Environmentally Friendly Pest Control: An Overview of The Sterile Insect Technique

In many cases, we can use the insects themselves to aid us in their elimination. One method, called the Sterile Insect Technique (SIT) involves using sterilized insects to drive the population down.

First, insects are raised in rearing facilities to adulthood. Then, males are singled out with a variety of methods (which I won't go into here...feel free to dig up the sources via google scholar), sterilized and released into the field in droves. This is preferable to pesticides because the technique is generally very environmentally friendly and species specific-no chance innocent bugs getting caught in the crossfire or people accidentally being exposed to pesticide.

This technique has been used with great success against the tsetse fly of Africa and on the screw-worms of North America. The tsetse flies (Glossnia ssp.) are best known for transmitting trypanosomaisis, or sleeping sickness as it's commonly known. It's a horrible disease, and some of the treatments are fatal about 10% of the time. The disease is usually fatal in most people who remain untreated. Fortunately, we can control it's vector. If we control it's vector, it can't pass from person to person. If it can't pass from person to person, the disease dies out. Screwworms aren't disease vectors for humans...and don't really affect us but their effects on cattle are even more horrifying. Adults are attracted to open wounds, where they lay their eggs. The larvae hatch, start eating the living flesh, and the scents released while they feed attract more female screwworm flies. At the very least, the cattle lose value and lose weight. Infestations resulting in death weren't uncommon before the measures were taken to eradicate the pest.

In controlling trypanosomiasis and screwworm flies, scientists use radiation (usually Cobalt-60, but also X-rays) to sterilize male flies and release them on the wild population so they mate with females. Many insects mate only once, and this would cause the female to lay infertile eggs or in the case of tsetse flies whose larvae develop internally, expel dead larvae. This causes a drop in the population of the target insect species, and the process is repeated for the next generation. Sooner or later, the number of sterile males outnumber the wild-type fertile males and eventually the population goes extinct.

Unfortunately, there are some drawbacks to this procedure. For example, one has to know that there will not be much migration into an area. If outside females who have already mated can immigrate into an area on a regular basis and reproduce, this tactic only becomes good for suppression. One of the biggest drawbacks is the fact that it's simply not economical. It has to have backing from a wealthy country like the US or United Nations in many cases and it is very labor intensive. This technique has been used for some agricultural pests (pink bollworm and the Mediterranian fruit fly to name a few), but would be ineffective for parthenogenic sawflies and aphids because they do not rely on males to reproduce. So it's not a silver bullet...but for many species which reproduce sexually, it's definitely effective. Many areas of Africa are now free of tsetse flies because of this technique, and the US hasn't seen an infestation since 1966

Many times, the flies are sexed manually when pupae by trained professionals. Other times, insects may be genetically modified with a gene coding for insecticide resistance on the Y chromosome. After this, they need to be carted into packages, refrigerated and dispersed around the habitat...sometimes by air. Of course, the biggest problem is when the equipment breaks down. In one case, a facility using the SIT had it's irradiation equipment fail and accidentally released millions of fertile male screwworms into the environment. These types of mistakes would simply set the project back awhile, but not render it ineffective.

This technique creates a lot of waste in terms of insects. Only about half the insects produced by any given facility can be used for two reasons. One reason is that in many cases, it's the female and only the female who can transmit disease. A female with non-working reproductive parts can and will take blood meals, which means they can still be disease vectors. The second reason is that mixed releases are simply inneffective. The goal is to get the males to spread throughout the area. Unfortunately, male insects have the 'dude in a nightclub' mentality-they won't spread out if they're released with females.

Why go prowling if you can get laid right at home? I've stayed in many a crappy nightclub for no other reason than because I was having success with the women there...and the same principle applies here.

http://www.ars.usda.gov/is/pr/2002/020828.htm

Alphey, L. (2002). Re-engineering the sterile insect technique. Insect Biochemistry and Molecular Biology, 32(10), 1243-1247. DOI: 10.1016/S0965-1748(02)00087-5

Pedigo, Larry P., Rice, Marlin E. (2009). Entomology and Pest Management (6th ed). New Jersey: Pearson Education

Vreysen, M.B., Saleh, K.M., Ali, M.Y., Abdulla, A., Zhu, Z., Juma, K.G., Dyck, A., Atway, M.R., Mkonyi, P.A., , . (2000). Glossnia austeni (Diptera: Glossinidae) Eridicated on the Island of Unguja, Zanzibar Using the Sterile Insect Technique. Journal of Economic Entomology, 93(1), 123-135.

Bacterial endosymbiont is a major causative agent of morbidity associated with filarial nematode infections.

Wolbachia is one of my favorite bacteria, I've actually given it it's own label on the blog. It does all sorts of strange things, like dictate the gender of the host’s offspring. Wolbachia lives in the eggs of it’s insect hosts, being passed on from mother to daughter. If they end up in a male, they dead-end because they cannot be passed on through sperm. Instead, they kill any potential male offspring the female has or makes infected males unable to have offspring with uninfected females depending on what species they infect.

However, Wolbachia is actually a somewhat common endosymbiont in insects and nematodes. Although it’s famous for the effects on insects I mentioned earlier, Wolbachia actually has a major role in medicine despite not actually being a human pathogen.

200 million people around the world suffer from a disease called river blindness. This disease is spread by parasitic flies through the bite. When a fly bites a human, it injects nematode larvae in it’s saliva. Once inside the body, these nematodes form nodules under the skin. They mate and then produce larvae which migrate through the skin, looking to be taken up again by a Simulium host.

The larvae when alive don’t really cause a whole lot of damage. Being a parasite, they’ve evolved ways to become invisible to the host’s immune system. The damage from river blindness comes from when the nematodes die. When they die, they become visible to the host’s immune system which subsequently responds, with many different responses but inflammation is the response responsible for the damage that causes the blindness. If the larva happens to be in the eye when this happens, then this can be very serious.

However, the nematode’s body isn’t the only thing that causes the immune response. Scientists studying Onchocerca volvulus have discovered that the effects of the dying larvae are greatly excasterbated by their Wolbachia endosymbiont.

Scientists took extracts from nematodes, nematodes treated with an antibiotic and nematodes that didn’t harbor Wolbachia and injected them into the eyes of mice. Nematodes treated with the antibiotic doxycycline as well as nematodes which don’t harbor Wolbachia triggered less of an immune response than did nematodes who had Wolbachia endosymbionts. To the scientists, this indicated that something in the Wolbachia cells and not the nematode cells caused the inflammation and other immune responses.

But what in the Wolbachia cells could trigger a response?

Wolbachia are a gram-negative bacteria, which means that a major portion of their outer cell wall is formed from a macromolecule called bacterial lipopolysaccaride (LPS). A receptor called Toll Like Receptor 4 (TLR4) is a major part of response to bacterial infection. Since TLR4 responds to LPS, it was a natural candidate for testing.

To test the link between the Wolbachia LPS and the immune response, the researchers used mice with a mutation in the TLR4 gene that made them less sensitive to LPS to determine if this was the cause. Once again, extracts containing Wolbachia were injected into the mice and their immune responses measured.

As one would expect, those mice with an underresponsive TLR4 receptor displayed less severe symptoms than did mice with a normal TLR4 gene. This means that instead of the nematodes causing the inflammation and other immune responses associated with river blindness, it’s actually their endosymbionts that cause those types of problems.

This opens up a whole new avenue of potential research into new treatments for river blindness. Since we now know that it is not the larvae that cause river blindness we can focus on the real culprit, Wolbachia. The Wolbachia are vital endosymbionts-the nematodes don’t properly develop without the bacteria in the system. This means by focusing our efforts on Wolbachia we not only prevent the LPS from the Wolbachia being released when the filarae die, we drastically reduce the numbers of said filarae because without the Wolbachia the nematodes are unable to reproduce.

Saint Andre, A.V., Blackwell, N.M., Hall, L.R., Hoerauf, A., Brattig, N.W., Volkmann, L., Taylor, M.J., Ford, L., Hise, A.G., Lass, J.H. (2002). The Role of Endosymbiotic Wolbachia Bacteria in the Pathogenesis of River Blindness. Science, 295(5561), 1892-1895.

Hymenorrhaphy

This blog is mostly an entomology/evolution/general science blog because political/human rights bloggers are a dime a dozen, but I do dip into culture and politics every once and awhile. I'm also not a medical blogger, so this is also kind of new for me. Aside from reading about science, I also read up on human rights and such. The rights of women are important to me and they should be important to anyone who reads this.

One of the things that's always puzzled me about religion is the concept of virginity until marriage. I've always lived in a culture where it was considered unrealistic. According to the CDC, well over half of people are sexually active by their twenties. And here in America, it's usually considered a surprise if you're a virgin when you exit high school. If you're a male, it's considered a dishonor.

It's always struck me as just a way for men to stake their territory. While great significance is placed a woman's virginity, a male's virginity is considered a burden. Examples of double standards abound and there's no reason to expound on them.

Virginity is a very important part of many cultures in the world, but nowhere else is it more important than the Mideast. Women who have sexual relations before marriage risk being disowned by their families, or worse.

In many parts of the world, women are still treated as nothing but property...and little valued property at that. Nobody would beat their motorcycle because somebody has ridden it, however in many parts of the world women are beaten to death for precisely this reason. There have been cases in middle eastern countries where women were beaten to death for talking to westerners. Women have been beaten to death for standing up to or leaving their abusive husbands.

As late as 1994, virginity tests for schoolgirls were still common in Turkey.

Usually, virginity is determined by inspecting the hymen. The hymen is a thin, collagenous membrane that covers the vagina at birth. Many people believe that the hymen breaks during the first insertion, however this may not be necessarily true. It can break from trauma, strenuous physical activity such as gymnastics or biking or a multitude of other things. Some women may be born without one.

This creates a problem for women in cultures similar to the examples I mentioned previously. Women in Europe experience less stringent sexual norms than we have here in America, and since the population of Muslim families is increasing this results in women who may feel like they're caught between the worlds of their family and the culture they know. Similar pressures are felt by women in America who hail from places in Central and South America.

If the hymen breaks, either through excersize or intercourse, this could create a problem for women in hyper-conservative cultures. They risk dishonor, violence and death. In some cultures, this will go so far as to force the women to marry her attacker to maintain her honor.

Fortunately for them there is a solution in the form of hymenorrhaphy, or 'hymen reconstruction' in laymen's terms. This surgery, in some parts of the world, can literally save the lives of women in many cases.

The surgery is a relatively minor procedure. Patients may remain conscious after being given a local anesthetic or may be unconscious during the procedure after being given a general anesthetic.

In many cases, the hymen is barely damaged and can be reconstructed by simply stitching the remnants together with dissolveable sutures. In surgeries such as this, gelatin capsules may be inserted to simulate post-coitus bleeding.

In other cases, a flap of the vaginal lining may be used to create a new hymen. In this case, the new hymen will have it's own blood supply and the capsule will not be needed.

In many countries, these procedures are banned because they're viewed as dishonest. Many feminists also scoff at the notion of procedures used to restore the appearance of virginity. Moreover, these procedures aren't cheap...the cost can be between $2,000 and $4,000 in Europe.

Works cited/more information:

http://www.reuters.com/article/worldNews/idUSL2532025120070430
http://www.tcclinic.com/hymen-restoration-toronto.php
http://www.miklosandmoore.com/hymen.php
http://www.obgyn.net/english/pubs/features/presentations/hennawy13/hymenorrhaphy.ppt