# Contrasting Invasion Strategies, Convergent Outcomes: Establishment of Zaprionus tuberculatus and Ceroplastes ceriferus in Italy

## TL;DR

Two invasive insect species, a fruit fly and a wax scale, have successfully established in Italy despite limited genetic diversity, showing how ecological flexibility and human activity can aid invasions.

## Contribution

The study reveals how contrasting invasion strategies can lead to successful establishment despite low genetic variation, emphasizing the role of human-mediated transport and ecological plasticity.

## Key findings

- Zaprionus tuberculatus was found on ten host plants, with highest abundance on persimmon, and reproduced only on figs and blueberries.
- Ceroplastes ceriferus showed polyphagy and established on four host plants in southern Italy.
- Both species had limited genetic variation in Italy, yet successfully established, highlighting the genetic paradox in invasive species.

## Abstract

Two non-native insect species, the fruit fly Zaprionus tuberculatus and the wax scale Ceroplastes ceriferus, have recently extended their distribution range into Italy. Although they differ greatly in behaviour and biology, the fruit fly being highly mobile and the wax scale remaining fixed on the plant, both established themselves in local environments through different invasion pathways. This study examined where these species occur, which plants they attack, and whether they are able to reproduce under Italian conditions. The insects were also analysed genetically to understand how much variation they possess and how Italian populations relate to those from other parts of the world. Such information helps clarify how these species arrive, spread, and adapt to new areas. The findings show that both insects are already established on several host plants and can persist under Mediterranean climate conditions. Despite carrying only limited genetic variation, both species successfully settled in the region. This outcome reflects what is known as the “genetic paradox”, in which invasive species can thrive even with reduced genetic diversity, highlighting the need for continued surveillance and a better understanding of the mechanisms that enable successful establishment.

Global warming and international trade are accelerating biological invasions, making the Mediterranean basin a hotspot for alien arthropods. Two invasive species, the drosophilid Zaprionus tuberculatus and the wax scale Ceroplastes ceriferus, were recently detected in central-southern Italy. Surveys conducted between 2023 and 2024 detected Z. tuberculatus across several sites in Campania and Lazio, and C. ceriferus in Campania. Zaprionus tuberculatus was reared from ten host plants, including three new records, and reached its highest abundance on persimmon. Laboratory assays showed that Z. tuberculatus adults reproduced only on intact fig fruits and blueberry, indicating a limited risk for most crops. Ceroplastes ceriferus was found on four hosts, confirming its polyphagy and establishment in southern Italy. Molecular analyses revealed two COI haplotypes in the Italian populations of both species, while three haplotypes were detected globally in Z. tuberculatus and seven in C. ceriferus. Sequence divergences were moderate, indicating limited but appreciable mitochondrial differentiation among geographic populations. In Z. tuberculatus, the COII haplotype detected in Italy did not match available African sequences, underscoring gaps in reference data and complicating the reconstruction of invasion routes. Despite contrasting ecological traits and dispersal strategies, both species achieved successful establishment in Italy, showing that ecological plasticity and human-mediated transport can offset reduced genetic diversity. These records expand the known European range of both species and highlight the need for coordinated surveillance, genetic monitoring, and preventive measures to limit further introductions in the Mediterranean region.