Where to purchase a solid sampler?

[Ento_Joe]

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[GOM]

Hi Joe

Just catching up with your posts.

Fascinating study - I am envious - you are doing some sound practical work

Looking at your list at least 2 jump out as possible plant associated molecules

- methyl salicylate (Oil of Wintergreen)

- neophytadiene.

What is the plant that you are using to nurture the mites? I will look up my database of plant oils

It set me thinking about whether there would be anything at all to gain from tumbling an uncut plant leaf with the diatomaceous earth and seeing what you get from the GCMS. I have to admit, I don't know - it is a speculative thought

As Peter correctly noted, the fatty acids (not the methyl esters) and squalene are also found in human skin sebum, although from my analyses of skin sebum the lack of cholesterol may rule that out as a source

Out of interest (?) there are three major sources of excretion from the human skin
Sebaceous glands that produce the oils for skin maitainence/barrier
Eccrine glands that excrete water (sweat for cooling) and salt
Apocrine glands found under the armpits that excrete putative (amongst other precursor odour molecules) steroid signalling molecules

Cheers

Ralph

[Ento_Joe]

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[Peter Apps]

Hi Joe

Since you got clean procedure blanks you can safely say that the compounds from the tumbled mites are from mite skin not human skin.

If the methyl salicylate is on the mites it might still be a predation cue, even though it is a plant product.

A very long time ago I checked polypropylene pipette tips for extractables, and they were remarkably clean. They did not have filters in them though. Glass is good stuff, and a sintered filter of the right porosity would filter the grit out, but I do not know of anything readily available that can work with your small volumes. You could try using larger volumes of solvent, and then concentrating down after you have filtered, but putting the loaded silica into a filter pipette tip and then percolating 200 ul of solvent through it will be fast, repeatable and cheap. I do a similar thing with carnivore urine on sand.

Peter

[GOM]

Hi

I need some time to digest your interesting reply but

My initial thoughts are

1. Your sample handling and the lack of cholesterol seems to preclude skin contamination.
2. Unfortunately I don't have broad bean in my plant database
3. Any Green colour is likely to be chlorophyll
4. I have been speculating along the lines of distinguishing between plant volatiles that could be adsorbed into the mite cuticle rather than exuded from it. Could you cut a leaf off at the stem, pour some diatomaceous earth onto it and then gently wrap it into an envelope and possibly tie it off gently with some non flavoured ribbon dental floss? Leave overnight before extracting the earth.
Am I correct in thinking that the predators are attracted to the prey mites themselves and not to volatiles from damaged leaves caused by the prey mites - I may have asked this before

Cheers

Ralph

[Ento_Joe]

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[Peter Apps]

Carbon fiber will almost certainly adsorb compounds from the extract. What I had in mind for the filter tips was more like this:

http://www.sigmaaldrich.com/catalog/pro ... &region=BW

You will not be using them for what they were designed for - they are meant to stop aerosols form getting up into the pipette body. You will hold them vertically, put your extract in the top and collect what runs through - maybe with a bit of help from some pressure at the top. Or put the loaded silica in the top and percolate solvent through.

Don't worry about losing analytes by evaporating solvent - nothing that you are interested in will be lost unless you evaporate to dryness.

On the methyl salicylate in the olfactometer - it is entirely possible that a compund which is a contact cue will not act an an airborne attractant, and vice versa. If you want a contact cue you have to do a contact bioassay.

Peter

[Ento_Joe]

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[Peter Apps]

Good morning Joe

I prefer evaporating under a gentle N2 flow - just enough to blow a little dimple into the surface of the liquid. It goes quicker, which means that I am less likely to get busy with something else and forget all about it. Also it provides a bit of shielding from volatiles floating around in the lab air.

With the pipette tips I would routinely run a ml of solvent through them before I use them just in case there are some extractables.

Dicke must have very steady hands if he can do antennography on creatures that size !! If he got a response to the airborne chemical there would presumably also be a response to the salicylate on a surface, which would be an indicator that it could be a contact cue. Maybe the signal from the antenna does not stimulate approach but does stimulate the predator to sink its fangs into a prey that it already in contact with.

Edit -- In fact, come to think of it, a contact cue would NOT be expected to generate upwind movement in an olfactometer - once the predator has the prey in its grasp it needs to stay where is it, not go wandering away upwind.

Peter

[Ento_Joe]

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[Ento_Joe]

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[GOM]

Hi Joe

I will continue to digest your posts - they are an example of how posting as much information as you can is helpful.

With regards to my comment about looking at the leaf volatiles I was wondering if in the list that you have detected from the mites using the diatomaceous earth approach

1. Most are from exudate
2. Are any from adsorption of the leaf volatiles onto the cuticle? If so (and it is highly speculative) then knowing them might enable you to remove them from your list

My suggestion/explanation of looking at the leaf volatiles using the same procedure as a control was rather clumsy

Does this image help?



Kind regards

Ralph

[Ento_Joe]

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[GOM]

Hi

I was thinking uninfested but you do both - I just want to add to your work load

Yes, there is a risk of damage but if done gently and loosely that should be minimised. Or perhaps put it in a sealed chamber without folding

Regards

Ralph

[Ento_Joe]

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