| Resumo: |
Early monitoring and toxicological studies with invasive pest species, such as the Spotted Wing Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), are of importance. It took only about 3 years to D. suzukii become the worldwide most important pest of small soft-skinned fruits, such as strawberries, blueberries and cher- ries. This drosophilid lays its eggs inside undamaged fruits, and its larvae destroy the fruit tissues, making it unmarketable. While attention was driven to the search about D. suzukii bioecology and alternative control tools, the spray with broad-spectrum insecticides has being the most used emergency control strategy, increasing the proba- bility of insecticide resistance selection in this species. Thus, in the current study, field surveys were performed aiming to identify and report the arrival/presence of the D. suzukii in two Brazilian states. Then, preliminary insecticide susceptibility compar- isons were carried out on populations originally collected in these regions to evidence potential resistance sources. Finally, it was assessed the toxicity of lime-sulfur (i.e. an old alternative pesticide) on D. suzukii and its oviposition and development on sprayed strawberry plants. The field surveys demonstrated that D. suzukii is already present in both Minas Gerais (MG) and Espírito Santo (ES) states. The species was first collected in a strawberry field at the municipality of Ervália - MG in March of 2016 and in Juiz de Fora - MG in November of 2016. Later, in February of 2017, the species was also found infesting strawberry and blackberry fields at the municipal- ities of Domingos Martins and Santa Maria de Jetibá - ES. In the blackberry fields, the infestation of D. suzukii occurred simultaneously with its confamiliar, Zaprionus indianus Gupta (Diptera: Drosophilidae). The susceptibility comparisons among D. suzukii populations identified a potential source of resistance to imidacloprid in a pop- ulation originally collected at the municipality of Juiz de Fora - MG (P < 0.05), while no consistent differences among populations were found for permethrin (P > 0.05). Lime-sulfur was toxic (LC50 = 26.6 mL/L) to D. suzukii flies in low concentrations, and its spray on strawberry plants reduced the D. suzukii oviposition in both choice (48.6% of reduction) and no choice (47.6% of reduction) semi-field bioassays (P < 0.05). It was also found a slight delay in the pre-imaginal developmental time of individuals from eggs laid on lime-sulfur treated plants only in the choice bioassay, indicating a possible effect of the females oviposition choice on its offspring development. Two other alternative preparations based in mixture of sulfur, lime, potassium perman- ganate, salt and detergent and the insecticides azadirachtin and indoxacarb did not cause high D. suzukii mortalities. As conclusions, D. suzukii has extended its current distribution range in Brazil, with presence of resistance sources to imidacloprid. Alter- natives, such as lime-sulfur, might be recommended in rotations for both traditional and organic farming approaches. Further studies monitoring the occurrence of insec- ticide resistance in field populations, as well as better investigation of the sublethal effects and compatibility of lime-sulfur applications on other D. suzukii hosts should be performed. |
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