Pesticide resistance: its not just for bugs anymore

By: Dana Sackett

When a specific trait about an animal makes it more likely to survive and produce offspring, that trait will get passed on to the next generation becoming more frequent in successive generations than those traits that do not help individuals survive and reproduce. For example, if being able to swim away from a shark very fast so as not to be eaten is important in the environment an animal lives in, only those individuals that are fast enough to escape will survive and pass on those fast genes. Overtime, the population would have more and more fast individuals as a result of having parents that were fast enough to survive and reproduce. This change in the frequency of a particular trait (such as being fast) in a population overtime is called microevolution.

Mouth of a sea lamprey. These parasitic fish attach to the sides and gills of other fish to feed on them. Credit: T. Lawrence, GLFC. Source

The most common example of microevolution today involves species that have very short life spans (think bacteria, insects, and viruses with generation times of minutes to days or months). The reason we are generally able to see changes in these shorter-lived organisms versus longer lived organisms is because one generation will pass on those traits that give an individual some advantage in surviving and reproducing in a very short period of time. A classic example of this would be pesticide and antibiotic resistance (see here for more information on a previous article on antibiotic resistance).

A sea lamprey from the great lakes. Source

When a pesticide is used widely and consistently for extended periods of time it can often kill nearly every one of those pests. However, for those individual pests that happen to have a trait that allows them to be resistant to the pesticide, they survive and reproduce, passing on that resistant trait to the new generation. The practical effect is that the population becomes more and more resistant to the pesticide over time. Eventually, the pesticide becomes ineffective because the entire targeted pest population has evolved to be resistant to it.

Parasitic sea lamprey feeding on a fish. Source

The general rule that microevolution is only visible over our lifetime in short-lived species has recently been challenged by a study that found longer-lived invasive fish species adapted resistance to pesticides. This study found that a population of sea lamprey, a parasitic invasive species in the Laurentian Great Lakes, was able to develop resistance to a chemical used to control its population in as little as forty years

Wounds inflicted by sea lamprey on an economically important fish species in the Great Lakes. Source

Sea lamprey are native to the Atlantic Ocean, but were able to use shipping canals to invade the Great Lakes in the early 20th century. Following introduction, with no natural predators, little competition, and prey/host species that were not familiar with the parasite, sea lamprey populations grew rapidly and decimated native fish populations. Scientists began investigating different means to control the population using chemicals in the 1950’s. One compound called TFM was found to effectively kill larval sea lamprey with very few detectable effects on other fish species. The sea lamprey population was reduced by 90% using this method, which resulted in the recovery of many economically important fisheries in the Great Lakes.

Photo of a sea lamprey from the Great Lakes. Credit: John Lyons. Source

However, with a generation time of four to seven years, and such widespread and continuous applications of this pesticide, sea lamprey that had traits that were resistant to the pesticide were able to survive and pass on those resistant traits, rapidly evolving into a population that was resistant to the pesticide within forty to eighty years.

Sea lamprey parasitising a fish in the Great Lakes. Source

Controlling the spread and devastation of an invasive species can cost billions of dollars. A cost many see as worth paying to prevent the complete devastation of the Great Lakes ecosystems and the numerous fisheries that support the regions economy. Thus, understanding how effective different methods of controlling or trying to eradicate an invasive species are and how long those strategies are likely to be effective is an important aspect of invasive species management. This is particularly true given that sea lamprey have proven that resistance is not only something that needs to be considered for insects and bacteria anymore but longer-lived species as well.

Christie MR, Sepulveda MS, Dunlop ES. 2019. Rapid resistance to pesticide control is predicted to evolve in an invasive fish. Nature, Scientific Reports 9: 18157.

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