Over-populated free roaming species can pose a large problem for society. Certain methods of population control include surgical castration, however a great number of societies have recently imposed restrictions on this form of sterilizing, due to ethical reasons and animal welfare legislations. There is a possibility of many complications, including bleeding, infection, and risks of anesthesia. So, other forms of sterilization have been imposed, known as chemosterilants.
A chemosterilant is a chemical compound that causes reproductive sterility in an organism. They may be used to control pest populations by sterilizing males. More technically, a chemosterilant is any chemical compound used to control economically destructive or disease-causing pests (usually insects) by causing temporary or permanent sterility of one or both of the sexes or preventing maturation of the young to a sexually functional adult stage.
Some examples of chemosterilants include CaCl2 and zinc gluconate. These are specifically known as necrosis-inducing agents, which result in the degeneration of cells in the testes, resulting in infertility. These kinds of chemicals are generally injected into male reproductive organs, such as the testes, vas deferent, or epididymis. When injected, they induce azoospermia, which is the degeneration of the sperm cells normally found in the semen. If no sperm cells are present, reproduction can no longer occur. There is, however, one complication that results from the use of necrosis-inducing agents. A lot of animals generally exhibit an inflammatory response directly after the injection. To avoid the pain and discomfort associated with necrosis-inducing agents, another form of sterilization was being studied, known as apoptosis inducing agents. If cells are signaled to perform apoptosis rather than being eliminated by a foreign substance, this will result in no inflammation in the area. Experiments were tested using mice in vitro and ex vivo that have proved this. Using an apoptosis inducing agent, known as doxorubicin encapsulated in a nanoemulsion, and injecting it into mice, testicular cell death was observed. Inflammation was not observed in this case, however more research still needs to be conducted with these materials, as the long term impacts are unknown.
Another chemosterilant found to be effective is known as ornitrol. This chemosterilant was provided to sparrows by impregnating canary seeds, and this was used as a food source for a group of sparrows. There was a control group that was fed canary seeds without the ornitrol, and these birds laid almost twice as many eggs as group that was given ornitrol. It was deemed an effective chemosterilant in the study, however after the removal of the chemosterilant from the diet, the birds were able to lay viable eggs as soon as 1-2 weeks later. 
The mating of sterilized insects with fertile insects produces no offspring, and if the number of sterile insects is kept constant, the percentage of sterile insects will increase, and fewer young will be produced in each successive generation. Chemosterilants should be applied in the larval or pupal stage of the insect to give rise to sterile adults or in the newly emerged adults before they become sexually mature.
Two types of chemosterilants are commonly used:
- Antimetabolites resemble a substance that the cell or tissue needs that the organism's body mistakes them for a true metabolite and tries to incorporate them in its normal building processes. The fit of the chemical is not exactly right and the metabolic process comes to a halt.
- Alkylating agents are a group of chemicals that act on chromosomes. These chemicals are extremely reactive, capable of intense cell destruction, damage to chromosomes and production of mutations.
- Pagseesing, S.; Yostawonkul, J.; Surassmo, S.; Boonrungsiman, S.; Namdee, K.; Khongkow, M.; Boonthum, C.; Iempridee, T. et al. (28 April 2021). "Formulation, physical, in vitro and ex vivo evaluation of nanomedicine-based chemosterilant for non-surgical castration of male animals". Theriogenology 108: 167–175. doi:10.1016/j.theriogenology.2017.12.014. PMID 29223654. https://www.sciencedirect.com/science/article/abs/pii/S0093691X17306039.
- HAYES WJ Jr (1964). "The toxicology of chemosterilants". Bulletin of the World Health Organization 31: 721–36. PMID 14278008.
- Baxter, Richard H. G (2016). "Chemosterilants for Control of Insects and Insect Vectors of Disease". Chimia International Journal for Chemistry 70 (10): 715–720. doi:10.2533/chimia.2016.715. PMID 27779930.
- Mitchell, Carl J.; Hayes, Richard O.; Hughes, T. B. (28 April 2021). "Effects of the Chemosterilant Ornitrol on House Sparrow Reproduction". The American Midland Naturalist 101 (2): 443–446. doi:10.2307/2424610. https://www.jstor.org/stable/2424610.
- Carson, Rachel (2002) [1st. Pub. Houghton Mifflin, 1962]. Silent Spring. Mariner Books. ISBN:0-618-24906-0
Original source: https://en.wikipedia.org/wiki/ Chemosterilant. Read more