ncbi.nlm.nih.gov/pubmed/14977099


Though thats only one study, with not really reliable findings. My opinion is that it depends on your apiary, type of hive etc.
I learned to leave it out as possible in all climates except with high humidity. This year i will go for leaving it in and make a TTBH with a solid bottom - Lets see how this turns out.

 

As other's have pointed out by now, bees have to COOL the hive whenever it's over 93 F outside. They cannot do this if they cannot control the ventilation. They do not need a lot of openings to do so nor does a chimney effect help them keep it cool.

 

It is my opinion that the honey bee controls the air flow over the combs and cooling just as Tarpy said by fanning and evaporation of water. They also control the amount of air passing over the face of the comb in the brood nest by the same method they use to control heat in winter, by forming a "shell" using their bodies in the seams between the comb to open or close the area of the brood nest. I also think they are able to control to a limited extent the humidity in the brood area by these methods.

I do not disagree that the bees control temps in the hive by air movement and evaporation of water, I just disagree that maintaining a small entrance so that they must use large numbers fanning to cool the hive is more efficient than allowing more heat to escape through a screened bottom. The bees will fan the comb surface and have air movement that will cool that surface, just as they do when they fan the outside surface of the hive to try to cool it on very hot days.

If you have ever experienced a hive meltdown was it a colony on a solid bottom board or a screened bottom?

I think Iskentenjack has the right idea, try both and see.

 

Any time, during the year or during the day, the outside temp drops below 93 degrees they need to heat the hive. If you have screened bottom board open you are performing this experiment only to a lesser degree;

http://beesource.com/resources/usda/overwintering-of-honey-bee-colonies/

 

A fireplace

 

No, a pile of equipment you use when moving bees.

 

I vote NEVER.

cchoganjr

 

I had a bottom board with a screen on it. The bees didn't like it open. I put that plastic thing on it that slides under it and my bees did so much better. Like others have said, it allows too much air flow. If you build a bottom board with an oil tray, thats your best fit for the bees. prevents drafts and oil kills the bugs that drop in.

For heat. I have a shade cloth 16ft x 16ft 16ft 2 of them that overlap. 5 posts that are holding them up. The bee hives get direct sun parts of the day. I put it on when the temp hits 100 degrees.

 

I use the enclosed sbb with oil tray. Used the design from Rusty Farm website with a few mods. It gives me a sneak peek into the hive with out opening it up... my little daily fix.

 

Here is a link to Rusty's oil tray bottom board plans that are referenced above:
http://schoonerbay.net/rustysbees/ipm.html

 

Thanks!

 

I do use them when moving bees. Bees often overheat when moving and often have trouble ventilating because they are confined. They do not have that issue when not confined... so yes, I find screened bottoms useful when moving bees.

 

What is the consensus among commercial beeks?

 

So, I'm wondering if that is really an "always" or just a "sometimes" suggestion for the summer months?

Screened bottom boards. Some swear by them, some swear at them.

This is one of the top ten or twenty regularly debated topics. I don't use them, mostly because I already have all the solid bottoms I need. I don't think they'd benefit me much, if at all.

 

>What is the consensus among commercial beeks?

From my observation they are 99.99% solid bottom boards...

 

Any of y'all ever find a cluster of bees on the underside of your screen where a newly mated queen didnt quite make the entrance and is stuck there?

 

>Any of y'all ever find a cluster of bees on the underside of your screen where a newly mated queen didnt quite make the entrance and is stuck there?

Yes.