Rules probably vary by country. I would expect that if you were to apply DDT at 500 lbs/m2 and turn several hundred hectares into a superfund site that there would be legal consequences. So there are restrictions in that sense. Within the context of your question there are no restrictions. Depending on how and where you are applying the materials you might need a pesticide applicator's license. I need an applicator's license, but I check the box that restricts the license for research purposes.

Essentially some equivalent must exist in all countries because otherwise there is no mechanism for developing new products. On the other hand, regulation is necessary otherwise one could dump toxic waste under the ruse of pesticide application. Someone at your university must know the relevant regulations as it applies to your university. You need to find them.

Also know the regulations for disposal of hazardous waste. If you are building microcosms in isolated tanks you may not need an applicator's license, but you will generate considerable waste that will need to be handled properly.

For this type of study it is important to use the formulated product. The formulation changes how the product is atomized, how droplets stick to the surface of the plant, and how long it lasts. It would affect penetration into the plant and how much toxicant is available for translocation. It would affect how much toxicant is transferred to the insect if the insect contacts a wet deposit while walking over a leaf surface. Atomization affects the distribution over the plant surface as the number of deposits and deposit size per square cm. Depending on how you are applying the product, you may want to address how your application method was different from a field application and how such differences might influence your outcome relative to a field outcome.

hello Sophie, I agree with Timothy...

I think the only drawback of using formulated product is that sometime you don't know exactly if/what kinf of adjuvants are used in the formulation which in turn may have an effect on the biological trait you are studying (e.g. effect not cause by the active ingredient itself)...

however, if I were you I would go for the formulated product.

To add to what Jean-Phillipe has advised to make sure you mimic real-world application scenarios as much as possible, I would also add that you should make sure the formulation you use is relevant to the test crop (there may be different formulations for use in different settings?) and if using under outdoor/field conditions that you apply within the window that it would normally be used (depending on growth stage of the crop in question etc). As Timothy pointed out most countries require those who use or apply agrochemicals to hold some form of permit. This may only be required for "commercial" operations, but even so I don't think it should be a problem for you. There should be no restrictions that might be applied by the manufacturers and you should be able to find the content of the formulation through MSDS (material safety data sheets) that they are obliged to produce and make publically available.

At least in the USA the MSDS does not cover what is termed on the pesticide label "inert ingredients." These formulation components are considered proprietary. The components and their relative proportions are difficult to figure out except in very general terms.

Know that everything makes a difference. The formulation, the nozzle, the tractor speed, the concentration, the target plant/insect, growing conditions, temperature, humidity, leaf wetness, leaf waxes, leaf trichomes, and on and on.

Thanks for all your answers. It greatly reinforce me in the idea that using commercial formulation is the best option and the more representative one. As I plan to study this question through lab experiment (microcosms) i thinks this won't be a problem in an environmental point of view. My main problem with that is the fact that, as Dr Ebert pointed it, we don't have access to the exact composition of the 'ready to use' formulation (only the % of content of the active compound). Will it not be a problem for data publication ?

From the industry perspective I don't see any legal problem if you buy and use final plant protection products commercially available in your ecotoxicity experiments . I havent heard of anybody not being allowed to do this in the past and I have seen lots of papers published containing such work. You will know from the label/SDS the amount of active substance(s) contained. Regarding the other ingredients and their concentrations in the final product, this is extremely sensitive commercial information and I can tell you now that you will not be able to have it. Nevertheless, this should not be a problem for publishing your data. Many other researchers have worked with final PP products in the past and I can assure you none of them would have know the full composition of these produts; but that did not stop them from publishing their work if it was of good quality. Usually the conclusions are focused on the a.s. effects and using a formulation as a test item instead of the technical a.s. makes it easier in terms of solubility etc. 

One option you could consider is to have two controls. Companies are sometimes willing to provide blanks (all the formulation components but no toxicant) for research purposes. You then have a water control, a blank control, and the full product. You probably don't need to bother with the "toxicant alone" treatment unless you are specifically looking at the synergistic effects of toxicant and formulation.

There is no problem with publication. Be a little careful in presentation. Your observed effect is due to the formulated product and not the active ingredient (alone).