Scientists combine spider venom and virus protein to target whiteflies

An artificial protein with insecticidal action could be a powerful tool for controlling whiteflies, a pest that attacks crops such as soybeans, cotton, beans and tomatoes. Biotechnology tools have allowed scientists at Embrapa Hortaliças (DF) to develop a protein formulated from the association of two others: one toxic and the other belonging to a begomovirus, a microorganism transmitted by the whitefly itself.

The artificial protein is obtained through the fusion of the virus's protein coat protein (CP) – responsible for forming an envelope that covers the genetic material of this microorganism – with a toxic molecule isolated from spider venom. This molecule has a lethal and specific effect on insects as long as it reaches the hemolymph (a liquid that circulates in the vessels of invertebrate animals, analogous to blood in vertebrate animals) and reaches the insect's central nervous system, 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 neurotransmitters are blocked that cause spasms in the pest insect until it causes its death.

Ingestion of just the toxic molecule by the whitefly has no effect because, once in the digestive tract, it is excreted by the insect before reaching the hemolymph. It is exactly at this point that the virus' CP comes in to act as a Trojan horse and allow the poison to reach its destination. In the insect's body, the virus has a circulatory cycle and this allows it to travel from the digestive system to the hemolymph. Therefore, the fusion protein adds the effect of the toxic molecule of spider venom to the virus circulation mechanism within the insect and, thus, causes a breakdown in the functioning of the whitefly organism.

For biologist Erich Nakasu, Research and Development analyst at Embrapa Hortaliças (DF), the biggest challenge of the research is not to synthesize the fusion protein, but to ensure that the toxic protein is produced together with the viral protein coat, and that it keep it protected inside the insect's body against its natural defense mechanisms to then reach the site of action in a condition to express the toxic effect, causing the insect's death.

“There are two possibilities outlined to achieve the toxic effect: developing a plant that expresses the fusion protein, being the source of the toxic product, or feeding the insect with an artificial diet”, he states, highlighting that the next step will be to test this method. pest control in greenhouses under controlled conditions.

Specific action for whiteflies
As the fusion protein is formulated based on the coat protein of the begomovirus, a microorganism transmitted exclusively by whiteflies, the specificity of the toxic action is assumed only for this insect pest. In this way, the fusion protein has a harmful effect only on whiteflies and does not compromise a non-target insect, preserving ladybugs, for example, which are natural enemies of the pest, and bees, important pollinators.

In nature, animals that feed on pests often produce and inject toxins into their prey. “The specific toxin being evaluated in the project, extracted from spider venom, has a specific action and causes damage only to insects. In vertebrates, in general, including humans, this toxin does not cause any harmful consequences or deleterious effects”, explains the biologist who also highlights that the experiments follow the standards of the National Technical Commission for Biosafety (CNTBio) and that the laboratory has quality certification. .

There is a tendency in scientific circles to test the use of fusion proteins in pest control, however, the application of this methodology to whiteflies is unprecedented and, if the results are positive, a major advance could occur in the integrated management of this pest that , currently, is mainly based on chemical control, which can be detrimental to the sustainability of agricultural production.

The prospect of research success is mainly due to the expertise of the team of scientists. Nakasu, in his doctoral thesis, carried out at Newcastle University and Durham University, in the United Kingdom, worked on the evaluation of a fusion protein originating from the combination of the venom of a certain species of spider with a substance found in flowers of the Amaryllidaceae family. , but at the time the control target was aphids. He also analyzed the effect of this fusion protein on the memory and learning capacity of beneficial and non-target insects, such as bees, concluding that there are no complications for these insects.

The whitefly
The whitefly is a pest that does not distinguish between food and, due to the high degree of polyphagy, keeping it under control is a task that has mobilized efforts from several production chains that are concerned about the negative impact on productivity. Large crops such as soybeans and cotton host the pest and feel the damage caused by sap suction, however, these are secondary to the damage caused by rust and boll weevil, the main pests of these crops, respectively.

In the case of tomatoes, in addition to acting as a sucking insect that compromises the plant's development and injects toxins capable of damaging the fruits, the whitefly also transmits viruses that affect crop productivity and generate losses of up to 50%. Some producing regions have adopted a sanitary vacuum, which provides for a period without live tomato plants in the field, to try to control the whitefly population level. However, to guarantee success in controlling this pest, more than relying on public policies implemented by plant defense bodies, it is necessary to propose rational management to farmers in order to maintain the sustainability of the entire system and, in this part, the scientific research.

The whitefly is a sap-sucking and virus-transmitting insect. In addition to harming the normal development of the plant, which naturally reduces production, during the feeding process, the whitefly injects toxins that, in the case of tomato plants, cause uneven ripening and the isoporization of the fruits. As for viruses, the pest can transmit begomovirus, crinivirus or both to tomatoes, which is called a viral mixture. This possibility concerns research, which is already questioning whether the combination could interfere with the management of other tomato viruses, such as tospovirus, transmitted by thrips. With mechanisms that favor adaptation in extreme conditions, the whitefly has a high fecundity rate, in addition to having parthenogenesis as a characteristic, that is, the female is capable of producing clones that will maintain possible genes for resistance to chemical products, the which facilitates the settlement of the population.

Origin of the whitefly
It is believed that the whitefly originated in the Middle East and, from there, expanded to regions of Africa and Europe until crossing the ocean and reaching the Americas in the early 1990s. The pest's population explosion was practically simultaneously in the United States and Brazil and, in our country, it found very favorable conditions for development. The viruses transmitted by insects to tomatoes, for example, come from Brazilian flora. “The whitefly facilitated the transfer of native viruses that were previously restricted to weeds. Before, there was no insect vector that was efficient in acquiring the virus from the weed plant and transmitting it to the tomato”, explains researcher Miguel Michereff Filho, from the Entomology area at Embrapa Hortaliças.

Production hub made unviable by whitefly
Due to inadequate management, in the mid-1990s, tomato farming in the agricultural hub of Petrolina (PE) was severely damaged by whiteflies and, as a result, the processing industry had to migrate production to the Center-West. 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 production system in the region, as happened in the Northeast, the agricultural defense body State approved a normative instruction that provides for the implementation of the sanitary void for tomatoes between the months of November and January. “This period of the year is problematic because there are other crops that are hosts to whiteflies, for example, soybeans. Therefore, the longer the tomato producer delays planting so as not to coincide with the soybean harvest, which is when the whitefly moves in search of other crops, the lower the chances of there being a high population of insects at the beginning of the season. establishment of tomato crops, when the plants are most vulnerable”, analyzes the researcher who recommends the months of February and March to begin tomato planting.

In order to guarantee the effectiveness of the sanitary vacuum, the defense agencies supervise seedling production nurseries, which must present reports with information on buyers, volume sold and time of sale. Another aspect of inspection is the sampling of production centers to check whether, in the off-season, there is cultivation of tomatoes in the field or tigueras, that is, vegetable remains that are not harvested and remain in the field until they sprout again. These plants are a concern because they can serve as a source of viruses and harm the break in the disease cycle, which is the main objective of the sanitary vacuum. According to Michereff, research has identified that the rate of virus transmission between tomato plants is much higher than that from weeds to tomatoes, hence the importance of eliminating any green plant from the field.