As the number of insecticides available to growers continues to dwindle because of tightening regulations and development of pest resistance, the quest for new products increases. These new products will have to conform to strict regulations due to concerns about human, animal, environmental and pollinator safety.
Ideally, new insecticides need to have a unique mode of action to counter insects’ ability to develop resistance. In addition, many synthetic chemicals currently rely on single-molecule technology, and it’s easier for pests to develop resistance to one molecule at a time.
“Plants have been using their own essential oils to defend themselves against pests for millions of years,” he says. “They are pretty complex structures. Rosemary oil, for example, contains 14 to 20 individual pure compounds. Typically botanicals were used for very specific applications — as repellants for fleas, ticks, mosquitos, etc. But no one applied modern science to identify what actually was going on within this complex extract called peppermint oil or rosemary oil. We did seven years of pure basic research to understand how these natural chemicals work, their mode of action and their stability in an agricultural setting as opposed to a homeowner setting. We started breaking them down into individual compounds to see which ones contribute to activity and how this chemistry interacts with specific neuro-receptors in insects.”
Multiple Molecules Prevent Resistance
Bessette says there may be three different classes of chemistry within a single plant extract. Some may be relevant to the pesticidal activity and others not at all. And while the complexity makes the process longer, Bessette says it is that same complexity that helps with resistance management and pesticidal activity.
“Most of the folks in the pesticide industry wanted to look at a single, synthetic compound and set up a manufacturing plant where they could patent and control the manufacture, use and distribution of that molecule,” he says. “It was very effective, but also sometimes expensive, and you could get massive resistance and some adverse toxicity issues as well. The likelihood of resistance with botanicals is much lower than if you had a synthetic chemistry because there are multiple molecules and related modes of action. That’s why the natural compounds will be at least a significant part of biopesticides in the future.”
Insects can also develop resistance to synthetic derivatives of natural chemistry, such as the synthetic pyrethroids, because they also rely on the single-molecule technology. In this case, the active compound within a natural extract is modified and then synthesized for commercial use. The resulting molecule is no longer natural and remains a single molecule.
“Synthetic pyrethroid chemistry has already moved through 4 or more generations,” Bessette says. “From what we’ve seen, they just keep adding a structure to the original molecule, but the insects are evolving resistance to every single one of these generations of synthetic pyrethroid. And even if it is still somewhat effective, now you have to go to the highest rate, which costs more money and creates more exposure in terms of humans and the environment. I don’t think anyone would argue that there’s significant potential for insect resistance when you only use a single-molecule type compound.”
Bessette’s team found that compounds in peppermint, rosemary and geranium essential oils target a nerve receptor system found only in insects – the octopamine receptor. Knowledge of this receptor system was not new, but nobody had yet been able to target it with a safe molecule. The agricultural product Keyplex developed from this basic research is called Ecotrol, and it includes all three botanical oils.
“We won’t use single-molecule applications because we don’t want to have any resistance build-up, no matter how remote the possibility might be since plants have been using these defenses for millions of years,” Bessette says. “There is also some insect specificity among the oils as well. They all have the same mode of action, but one oil may be more active on a particular insect over another due to biology. A tick that has a very hard exoskeleton is more difficult to control than an aphid, which has a very soft cuticle. Some of these essential oil compounds are also very good solvents, so you want one that will penetrate through that wax cuticle and reach the target receptor sites.”
Because the essential oils are a complex blend of compounds that have a unique mode of action, they are a valuable tool for rotation and/or tank mix with other chemistries.
Botanicals Offer Unique Mode of Action
“At the end of the day, that’s what we want our products to be – an effective tool in the toolbox,” Bessette says. “It’s not a magic bullet, but we can definitely offer a variety of applications and advantages with our chemistry if we have multiple modes of action over and above what the synthetics are doing.”
Bessette says the team’s years of research will result in other new products soon.
“We’ve identified the structure/activity relationship of chemistries that bind to the octopamine receptor site and some others that don’t,” he says. “Our future direction is to start looking at those that don’t and evolve the products so you have multiple modes of action within a single formulation. If another compound doesn’t target octopamine, but works on another receptor, we will start putting these two natural essential oil compounds together. You’ll have a more effective product because you’re targeting two receptors in the insect. It will be almost impossible for that insect to develop resistance, because it is not a single molecule or single mode of action. It would be purely random as to which one would survive.”
In addition, Bessette says Ecotrol can be used to bring back some older chemistries that aren’t currently very active because of massive resistance.
“If Ecotrol is tank-mixed or rotated with these products, you could potentially make the highest label rate active again where it wasn’t before,” he says. “You now have two different modes of action active and working on the insect system. Plus there is the additional effects of the oils, such as the solvent/penetration aspect. You’re doing something completely novel, for which the insect system is not evolved. You’re now shooting them in the hand and the foot, instead of just the foot. The Ecotrol actually enhances the ability of the original application.”