Mapping highlights areas and periods most susceptible to the occurrence of spotted wing drosophila in Brazil

Embrapa studies mapped municipalities across the country with more favorable conditions for the development of spotted wing drosophila (DAM), a pest that attacks small fruit orchards and can cause losses of up to 100% of production. Identified in Brazil in 2013, it mainly affects plum, blackberry, persimmon, citrus (orange, lemon and tangerine), fig, strawberry, nectarine, pear, peach and grape plantations. The research, which is part of the DefesaInsetos Project and involves three Embrapa Units: Environment (SP), Territorial (SP) and Semi-Arid (PE), also aims to detect potential biological control agents and minimize the environmental impact of the use of chemicals against the insect.

The studies showed that the month of November is the one with the largest number of municipalities with favorable conditions for the development of the spotted wing drosophila: 2.288, in total. On the other hand, June has the smallest number: 884 municipalities. The most susceptible area is in the Southeast region, where the presence of orchards and temperature and humidity conditions favor the insect's development throughout the year. In the South region, favorability predominates from October to April, while in the Northeast, suitability prevails from May to October, peaking in July. In the Central-West region, the four federation units have favorable conditions between December and June. The shortest period is in the North region, from June to August. 

Periods of unsuitability for the development of the DAM were also signaled by the monthly zonings carried out by the Embrapa team. To this end, agricultural production data from the Brazilian Institute of Geography and Statistics (IBGE) were analyzed in order to identify the municipalities in which the main host fruit plants are produced. Another source used was the National Institute of Meteorology (INMET). Embrapa Territorial analyst Rafael Mingoti highlights that, by revealing the areas and periods in which the insect has optimal conditions for development, the work highlights which places and moments require more attention to avoid damage.  

Spotted wing drosophila (DAM) 

Drosophila suzukii is a polyphagous insect, an exotic pest of economic importance for crops in Brazil, where it was identified in 2013. It is known as Spotted Wing Drosophila (DAM) or Spotted Wing Drosophila (SWD), in addition to the black fly. cherry or vinegar fly. 

Originally from Southeast Asia, DAM is considered one of the most important pests of small fruits in different countries in North America, South America, Asia and Europe. The insect pest has a wide range of host crops, including blueberries, strawberries, raspberries, peach, grapes, blackberries, blackberries, cherries, plums, persimmons, figs, citrus fruits (orange, lemon and tangerine) and pears. It can also occur in apricots, nectarines, oak sap and flowers. 

Losses can reach 100% of production and its main management strategy is based on chemical control. However, some characteristics of biological control also make it a good strategy for managing this insect. Among them, the ability of many parasitoids to attack larvae inside fruits, where pesticides are generally less effective, stands out. Furthermore, natural enemies are capable of interfering with the natural mortality of pest populations present in natural areas, in which wild hosts are present and control is not employed. 

Biological control: parasitoid wasps are promising against the pest

To try to reduce these losses, producers generally resort to chemical control. Therefore, one of the priorities of agricultural research is to seek alternatives and more appropriate ways of using these products, in addition to disseminating knowledge that favors the successful use of biological control. 

The Embrapa research team has been seeking information on various natural enemies – fungi, bacteria, viruses, nematodes, predators and parasitoids – that could act as biological control agents for the spotted wing drosophila. In the assessment of Embrapa Environment researcher Jeanne Prado, responsible for prospecting these control bioagents, “studies that deepen knowledge about the pest and control strategies are always necessary, as they open up a range of national options for controlling the insect”. Work based on national and international technical-scientific information about the spotted-wing drosophila and its natural enemies favors prospecting for control bioagents, even before laboratory or field studies are carried out, he adds. 

“We sought information about natural enemies that have already appeared abroad as important control strategies and identified those already present in our territory or that have abilities to adapt and possibly be successful in controlling the pest. When integrated into the management of agricultural crops, the strategy can help reduce the use of chemical products”, explains Prado. A more in-depth analysis of the technical-scientific literature resulted in the prioritization of two wasps as most viable for use in national conditions.

The scientists then carried out a second mapping exercise to assess whether the areas most affected by the proliferation of the pest would also present good conditions for the development of one of these parasitic wasps, Ganaspis brasiliensis. The study showed that it is suitable for use in all areas indicated as also favorable to the spotted-wing fruit fly, which would allow the use of this biological resource.

Based on the results of this second zoning, studies on Ganaspis brasilienses were deepened based on information about Chinese and Korean populations of the parasitoid, which have already been used abroad. Among the various municipalities identified as suitable for the development of both spotted-wing drosophila and the wasp, five were prioritized for estimating the development times and the number of annual generations, both of the pest and of each of the parasitoid populations: Bento Gonçalves, RS; Morro do Chapéu, BA; Oiapoque, AP; Petrolina, PE and Vacaria, RS. 

These estimates considered the minimum energy needs acquired by insects, based on the temperature of each location, so that they survive and are able to go through all their life stages, generating offspring, separately by municipality evaluated. For this reason, they also demanded information on average monthly maximum and minimum temperatures, obtained from information made available by INMET. The results presented the development times of the immature phase and the number of generations of the pest and parasitoid (for each population) in each municipality, as well as in different periods of the raspberry harvest, in Bento Gonçalves, RS, and strawberry, in Morro do Chapéu, BA. 

Mapping supports preventive control and monitoring of DAM

Embrapa Environment researcher Maria Conceição Pessoa, responsible for making the estimates, explains that these calculations support integrated management strategies for the spotted wing drosophila, both focusing on biological and chemical control. “Both require knowledge of the periods of greatest availability of immature and adult phases of the pest, as well as that necessary for the parasitoid to reach its adult phase, in each location”, says the researcher.

For strawberry cultivation in Morro do Chapéu, BA, Embrapa researcher Beatriz Paranhos, who works in the Semiarid region and participated in the joint evaluations of the results obtained, provided information about different fruit harvest periods.

In Mingoti's assessment, mapping has the role of supporting, mainly, technical assistance agents and other professionals and institutions that provide information to farmers. “For people who provide guidance aimed at controlling the pest, this information is important. Zoning, which indicates whether or not the area is favorable to the proliferation of the insect, also helps with preventive monitoring. The mapping of bioagents indicates those that are most successful in joint adaptation with the pest and, thus, with local control”, he details. The data can also guide companies and institutions interested in investing in biological control of DAM.

Mathematical models minimize the environmental impact of pesticides

The Embrapa team also evaluated active principles of pesticides used in the chemical control of spotted-wing drosophila in Brazil and abroad to identify the most suitable ones in terms of protection, mainly, of water and soil quality, as well as insects pollinators, in places where they could potentially be used.

The Embrapa Environment researcher, Vera Ferracini, who coordinated this part of the work, informs that it was necessary to collect information about each active ingredient with potential application for controlling the drosophila in question in order to subsequently carry out screening. ) of those that require greater attention in use, mainly in relation to transport (leaching into groundwater or surface runoff to rivers and lakes) or in soils in locations favorable to the greater development of the spotted-wing drosophila. In this approach, a zoning was proposed covering the municipalities, by region of the country, where there are more favorable conditions for the development of the spotted wing drosophila. 

The screening was done using mathematical models that signal the trend of transport in water or on land. One of these mathematical models required the creation of another territorial zoning indicating the location of fragile areas throughout the national territory, identified by the presence of free aquifers, whose soils are typically sandy, with high porosity and rainfall levels favorable to the development of the DAM. 

The geologist and researcher at Embrapa Meio Ambiente, Marco Antonio Gomes, participated in the identification and selection of fragile areas. According to him, “from a more detailed analysis of these areas, it was verified that the majority of sandy soils occur in areas of outcrop or direct recharge of sedimentary aquifers, a condition that poses a great risk of contamination to the groundwater, if pesticides with high leaching potential are used”. 

The researcher also highlights that “it is important to remember that areas of sedimentary aquifer outcrops occupy large portions of the Brazilian territory, including a large part of the Amazon Basin (Alter do Chão Aquifer), part of the São Francisco Basin (Urucuia Aquifer), part of the Paraná Basin (Guarani Aquifer), part of the Pantanal Basin (Cenozoic Bauru - Serra Geral and Guarani Aquifers) and part of the Maranhão Basin (Serra Grande Aquifer)”. Thus, Gomes also highlights that, “in view of this scenario, the screening of pesticides carried out by the project makes it possible to select those with lower leaching potential for application in fragile areas”. Therefore, “the results support strategies for using chemical control of the pest, aiming for greater environmental sustainability”, summarizes Ferracini.

The group continues research to support strategies to combat the spotted wing drosophila. New evaluations of pesticides used for chemical control and a study on the second species of wasp with potential for use in biological control are being carried out.