Environmentally Friendly Pest Control: Potential and Efficacy Test of Bacillus thuringiensis as an Insecticide

The extensive use of chemical pesticides since the introduction of DDT in the 1940s has had a significant impact on agriculture and public health. DDT and other synthetic insecticides have proven effective in protecting crops from pests and controlling human disease vectors. However, uncontrolled use over a long period of time has caused serious problems such as environmental pollution, damage to beneficial insect populations, and the emergence of pest resistance to these chemicals.

Awareness of these negative impacts has triggered a shift towards more environmentally friendly pest control methods. One emerging approach is the use of microbial-based insecticides, especially Bacillus thuringiensis (Bt), which is a Gram-positive bacterium that produces insecticidal proteins. Bt and other entomopathogenic microorganisms, such as bacteria, viruses, and insect-pathogenic nematodes, offer a safer solution for the environment and human health. They are effective in controlling specific pests without damaging the ecosystem as a whole.

However, before being widely used, microbial-based insecticides, including Bt, need to go through rigorous efficacy tests. This efficacy test is important to ensure that the insecticide is truly effective in controlling the target pest, without affecting non-target organisms. This testing process also ensures that the microbes used can be mass-produced and remain stable in commercial formulations. Thus, microbe-based insecticides are not only environmentally friendly, but can also be relied upon for sustainable pest control. 

What is Bacillus thuringiensis?

Bacillus thuringiensis (Bt) is a Gram-positive spore-forming bacterium that produces several types of insecticidal proteins that are effective against a variety of insect pests. For decades, Bt has been proven to be safe and potent as a biological pest control agent.

Insecticidal proteins produced by Bt include crystalline proteins known as delta-endotoxins (such as Cry and Cyt toxins) and vegetative insecticidal proteins (Vip) such as Vip1, Vip2, and Vip3. Vip1 and Vip2 toxins are primarily active against insects of the order Coleoptera, while Vip3 is effective against insects of the order Lepidoptera.

The toxins produced by Bacillus thuringiensis (Bt) work by causing lysis of the epithelial cells of the midgut of insects, particularly Lepidoptera. After the toxin is ingested, within the first 5 minutes there is an increase in glucose absorption in the intestinal cells, followed by histopathological changes. The midgut becomes paralyzed, columnar cells begin to swell, and microvilli swell. Goblet cells also undergo changes, although more slowly. Within 30 minutes, potassium ion activity in the intestinal cells increases, causing a decrease in blood potassium levels, as well as a decrease in leucine and glucose, which ultimately triggers metabolic damage to the intestinal cells. The cells begin to lyse and detach from the basement membrane. General paralysis occurs within 1 to 7 hours, and within 1 to 3 days, the insects die from starvation. 

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Advantages of Using Bacillus thuringiensis as a Pesticide.

The use of Bacillus thuringiensis (Bt) as a pesticide has several advantages compared to chemical pesticides. First, Bt is an environmentally friendly bioinsecticide because it works specifically on target insect pests without harming other organisms, including pollinating insects, natural predators, and non-target animals. This is different from chemical pesticides that often kill beneficial insects and pollute the environment. Second, Bt has a lower risk to human and animal health because its toxins are only active on certain insects, making it safe to use on food crops. Third, the use of Bt can help reduce pest resistance to pesticides, because the proteins it produces have unique and diverse working mechanisms. In addition, Bt can be mass-produced and applied in the form of sprays or inserted into transgenic plants, such as corn and cotton, which makes it effective for long-term control. Thus, Bt offers a more sustainable and safe pest control solution compared to chemical pesticides. 

The use of Bacillus thuringiensis (Bt) as a pesticide not only provides advantages in terms of environmental friendliness and safety, but also high work efficiency. When applied as an insecticide, Bt particles that miss their target insects and fall to the ground can degrade and act as a pesticide-based fertilizer. This process helps enrich the soil with organic matter while maintaining its pest control properties, creating a beneficial cycle for soil and plant health. In addition, Bt works effectively by attacking the digestive tract of target insects without affecting non-target organisms, making its use more economical and targeted than chemical pesticides. This efficiency also extends the life of crop protection because Bt toxins remain active for a period of time after application, providing long-term protection against pests. With the ability to control pests specifically and sustainably, as well as providing the added benefit of being a fertilizer, Bt is an efficient and economical choice for pest management.

Bacillus thuringiensis Efficacy Test

Efficacy testing of Bacillus thuringiensis (Bt) as a pesticide is an important step to ensure its effectiveness in controlling insect pests before its widespread use. There are several methods that are often used to test the efficacy of Bt, including:

Laboratorium Bioassay Test

This method is carried out in the laboratory using target insects in a controlled environment. Insect larvae are fed food mixed with Bt suspension, then observed to see the effects of the toxin on mortality and physical changes in insects. The results of this bioassay test provide important information about the level of Bt toxicity to different pest species.

Limited Field Test

Limited field trials are conducted on a small scale in agricultural areas to assess the performance of Bt under real environmental conditions. In this method, Bt is sprayed on crops susceptible to pest attack, and the pest population is monitored over a period of time. This method helps determine the effectiveness of Bt in reducing pest populations in the natural environment while ensuring that there are no negative effects on non-target organisms.

Stability and Residual Test

This method tests how long the Bt toxin remains active in the field after application. Plants that have been sprayed with Bt are tested periodically to see if the toxin is still effective at killing pests after some time. The stability of Bt under various environmental conditions, such as exposure to sunlight and rain, is also tested to determine how often applications need to be repeated.

All three of these methods are critical to ensuring that Bt is effective, safe, and sustainable as a bioinsecticide.

 

Author: Dherika

References

Kumar, P., Kamle, M., Rituraj, B., Dipendra, K.M., & Bharti, S. (2021). Bacillus thuringiensis as Microbial Biopesticide: Uses and Application for Sustainable Agriculture. Egyptian Journal of Biological Pest Control, 31(95): 1-7. https://doi.org/10.1186/s41938-021-00440-3.

Peralta, C., & Palma, L. (2017). Is the Insect World Overcoming the Efficacy of Bacillus thuringiensis?. Toxins, 9(39): 1-5. Doi:10.3390/toxins9010039.

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