Need to manage a pest problem? Luckily, there are many ways to do that! From physical to biological to chemical controls, Steve covers an array of pest management strategies farmers can use when an issue arises.
Remember when Bill Murray’s character uttered, “Anything different is good” in the classic movie Groundhog Day? Well, that idea can also be applied to farming and pest control. There are many different ways to farm and many different methods, tools and strategies that farmers can use to control the pests and disease that prey upon our food. This is not unlike the journey Murray’s character, Phil, takes in the movie, hilariously trying to make it out of the time loop he finds himself in and to make it to tomorrow. Groundhog Day is a great example of finding different ways to solve a problem, and recently there have been a crop of these types of movies and tv shows making their way to our screens, like Happy Death Day and Russian Doll. They are great reminders that ingenuity and original thinking can help you out of many jams!
If the jam you find yourself in concerns “bugs,” then we are typically quite open to a few options that involve killing the invaders ourselves or we are willing to hire an expert service to do the job. If your house or apartment is overrun with ants, roaches or fleas, you are probably going to do something about it! If you are unfortunate enough to get a bedbug infestation, you may have to consider some pretty extreme solutions to eliminate that threat. In an earlier podcast, I described the recently introduced pest, the Brown Marmorated Stink Bug, a pest that likes to migrate in the thousands to the inside of houses in the weeks leading up to winter. In these situations, “killing” something makes sense.
Figure 1: Brown Marmorated Stink Bugs. Image from Penn. State https://extension.psu.edu/brown-marmorated-stink-bug
Farmers often find that their crops are being attacked by “bugs” of various types, and they want and need to do something about it. So, farmers and non-farmers can both relate to times when they need to do something about a pest. But there are actually lots of different options for how to do that, and so the title of today’s podcast is: “there’s more than one way to kill a bug.”
Physical methods
Perhaps the most familiar way to “kill a bug” is using physical methods like a fly swatter or a shoe. That isn’t a practical approach for an entire farmed field, but there are physical approaches used by farmers. For instance, the California strawberry growers have found that by running a big vacuum machine over the rows they can keep the population of Lygus bugs in check. That means that you and I will be able to buy strawberries that are not marked and deformed by the feeding of this large, true bug. Homeowners can also buy special bug vacuums that are a good way to deal with something like those stinkbugs if they invade your house (apparently you shouldn’t just squish them because of the “stink” part).
Figure 2: Lygus vac in strawberries, image from Univ. California Extension http://calag.ucanr.edu/Archive/?article=ca.v049n02p19
Perhaps the simplest kind of physical control is a barrier. For something like a greenhouse growing vegetable crops, screens are a simple and practical way to keep out bugs, just as they are for our homes.
Traps
Another physical way to deal with pests is with traps. Many homeowners from areas Another physical way to deal with pests is with traps. Many homeowners from areas where there are lots of mosquitoes use a “bug zapper” to protect themselves while on the porch. The mosquitoes are attracted to a light or source of CO2, and then there is an electrical discharge to kill them. In agriculture, the traps might just have some sort of juice with a smell that attracts the bugs, or it might be loaded with an insect sex pheromone that is being used to lure the pest and get it into a container from which it can’t escape or get it to land on some sticky surface. Traps used in farming are usually more for getting a feel for what kind of pests are showing up in big numbers than a way to actually achieve pest control solely through trapping.
Figure 3: Pheromone Trap: Univ. Kentucky http://entomology.ca.uky.edu/ef112
Drowning
Another way to kill a bug is to drown it. Insects and mites breathe in and out through small openings all over their body called spiracles. Particularly for insects that are small and soft-bodied, they can be effectively control them with water that includes a surfactant, or “insecticidal soap.” You can actually make such a spray yourself using a bit of dishwashing detergent in water. For this approach to work, the spray has to completely cover the entire plant, including the underside of the leaves, which is often where the pests are feeding. If you have white flies or aphids or mealy bugs in your garden or landscape, this can be a good approach. EPA registered “soaps” of this nature are commonly used in farming.
A similar drowning strategy can be done using various oils. Particularly in organic farming, oils derived from plants or from petroleum (mineral oil), are used extensively for the control of certain insects and mites.
Interference With Reproduction
Most insect pests start each new season with a relatively small population that has successfully “overwintered”. The pest only becomes a serious threat for crop damage if it can greatly increase its numbers over several generations. So, there are a number of pest control strategies that involve disrupting the bug’s reproduction.
In some cases, there are pest species that can only survive on one specific crop and not on any local weeds. In that scenario, it is possible for the farmers to organize a “crop-free period” in a given region so there is no way for the pest to keep going except maybe to re-enter from a distant point.
There are certain crop protection chemicals “called “insect growth regulators” which don’t actually kill the bug, but keep it from going through its various larval stages and thereby preventing it from reaching the reproductive, adult stage. There is another method called “pheromone confusion”, where many small emitters loaded with the insect-specific pheromones are spread around in something like an orchard or vineyard so that the male insects are diverted and don’t find a real mate.
There is another strategy called “sterile male release” in which pest insects are raised in captivity and then treated in such a way that the males are sterile (usually by exposure to gamma radiation). If large numbers of these males are released, they mate with the wild females and the result is far fewer bug babies. This approach has frequently been used for mosquito control to protect people, and in some cases where there is a new, invasive pest of a crop such as when the Mediterranean Fruit Fly became a threat to California crops a while back.
Several years ago, researchers at Oxford University in the UK used a genetic engineering approach to raise a population of a pest in captivity and then guarantee that there were only sterile males left for a release. These males are more competitive for breeding than those partially compromised by the radiation exposure. This method has been quite successful for dealing with Zika Virus in various areas around the world, but sadly it is used far less than it could be due to GMO-phobia. It would be an ideal solution for a new invasive pest like the spotted winged drosophila, a fruit fly that has recently become a big problem in many fruit crops in the Americas.
Repellents
Another pest control strategy that can work in certain cases is to simply repel the insect and not actually kill it. For instance there are reflective plastic mulches that make some insects avoid the fields where they are used.
Figure 4: A reflective mulch for use in tomato culture. Image Colorado State University Extension http://wci.colostate.edu/shtml/CTV2008.shtml
DEET for example, is a familiar chemical repellent that humans use on their skin to protect themselves from mosquitoes and ticks. There are also chemical repellents used in agriculture. Some just generally drive the pest away while others are particularly good at convincing the female insect to avoid laying eggs on the sprayed crop.
Biocontrol
There are also approaches to bug control based on biological agents. This method leans heavily on the “survival of the fittest” theme and is tinged with a bit of The Hunger Games flavor. There are bugs that eat other bugs, like the familiar Lady Bugs or Lace Wing. These and other predators can often keep pest bug populations in check. There are also things called “parasitoids,” often tiny wasps, that lay their eggs in the pest insect so that later their larvae can hatch out and eat their host.
When a new pest arrives in an area, it often doesn’t have many of these “natural enemies.”The Glassy Winged Sharpshooter was a new pest introduced into California about 10 years ago. It is particularly troublesome because it spreads a bacterium that can kill grapes. Another such new pest is the Asian Citrus Psyllid that spreads the HLB bacterial disease that kills citrus trees
Figure 5: The Glassy Winged Sharpshooter, Image from Univ. California Riverside https://cisr.ucr.edu/slideshowpro/albums/album-9/lg/glassy-winged_sharpshooter_gwss-2.jpg
For both of these pests, California researchers have explored the parts of the world they came from originally and found some of their natural enemies. After doing the homework to make sure that these insects won’t become pests themselves, they have brought the good candidates to California to start building new populations of these beneficials to make it a little bit easier for California farmers to deal with these new invasive pests.
There are predatory mites that eat crop-damaging mites. There are companies that raise these tiny creatures so that they can then be gently spread throughout a field. That spreading job has usually been done by hand, but lately people have been experimenting with small, low flying drones to do that job.
Figure 6: A predatory mite taking out a two spotted spider mite that is a severe pest of strawberries. Image Univ. FL http://entnemdept.ufl.edu/liburd/fruitnvegipm/images/research/Californicus.png
There are also bio-control strategies based on certain fungi and certain nematodes that specifically attack bugs. These can be raised in captivity and then introduced into the field to attack the pest.
Toxins
The last big category of “ways to kill a bug” are the chemicals that are toxic to the pest - things we usually call insecticides. But even within this category, there are many different mechanisms by which the insect is killed. Again, many way to kill a bug. Chemicals for killing insects isn’t something that started with people. In fact, many plants produce their own chemicals for the purpose of defending themselves against pests. In some cases, it is possible to extract such chemicals from one plant species and use them as “natural product” spray on another crops. There are also other organisms like bacteria, fungi and actinomycetes that naturally produce insecticidal chemicals as they grow. These can be fermented in a tank in the lab and then the chemical produced is formulated into an agricultural pest spray.
Some very old pesticides, based on things like sulfur or copper, do what they do in a rather non-specific way, disrupting many functions at once. This usually takes substantial doses. Modern insecticides generally require far smaller doses because they act by inhibiting some particular enzyme, an enzyme that is critical for the pest to survive.
Some of the earliest synthetic chemical pesticides, called organophosphates or carbamates, inhibit an enzyme called Choline esterase that plays a key role in neural function in both insects and animals. It was possible to use these products with relative safety because the dose needed to kill the bug was much lower than what would be take to injure larger animals or people. Still, chronic exposure to these “CEI” compounds or choline esterase inhibitors could eventually cause trouble.
So over the last few decades, the use of CEIs has declined dramatically as new pest control options have been discovered. The best part about these new generations of insecticides is that they have been designed to specifically inhibit enzymes that only occur in insects and not in animals.
The classic example of toxin specificity comes with another example of “biocontrol.” Its based on a particular soil dwelling bacterium called Bacillus thuriengensis – usually know as Bt. Different subspecies and strains of this bacterium make unique proteins that are specifically toxic to just a certain subset of pests. When the protein gets into the right insect’s gut, it is partially digested and a part of it can very specifically bind with and disrupt the bug’s gut lining, eventually killing it. One type of Bt only affects caterpillars. Another only affects the larval stages of beetles. Another type only works on things like flies and mosquitoes. These bacteria can be brewed up in a fermentation tank, dried, and sprayed on crops to control insects but with minimum disruption to beneficial insects because of the selectivity of the toxin. The bacterium does not have to be alive or active, it is really just there for its protein toxin. Bt sprays like this have been used in agriculture since the 1960s, but the protein is not very stable in sunlight. So it has to be applied over and over again.
Since the mid-1990s, there have been several genetically engineered crops in which the bacterial gene for the protein toxin is inserted into the plant’s genome so that it makes its own Bt toxin protein. These crops have been extremely attractive to farmers, but only a small subset of the possible uses have been commercialized because of anti-GMO fears and the related brand protectionism in the food industry.
As I mentioned before, most modern, synthetic insecticides have been designed to inhibit enzymes that are not found in animals. There is an organization called IRAC standing for Insecticide Resistance Action Committee, and they keep track of how the various classes of insecticides work, and which enzymes they inhibit. This is important because farmers need to mix and match those tools so that they don’t drive the pest to evolve resistance to those insecticides.
So as you can see, there are “many ways to kill a bug.” The more different strategies that a farmer can combine or use in sequence, the less chance there is that the pest will evolve resistance to any of the specific tools. This sort of “resiliency through diversity” is central to sustainable pest management programs – and the continued ability of farmers to produce the crops we all need. So it’s a good thing that there’s more than one way to kill a bug.