Glue science: How we get insects to “stick” around in traps
One of the biggest issues, when monitoring for insects, is that the insects don’t really want to be caught. Go figure.
Regardless of the trap style, whether it be a pitfall trap or a sticky blunder trap, the insects that approach them tend to, by and large, avoid hurtling headlong towards death. We do our best to design traps to outwit these crafty bugs and if you spend some time watching a trap, you’ll see what I mean.
Take a pitfall trap for example, you’ll probably see a number of insects walking around the trap and leaving.
Sticky note adhesive is designed to exacting specifications. The glue on the back of each note has the ideal balance of tackifier and elastomer to make peeling easy, not leave behind any residue, and have high enough shear resistance to hold the note on a vertical surface without sagging or sliding.
You might also see insects walking up the ramp and changing their mind as they reach the edge and begin to lose footing. Sticky blunder traps have the same issue. Observation of a glue board will reveal that a decent number of potential visitors might get right up to the glue line, test a toe in the water, then pull themselves free and head the other direction. This tendency towards self-preservation keeps us always working towards the perfect trap. In the meantime, we do catch a percentage of them. This is why so many insect traps are used primarily as monitors instead of eradication methods.
It is All about the Glue
In the pursuit of a better insect trap, manufacturers put a lot of effort into developing glues that balance all the important qualities required to catch the best percentage of unlucky insects. We probably don’t give glue that much thought on the average day, but they really are all around us and come in a variety of forms and chemistries.
Take white school glue for example. It falls under the category of a “structural” adhesive. Structural adhesives are those that cure or harden based on one or more factors. Our white glue starts as a liquid using water as a solvent. As the water evaporates, the glue begins to dry out, harden, and bond surfaces together. Not all structural adhesives require “drying” out. Others, like epoxies, rely on chemical reactions that are independent of exposure to air.
Other common structural adhesives, like hot-glue, use high temperatures to liquify the adhesive material until it can return to normal temperatures and provide a strong bond between surfaces. Structural adhesives, with the exemption of hot glue, are good at doing their job of sticking one thing to another, one time.
After that, should the bond be broken, it can’t be reestablished without the addition of fresh adhesive. None of these structural adhesives are going to do us much good with insect trapping which is why we are lucky to have another category called “pressure-sensitive” adhesives.
Pressure sensitive adhesives are types of glue that don’t require solvent evaporation or curing of any kind. When it comes to pressure sensitive adhesives, think about tape, adhesive labels, and sticky notes. The glue on these products doesn’t have to dry or cure to do its job. Simply press the tape or sticky note onto a surface and there you go, it’s stuck. The precise formulation of these adhesives is manufacturers, but they generally feature two usually kept fairly close to the vest by their main components. These two primary components are an elastomer, and a tackifier.
In order to work, a pressure sensitive adhesive needs to be able to “wet” the surface that it is applied to in order to provide initial “stick”. This is where the tackifier comes in. It provides the initial stickiness in the process, Think maple-syrup, nice initial stick, but doesn’t really hold anything together when wet. That’s why we need the next step for good adhesion, the elastomer.
The elastomer, combined with the tackifier, adds a “rubbery” component to the mix that helps resist shear and peeling forces. Imagine 3 sticky notes. One has a backing that has the tackifier only. The tackifier is semi-liquid and initially sticks nicely to a horizontal surface but you find that you can still slide it around with relative ease.
The second note has the elastomer only. If has a good “rubbery” quality to it and it resists sliding around, but it’s not really attached to the surface at all.
The 3rd note, has the best of both worlds, it sticks to the surface, resists sliding and peeling, and it’s perfect for sticking futile reminders to perform tasks that are not worthy of today’s efforts and are best left to future you.
Pressure sensitive adhesives can be manipulated for maximum performance. Cold weather formulas, like on this board, work down to 0 degrees Fahrenheit!
Some sticky trap glues are relatively hard, some are more liquid, some are specially designed to work in extreme low temperatures.
All of them however, are picked purposefully for the kind of insect or pest they are aimed at catching.
The harder glues skew heavy towards elastomer and are good for, stout, crawling pests, and some flying insects.
The more liquid glues skew towards more tackifier and are ideal for catching light, flying insects, by immediately wetting and entangling their wings. Heavy tackifier glues also have some additional capacity to continue to perform in dusty environments.
The goal when designing a sticky trap adhesive, is to formulate a glue that has the best chance of holding onto the insects that make contact with the glue.
“Wet” glues like in this NoSurvivor™ trap are most common in traps designed to capture flying insects. The tackifier-heavy glue helps to immediately wet and tangle the wings of the insects to disable it inside the trap. Photo by James Feston
Because the insects resist being caught, the adhesive needs to have the right balance of tackiness to grab them, and elastomer to hold them.
Ultimately, the efficacy of our insect traps relies on its ability to overcome the survival instincts of our insect quarry.
Which is why, when you are choosing a trap for your IPM program, you might take a moment to think about the many factors that go into designing the humble sticky trap.
There is more science to the stick, than meets the eye.
Insects Limited, an Insect Pheromone Company
Insects Limited, Inc. researches, tests, develops, manufactures and distributes pheromones and trapping systems for insects in a global marketplace. The highly qualified staff also can assist with consultation, areas of expert witness, training presentations and grant writing.
Insects Limited, Inc. specializes in a unique niche of pest control that provides mainstream products and services to protect stored food, grain, museum collections, tobacco, timber and fiber worldwide. Please take some time to view these products and services in our web store.
