Is it better to evaluate a product in real conditions or is it better to simulate the conditions of use?
To register an insecticide under the BPR, testing in field is required when the product is against cockroaches or ants, for professional use. In some situation testing in field against mosquitoes (when the simulation cannot be realistic) and flies (use in stable or in waste dumps) is also necessary. But what is a “field test” and what does it entail? A “field test” is when the product is applied in real conditions, when the infestation is natural, spontaneous and the product is applied strictly following the indications of use. We can modified something in the environment, maybe to reduce/avoid the reinfestation, or to reduce the possibility of the insects to hide, like it would be done anyway during a professional pest contro application, but we cannot create conditions which cannot be naturally found.
For sure when we want to test an insecticide in field, we have to face the fact that the replicates will be very different between themselves because we have limited choice. When the test is in the field we have to find the infested place, where we are free to monitor and treat, where there aren’t other activites which can affect our test. This is not easy so we have to adapt. Another aspect are the parameters like temperature, humidity, light , rain, sun etc, which are completely out of our control. All these variables make that the results between replicates can be very difficult and the result of our test can be very different from the results of another test performed by somebody else. In a field test the efficacy of the application is strongly affected by the ability of the tester, the capability of the tecnician in applying the product in the way to get the best results.
The simulated use test is when we build the environement and we release the insects to create the infestation. The concept of “simulation” is indeed very wide. If we want to test an insecticide against the Oriental cockroach simulating a spot application, for example, we can treat part of an arena 0.5 m2 where the insects have available on the non treated area shelter, food and water. The insects have the choice to stay or not in contact with the insecticide, so the simulation is fulfiled. But we can release the insects into a 40 feet shipping container, and this will also be a simulated use test because we created the infestation.
The simulated use test can be much more standardized and the environmental parameters can be kept under control, making the test reproducible. The test is less affected by the capablity of the applicator and of the availability of infested places, reducing also the time and the costs.
It is true that a test simulated in laboratory, especially for some type of products like fumers and thermofoggers, cannot provide reliable results. Other typology of products, like adulticides for outdoor use against mosquitoes cannot be tested simulating the use because the mosquitoes are not free to escape, if they want, not so far like in the real conditions. Other products, like mosquito repellent coils, can be very well tested in simulated conditions just if the environment is big enough to allow the product to disperd like in the outdoor and the mosquitoes are free to flay away from the product, conditions which cannot be reproduced in laboratory but which can be fuflied in screenhouses or big greenhouses.
To conclude, the field test can be expensive, complicated, often unreliable and should be limited to specific uses which cannot be simulated. Otherwise for professional products, the simulation of the test in the field it should be preferred for the reproducibility, the possibility to keep environmental parameters under control, the costs and the timing.