Residual studies are tests that involve applying a product over a surface and then allowing it to dry for a specified period of time before insects are placed on the treated surface. The budgets for a residual test need to be 4-10x higher because these tests can get very involved. The most compounding budgetary factors typically come from the ages you choose to test (and that should depend on how long it is actually performing. Cut it off when it stops providing suitable results). However, in this blog entry I will focus on the selection of the appropriate surfaces for your test.
First, you need to consider the relevance of the surface to your target pests and application.
Plant pests are easy decisions… we test on leaves. But you do need to consider how waxy the surface of the leaves should be, if you should be testing on the undersides or tops of the leaves, what plant species is suitable for your target pests/uses, etc. Most of these questions are answered with a simple review of the key plants that your product will treat.
Household pest species leave us with a wide range of options: stainless steel, ceramic tile, linoleum, unpainted wood, painted wood, carpet, fabrics, laminated wood, vinyl paneling, mulch, soil, sod grass, gravel, concrete, concrete paneling, and so many more. Again the most relevant questions are ‘where are the target pests living’ and ‘where will the applicator be applying the product?’
Second, you need to consider the larger questions: ‘What does EPA expect’ and ‘what will show my product in it’s best light?’ Sadly enough, these 2 factors are a bit mutually exclusive.
EPA’s expectations: Of course I can’t speak for EPA and this is one of thousands of critical factors that are not in writing by EPA. But history, experience, and common sense can go a long way (and save the time of asking them directly). In a nut shell, you should be looking to use surfaces that are critical to the species and treatment site. More importantly, EPA tends to expect to see some ‘worse case’ and ‘best case’ surfaces. This really means that you want the hardest surface that can be typical for the application of your product because the hardest surface will almost always give you the longest residual life and best performance. Next, you ALSO will want to provide EPA with a representative ‘absorbent’ surface from the target site/pest. While these absorbent surfaces will tend to show your shortest residual life and possibly not even work when the product is ‘freshly applied’, they are critical for the purposes of showing EPA that you ‘went the extra mile’ in testing your product.
- German Cockroaches are common in kitchens, both commercial and residential. Stainless steel, ceramic tile, and glass are all ‘hard’ surfaces you can find in kitchens and are ideal for showing your longest residual and fastest kill. But the backs of cabinets are the most common harborages for German cockroaches, so the far extreme is to include unpainted wood in your data set.
- Bed bugs mostly only live on textured surfaces so EPA wants to see unpainted wood and mattress ticking as the standards. We also like to include laminated wood because it is a surface that is common in their environment and will show your product in its best light.
- Perimeter pests around the outside of a house or business are more complicated because brick, concrete, soil, sod, and mulch are all VERY, VERY difficult but also very common surfaces for your products. Our favorite outdoor perimeter surface is vinyl siding. Painted wood is a similar ‘semi-hard’ surface option. However, at some point you have to bite the bullet and pick one of the tougher surfaces around a perimeter.