When we think about epigenetics and the phrase “environment determines genetic expression”, we should think about what this means not just for the plants and species we are trying to optimize, but also for all the plants, fungus, bacteria, nematodes, and mites commonly called ‘pests’. If environment determines their genetic expression, that means we can manage their virulence or pathogenicity to the degree we can manage the environmental factors they depend on.
Tom Dykstra shares an interesting perspective on healthy vs unhealthy mosquitos, and their capacity to resist infection from malaria or other ‘pathogens’.
John: You and I have discussed before how environment determines genetic expression. And you expressed that you have had difficulties infecting some mosquitoes with malaria. As we’ve been having this conversation about mosquitoes, that popped back into my mind. What are the differences between healthy and unhealthy mosquitoes as vectors of infectious disease?
Tom: Well, I personally have not infected mosquitoes with malaria, but I’ve talked to researchers who’ve worked on this. Let me put it this way. Most Anopheles mosquitoes do not transmit malaria. Most Aedes mosquitoes do not transmit dengue, yellow fever, or Zika. Most Culex mosquitoes do not transmit encephalitis.
When you observe this, you understand that not all insects are infected with the disease. So you can get bitten by thousands and thousands of Anopheles mosquitoes and not get malaria. But all you have to do is be bitten by one mosquito that does have malaria in order for you to get it.
And this is one of the truths of biology that has been revealed to us—that insects also have various states of health and lack of health. In order for them to be relatively healthy, they need digested components. Their food sources need to be as such. But if their food source is not that good, or if it’s missing something, they can suffer. Insects have died in the field. I’ve seen it many times. Sometimes people try to keep them as pets and they die. We see them dying in the field all the time. They are susceptible to disease. They also have states of health and lack of health that are somewhat analogous to what you would find in a human.
If you’re working with mosquitoes in the laboratory, and you try and infect them with the particular disease that they’re supposed to be infected with—Anopheles mosquitoes with malaria, for example—you will not get a 100 percent infection rate. And that is amazing. This is in part because when you’re raising them in the laboratory, they’re coddled. They’re given everything they need. Therefore, they’re in pretty good shape, and it becomes a little difficult to infect them. Out in the field, they might be more susceptible. Ones that are more susceptible might die. Others would be more susceptible to actually getting a disease—like the malaria protozoan or the Zika virus or anything of that sort. And it can actually take hold of the system, because the insect doesn’t have the immune system to take care of it. It kind of sets up shop inside the insect.