For hidden stored grain insects, counting of insects can be done by x-raying the sample and then count the insects from developed flim. If you can collect your sample leaf/plant, then you can try this method.

1. Will an abundance estimate do? E.g. tapping into a funnel 5 times.

2. Alternatively count each plant by hand for e.g. 3 minutes. Redo as destructive sampling in the lab as for a subsample of plants, and develop a fudge-factor (%insects seen in field/ all insects present )

3. Use catch per unit effort and models borrowed from fisheries for depletion estimates. Record the # bugs found on each plant / 30 second interval for e.g. 10 minutes. Model the number of bugs you would have to find until you have them all. A good ref is Hilborn R. and Walters C. J. (1992). Quantitative fisheries stock assessment: Choice, dynamics and uncertainty. Chapman and Hall, New York.

Once you have done this for a sample of plants (high and low bug density), you can predict how many bugs in total as a function of how many you see in e.g. 2 minutes.

(It'd be a great paper in itself).

Thanks for the replies, a x-ray in the field sounds great, but we don't have it and perhaps difficult to get one portable.

And yes we decided to do an estimate to compare controls with other plants and the curly endives. Therefore we use a similar approach. Anyway since there are many plants and it's one part of many others, there's no time left to do an more exhaustive research (unfortunately, as it sounds interesting).