Scale insects like to be parasitic on many kinds of fruit trees, flowers, and crops. For example, succulent plants, apricot, and apple trees attract them a lot. Besides, the honeydew they secrete can cause sooty mildew. Therefore, it is extremely important for the farmers to prevent the rampancy of scale insects. Scale insects vary in appearance, but the common thing is that they all secrete a waxy coating as their “armor”.
To control the effect of the scale insects on farming, nowadays farmers kill scale insect by injecting pesticides into the trunk. So when the scale insect bites the trees, they would be killed. However, chemical method would result in the resistance of the insects to drugs. And there is a possibility that the whole food chain would be changed and the ecological balance would be destroyed. In order to bring convenience and safe to farmers, we decide to create a special bio-safe pesticide, making the deinsectization process faster, stronger and better.
Introduction
Our thought of this project comes from the basic structure of the scale insect. According to other researches, the thick shell of the insect is made of three different kinds of material: a layer of wax secreted by the insect, a layer of chitin, and a layer of protein. These substances compose the harsh shell of the scale insect. Since it is a combination of wax, chitin and protein, we consider that maybe we can decompose them layer by layer, and finally destroy its shell. Without its shell, it is extremely difficult for it to stay alive, and any kind of pesticide would be able to kill that insect easily and immediately. Therefore, we put this idea forward: decompose its shell layer by layer, and finally get the result that its harsh shell is destroyed.
Since this kind of insects always damage fruit trees and succulent plants, it is important that we should keep them safe while killing those insects. Otherwise, those fruits may be stained. Thus, we design a suicide process to let bacteria suicide after wipe out those pests. After killing the insect, bacteria would kill themselves because of the suicide gene. In this way, we can ensure that our method won’t affect any plants or fruits.
Parts Description
According to the thesis*1, we know that chitinase and protease are playing the most important role when the entomopathogen is trying to infect the scale insects. Entomopathogen needs chitinase to resolve the chitin layer of insects and needs protease to resolve the protein layer of insects. Base on this information, we transmit the chitinase gene and the protease gene to E. coli so that our E. coli can “open” the Chitin layer and Protein layer easily.
In another thesis*2, we found a specific entomopathogen named Verticillium lecanii. These kind of fungi are parasitic on scale insects, and they use chitinase, protease to “open” the shell of scale insects just like the description in thesis1. Thus, we use the chitinase gene (Genbank number: ) and Protease gene(Genbank number: )that has been found in Verticillium lecanii. Now our E. coli has two incisive “swords” and we can achieve our final goals.
Now we can “open” the shell of scale insects easily, but how can our E. coli distinguish the scale insects successfully? We do not want our E. coli to produce chitinase and protease all the time, since those two enzymes may cause damage to plants. We solve this problem by using a special promoter. SacB promoter is a great promoter that can recognize cane sugar. And we know that scale insects secrete honeydew that contains amino acid and sugar, such as cane sugar. Those secretions can cling on the surface of the scale insect’s shell. Above all, if we put SacB promoter gene into our E. coli, they would recognize scale insects easily and specifically. Then, if our E. coli meet some cane sugar that is placed on the surface of scale insects, another gene will be waken and start to be translated.
You may be confused now, but I am going to explain that. First, you should know that the two enzymes, chitinase and protease, are not exocrine enzymes. So how can they touch the layers of scale insects? The special gene mentioned above – S-RRz will do this job. This gene can split the cytomembrane of E. coli in 30 min and let our enzymes come out. And now, our enzymes can start working and destroy the shell of scale insects.
Expected Result
According to our explanation above, it is necessary to predict the result we would get from this project. As we all know, scale insect is the nightmare of many succulent plants and fruit, so probably this project would be used in agriculture and farming. We can design a pesticide kit that contains 3 kinds of engineered E.coli, which are separately designed to produce 3 kinds of enzymes. Farmers can easily mix them together at a certain portion and spread the pesticide to the scale insect. Since we don't want E.coli to have any competition with each other, those 3 kinds of E.coli should be cultivated and kept separately, and they would only be mixed just before people spray trees or crops with the final insecticide.
In order to eliminate the possibility of damage during transportation process from the lab or pesticide company to the customer, we collaborate with team SIAT-SCIE. The special technique developed by team SIAT-SCIE would keep our product safe and make it convenient enough for long-time transportation. Thanks to team SIAT-SCIE, our project becomes more reliable, controllable and applicable.
