Since its first detection in Trentino fifteen years ago, Drosophila suzukii, an invasive species originating from East Asia, has become the main harmful insect for a wide range of fruit crops, particularly berries and cherries.
Thanks to its polyphagy and high mobility, it can reproduce massively in natural habitats surrounding cultivated plots, rich in host plants that provide fruits to infest almost all year round. The spillover of adults from semi-natural and forested habitats to crops is one of the phenomena that most complicates infestation control.
In this context, management strategies based solely on the use of insecticides for adult control have proven ineffective and must be integrated with appropriate agronomic practices and biological control techniques.
Photo 1. Damage caused by Drosophila suzukii on cherry fruits (Source: Boselli, Emilia Romagna Region)
The study day on February 19, promoted by the North-East section of the Accademia dei Georgofili under the patronage of the Edmund Mach Foundation, and hosted at the auditorium of the Sant’Orsola Cooperative in Pergine Valsugana (TN), was an opportunity to update technicians and producers on the effectiveness of currently implemented control methods and the prospects offered by the application of biological control.
It was reiterated that there is no single technical solution capable of ensuring effective control of D. suzukii, but that it is essential to integrate various available techniques, from insecticide treatments to agronomic practices, up to the organization of the harvesting process.
Among well-established practices are frequent mowing of ground cover, canopy management through proper pruning, and wider planting spacing to promote light penetration and canopy aeration.
Additionally, shortening harvest intervals and removing waste fruit, or using an augmentorium to isolate infested fruit and support the proliferation of native and introduced parasitoids active on D. suzukii, are recommended.
Where possible, it is advisable to review the scheduling of production cycles to avoid the periods most favorable for D. suzukii infestation.
Installing anti-insect nets in a monobloc version, rather than the single-row type, has shown significant advantages, allowing easier access for treatments against other plant diseases and for routine cultivation activities.
Monitoring flight activity is also crucial to determine the optimal timing for intervention and the best moment to close the nets.
Photo 2. Single-row multitasking covers on cherry trees (Source: SL Fruit Service)
Traditional Biological Control
Regarding the classical biological control program through the release of the alien parasitoid Ganaspis kimorum, now in its fourth year of implementation, sampling data show a constant increase in the absolute number of G. kimorum individuals from 2021 to 2024.
In Trentino, findings have been higher than in other regions, with an increase over previous seasons: in 2024, 25% of sites showed presence in pre-release, and 60% in post-release. All captured individuals emerged from D. suzukii pupae, confirming the parasitoid’s specialization towards the target species.
Photo 3. Leptopilina japonica, larval parasitoid of D. suzukii (Source: Senesaica)
The discovery of the alien larval parasitoid Leptopilina japonica in the provincial territory in 2019 has opened new prospects for the biological control of D. suzukii. Extensive monitoring in the following years confirmed its near-ubiquitous distribution, with D. suzukii parasitization rates varying according to different spontaneous host plants, seasonality, and environmental context.
Currently, L. japonica represents the main antagonist of D. suzukii in areas where it has naturally arrived, with parasitization rates averaging around 20% (0-70%). Monitoring has also established that, although L. japonica is not a host-specific parasitoid, its parasitization is limited to very few species phylogenetically close to D. suzukii.
However, adventive populations of L. japonica cannot yet be manipulated for augmentative biological control. The idea of planned releases at specific seasonal moments or in areas with low natural populations could significantly increase its impact on the pest.
Ongoing studies aim to gather evidence demonstrating the absence of risks in using L. japonica, with the goal of requesting authorization for its augmentative application.
Among innovative strategies for controlling D. suzukii, the "Sterile Insect Technique" is emerging as a promising and sustainable approach, particularly effective when integrated with classical and augmentative biological control.
Sterile D. suzukii males, obtained through irradiation, are already available on the market, and the first field trials have been conducted in the United Kingdom. In addition to classical SIT, a genetic SIT based on the concept of self-limiting gene drive is under development.
Studies on specific genetic lines are ongoing to assess their fitness and reproductive behavior. Although current European regulations still prevent the full-field release of genetically modified insects, new genome editing technologies are evolving rapidly and could soon change regulatory scenarios, opening new perspectives for large-scale genetic SIT application.
Video of the seminar presentations:
Claudio Ioriatti
Source: Accademia dei Georgofili
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