Brine and Oil in Traps and Update

[Droege, Sam]

Update on use of Brine and Mineral Oil in Traps

All

We are still identifying species and putting together analysis, but thought I would send out an update on brine experiments this year as the results are potentially useful already.

Goal: In bowls and similar type traps, develop a trapping liquid that lowers cost, increases preservation, decreases evaporation.

We have experimented with Brine, Stearic Acid, Oleic Acid, mineral oil. 

Brine and mineral oil are useful in some cases, stearic acid and oleic acid had issues and were dropped.

Brine = Gallon water + 1 cup salt (NaCl)

Capture rates: soapy Brine, Propylene Glycol, soapy water:  No significant differences in captures of bees.

Brine (as long as not diluted by rain) appears to keep specimens from rotting for weeks (6 weeks was the longest run), perhaps indefinitely?

Brine decreases evaporation (we are running experiments, but appears to be about 1/2 the rate of soapy water.

Hanging stadium cups (yellow, blue, white) in blooming (or about to bloom) shrubs and trees is an effective way to sample those trees...captures are high and include specialists (more details after we analyze all the data).  Traps can be set out at start of bloom and then picked up after bloom is done....an efficient way to sample many plants.  A telescoping pool cleaner or similar can be used to hang traps in trees. 

Adding 3ml or more mineral oil to brine (without soap) stops evaporation almost completely.

Bees are captured at what appears to be similar rates in traps with and without oil

Oil has relatively low surface tension as does water (brined or not) with dish soap added. 

However, Oil cannot be used atop soapy water as the soap will degrade the oil. 

Oil can be added to any type of water trap but appears to be most effective for use in blue vane traps or stadium cup traps when you want those traps to be left out for long periods of time...particularly in dry environments. 

When captured, bees stay in the oil layer as the water still retains its surface tension (because there is no soap in the water).  To be safe, brine not plain water should be used in case specimens do eventually drop into the water below the oil layer.

Basic procedure for a long-term oil trap would be to fill receptacle of trap part full with brine leaving some head room in case of rain.  More salt should then be added which will sink to the bottom so that if it does rain that excess salt can go into solution and keep the preservation level of the water near the saturation level.  Mineral oil is added such that there is at least 3ml of oil on top of the water.  More oil can be added but it won't change the evaporation rate....however, it is possible that having more oil could be important if a lot of bees are captured and none sink into the brine...to be determined. 

Salt is extremely cheap, mineral oil in the quantities being used is also not expensive.  Mineral oil is often sold as "baby oil" and comes scented which could decrease captures, but pure mineral oil is readily available online or perhaps at pharmacies. 

Cleaning oily bees needs a strenuous approach.  We have had good luck doing a quick initial wash and then soaking them overnight in 70% alcohol or 100% dawn liquid.  We are doing more experiments to see if less intense methods can work.

We will work up the species information on capture rates in blooming shrubs and trees for something more definitive during the winter.

It remains to be determined what the impact might be on DNA with these fluids.

We encourage everyone to run some trials of this approach in their area and report back.

Your federal worker

sam

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- ERIC PANKEY

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[Walker Darby Bensch]

I would like to add that brine solutions could be useful in cold climates. 

I used emergence traps in my project these last two summers here in Wyoming. Deploying emergence traps in early spring meant competing with freezes and even the occasional snowstorm when cold fronts pass through. This past summer, I added salt to the soapy water in my emergence traps to prevent freezing with good success. Had the soapy water froze, I think it would have burst and broken the plastic bottles. 

Glad to see that adding salt seems to not have a negative effect on catch and may even benefit preservation. 

Best, 

Walker Bensch. 

Walker Bensch B.Sc.

Master's Student

Tronstad Lab Group, Wyoming Natural Diversity Database

University of Wyoming - Zoology & Physiology Department

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Subject: [Beemonitoring] Brine and Oil in Traps and Update

 

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[Erik van der Spek]

Dear Sam,

Thank you for this interesting information; it raises a number of questions for me:

How do insect groups other than bees react to brine, particularly flies, which I also frequently encounter in color traps?

What happens to flies when a layer of oil has been applied; are they easy to wash as well? My experience is that they are much more fragile, and I always try to pass on my by-catch to others for identification.

Kind regards,

Erik van der Spek

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[Droege, Sam]

Greetings Erik

I have to say that I am not paying much attention to the fly bycatch.  I know that we catch quite a number with the brine...but haven't done any counts to see if there are more or fewer..

Ditto on the oil.

We are in the middle of washing experiments so will let you know how that goes and will try to pay attention to the flies to see what happens to them.

We are seeing that soaking overnight in 70% alcohol or high concentration dish detergent results in acceptable specimens, but now are going to try working with specimens that have been sitting in oil for >1 week...could be a different beast considering that the oil may have migrated more internally through the spiracles....

Onward!

Sam

Thanks  for writing...helps to have feedback.

Let me know if you try this and your experiences.

Sam

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From: Erik van der Spek <spek-...@introweb.nl>
Sent: Monday, August 24, 2026 1:47 AM
To: Droege, Sam <sdr...@usgs.gov>
Cc: 'Google Groups' via beemonitoring <beemon...@googlegroups.com>
Subject: [EXTERNAL] Re: [Beemonitoring] Brine and Oil in Traps and Update

 

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