Hi Johan- this is commonly expressed simply as "gallery length" in cm. Different feeding galleries can be averaged together. This can be measured with a map measurer or a piece of string that is then compared to a ruler. Another option is to make a grid on a clear surface (such as an overhead sheet) and overlay the grid on the twig or bark surface to count the number of square mm or cm of "gallery". Different depths could be due to larval vs adult feeding, or potentially seperate species. Hope this helps!

Thanks for your answer Thomas. The issue that I am facing is actually that this is not a gallery type damage. The weevils are all adults and feed on the bark of the twigs from the outer to the core. There fore, the two type of damages would be some sort of scratching the surface of the bark (about to half the depth) and galls that are the full depth of the bark.

The problem is that these insects are not feeding continuously and so are not making a pattern that I could follow with a string (great idea though) but they are feeding by tiny patches which at the end of my experiment become areas.

Another option might be to use a grid approach.  Try using a small grid (square) 10 cm on each side and estimate the amount of damage occurring in this grid.  You could either measure the amount of area that is damaged or measure the number of damaged areas you see.  Do this randomly where damage might occur.  You would need many samples so as to not bias your estimate. The nice thing about this approach is that you can use paper to make your grid or even plastic sheet with lines on them.  These will be flexible enough to bend around the branch or twig. Ultimately, the number you would come up with would be X number of damages per cm2 or the amount of damage caused per cm2 . Then the next step would be to normalize by the total surface area of the branch to get an actual estimate of feeding damage.

Maybe this will help?

For better clarity, this is the type of damages I have. I've been trying to use cling film and mark them with two different colors but then I need to use a software to actually measure the two different colors. Anybody knows which software I could use?

Have you looked into Assess 2.0.  Check it on aps website.

http://www.apsnet.org/apsstore/shopapspress/Pages/43696.aspx

this works great for leaves.

Hello Johan,

Maybe you can try with ImageTool. It is old software but I think that you can use it to separate area with different colors.

http://compdent.uthscsa.edu/dig/itdesc.html

Regards,

Slobodan

I had areas traced on transparencies that I scanned and then used Photoshop to calculate number of pixels in the area/polygon and then converted that to area (cm2). (Make sure scale doesn't change in scanning and viewing on screen in Photoshop).  I've also heard that ImageJ is really good for this.

I actually had a try with ImageJ yesterday using a similar method Katherine. The only issue is that it will count some red pixels in the white areas but I think I have the technique now and will improve it before my next experiment.

Thanks all for your ideas

DEar Scientist, I am afraid that I think the answer is very easy, when  you are looking for damage there is no need to go for such problematic measures , you can easily weigh the twigs before and after the application and compare different tries with a control if it is a vital experiment. Otherwise, please let me know what is your aim of that experiment. thank you for your further explanation to me.

Dr. Abdigoudarzi, Iran

Hi Mohammed. We actually excluded the use of weight scale for several reason. The main one is that over the time of the experiment, the moisture will increase the weight of the wood and we don't know how each twig will react to these kinds of moisture changes. A second reason is that I am also interested to measure the surface area and the volume of bark eaten by my insects and therefore I won't be able to extrapolate the weight to the surface area of treated bark eaten.

Hi Johan. Could you not measure volume by comparing displacement of a fluid before and after your experiment? Or using a substance to fill the eaten areas and measuring the volume of this - similar to measuring the volume of a skull using small beads?

Hi,

I estimated consumption rate of a xylem-feeder based on the dimensions of the corridors made by larvae. Below is the methodology description copied from my article (Walczyńska 2009, Journal of Insect Physiology, 55, 1107-1117).

"Consumption rate was estimated based on the dimensions of the corridors made by larvae during a period between the change of slices (Hosking and Hutcheson, 1979). To achieve this, each slice was scanned and the area of the corridors

was measured using ImageJ 1.36b software (National Institute of Health, USA). The depth of a corridor was measured with millimeter paper, to an accuracy of 0.5 mm. Moreover, all the faeces and uneaten parts were removed from the corridors,

weighed, dried for 24 h at 105 8C and weighed again. The difference in mass was treated as moisture content in further analyses. Finally, the faeces were mechanically removed from the pinedust. The volume of a corridor was then recalculated to mass. Density of a pine slice was calculated according to the formula:

d ¼ DMC 0:49mg=mm3 þ ð1 DMCÞ 1:00mg=mm3;

where d is the estimated density, DMC is the content of dry mass in pinedust and faeces (assumed to be equal to the dry mass of wood), 0.49 mg/mm3 is the density of dry pinewood (Surmin´ ski, 1993), 1 mg/mm3 is the density of water. Consumption was finally calculated as the difference between the dry mass of wood and dry mass of pinedust, and the rate of consumption was achieved by

dividing this value by the number of foraging days."

Good luck with your studies!

Best regards,

Aleksandra

@Kevin: Yes, I had this idea but the most important measure I needed was the surface area eaten and by having the volume, I wouldn't be able to correlate it to the surface area. I actually tried this method and unfortunately, bubbles of air get stuck in the damaged areas due to its discontinuity but I'll definitely tried that again.

@Aleksandra: The insects I am working with are adults feeding on the outside of the bark. Therefore, they are not creating any galleries but patches of  small damages here and there which makes it much harder to measure. But I use ImageJ and I had a good estimation. Now I just need to improve the technique and the accuracy