Mosquitoes might be just pesky little insects that might start appearing again in a few months. They leave their saliva in your skin, and this causes an itchy bump. But in other parts of the world. Estimates report that mosquitoes have killed up to 52 billion people in history by spreading malaria, yellow fever, and dengue. It is currently killing 1 million people per year, even with advanced medicine and healthcare around the world. Doesn’t that horrifying statistic shock you?
To drastically lower this number, researchers took a smart approach and decided to eliminate the source of the problem. They decided to use CRISPR to genetically alter the male flies so that they become sterile. Professor Craig Montell from UC Santa Barbara altered the gene of Aedes aegypti, the main type of mosquito that transmits dengue, yellow fever, Zika, etc.
Previously, scientists just radiated and applied chemicals to sterilize male mosquitoes in hopes to alter their genes since “there are enough genes that affect fertility that one will likely be altered,” making them infertile. However, this would leave, many of the mosquitoes to be sick and die prematurely since other genes that don’t relate to fertility are also changed.
Using CRISPER/Cas9, researchers removed B2t, a gene that specifically affects male fertility in mosquitoes. Unlike in previous efforts, the sterile mosquitoes were completely healthy.
This whole effort to sterilize insects is part of a greater method called the sterile insect technique (SIT). Scientists release way more sterile insects than there exist in the wild. The population will crash as females will not be mating with a lot of males that are capable of making offspring. A benefit of releasing males instead of females is that males feed on nectar, not blood, so it will not cause major disturbance to communities.
To sexually reproduce, a sperm cell must meet an egg. Each gamete is a haploid that has a single set of chromosomes. The sperm and egg combine to produce a zygote making it a diploid with a complete set of chromosomes. If a male is sterile, then they are not able to produce or release their sperm, making it impossible for those insects to reproduce.
The effect of this technique is more effective after each cycle, so when you release the same amount of mosquitoes after 3 cycles, the population change will be way more drastic. A downside to this is that sterile male mosquitoes need to be reintroduced after they die off since they cannot pass on their mutated gene.
Although researchers have successfully identified a way to isolate the gene and remove it to make male mosquitoes fertile, they still needed to find the optimal ratio of lab mosquitoes to wild type to ensure that they do not wipe out the species in an area since that has dramatic effects on the whole ecosystem. The researchers conducted many trials and found that, in a week, a ratio of about “5 or 6 sterile males to one wild-type male” decreased female fertility by 50% while, a ratio of 15:1 suppressed female fertility to about 20%, where it leveled off. So depending on the situation, they now release the more precise amount.
I think that this is one of the brilliant uses of CRISPR, and it only goes to show how far we can go if we master this technique. An ethics question that this research brings up is, do humans have the right to wipe out an entire species just because it is causing harm to humans?