Lorenzo Tonina

Non-crop plants used as hosts by Drosophila suzukii in Europe

The invasive spotted wing drosophila Drosophila suzukii, a fruit fly of Asian origin, is a major pest of a wide variety of berry and stone fruits in Europe. One of the characteristics of this fly is its wide host range. A better knowledge of its host range outside cultivated areas is essential to develop sustainable integrated pest management strategies. Field surveys were carried out during two years in Italy, the Netherlands and Switzerland. Fruits of 165 potential host plant species were collected, including mostly wild and ornamental plants. Over 24,000 D. suzukii adults emerged from 84 plant species belonging to 19 families, 38 of which being non-native. Forty-two plants were reported for the first time as hosts of D. suzukii. The highest infestations were found in fruits of the genera Cornus, Prunus, Rubus, Sambucus and Vaccinium as well as in Ficus carica, Frangula alnus, Phytolacca americana and Taxus baccata. Based on these data, management methods are suggested. Ornamental and hedge plants in the vicinity of fruit crops and orchards can be selected according to their susceptibility to D. suzukii. However, the widespread availability and abundance of non-crop hosts and the lack of efficient native parasitoids suggest the need for an area-wide control approach.

Comparison of attractants for monitoring Drosophila suzukii in sweet cherry orchards in Italy

The invasiveness of Drosophila suzukii Matsumura is causing sizable damage to soft fruits and cherry. In order to define a targeted strategy for D. suzukii management, it is important to have access to highly sensitive trapping tools for detection, monitoring and control that are also selective, practical in use, economic, and with low environmental impact. The aim of this study was to compare different combinations of traps and lures to define a best practice approach for D. suzukii monitoring in Italy, extended over a wide elevational gradient and landscape complexity. The high attractiveness was not always combined with high selectivity, as in some cases up to 95% of the Drosophila spp. captured were belonging to species different from D. suzukii. The commercial Droso‐Trap was very efficient providing high capture ability. Overall, the most attractive lure was Droskidrink while Suzukii Trap was the most selective one. Lure attractiveness and selectivity, however, changed during the season in relation to environmental temperatures and phenological developmental stages, suggesting the need for implementing different lures in different periods and for the different purposes (monitoring or mass trapping). In terms of trap management, Droskidrink showed the problem of bacterial‐gel formation, while Suzukii Trap and Pherocon SWD were easier to handle as they did not need to be checked at weekly interval. Finally, these results were gathered to convey the most efficient combination of trap and bait able to efficiently perform mass trapping and attract and kill technique.

Spillover of Drosophila suzukii between noncrop and crop areas: implications for pest management: D. suzukii between crop and noncrop habitats

Semi‐natural areas may promote Drosophila suzukii population dynamics by providing alternative host resources, overwintering habitats and refuge areas during cold, warm or dry periods, or when crops are sprayed with insecticides. In the present study, we investigated the spillover of D. suzukii between noncrop and crop areas using sweet cherry as a model crop. We sampled the pest at different heights and at different distances from the forest, from the the winter dormancy stage to the post‐harvest period. Drosophila suzukii activity‐density in the orchards declined strongly with increasing distance from the forest margin and with increasing height above the ground. The observed patterns varied over the crop phenological development stages, indicating that the pest used multiple habitats throughout the year. When the host plant was not suitable for reproduction, D. suzukii preferred to fly closer to the forest margin and at lower heights. When the host plant was suitable (i.e. ripe cherries), D. suzukii further colonized the orchards both horizontally and vertically, exploring the canopy volume more in depth. The results of the present study will contribute to the development of more effective and practical approaches for protecting fruit crops from D. suzukii and improving chemical, physical or mechanical control measures.

Genetic variability in Italian populations of Drosophila suzukii

BackgroundDrosophila suzukii is a highly destructive pest species, causing substantial economic losses in soft fruit production. To better understand migration patterns, gene flow and adaptation in invaded regions, we studied the genetic structure of D. suzukii collected across Italy, where it was first observed in 2008. In particular, we analysed 15 previously characterised Simple Sequence Repeat (SSR) markers to estimate genetic differentiation across the genome of 278 flies collected from nine populations.ResultsThe nine populations showed high allelic diversity, mainly due to very high heterozygosity. The high Polymorphism Information Content (PIC) index values (ranging from 0.68 to 0.84) indicated good discrimination power for the markers. Negative fixation index (FIS) values in seven of the populations indicated a low level of inbreeding, as suggested by the high number of alleles. STRUCTURE, Principal Coordinate and Neighbour Joining analysis also revealed that the Sicilian population was fairly divergent compared to other Italian populations. Moreover, migration was present across all populations, with the exception of the Sicilian one, confirming its isolation relative to the mainland.ConclusionsThis is the first study characterising the genetic structure of the invasive species D. suzukii in Italy. Our analysis showed extensive genetic homogeneity among D. suzukii collected in Italy. The relatively isolated Sicilian population suggests a largely human-mediated migration pattern, while the warm climate in this region allows the production of soft fruit, and the associated D. suzukii reproductive season occurring much earlier than on the rest of the peninsula.

Temperature-induced phenotypic plasticity in the ovipositor of the invasive species Drosophila suzukii

Drosophila suzukii (Matsumura, 1931) is a highly successful invasive dipteran which represents a serious threat for global fruit industry. Among other adaptive traits, D. suzukii owes its success to the derived morphological features of its ovipositor, which allows the insect to exploit the exclusive ecological niche of fresh fruit, thus avoiding competition with other closely related species. With the aim of investigating temperature-induced phenotypic plasticity of D. suzukii ovipositor, we reared this insect in four different laboratory conditions, represented by the combination of two developmental temperatures and two diet regimes for the larvae. We recorded the effects of these two factors on ovipositor size and shape and overall body size through a combination of distance-based and geometric morphometric analyses. Results showed that insects attain the largest body sizes at lower temperature, whereas the diet does not determine significant difference in size. However, the effect on size of the two factors is less pronounced in the ovipositor, which shows a negative allometry with respect to body size in all treatments. At higher temperature, ovipositor shape tends also to co-vary with its own size. Neither temperature nor diet have significant effect on ovipositor bilateral fluctuating asymmetry. These results confirm the hypothesis that in D. suzukii the toughened valve of the ovipositor are subjected to effective morpho-functional constraints, while probably being under strong selection by reason of their mechanical role.

Temperature Alters the Response to Insecticides in Drosophila suzukii (Diptera: Drosophilidae)

Abstract Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive pest in Europe and is a major threat to the soft fruit industry. Because of an ample temperature range, the pest spans from low to high elevation crops in mountain areas of the Southern Alps. Starting from field observations on the variable efficacy of insecticides under different temperatures, experiments were designed to test the efficacy of chemical families of insecticides available against this pest. Pyrethroids and spynosins proved to be the most effective under all temperature conditions (14, 22, and 30°C) in all assays. Organophosphates and neonicotinoids showed significantly lower efficacy at low temperatures, indicating that they are not suitable to protect crops under those conditions. The management of the pest in cold habitats, which are suitable for the cultivation of high-quality berries as for example in mountain farming systems, is constrained by a limited number of molecules available for fruit protection. Temperature has to be considered among factors affecting the decision-making process for the choice of registered formulations to be used in pest control.

Erratum to: Non-crop plants used as hosts by Drosophila suzukii in Europe

The article was originally published Online First without open access. After publication in Volume 89, Issue 3, pp. 735–748 the author decided to opt for Open Choice and to make the article an open access publication. Therefore, the copyright of the article has been changed to The Author(s) [2017] and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons. org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.