A self-eliminating CRISPR-based solution to insecticide resistance

A novel CRISPR-based tool introduces insecticide-susceptible genes without them spreading uncontrollably.

Insecticide use and insecticide resistance form a vicious cycle – insecticides cause insecticide resistance, which causes more insecticides to be used, which causes more resistance, and so on. To help address this, researchers from the University of California – San Diego (CA, USA), have developed a self-eliminating CRISPR-based tool that cuts out insecticide-resistance genes and replaces them with susceptible wild-type genes. The system could help reduce the use of insecticides, and could even be applied to mosquitos and malaria.

Insecticides are commonly used to prevent damage to valuable crops by pests. However, over time, insects develop genetic mutations that make them resistant to insecticides, forcing farmers to increase the use and concentration of poisonous insecticides. When used at high concentrations, insecticides pose a risk to human health and the environment, as they kill all insects, not just pests.

Researchers have developed CRISPR-based techniques that remove insecticide-resistant genes and replace them with genes that are susceptible to insecticides. While these technologies can help protect crops and reduce insecticide use, there are concerns that once the genes are released into a population, they could spread uncontrollably.

To address this issue, the researchers of the current study developed a self-eliminating allelic drive, or ‘e-Drive’. The e-Drive encodes a group of DNA elements, including both Cas9 and a guide RNA to target a gene known as the voltage-gated sodium ion channel, or Vgsc, which is required for the nervous system to function normally. Cas9 cuts the targeted Vgsc insecticide-resistant gene, which is switched out for a native copy of the gene that is susceptible to insecticides.

To make the e-Drive self-eliminating, it is inserted on the X-chromosome and reduces the mating success of males, resulting in reduced offspring. This means that the frequency of the e-Drive declines through each population and eventually vanishes.

The researchers trailed the e-Drive in fruit flies, as a proof-of-concept study. They deemed it to be successful, with all of the offspring converting to native genes in eight-to-10 generations, which took around 6 months.

“Because insects carrying the gene cassette are penalized with a severe fitness cost, the element is rapidly eliminated from the population, lasting only as long as it takes to convert 100 percent of the insecticide-resistant forms of the target gene back to wild-type,” said first author Ankush Auradkar.

The self-eliminating nature of the e-Drive allows for its introduction and re-introduction when needed and when different types of pesticides are being used.

The researchers are now turning their efforts to mosquitos, hoping that a similar system in mosquitos might help prevent the spread of malaria.