The promise of mutant insects
By Carolyn Duncan

OTTAWA — Scientists around the world are working to create the 'ideal' insects to control infectious diseases and save crops.

A mosquito represents one of many insect disease vectors.

Imagine a world without insects. The annoying hum of mosquitoes on a summer night gone, silenced by a mysterious genetic mutation. What if the insects contributing to tropical parasitic diseases and mass destruction of crops were altered so they could no longer harm humans or the economy?

Crops have been destroyed for centuries by pests, and the solution to some insect problems may be within reach. ‘Designer insects’ are biotechnology’s newest contribution to both agriculture and the possibility of parasitic disease control.

Dr. David O’Brochta, associate professor of the Molecular Cell and Biology program at the University of Maryland focussed directly on transposable elements, or new artificial traits, that would attach to the DNA of an insect and change its characteristics.

“To figure out how genes work, isolate a gene, look at its structure, maybe change and then put it back into an insect.”

“Technology is important to significantly reduce the transfer of diseases,” says Dr. Carl Lowenberger Associate Professor, Canadian Research Chair in Parasitology and Vectors of Disease at Simon Fraser University. He added that the concept of disease eradication is still very far away, but researchers have made progress.

The idea of genetically modified bugs has been around since 1982. Researchers isolated transposable elements, or genes that could be replicated in other organisms in fruit flies (Drosophila) in the 1980s. According to Dr. Thomas Miller, Professor of Entomology and Entomologist at the University of California Riverside, these transposable elements were successfully copied for the first time in 1995.

“After 1995 there was a floodgate,” said Miller. “A number of insect transformists were reported in the next period after that.”

Researchers hoped to make major advances in disease control and agriculture. Genetic modification of insects promised to slow the spread of tropical diseases and to stop the destruction of crops.

‘Designer insects’ are created by injecting insects with new DNA strands. A piece of DNA that is coded for a new type of gene would be inserted to an insect’s reproductive tissues during embryonic development. For example, one could inject a DNA strand coded for red eyes into the fertilized egg of a fruit fly with white eyes. When the egg is laid, and the larva grows, it would have red eyes rather than the white eyes that its parent’s DNA would have dictated.

The bollworm's story

Miller’s research is specifically with the pink bollworm, a pest that eats and burrows in cotton plants, costing the U.S. cotton industry $30 million annually. It was an alien species, likely introduced from cotton shipments of Australian or Indian origin, and according to Miller, a worldwide problem.

“It’s a dry climate pest,” he said. “You wouldn’t find it anywhere east of the Mississippi River, and you won’t find it in a wet climate.”

“Well we try to get bollworm eggs within an hour after they’re laid,” explained Miller. “We know when the females lay eggs, so we reverse the life cycle in an incubation chamber, and we convert their time to our convenience.”

Miller said that the DNA injected has codes for enzymes that cut into the insect’s own DNA, and therefore it continues to be replicated as a part of its own genes. From there, research would determine what can be done with different traits to different types of insects.

The trait that he has introduced into the bollworm’s DNA is a conditional lethal gene. This ‘conditional lethal gene’ works against a bollworm embryo’s natural ability to grow and survive at cooler temperatures. The process has yet to be perfected, but Miller hoped it would work to eliminate the pink bollworm.

Another method he used to reduce the number of pink bollworms in the wild was mass rearing and release of sterile insects. The insects are exposed to radiation just strong enough to render them sterile, then released. They then contaminate the wild population and prevent reproduction.

He said his team is doing the required regulatory paperwork to get the transgenic pink bollworms released in the wild.

“If you really want to eradicate pink bollworm you have to do it on an area-wide basis where everyone is doing the same thing,” said Miller. “You have to maintain yourself pest-free for at least five years to be absolutely certain you’ve done a good job.”

Miller explained that it is a regulatory process, and that many people are not willing to accept the genetically engineered insects.

Malaria-resistant mosquitoes?

Lowenberger works with genetically modified insects and transposable elements, too. His specialty is the concept of manipulating the genes of insect vectors, such as mosquitoes, to kill parasitic diseases.

“We’re looking to solve problems like the West Nile virus, dengue and yellow fever,” Lowenberger said. “Insect vectors are the causes of many diseases.”

Methods of solving diseases are similar to those that Miller used with the pink bollworms, but Lowenberger said it is more uncertain. His work would ideally end up manipulating the DNA of mosquitoes to kill parasitic diseases such as malaria so they could no longer transfer the disease to humans.

“Back in the 1960s we used DDT to kill off all kinds of mosquitoes,” said Lowenberger. “But that obviously didn’t work, and now human health has even suffered from it.”

A DNA strand is the basis of genetic engineering.

“Malaria is an enormous killer,” said O’Brochta. “One of the reasons for developing this technology is that there are 400 million clinical cases of malaria in the world in a year.”

The disease kills more people annually than HIV/AIDS, and, according to O’Brochta, and it has been around “forever.”

Insect vectors act as a catalyst to parasitic diseases in many tropical countries. According to Lowenberger, a parasite such as malaria has the ability to hide in a mosquito without being detected by its immune system.

“In the gut of bugs is where changes occur,” said Lowenberger. “The insect vectors host bacteria and viruses into their immune system.”

When the parasite has matured, it would transfer into a human host and make that person sick. Lowenberger said it is a hit and miss process in manipulating the DNA for an insect’s immune system.

“The main problem with creating these types of insects,” he said, “is that we cannot detect where the DNA sequence will enter the insect.”

O’Brochta said the transposable elements are something that he can attach any gene to, and it will eventually be replicated into the DNA of an insect. He found that the most effective time to inject the insects in their reproductive organs, where chances are greater that the new traits will be passed on to the next generation of mosquitoes.

Detecting whether the immune system change actually occurred was based on the presence of a different indicator gene. For example, some traits are linked, and when Lowenberger injected a strand of DNA with two specific, different traits, he might see the phenotype, or physical trait, and can therefore determine that the genotype, or genetic trait, was also changed.

“Our goal is to make the insect produce (as a genetic model) an antibody to neutralize the parasite,” said Lowenberger. “This would block the parasite from reproducing in cells, and reduce its access to humans.”

A buggy future

All types of research with these transgenic insects could ideally lead to constructive changes in the world. The catch: the uncertainty of how genetically engineered insects react in the wild. The issue raised environmental ethical concerns. Studies that would determine the effects of genetically engineered insects in an ecosystem are difficult to control.

Lowenberger pointed out that especially in developing countries where parasitic diseases are most prevalent that the people would not necessarily have the education required to understand a test study of the release of genetically engineered insects.

“Once you let the genie out, you can’t get it back,” he said. “It’s an ethical situation, a village of a developing country or a problem area, you can’t easily measure the impact on human health.”

Lowenberger expressed other concerns about the fitness of transgenic insects. “Genetically engineering insects in the lab, they have fitness tests, but can they be used practically? Then if you can, how do you drive the ‘new’ insects into the wild population?”

His questions are part of what he referred to as part of the “pie in the sky” situation. Lowenberger said the concept of using these insects could work, but there are so many things to be considered before releasing them.

O’Brochta referred to the genetic engineering of mosquitoes to reduce the prevalence of malaria as “fairly speculative, and pretty ambitious, and not really that close to being accomplished, but we’re sort of getting all the tools together…”

Would these insects manage to mutate in a natural way in order to survive? Studies have not yet determined if genetically modified insects would overcome their differences. It would take an extended period of time, and according to Lowenberger, hundreds of different effects of all kinds of transgenic insects are unknown.

“We’ll be altering the insect’s ability to serve as a host to a pathogen, or cause of a disease, and it might become a poor host for that one pathogen,” said O’Brochta. “One risk is that we might make it a better host for another new pathogen.”

O’Brochta added that he tried to address as many concerns as possible in the laboratory, where he can immediately fix any problems.

“How do we get that characteristic into the entire population of mosquitoes?” O’Brochta wondered. “It’s not going to be just a matter of opening a window and letting them go…”

Regulatory processes for the United States and Canada would be very similar regarding the release of genetically engineered insects. Miller said it involved a lot of paperwork and background research.

Miller was optimistic about the future of pink bollworms in agriculture. Genetically engineered insects would certainly be effective. He said that the only problem he encountered was the fitness of the insects, and that his team was working on making them survive in the wild.

Grasshoppers are a pest to crops. Are they next up for genetic modification?

“If you release a genetically modified pink bollworm to the environment, there’s nothing in the environment to mate with for one thing, for another thing, it’s in the soil for the most part,” said Miller. “It’s not something that intrudes in the environment at all because it’s a brand new pest. You can follow the infestation from the early 1900s,”

Environmental impacts would still be difficult to gage. Lowenberger pointed out that humans have never been able to fully eradicate pests. Biological evolution could compensate for the changes made to insects.

“We would look to replace the wild population with one that would not be able to transmit the parasite – a new mosquito,” said Lowenberger.

‘Designer bugs’ might not have made any major impacts on disease eradication or agricultural practises yet, but it is still early in the research phase. O’Brochta, Lowenberger and Miller all pointed out the massive potential for their research. They would not silence today’s insects, but the goal is to make them less dangerous and destructive for people.

“We can make the bugs,” said O’Brochta. “In the near future we’ll make them do exactly what we want them to do.”