Saving the maize crops

“The results of the research we have carried out on the genome of viruses, specifically on nucleopolyhedroviruses (NPVs; Baculoviridae) will help to understand how genetic systems evolve. This discovery is of great importance when we take into account that NPVs have shown to have great insecticide potential for the control of agricultural and forestry plagues, above all for the cultivation of maize in countries such as Mexico and Honduras”. This is one of the conclusions of the PhD thesis “Functional importance of genotypic and phenotypic diversity in a Spodoptera frugiperda multiple nucleopolyhedrovirus population” that researcher Oihane Simón De Goñi recently defended at the Public University of Navarre.

How the virus affects the plague

The nucleopolyhedrovirus (NPVs; Baculoviridae) have shown to have great insecticide potential for the control of agricultural and forestry plagues. It involves an infectious virus for insects that cause plagues, the size of which is 2 to 3 micras and which can be found, according to Ms Simón de Goñi, “contaminating a plant leaf which the insect feeds off. This virus is composed of a protein that includes the infectious viruses, known as virions. The larva, on eating the contaminated leaf, ingests the virus which, when it arrives at the digestive tract of the insect, it dissolves the protein surrounding the virions and these are released. Then the virions unite with the epithelial cells and enter the nuclei thereof where they multiply to produce new virions which then infect the cells of other internal tissues of the insect’s body. Thus, the infected cells burst (lysis) and, finally, the whole insect becomes a pool of liquid in a matter of 3 or 4 days, releasing thousands of millions of viral particles that contaminate other leaves to commence a new cycle. This is the useful insecticide action of this virus”.

Population genetics of the virus

The study was designed to resolve the question of why the deleterious genotypes – which are unable on their own to infect the insect – are maintained in the virus population. “Until now it was believed that the genotypic variants with deletions were defective and, thereby, these variants would tend to disappear with evolution. In consequence, it was believed that in order to produce good insecticides, the logical thing would be to use only those genotypes that were complete. However, on analysing the genetic sequence of this virus, characterising the genotypic variants present in this isolated sample, we have been able to show that the genetic diversity present in this virus is important for the biological activity of the virus and its potential”.

The main consequence of this is that “these variants do not disappear because they contribute to enhancing the overall set of pathogenic characteristics of the viral population. Thus, in the elaboration of insecticides, it is better to work with mixtures of genotypes, given that a much more powerful insecticide is obtained”.
The characterisation of the virus reaffirms the discovery. “There are variants that act synergically between each other and that make the activity of the virus increase. This causes certain genes to be involved in this synergic action and so the next step will be to determine which genes are involved and thus we will be able to extrapolate them to other viruses also”.

The results will be applicable to the development of bioinsecticides “that can be used in countries like Mexico and Honduras, where significant damage is incurred in maize plagues, affected by this virus”.

But moreover these results can “be extrapolated to the elaboration of other bioinsectides because the importance of the discovery of the retention of these variants lies in the fact that it can be valid for other viruses”.

The advantages of using bioinsecticides instead of chemical insecticides are many, states the research scientist, “Their high-specificity insecticide action does not contaminate the environment and are not toxic for the rest of the (beneficial) insects, plants, land and marine animals nor for humans. This means that products based on these viruses are ecologically very sound, desirable and compatible with most control agents and thereby an interesting alternative in any plague control programme”. One of the main drawbacks in marketing the product “is precisely its high specificity, together with its high production cost. Thus, it is necessary to continue researching new techniques to enable the production of a virus with a wider spectrum of potential hosts, in larger quantities and at a lower cost”.