Introduction

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), world-renowned as the spotted-wing drosophila or by its acronym “SWD”, is a frugivorous fly native to Eastern Asia that has been accidentally introduced to the Europe and Americas in the 2000s (Asplen et al. 2015). The accelerated spread within both continents and the subsequent agricultural losses in numerous countries, particularly to commercial soft and thin-skinned fruits, highlighted D. suzukii as one of the most important globally invasive agricultural species (De Ros et al. 2020; Garcia 2020a). Argentina is no exception to this situation, as D. suzukii has quickly become one of the most important fruit pest in the country (Funes et al. 2018).

The female of D. suzukii tends to lay eggs mainly on healthy, ripe fruits as it has a highly sclerosed serrated ovipositor, which makes it different from other sympatric drosophilid species into invaded areas (Atallah et al. 2014). In addition, D. suzukii has a broad host range, which includes numerous crops, non-crop and ornamental plants, although soft fruit are the primary hosts of this novel pest (Wollmann et al. 2020). Kirschbaum et al. (2020) summarise both naturally infested fruit species in the field and those artificially infested in laboratories on a worldwide basis. Several non-crop fruit species growing in wild vegetation areas may provide suitable hosts in order to maintain and multiply D. suzukii populations within invaded areas (Lee et al. 2015; Kenis et al. 2016). In this regard, evidence on wild host status on which invasive D. suzukii may increase in numbers is critical to support management strategies of this novel pest, particularly in habitats surrounding commercial berry crops (Lee et al. 2015, Wang et al. 2016). In addition, in e wild host fruits, there may also be a natural biological regulation of D. suzukii populations by resident natural enemies, including some parasitoid species (Arno´ et al. 2015; Gabarra et al. 2015; Daane et al. 2016; Garcia et al. 2022; Abram et al. 2022). In this framework, parasitoid surveys revealed a large assemblage of resident species associated with D. suzukii in both crop and non-crop areas throughout Argentina. Particularly larval parasitoid species belonging to Figitidae were recorded, such as Leptopilina clavipes Hartig, Ganaspis hookeri Crawford (Lue et al. 2017), Leptopilina boulardi Barbotin, Carton and Kelner-Pillault (Garrido et al. 2018), Dieucoila octofagella Reche (Reche et al. 2021), Euxestophaga argentinensis Gallardo, Hexacola bonaerensis Reche (Gallardo et al. 2022a), Ganaspis brasiliensis (Gallardo et al. 2022b, Funes et al. 2023), Leptopilina heterotoma Thomson and Hexacola hexatoma Harting (Fischbein et al. 2023). Both D. octofagella and G. brasiliensis were the only figitid species recovered from D. suzukii puparia, while the remaining species were only recorded from liquid traps together with D. suzukii adults. However, D. octofagella and G. brasiliensis were not abundant nor did they exerted control over D. suzukii. However, resident pupal parasitoid species has lately been associated with D. suzukii through tested trophic relationships in non-crop areas of northwestern (NW) Argentina (Buonocore Biancheri et al. 2022, 2023), as well as in southern Brazil (Wollmann et al. 2016, da Costa Oliveira et al. 2021). Particularly, three resident idiobiont pupal parasitoids, Pachycrepoideus vindemiae Rondani, Spalangia cf. endius Walker (Hymenoptera: Pteromalidae) and Trichopria anastrephae Lima (Hymenoptera: Diapriidae) were mainly found in close trophic association with D. suzukii on feral peaches [Prunus persica (L.) Batsch] (Rosaceae) occurring in wild vegetated environments of NW Argentina (Buonocore Biancheri et al. 2022). Both P. vindemiae and T. anastrephae were the most abundant and significant parasitoid species associated with D. suzukii (Buonocore Biancheri et al. 2022). The pteromalid P. vindemiae is a worldwide cyclorrhaphous dipteran parasitoid that was introduced in several American countries as a biocontrol agent against tephritid pests (Garcia et al. 2020), although it was first record in Argentina dates back to the 1940s, but misidentified as Pachycrepoideus dubius Ashmead (Ovruski et al. 2000). Pachycrepoideus vindemiae is a pupal ectoparasitoid, because the female lays the egg inside the space between the puparium shell and host pupal body (Wang and Messing 2004). In contrast, the diapriid T. anastrephae is native to the South American Neotropical region (Garcia et al. 2020), and it is an endoparasitoid because the female lays the egg into the hemocoel of the host pupa (da Costa Oliveira et al. 2021). The cosmopolitan S. endius is also a polyphagous dipteran ectoparasitoid, but mainly associated with tephritid and synanthropic flies (Morgan et al. 1975). The three pupal parasitoid species can be successfully lab reared (Wang et al. 2016; Krüger et al. 2019; Zheng et al. 2021), but both P. vindemiae and T. anastrephae have shown potential as D. suzukii biological control agents in the Americas (Garcia 2020b).

In view of the above, the hypothesis of the current study argues that the combined action of both pupal parasitoid species, occurring most frequently in non-crop fruit areas, has a significant impact as a natural regulation factor on D. suzukii populations. Therefore, in order to test this hypothesis, three aims were set as follows: (1) to assess the abundance of D. suzukii and associated parasitoids in non-crop hosts such as feral peach and guava (Psydium guajava L.) (Myrtaceae); (2) to analyse the influence of the host puparium origin, i.e. recovered from fruit or the soil adjacent to the fruit, associated with the sampled fruit species on the D. suzukii parasitism and (3) to determine the relevance of parasitism individually inflicted by P. vindemiae and by T. anastrephae on D. suzukii puparia recovered from both fruit and soil. The findings of this research are discussed with regard to the potential use of both P. vindemiae and T. anastrephae against D. suzukii within an area-wide integrated pest management approach (Haye et al. 2016; Garcia 2020b) in the fruit-growing NW region of Argentina, in which the pest populations apparently thrive on alternative, non-crop host plants (Buonocore Biancheri et al. 2022). This subtropical fruit-producing region, where the rainforest is an important part of the landscape, is a major soft fruit producer and exporter from Argentina (Funes et al. 2017, 2018). However, results of the study may be used for developing biological control strategies against D. suzukii in the remaining fruit-growing regions of Argentina and in other places in America and the world.

Material and methods

Sampling area

The study was carried out in a 14,174-ha area of protected wildlife known as “Sierra de San Javier” Park. It belongs to the Universidad Nacional de Tucumán and it is located in Horco Molle, Yerba Buena district, Tucumán province, in NW Argentina. This wilderness area belongs to the southernmost extension of the South American subtropical montane rainforest, locally known as “Selva de Yungas”. In this region, the climate is humid warm-temperate with a rainy-warm season between October and April, and a dry-cold season between May and September; mean annual rainfall and temperature are about 1500 mm and 21.5 °C, respectively (Schliserman et al. 2016). Sampling sites were located on the eastern slope of the San Javier Mountain at 26°43′00″S latitude, 65°22′00″W longitude, and 600–800 m altitude. Sites consisted of tropical rainforest environments of low and medium disturbed secondary structure, with combined fruit species such as exotic guava, peach, and Citrus aurantium L. (sour orange) (Rutaceae) and natives to the Neotropic such as Juglans australis Grisebach (wild walnut) (Juglandaceae) and Myrcianthes pungens (O. Berg) D. Legrand (mato) (Myrtaceae).

Drosophila suzukii puparia sampling and processing

Puparia of D. suzukii were collected from both fallen fruit and soil in feral peach and guava tree-dominated environments. Samplings were performed throughout two peach and guava fruiting seasons, i.e. December 2016- January 2017 and December 2017-January 2018, and March 2017-April 2017 and March 2018-April 2018, respectively. Feral peach and guava were chosen because both host species are abundant in disturbed wild vegetation areas adjacent to berry crops, and fruiting periods cover from late spring to early autumn in northern Argentina (Schliserman et al. 2014, 2016). Mean (± SE) air temperature and relative humidity (RH) recorded during both peach and guava fruiting periods were 26.9 ± 0.6°C–82.9 ± 1.1% and 21.8 ± 0.9°C–68.4 ± 3.1% for the first collecting period, respectively, and 26.3 ± 0.8°C–82.5 ± 2.1% and 21.3 ± 0.4°C– 72.4 ± 1.7% for the second collecting period, respectively. The meteorological data were recorded by a weather station located at 700 m in the Sierra de San Javier Park. Forty peach and guava trees were selected for D. suzukii puparia sampling. On each sampling date, four peach or guava trees were randomly selected, and then, five fallen ripe fruit per each fruit tree were sampled. In addition, all D. suzukii puparia located on the soil underneath each fruit or close to it were also collected. Each sampled fruit was placed individually into a cloth bag, and its top was closed with a rubber band. Likewise, the soil underneath each fruit and the soil close to the fruit were dug with a hand shovel up to ~ 2 cm deep to find buried puparia. Then, the extracted soil from the sector relating to each fruit sampled was also placed individually into another cloth bag. All bags with fruit or soil were placed in plastic crates (32 × 24 × 12 cm) and taken to the Pest Biological Control Laboratory from the Planta Piloto de Procesos Industriales Microbiológicos y Biotecnología (PROIMI), in San Miguel de Tucumán. Fruits were removed from bags and individually placed in a plastic crate (20 × 15 × 5 cm) with a ½-cm layer of sterilised vermiculite Intersum® (Aislater S.R.L., Cordoba, Argentina) on the bottom as a pupation medium. Fruits and vermiculite were daily checked to remove drosophilid puparia. All puparia found inside pulp fruit, attached to the fruit rind or buried in the vermiculite were removed with a blunt-tip tweezer. Puparia were previously identified and then those of D. suzukii placed into 8 × 5 cm (diameter × height) voile cloth-covered plastic cups, with sterilised, moistened vermiculite on the bottom. Soil samples were removed from bags and sieved. Puparia thereby recovered were identified in order to select out those of D. suzukii. After that, all puparia were placed into cups described above. All cups were housed in a room at 25 ± 1°C, 75 ± 5% RH and 10:14 h L:D until adult D. suzukii and parasitoids emerged.

Drosophila suzukii puparia and adult parasitoids identification

Hauser’s (2011) work was used to identify both the D. suzukii puparium and adult, and the Risbec’s (1950) and Gibson’s (2000) keys were used to identify pteromalid and diaprid adults, respectively. Voucher fly and parasitoid adult specimens were stored at the entomological collection of the Fundación Miguel Lillo, in San Miguel de Tucumán.

Data analyses

Numbers of recovered D. suzukii puparia, emerged adult flies and parasitoids, non-emerged parasitoids, non-emerged host puparia and parasitism, were used as response variables for statistical analyses. The parasitism percentage was calculated as the total number of emerged adult parasitoids and non-emerged parasitoids recovered from D. suzukii puparia sampled in a particular microhabitat (fruit or soil) and on a particular fruit species (peach or guava), and divided by the total number of host puparia recovered from those microhabitat and fruit species × 100. Given the lack of normality, data were ranked transformed prior to analyses (Conover and Iman 1981), but, untransformed data are shown as means (± SE) in tables and figures. All variable responses were analysed by one-way univariate general linear models (GLMs) with type III error at p = 0.05. This analysis allowed to identify significant effects of the fixed factor “host puparium origin related to tested fruit species”, with four levels, namely, host puparia from peach fruit (= Fruit_Peach), host puparia from guava fruit (= Fruit_Guava), host puparia from soil next to peach (= Soil_Peach), and host puparia from soil next to guava (= Soil_Guava). Parasitism levels caused by a particular parasitoid species were analysed by two-way univariate GLMs. Fixed factors were “parasitoid species” with two levels, namely, species n° 1 and species n° 2, and “host puparium origin related to tested fruit species”. Data from first and second collecting periods were separately analysed. Mean values were analysed by Tukey’s honesty significant difference (HSD) test at p = 0.05. A Pearson product moment correlations at p = 0.05 was carried out to establish the level of relationship between the mean air temperature and the RH recorded during peach and guava fruiting periods. Air temperature, which it is correlated with RH, was chosen as a covariable when parasitim was analysed by one-way univariate GLMs. Temperature is a standard predictor of insect development dynamics (Terblanche et al. 2010). Statistical analyses were performed using STATISTICA software, version 10.0 (StatSoft Inc 2011).

Results

From 480 fruits, 50% feral guava and 50% feral peach, collected over two consecutive fruiting periods, 3437 D. suzukii puparia were recovered. A significantly higher number of D. suzukii puparia were found inside the fruit than buried in the soil underneath or close to the fruit sampled, with a significantly higher incidence on peach than on guava at both collecting periods (first collecting period: F(3, 92) = 60.495, p > 0.0001; second collecting period: F(3, 92) = 68.919, p > 0.0001) (Table 1). Overall, 78% of host puparia recovered were from fruit. The same pattern was recorded for the adult fly and parasitoid emergence in both surveying periods. Significantly, higher numbers of flies and parasitoids emerged from puparia recovered from fruit than from the soil, but predominantly from peach (first collecting period; adult flies: F(3, 92) = 90.830, p > 0.0001, adult parasitoids: F(3, 92) = 34.001, p > 0.0001; second collecting period, adult flies: F(3, 92) = 85.161, p > 0.0001, adult parasitoids: F(3, 92) = 31.495, p > 0.0001) (Table 1). However, significantly similar numbers of adult parasitoids were recovered from host puparia collected from both guava and peach fruits at the first sampling period (Table 1). Overall, 1163 and 566 emerged adult flies and parasitoids were recovered, respectively, from D. suzukii puparia. Additional 219 parasitoids were recovered from the dissection of non-emerged puparia. A significantly higher number of those parasitoids were from puparia recovered from the fruit than from soil (first collecting period: F(3, 92) = 15.746, p > 0.0001; second collecting period: F(3, 92) = 52.799, p > 0.0001) (Table 1). There were no significant differences between parasitoids not emerged from puparia collected from guava and peach fruits at both collecting periods (Table 1). There was no insect emergence from 1708 puparia. Significantly more non-emerged host puparia were disclosed from fruit samples than those from soil (first collecting period: F(3, 92) = 22.699, p > 0.0001; second collecting period: F(3, 92) = 47.938, p > 0.0001) (Table 1).

Table 1 Mean (± SE) numbers of Drosophila suzukii puparia and emerged adults, non-emerged host puparia, and emerged and non-emerged parasitoids recovered per sample from both infested peach and guava fruits, and from soil underneath or close to the fruit during two collecting periods, December 2016 - April 2017 and December 2017 - April 2018, in Horco Molle, Tucumán, northwestern Argentina
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Three parasitoid species, T. anastrephae, P. vindemiae, both pupal parasitoids, and an unidentified species of Leptopilina Förster (Figitidae), a larval parasitoid, were recovered from the total number of D. suzukii puparia collected in the study area. Pupal parasitoids accounted for 99.8% of the total number of individuals collected, as only two specimens of Leptopilina sp. were found. Trichopria anastrephae was the most abundant parasitoid species, with 460 identified specimens, accounting for 72% of both pupal parasitoids. Of all T. anastrephae specimens, 94% were from host puparia found inside the fruit, whereas 61% of the 180 P. vindemiae specimens were from puparia collected directly from the fruit

Parasitism recorded on D. suzukii puparia recovered from fruit, either peach or guava, was significantly higher than that recorded from host puparia recovered from the soil next to the fallen fruit, at both the first and second collecting periods (first collecting period: F(3, 92) = 18.941, p > 0.0001; second collecting period: F(3, 92) = 9.246, p = 0.0002 ) (Fig. 1). The analysis showed the same parasitism pattern as previously described when the covariate “air temperature” was incorporated, which did not significantly influence parasitism (first collecting period: F(3, 92) = 18.921, p > 0.0001, covariate, F(1, 91) = 1.211, p = 0.2741; second collecting period: F(3, 91) = 9.212, p > 0.0001, covariate, F(1, 91) = 1.846, p = 0.1776). Air temperature and RH were positively correlated (r = 0.98, N = 96, P < 0.0001); therefore, RH did not influence parasitism during the study.

Fig. 1
figure 1

Mean (± SE) parasitism percentages recorded from Drosophila suzukii puparia recovered from peach (Prunus persica) and guava (Psidium guajava) fruits, and from soil next to the fruit, during two collecting periods (A December 2016-April 2017; B December 2017-April 2018) in Horco Molle, Tucumán, northwestern Argentina. Bars with dissimilar letter indicate significant differences (Tukey HSD test, p = 0.05)

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Significant differences in the D. suzukii parasitism were found when individual categorical factors, host puparium origin related to the fruit species and pupal parasitoid species and their interaction were analysed at both the first and second collecting periods (Table 2). Parasitism by T. anastrephae on D. suzukii puparia was significantly higher in those host puparia recovered from fruit than in those from soil parasitised by this diaprid (Fig. 2). In turn, T. anastrephae parasitised significantly more D. suzukii puparia on fruit than P. vindemiae. This pattern was evident in both study periods (Fig. 2). Pachycrepoideus vindemiae parasitised significantly more D. suzukii puparia on soil than T. anastrephae only in the first collecting period, whereas in the second study period there was no significant difference in the parasitism due to both parasitoid species on host puparia recovered from soil (Fig. 2).

Table 2 Summary of two-way univariate general lineal models on the effect of the host puparia origin related to the tested fruit species (PuOr), the parasitoid species (PaSp) and their interaction on parasitism due to Trichopria anastrephae and Pachycrepoideus vindemiae on Drosophila suzukii puparia collected from both peach and guava fruits, and from soil next to fruit, during two collecting periods, December 2016 - April 2017 and December 2017-April 2018, in Horco Molle, Tucumán, northwestern Argentina
Full size table
Fig. 2
figure 2

Mean (± SE) parasitism on Drosophila suzukii by Pachycrepoideus vindemiae and Trichopria anastrephae based on the interaction between both parasitoid species and host puparium origin related to tested fruit species fixed factors, during two collecting periods (A December 2016-April 2017; B December 2017-April 2018) in Horco Molle, Tucumán, northwestern Argentina. Bars with dissimilar letter indicate significant differences (Tukey HSD test, p = 0.05)

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Discussion

All integrated pest management programmes incorporate regular monitoring of the pest and its resident natural enemies in both crop and non-crop areas as critical tools for implementing a combination of pest management techniques for controlling the target pest (Garcia et al. 2022). These strategies are selected to minimise the extent of environmental degradation, reduce the impact of chemical inputs on humans and non-target organisms, improve on- and off-farm sustainability and reduce production costs to the farmer (Pretty and Bharucha 2015). Against this backdrop, results of the non-crop fruit field survey carried out in a protected wild forest area of the province of Tucumán, NW Argentina, highlight the combined role of two resident pupal parasitoids, T. anastrephae and P. vindemiae, as a natural regulating agent of the D. suzukii population in two host feral fruit species, P. persica and P. guajava. Particularly, the study provided three relevant findings on the trophic ecology of the non-crop fruit-D. suzukii - parasitoids system as follows: (1) the long-term use of both feral fruit species, P. persica and P. guayava, in non-crop areas as relevant alternative hosts by D. suzukii; (2) the importance of both T. anastrephae and P. vindemiae with regard to D. suzukii natural mortality and (3) the co-performance of the two pupal parasitoid species for targeting D. suzukii puparia located at different microhabitats.

The first finding highlighted the importance of feral peach and guava as D. suzukii alternative exotic hosts in the NW, from their first record in wild vegetation areas between March and November 2016 (Escobar et al. 2018; Buonocore Biancheri et al. 2022). In fact, Rosaceae and Myrtaceae include the largest number of D. suzukii host fruit in Latin America, accounting for nearly 50% of all fruit species recorded as hosts of this novel invasive pest (Garcia et al. 2022). Evidently, both feral guava and peach play an important role in the maintenance of D. suzukii populations in environments with different wild vegetation disturbance levels, particularly when economically important crops, such as susceptible berries (Funes et al. 2018), are not present in the region. For example, both non-crop alternative hosts provide food and reproduction resources for D. suzukii population growth in NW Argentina, as shown in the current study. Thus, D. suzukii adults switch from peach, which fructifies between late spring and early summer, to guava, which bears ripe fruit from mid-summer to late autumn. This scenario may enable D. suzukii overwintering morphotype adults to be present in NW Argentina. Winter females are the ones that may infest berry crops at the beginning of spring, which leads eventually to the development of the first generation of summer morphotype adults (Panel et al. 2018; Kirschbaum et al. 2020).

With regard to the second finding, overall parasitism levels on D. suzukii recorded in the current study on feral guava and peach, which averaged 16 and 22%, respectively, were essentially caused by both T. anastrephae and P. vindemiae. These values outperform slightly the parasitism of D. suzukii by resident parasitoids reported for Europe and North America, which have remained below 10% for a long time (Jarret et al. 2022). Within a broader context, the two pupal parasitoid species were accountable for 12–18% and 19–23% of the total host puparia mortality in guava and peach, respectively. The remaining percentage of dead host puparia was mainly due to unknown causes and other organisms, such as mites, entomopathogens and, perhaps by some predators injuring puparia. The strong incidence of ants removing D. suzukii puparia from soil, such as documented by Woltz and Lee (2017), was not assessed in this study. However, it is likely that a high percentage of the unknown host mortality was due to the injury caused by parasitoid females when introducing the ovipositor into the host or to the host-feeding behaviour. In this regard, it has been found that P. vindemiae females are able to kill D. suzukii pupae due to the host-feeding behaviour (Bezerra da Silva et al. 2019). Because P. vindemiae has been recurrently recorded as an abundant species parasitizing tephritid and drosophilid puparia in both crop and wilderness areas of Tucumán (Turica and Mallo 1961; Ovruski 1995; Bunocore Biancheri et al. 2022), its impact on D. suzukii mortality may be even higher than that recorded using the parasitism rate alone. It is also noteworthy that T. anastrephae was the parasitoid species with the highest level of parasitism on D. suzukii in the surveyed area. The latter is highlighted because T. anastrephae is a native Neotropical parasitoid mainly associated with saprophytic drosophilids, although it has been recorded from tephritid puparia belonging to the Anastrepha genus (Ovruski et al. 2000; Garcia et al. 2020). That is, despite the lack of a co-evolutionary relationship in sympatry with D. suzukii, T. anastrephae has been successfully able to adapt to this novel pest immediately at the onset of its invasion and dispersal in NW Argentina. The cosmopolitan P. vindemiae has a distinctive background because it is a highly polyphagous parasitoid on Cyclorrapha Diptera (Wang and Messing 2004), which enables it to adapt easily on novel hosts species (Hogg et al. 2022). Therefore, the current study and the previous one by Buonocore Biancheri et al. (2022) have shown both pupal parasitoid species displayed a swift and successful host-parasitoid co-adaptation process. Nevertheless, both pupal parasitoid species are not apparently exerting a substantial regulating effect on the D. suzukii abundance. Although parasitism did not abruptly reduce the D. suzukii abundance, both pupal parasitoid species were relevant mortality agents in the surveyed area, which was recently invaded by this novel pest. Therefore, both T. anastrephae and P. vindemiae can be valuable components into a framework of biological control measures in combination with other D. suzukii management strategies (Garcia 2020b). Larval parasitoids, particularly figitid species, for which trophic relationship with D. suzukii has been genuinely proven (Reche et al. 2021; Gallardo et al. 2022b), have displayed too low parasitism on this exotic pest in NW Argentina. A strong immunological response of D. suzukii larvae against attack by indigenous larval parasitoids at sites invaded by this exotic pest may be the cause of the parasitism shortage (Wang et al. 2016).

The third finding corroborated the availability of both pupal parasitoids to attack D. suzukii puparia located either inside the fallen fruit or on the soil underneath it, or buried near the fruit. This ability of the parasitoids made it possible to cover at least two microhabitats in which the D. suzukii larvae develop their puparia. Thus, both P. vindemiae and T. anastrephae have a more extensive impact on the D. suzukii abundance. However, this combined action of the two pupal parasitoid species in both tested microhabitats may imply a competitive interaction between females for the same resource (the host puparium). Therefore, such mutual interference may influence the parasitoid species performance as regulating agents for the D. suzukii abundance. This has been shown in studies under lab conditions, in which T. anastrephae outperformed P. vindemiae in the ability to attack D. suzukii puparia (da Costa Oliveira et al. 2021). Similar competitive superiority was also recorded for Trichopria drosophilae Perkins, a parasitoid taxonomically and biologically related to T. anastrephae (Masner and Garcia 2002), when interacting with P. vindemiae in both lab and semi-field trials (Wolf et al. 2021). Laboratory functional response studies showed that T. drosophilae has a higher egg load than P. vindemiae which allows it to parasitise more D. suzukii puparia in less time (Kaçar et al. 2017). However, in ecosystems, sympatric species reduce competition by, among other actions, using different resources or habitats (Amarasekare 2003; Bonsall et al. 2002). This was tested for both parasitoids, which can reduce or avoid the negative effects of this interspecific interaction through the ability to discriminate hosts previously parasitised by the other species and/or through differentiated foraging behaviour patterns for targeting of available resources (Buonocore Biancheri et al. 2023). This divergence in foraging behaviour can be corroborated through parasitism levels caused by both parasitoid species according to the microhabitats tested in the present study. The results showed a tendency of T. anastrephae to forage and parasitise D. suzukii puparia located on the fruit. The preference of T. anastrephae, previously proven in field studies by Buonocore Biancheri et al. (2023), was also recorded for T. drosophilae in studies under lab (Wang et al. 2016), semi-field (Wolf et al. 2021) and field conditions (Trivellone et al. 2020). However, parasitism by T. drosophilae on D. suzukii puparia located on the soil was rather high. Previous studies (Buonocore Biancheri et al. 2023) suggested a preference of P. vindemiae to parasitise D. suzukii puparia in microhabitats away from inside the fruit when females are under an interference situation with T. anastrephae females. Interestingly, data from the current study demonstrated that P. vindemiae females exhibited a higher behavioural plasticity than T. anastrephae for locating host puparia, as they similarly parasitised D. suzukii puparia on both fruit and soil. Such ability of P. vindemiae females to forage over a wide range of microhabitats was also supported by studies in Switzerland (Wolf et al. 2021; Trivellone et al. 2020). The abovementioned authors revealed some preference of P. vindemiae females to forage on D. suzukii puparia located in fruit on the foliage, but at the same time, T. drosophilae displayed foraging preference for host puparia on fruit scattered on the soil. Host foraging plasticity spanning different microhabitats, coupled with high polyphagy, are likely behavioural strategies that enable P. vindemiae to avoid interference with resident competitors and to be plentiful in the surveyed area.

In conclusion, the results evidenced an interesting new system of trophic interactions in a non-crop area of NW Argentina between two exotic feral fruits widely abundant in the region, the recently introduced D. suzukii and two resident pupal parasitoids well adapted to the newly established host. Both peach and guava turned out to be important D. suzukii multiplier hosts, whereas both P. vindemiae and T. anastrephae contribute to the natural mortality of this invasive pest. Both pupal parasitoid species killed about one-quarter of the total D. suzukii puparia scattered in two different microhabitats, fruit and soil. This suggests targeting them when analyzing D. suzukii integrated management strategies, because T. anastrephae and P. vindemiae are promising D. suzukii biological control agents. The current incidence on the novel pest population by T. anastrephae and P. vindemiae may properly be managed to improve the D. suzukii mortality in natural settings with many alternative fruit hosts. A first advisable step may involve lab studies based on replicated experimental adaptation for increased developmental success rate of both pupal parasitoid species (Kruitwagen et al. 2018, Woltering et al. 2019, Jarret et al. 2022). A recommended second step may address conservation biological control (Barbosa 1998) in wilderness areas of the Yungas forest or in patches with mixed stands of native and introduced fruit species adjacent to commercial fruit crops. Non-crop habitats particularly provide D suzukii multiplication and overwintering sites as well as shelter and food (Schmidt et al. 2019). Both resident pupal parasitoids, T. anastrephae and P. vindemiae, can exert an interesting natural control of the D. suzukii population, based on the data provided in the current study. Therefore, wild vegetation areas, where insecticide use is precluded, may preserve and multiply resident D. suzukii parasitoids. Thus, as suggested by Aluja (1999) to control tephritid fruit flies by native parasitoids, keeping areas with native vegetation interspersed in large-scale fruit crops may be an approach to encourage conservation biological control. This procedure may be suitable in berry-producing regions of Argentina. In a further potential third step, when natural populations of pupal parasitoids are not large enough to suppress D. suzukii natural populations, the augmentative release from such agents may help to enhance their impacts. Thus, field trials in Italy showed that augmentative release of the diaprid T. drosophilae substantially reduced fruit damage by D. suzukii in both a managed closed (Rossi Staconi et al. 2018), and an unmanaged open cropping system (Rossi Staconi et al. 2019). Similarly, augmentative releases of T. drosophilae in Mexico in commercial crops of Rubus fruticosus L. reduced the D. suzukii population up to 50% D. suzukii (Gonzalez-Cabrera et al. 2019). Recently, augmentative releases of P. vindemiae reduced, but on a relatively small scale, D. suzukii populations in caneberry hoop houses in Minnesota, Oregon and California (USA) (Hogg et al. 2022). Those results suggest that augmentative releases of resident pupal parasitoids may reduce D. suzukii outbreaks (Wang et al. 2020). Consequently, developing biological control strategies for D. suzukii using local biocontrol agents seems achievable in berries-growing regions of Argentina, as elsewhere in the world.