Introduced in Central America twenty years ago, the Guatemalan potato moth is wreaking havoc in potato crops in Venezuela, Colombia and Ecuador. Its larvae can devour entire stocks of potato tubers, one of the main crops and the staple food of Andean populations. Control measures exist, but are toxic or financially out of reach for farmers. To combat this scourge, researchers at the Institut de recherche pour le development (IRD) and their Ecuadorian partners have developed a promising alternative: a biopesticide based on a virus that infects the moths in order to preserve the ecosystem and reduce the risk of pollution as well as the resistance of these destructive insects.
New biological insecticides have emerged in recent years which make use of so-called “entomopathogenic” viruses that are harmful to insects, in particular the baculovirus. To identify the virus in this family that will most effectively control the Guatemalan potato moth, the French-Ecuadorian research team have analysed the pathogens among moths from all over the world. And the winner is… the granulosis virus, or granulovirus, which appears to be the most wide-spread. The researchers detected it in moths from twelve different countries. Moreover, it has the widest activity spectrum: it also attacks five other tuber pests. The researchers then did a laboratory test of a formula based on this virus. The result was as efficient as chemical products: it produces a mortality rate among Guatemalan potato moth larvae of more than 98%!
Pulverised on the surface of potatoes or the eggs of the invasive species, the granulovirus contaminates the larvae through ingestion. It then spreads through the digestive tract and to the entire organism of the host, causing a lethal infection within two or three days. The action is therefore relatively slow compared to chemical insecticides that have an immediate effect upon contact. Its use also requires expert knowledge and detailed monitoring of the moth’s biological cycle, ecology and behaviour, which could hold back its deployment for biological control.
Nevertheless, such a biopesticide has many advantages and is a worthwhile alternative to chemical insecticides which are still the primary method used by farmers in Ecuador. Phytosanitary products are toxic for the environment and potentially for the user as well. Using biological pesticides that rapidly degrade in the environment would reduce the risks of pollution.
Another advantage of baculoviruses is that they are innocuous to man, vertebrae and plants. Moreover, each viral strain attacks a very limited number of insect species. This host specificity means that the Guatemalan potato moth can be targeted while preserving the ecosystem, in particular useful insects like pollinators. Lastly, unlike the molecules in chemical plant-protection products, viruses are able to mutate, which limits the development of resistance in their host.
For efficient control of the Guatemalan potato moth, the use of this viral pesticide must therefore necessarily form part of an integrated control strategy. To this end, the French-Ecuadorian team has since 2006 been doing genetic, agronomic and ecological studies: molecular analyses to describe the genetic structure of the pests, a study of the impact of temperatures on their ecology by means of drones with thermal cameras. The aim is to get a better understanding of the insects’ population dynamics and define good practices to limit their proliferation. In this respect, the researchers have developed methods like role-playing games to raise awareness among farmers. Recent surveys have shown their efficiency on a regional scale (Ecuador, Peru and Bolivia). Training remains a key element in efficient crop-pest management.