4 Keys to Managing Insecticide Resistance
November 7, 2021 My previous article on insecticide resistance discussed the reasons for insect pests losing sensitivity to insecticides, and the mechanisms of this unfortunate process. Now it is time to talk about what can be done to prevent resistance from happening, or at least to delay it by as long as possible. Despite a long and discouraging history of failures, it is very much possible to do so, given some effort is made towards achieving this goal.
Recognizing the Problem
So, what is there to be done to save a family farm from being devoured by mutant superbugs? The first step to solving one’s problem is always acknowledging that it exists. This acknowledgement consists of two parts. Part one understanding that something undesirable is either happening already or will happen in the foreseeable future. Part two is realizing that the problem is one’s own problem, not somebody else’s problem. Regarding insecticide resistance, very few people who are involved in agriculture deny that it is a real thing rather than a theoretical construct cobbled together by aloof academics sheltered in the Ivory Tower. However, substantially more than a few people do not consider it to be an important enough concern to take an action.
Common thinking is that chemical companies will take care of insects evolving resistance to their products, just as they did in the past. However, this may or may not be the case. Developing a new active ingredient and bringing it to the market is considerably more difficult and expensive than it used to be, in large part because of much stronger scrutiny of its environmental impacts. Companies themselves have also become humongous semi-monopolies through mergers and acquisitions. Therefore, they are likely to have sufficient resources to forfeit a product or two while still staying in business, especially if their patents on these products have expired.
For some of the companies, insecticides are not even the main part of their portfolios. Plus, nowadays trading cryptocurrencies or other creative financial instruments is more lucrative than growing food and fiber. It is somewhat surprising that people still bother with the latter. It may be a sound business decision to phase out research and development on new insecticides altogether and redirect funds towards opening some kind of a crypto derivative virtual reality quantum vision trading desk.
Diversifying the Management Techniques
Once a problem is defined and its existence is fully accepted, solutions can be found. For insecticide resistance, they are actually rather straightforward. It is very important to avoid relying on a single insecticide as a sole tool for resistance management. Probability of a mutation that makes an insect resistant to different control methods is significantly lower than probability of a mutation conferring resistance to a single control method. So, if multiple methods are used, a mutant that is resistant to one of them will still succumb to the other.
Combining insecticides with different modes of action is the most common approach to diversifying pest control for the purpose of resistant management. One way to do it is spraying one insecticide after another in an alternating sequence of active ingredients. Another way is to use on-farm tank mixes or pre-mixed products containing several active ingredients (for insect-protected transgenic plants, such an approach is known as pyramiding). There are different opinions on which method is better, but both are superior to using a single insecticide.
Better yet, insecticides can be integrated with other control techniques, such as biological control, crop rotation, removal of crop debris that may harbor insect pests, etc. This further diminishes probability of failure because a physiological or behavioral change that simultaneously helps, for instance, digesting a poison and dodging a predator is highly unlikely.
When talking about non-chemical control techniques, it is also important to realize that by themselves, they are not immune to failure due to the evolution in populations of target pests. For example, northern corn rootworms have adapted to crop rotation between corn and soybean by waiting out the soybean year while diapausing as eggs in the soil. Along the same lines, western corn rootworms started laying eggs in current-year soybean fields, so that larvae hatch when these fields are rotated to corn in the next year. So, contrary to a common misconception, a simple substitution of insecticides by some other approach will not solve the problem of resistance. However, when chemical and non-chemical methods are used together, the probability of them failing simultaneously becomes very low.
Going (Somewhat) Easy on Pests
Besides diversifying control methods, it is also important to keep selection pressure on pest populations as low as possible. Killing pests is not the end goal of crop protection; the end goal is, as strange as it may sound, protecting the crop. This is better achieved by preventing pest populations from reaching economically damaging densities. Trying to kill every single bug will inevitably lead to only the most resistant of them surviving. When these mate with each other, their offspring is also resistant and can no longer be controlled with the same chemical. To the contrary, if a resistant insect mates with a susceptible insect, their offspring is usually less resistant than their resistant parent. As a result, it can be controlled by a sufficiently high rate of the same insecticide.
There are several ways to lower selection pressure. One is to monitor insect populations and spray only when they exceed economic thresholds. This requires extra effort, but usually cuts the number of insecticide applications and associated expenses. Another is to leave a certain portion of a field untreated, so that susceptible insects can survive over there and then interbreed with resistant mutants in the treated portion of the field. Leaving such refuges is a legal requirement when growing insect-protected transgenic plants. At the same time, it is not commonly practiced with sprayable insecticides because of obvious concerns about the damage to untreated plants. Still, it is worth considering for lasting insecticide efficacy.
Although this may seem counterintuitive, lowering insecticide application rate below label requirements in an attempt to lower selection pressure is a bad idea. As discussed above, progeny of one resistant and one susceptible parent is somewhere in between the two of them in its level of resistance. Therefore, it may be able to survive low doses of the toxin. The way the laws of inheritance work, once these survivors mate with each other, some of their offspring will have resistance genes received from grandparents on both mother’s and father’s sides. As a result, they will be highly resistant even to insecticides applied at the highest label rates.
Short-Term Effort for Long-Term Success
Agricultural sustainability is a popular buzzword that is constantly brought up in publications, advertising materials, at conferences, and even in informal conversations among a variety of stakeholders. It may have different meanings to different people, but the bottom line is that production of food and fiber must continue for as long as humans inhabit the Earth. Soil erosion and overreliance on non-renewable resources are often brought up as threats to sustainability, while insecticide resistance often goes unmentioned. However, retaining an ability to suppress insect pests is an important component of an overall agricultural sustainability. Therefore, practices directed towards preventing pest adaptation to insecticides and other control methods should not be overlooked when devising long-term plans for agricultural operations.
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