Seed wasp invasions promoted by unregulated seed trade affect vegetal and animal biodiversity

Abstract

Cone and seed insects are considered the most important predators of tree seeds during the pre-dispersal phase of development. Among them, exotic seed chalcids in the genus Megastigmus invaded Europe as a result of the rapidly-increasing and mostly unregulated seed trade for afforestation and ornamental plantations. Unlike their economic impact in seed orchards, until recently, little attention was paid to the ecological impact of these insects. In the present study, selected case studies of alien Megastigmus spp. were considered to assess their specific impact on the potential of natural regeneration of native woody plants and on the native entomofauna competing for seed resource. We re-analyzed data from former studies that did not focus on these ecological interactions and, here, present previously unpublished results. Seeds of Douglas-fir, true cedars, true firs and wild roses were sampled all over Europe, and the relative importance of the native and invasive chalcid species was assessed as well as their specific impact on seed yield. In most cases, the recent arrival of alien chalcids resulted in a significant decrease in the regeneration potential of the host trees. In the absence of competitors, alien chalcids occupied the entire seed niche in Douglas-fir, but their impact tended to decrease after the arrival of invasive seed bugs. In firs, alien chalcids tended to displace the native chalcids, but not in wild roses and cedars, where their damage was increasing. Different biological traits that might explain invasive success of alien chalcids are discussed. However, no general invasive patterns seem to exist.

Megastigmus seed chalcids (Hymenoptera, Torymidae) radiated much more on Angiosperms than previously considered. I- Description of 8 new species from Kenya, with a key to the females of Eastern and Southern Africa

“…The seed trade, in particular, has been identified as highly prone to pest invasion as a result of the limited measures in place to regulate seed traffic and the specific biology of the associated alien organisms (Auger-Rozenberg and Roques 2012). Indeed, phytosanitary regulations regarding the trade in tree seeds are non-existent in a number of countries, including those of the European Union, whilst the exploding development of trade through the internet allows seeds to move quite freely all over the world.…”

“…In addition, the endophytic way of life of most insects associated with seeds makes it difficult to detect their presence during the transport and importation processes. In most cases, examining the outside of the seeds does not provide any evidence of insect larvae which can be detected only when seeds are X-rayed (Auger-Rozenberg and Roques 2012). As a result, 11 of the 21 seed wasp species in the genus Megastigmus (Hymenoptera, Torymidae) known to date in Europe are of exotic origin (Roques and Skrzypczyńska 2003).…”

“…As a result, 11 of the 21 seed wasp species in the genus Megastigmus (Hymenoptera, Torymidae) known to date in Europe are of exotic origin (Roques and Skrzypczyńska 2003). This level of invasion has already had negative consequences for both natural regeneration of native trees and seed niche exploitation by native seed feeders (Auger-Rozenberg and Roques 2012). Therefore, it is important to increase our knowledge about the species that may be introduced with tree seeds.…”

Linking niche theory to ecological impacts of successful invaders: insights from resource fluctuation‐specialist herbivore interactions

“…Accordingly, we focused on the sequential invasion of French true cedar ( Cedrus atlantica ) forests by the two seed‐specialized wasps, Megastigmus pinsapinis and Megastigmus schimitscheki (Hymenoptera: Torymidae). Wasps of the genus Megastigmus are highly invasive pre‐dispersal seed predators, for which the global and largely unregulated seed trade has generated many recent and unique species assemblages in both urban and forest ecosystems (Auger‐Rozenberg & Roques ). All Megastigmus species share the same cryptic life cycle, reflecting their strong specialization on seed resources (Roques & Skrzypczynska ).…”

Temporal Population Genetics of Time Travelling Insects: A Long Term Study in a Seed-Specialized Wasp

“…Although those two cedar species were introduced to many Mediterranean countries as ornamental trees, invasive populations of M. schimitscheki have been observed to date solely in southeastern France. M. schimitscheki progressively invaded most of the planted C. atlantica stands in France, even showing a competitive advantage over its direct and closely related resident competitor M. pinsapinis (Hoffmeyer) [30], [31]. C. atlantica is considered a masting tree species [32], [33] and is thus thought to impose drastic and quite unpredictable variations in resource supply on its seed-specialized predators [29], [30].…”