Scientists combine spider venom and virus protein to target whitefly
An artificial insecticidal protein could be a powerful control tool for the whitefly, a pest that attacks crops such as soybeans, cotton, beans and tomatoes. Biotechnology tools have allowed scientists from Embrapa Hortaliças (DF) to develop a protein formulated from the association of two others: a toxic and another belonging to a begomovirus, a microorganism transmitted by the whitefly itself.
Artificial protein is obtained by fusing the protein coat protein (CP) of the virus - responsible for forming an envelope that lines the genetic material of that microorganism - with a toxic molecule isolated from
the venom of spiders. This molecule has a lethal and insect-specific effect as long as it reaches the hemolymph (blood circulating in the vessels of invertebrate animals analogous to blood in vertebrate animals) and reaches the central nervous system of the insect, causing paralysis. In general terms, the hypothesis is that when the insect ingests the fusion protein, CP transports the toxic molecule from the digestive system to the circulatory system and from there to the nervous system, where the neurotransmitter blockage occurs Spasms in the insect-plague until it causes his death.
The ingestion of only the toxic molecule by the whitefly does not have an effect because, once in the digestive tract, it is excreted by the insect before it reaches hemolymph. It is precisely at this point that CP enters the virus to act as a Trojan horse and allow the venom to reach its destination. In the body of the insect, the virus has a circulatory cycle and this allows it to transit from the digestive tract to the hemolymph. Thus, the fusion protein adds the effect of the toxic molecule of spider venom to the mechanism of circulation of the virus within the insect and thus promotes a breakdown in the functioning of the whitefly organism.
According to biologist Erich Nakasu, Research and Development analyst at Embrapa Hortaliças (DF), the major challenge of research is not to synthesize the fusion protein, but to ensure that the toxic protein is produced in conjunction with the viral protein coat, and that Keep protected inside the body of the insect against its natural defense mechanisms to then reach the site of action in a condition to express the toxic effect, causing the death of the insect.
"There are two possibilities outlined to achieve the toxic effect: developing a plant that expresses the fusion protein, being the source of the product toxic, or feeding the insect with an artificial diet," he says, noting that the next step will be to test this method Of control of the pest in greenhouse under controlled conditions.
Specific action for whitefly
As the fusion protein is formulated based on the begomovirus cover protein, a microorganism transmitted exclusively by the whitefly, the specificity of the toxic action is assumed only for this insect-plague. In this way, the fusion protein has a detrimental effect only on the whitefly and does not compromise a non-target insect, preserving ladybugs, for example, that are natural enemies of the pest, and bees, important pollinators.
In nature, animals that feed on pests generally produce and inject toxins into their prey. "The specific toxin being evaluated in the project, extracted from the venom of the spider, has specific action and causes damages only in insects. In vertebrates, in general, including humans, this toxin causes no harmful consequence or deleterious effect, "explains the biologist who also points out that the experiments follow the standards of the National Technical Commission on Biosafety (CNTBio) and that the laboratory has quality certification .
There is a scientific tendency to test the use of fusion proteins in pest control, however, the application of this methodology in whiteflies is unprecedented and, if the results are positive, a great advance in the integrated management of this pest can occur. , Is currently based mainly on chemical control, which can be detrimental to the sustainability of agricultural production.
The prospect of successful research is mainly due to the expertise of the team of scientists. Nakasu, in his doctoral thesis at Newcastle University and Durham University in the United Kingdom, worked on the evaluation of a fusion protein originated from the combination of the venom of a certain spider species with a substance found in flowers of the family Amaryllidaceae , But at the time the target of the control were aphids. He also analyzed the effect of this fusion protein on memory and learning ability of beneficial and non-target insects such as bees, concluding that there are no complications for these insects.
The whitefly is a pest that does not distinguish between food and, due to the high degree of polyphagia, keeping it under control is a task that has mobilized efforts from various productive chains that are concerned with the negative impact on productivity. Large crops such as soybean and cotton host the pest and feel the damage caused by the sucking of the sap, however, they are secondary to the losses of rust and bulrush, the main pests of these crops, respectively.
In the case of tomato, in addition to acting as a sucking insect that compromises the development of the plant and injects toxins capable of spoiling the fruits, the whitefly also transmits viruses that affect crop productivity and generate losses of up to 50%. Some producing regions have adopted the sanitary void, which foresees a period without live tomato plants in the field, to try to control the population level of the whitefly. However, to ensure success in controlling this pest, rather than rely on public policies implemented by plant protection agencies, it is necessary to propose to the farmers a rational management in order to maintain the sustainability of the entire system and, in this part, scientific research.
The whitefly is a sap-sucking insect that transmits viruses. In addition to damaging the normal development of the plant, which naturally reduces production, in the feeding process, the whitefly injects toxins that, in the case of the tomato, cause uneven maturation and isoporation of the fruits. As for viruses, the pest can transmit to the tomato the begomovirus, the crinivirus or even both, which is called a viral mixture. This possibility worries the research, which already questions whether the combination may interfere with the management of other tomato viruses, such as the tospovirus, transmitted by the thrips. With mechanisms that favor adaptation under extreme conditions, the whitefly has a high fertility rate, in addition to parthenogenesis, that is, the female is able to produce clones that will maintain possible genes for resistance to chemicals, Which facilitates the establishment of the population.
Origin of the whitefly
It is believed that the whitefly originated in the Middle East and from there it expanded to parts of Africa and Europe until it crossed the ocean and reached the Americas in the early 1990s. The population explosion of the pest was practically In the United States and Brazil and, in our country, found conditions very favorable to development. The viruses transmitted by the insect to the tomato, for example, come from the Brazilian flora. "The whitefly facilitated the transfer of native viruses that were previously restricted to weeds. Before, there was not a vector-insect that would be efficient in acquiring the weed virus and transmitting it to the tomato, "explains researcher Miguel Michereff Filho, from the Entomology area of Embrapa Hortaliças.
Production pole unviable by the whitefly
Due to the inadequate management, in the mid-1990s, tomaticultura in the agricultural center of Petrolina (PE) was greatly affected by the whitefly, and with this, the processing industry had to migrate production to the Midwest. Currently, Goiás is the largest tomato producer in the country, with more than 30% of the national production of the fruit, and to prevent the pest from compromising the sustainability of the productive system in the region, as happened in the Northeast, the agricultural defense agency State approved a normative instruction that provides for the implementation of the sanitary void for the tomato between the months of November and January. "This time of year is problematic because there are other crops that are hosts of the whitefly, for example, soybeans. Therefore, the longer the tomato producer delays the planting to not coincide with the soybean harvest, which is when the whitefly moves in search of other crops, the smaller the chances of having a high insect population at the beginning of the Establishment of the tomato crop, when the plants are more vulnerable, "analyzes the researcher who recommends the months of February and March to start planting the tomato.
In order to ensure the effectiveness of the sanitary void, the defense organs supervise nurseries producing seedlings, which must submit reports with information on buyers, marketed volume and time of sale. Another aspect of the inspection is the sampling of poles of production to check if, in the off season, there is tomato cultivation in the field or tigueras, that is, vegetable remains that are not harvested and stay in the field until it sprouts again. These plants are worried that they can serve as a source of virus and may hamper the breakdown in the disease cycle, which is the main objective of the sanitary vacuum. According to Michereff, the research identified that the rate of virus transmission among tomato plants is much higher than that of weeds for tomato, hence the importance of eliminating any green plant in the field.