Journal of Entomological and Acarological Research | 2019
Can exotic drosophilids share the same niche of the invasive Drosophila suzukii
Abstract
The presence of the four exotic drosophilids Chymomyza amoena (Loew), Drosophila suzukii (Matsumura), Zaprionus indianus (Gupta) and Zaprionus tuberculatus Malloch has been investigated in different orchards in Northern Italy for two consecutive years. The presence and the abundance of the population of the drosophilid flies were surveyed with apple cider vinegar traps, fruit baited traps, and fruit collection. Chymomyza amoena, Z. tuberculatus and D. suzukii have been identified in the ACV traps in both years. Only D. suzukii and Z. tuberculatus emerged from fruit baited traps. Except for D. suzukii, no other exotic drosofilid was captured from the fruit collection. Z. indianus was never observed. Analyses of the presence of the different species, seasonal occurrence and sex ratio are provided. Introduction In recent years, four exotic drosophilids, Chymomyza amoena (Loew), Drosophila suzukii (Matsumura), Zaprionus indianus (Gupta) and Zaprionus tuberculatus Malloch were detected in Italy. To date the most dangerous among them is the polyphagous D. suzukii, as it is able to lay eggs into the pulp of healthy fruits due to a serrated ovipositor which lacks in the other three species (Asplen et al., 2015). This destructive pest of small and stone fruits, native to Eastern and Southeastern Asia, was detected for the first time in 2008 in Tuscany, Italy (San Giuliano Terme, Pisa, Central Italy) simultaneously with Spain, near Barcelona (Calabria et al., 2012; Cini et al., 2012). Drosophila suzukii rapidly adapted to the climatic conditions of the Mediterranean countries, and nowadays it is widespread in Europe, including several Italian regions where it causes serious economic losses (Cini et al., 2014). In Lombardy, where this research was conducted, the pest was detected in 2011 (Griffo et al., 2012). The Nearctic C. amoena (Wheeler, 1965) was first found in Europe in Czechoslovakia in 1975 (Màca, 1985; Màca & Bächli 1994), probably introduced through imported fruits, and it is now present in mainland Europe (Bächli et al., 2004). In Italy this species was collected for the first time in Italy in Veneto (Northeastern Italy) in 1999 (Bächli et al., 1999) and later in Lombardy (Northern Italy) in 2000 in the Alps (Band et al., 2003). Chymomyza amoena is considered a broad-niched species able to develop and overwinter in a great variety of fruits and nuts (Band et al., 2005). Zaprionus tuberculatus, native to the Afrotropical region and the islands of the Indian Ocean, was detected for the first time for the European continent in Italy in Trentino (Northern Italy) and in Apulia (Southern Italy) in 2013 (Raspi et al., 2014; Antonacci et al., 2017). No information is available about its presence in Lombardy. Larvae usually develop on decaying fruits, but the insect was also observed laying eggs in flowers. Eggs hatch in a few days, and the feeding larvae make the flower wither and rot (Buruga, 1976). The species Z. indianus, also known as the African fig fly, is native to Africa, but it has widespread into several areas included Asia, North and South America (Vilela, 1999; van der Linde et al., 2006). Its presence in the Mediterranean Basin has been reported in several countries (EPPO, 2016). In Italy, the species has been detected for the first time in 1988 (TaxoDros, 2003), and reported again in 2010 by Yassin & David. Recently, the pest was observed in Southern France (Kremmer et al., 2017). The polyphagous Z. indianus is considered a secondary pest able to infests overripe, fallen, or rotting fruit. However, in Brazil it was reported as a primary pest of figs causing serious economic damages (Vilela et al., 1999). The objective of this two-year study was to evaluate the contemporary presence of the four exotic drosophilids in the same habitat and the possibility for them to share the same host plants. Information on biology and seasonal presence of the drosophilids were also acquired. Material and Methods Sampling areas Field surveys were carried out in four localities in Lombardy region, Northern Italy during 2014 and 2015 in crops infested by D. suzukii in the previous years (Table 1). Investigations were made in A cc ep te d P ap er Montanaso Lombardo (Lodi), Camnago Volta (Como) and Minoprio (Como) in 2014, and in Camnago Volta, Minoprio, and Guanzate (Como) in 2015. Guanzate was added as a research site in 2015 due to the decision of the farmer in Montanaso Lombardo to renovate the raspberry and blackberry plantation. Sampling methods and instruments The population levels and the presence of the four drosophilids were evaluated in each site by placing Apple Cider Vinegar traps (ACV), Fruit Baited traps (FB) or collecting fruits during the season. Details of samplings are given in Table 1. ACV traps consisted of a plastic bottle (1.5 L) with a screw-top modified with holes of 0.5-0.8 mm diameter in 10 rows and 10 column positioned on one side of the top half of the bottle. Each trap was hang on a plant at 1.5-2.0 m high. The number of ACV traps is indicated in Table 1; one trap every 1,000 sqm was positioned in each sampling site. Traps were baited with 250 mL of apple cider vinegar with 5% acidity. Trap content was replaced weekly during the trial period. The entrapped specimens were rinsed, collected and stored in 70% (v/v) solution of ethanol inside plastic vials (44 mm×10.8 mm, 2 mL volume) for subsequent identification. FB traps were positioned in the crops at about 1.5 m height and consisted of a delta trap where two plastic petri dishes (diameter 90mm), one with slices of banana and one with healthy blueberry fruits, were placed. Banana was chosen because it is highly attractive for drosophilids in general (Cha et al., 2012; Schubert et al., 2014), while blueberries were chosen as favorite hosts for D. suzukii (Mazzetto et al., 2016). Two delta traps were positioned for each crop. To evaluate if differently overriped fruits can allow the oviposition and development of different drosophilid species (associated to healthy or decaying fruits), as verified by Lasa et al. 2016, the petri dishes were removed every 7 days in one delta trap and every 14 days in the other. After removal, petri dishes were positioned inside plastic transparent boxes (750 mL) with a net on the lid for ventilation and prevention of insect escape and transferred to the laboratory of DeFENS, University of Milan. Boxes were maintained at room temperature and checked three times per week. Newly emerged drosophilids were removed during the first ten days in order to avoid overlapping generations; further observations were done in the following ten days to check for C. amoena and Z. tuberculatus presence, as these species are known to have a longer developing period (Band, 1988a; Buruga, 1976). After removal, specimens were stored in 70% (v/v) solution of ethanol inside plastic vials (2 mL) for subsequent identification. In 2015, the climate in summer significantly differed from the ten-year period 2004-2014 and was characterized by lower humidity and higher temperatures (ARPA Lombardia 2017) causing the desiccation of the fruits inside FB traps. Consequently, FB traps were discarded and blueberry, raspberry, and blackberry fruits were collected directly from plants. 50 fruits per week per crop were gathered in Guanzate and Minoprio during the fruit-producing season. Fruits were put in plastic aerated transparent boxes (750mL) and checked with the same methods detailed before. Identification of drosophilids in laboratory All specimens were observed under the stereomicroscope (Wild Heerbrugg M5A, Leica Geosystems Gmbh, Heerbrugg, Switzerland) for identification. The following taxonomic keys were used for species classification: Bächli et al. (2004) to identify C. amoena, Vlach (2010) for D. suzukii, Markow & O’Grady (2006) for Z. tuberculatus, and Yassin & David (2010) for Z. indianus. Among the collected drosophilids, adult males and females of C. amoena, D. suzukii and Z. tuberculatus were identified and counted under the stereomicroscope. When a specimen was not included in the previous four, it was considered and counted as native. Statistical analysis A cc ep te d P ap er SPSS Statistic (Version 24 for Windows, SPSS Inc. Chicago, IL, USA) was used for all statistical analyses. Prior to analyses, all data were tested for normality and homogeneity of variance with the Shapiro-Wilk Wtest and Levene’s test respectively. One-way ANOVA was used to compare the mean number of D. suzukii emerged weekly from blackberry, raspberry and blueberry fruits (weekly emergences and sites were considered as a replicates). A two way-ANOVA was used to compare D. suzukii ACV captures in different localities and months. Where significant differences occurred, Tukey-Kramer’s Honestly Significant Difference multiple comparisons test was applied for mean separation (P < 0.05). Results A total of 66,042 and 25,669 drosophilids were captured in 2014 and 2015, respectively (Table 2). This study evidenced the presence of three of the four exotic species in Lombardy region. In detail, D. suzukii was collected from all of the sites, traps, fruits and in both years; C. amoena was collected in both years only by ACV traps in all localities, exception for Montanaso Lombardo. Zaprionus tuberculatus was collected only in 2014 by ACV traps from all study sites and from FB traps in Montanaso Lombardo and Minoprio. No Z. tuberculatus was captured in 2015 even in the sites where it was present in the previous year. Zaprionus indianus was never collected in the present research. Only D. suzukii emerged from the fruit collected in 2015. In 2014, the population of drosophilids captured by all ACV traps, consisted of 65.95% of D. suzukii, 30.34% of native drosophilids, 3.69% of Z. tuberculatus, and 0.02% C. amoena. Among the adults emerged from FB traps, 1.31% were Z. tuberculatus, 0.87% were D. suzukii, and the remaining part consisted of native drosophilids. In 2015, most of