Takehiko Yamanaka

A negative consequence of international trade is the accidental transport of non-native insect species to non-native regions, but our understanding of how this risk varies among species and how it relates to species traits remains incomplete. We conducted a multi-continental analysis of historical border interception records for bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae), integrating 13,124 interception events (353 species) from Canada, Chile, Japan, New Zealand, and the United States. We estimated an intercontinental propagule pressure index and tested how species characteristics influence transport likelihood. Interception assemblages showed low similarity among countries, with 64% of species recorded in only one nation, indicating strong geographic structuring linked to trade pathways. Interceptions were taxonomically and biogeographically non-random: species native to the Palearctic Nearctic and Indo-Malayan regions were overrepresented, whereas Neotropical, Austro-Pacific and Afrotropical taxa were underrepresented. Host tree taxa emerged as the strongest predictor of propagule pressure. Species associated with conifers—particularly Pinaceae—exhibited approximately twice the propagule pressure of species restricted to broadleaved hosts. Ambrosia beetles showed higher propagule pressure than bark and twig/seed feeders. Propagule pressure also increased with the number of regions where species have already invaded, consistent with bridgehead dynamics. Synthesis and applications: Our findings demonstrate that intercontinental transport of bark and ambrosia beetles is strongly structured by host associations, feeding guild, and biogeographic origin, reflecting the composition of traded commodities and historical trade networks. Identifying taxa with consistently high propagule pressure provides a basis for prioritizing surveillance and strengthening global forest biosecurity.

Some animals exhibit large‐amplitude fluctuations with periods close to their generation length. These fluctuations can be caused by seasonal environmental influences, scheduled pesticide applications, or ecological factors such as intraspecific regulation and consumer–resource interactions. While theory provides various mechanisms for how environmental and ecological factors might generate generational fluctuations, there has never been a field experiment testing the relative contributions of seasonal demographic synchronisation and intraspecific regulation to generation cycles in natural populations. The smaller tea tortrix, Adoxophyes honmai , is a serious pest of tea plants and a temperate multivoltine insect that undergoes 3–5 large‐amplitude generation cycles each year under natural conditions in Japan. Theory suggests that these fluctuations may represent limit cycles driven by asymmetric intraspecific interference, where older larvae directly affect younger ones. However, in the field, these populations also experience strong seasonality and periodic insecticide applications that are thought to either generate or modify these fluctuations. We conducted a replicated field‐cage experiment on the tortrix populations to manipulate the initial degree of stage synchrony and the timing of introduction. The experiment included four treatments contrasting pulsed versus continuous age structures at the onset of spring, along with two introduction timings separated by 20 days (approximately half a generation time). We minimised artificial interventions, such as harvesting and insecticide application, as well as the effect of natural enemies while allowing meteorological influences during the season. To compare the field‐cage experiment results with theoretical predictions, we constructed an age‐structured population model featuring asymmetric larval interference. We executed simulations using the same introduction scenarios as in the field‐cage experiment. We observed the emergence of clear generational cycles in all treatments of the field‐cage even in the absence of any initial demographic synchrony. This suggests an internal mechanism regulating population cycles, possibly intraspecific interference. However, the generational cycles in the field‐cage were synchronised across treatments and with outer field populations. The results from the field‐cage experiment and simulation analyses indicate that external environmental factors, such as precipitation, acted as a pacemaker for the generational cycles created by the internal regulatory mechanism.

Many organisms overwinter in a specific life stage, which means their phenology must be well‐timed with seasonal changes in the environment. As environments warm, we expect a delay in the onset of winter. For organisms where temperature is the primary driver of development rate, warming environments also mean faster development. If temperature dependence in the development rate of individuals does not also change, this will cause a mismatch between the seasonal timing of the critical overwintering stage and the onset of winter. There are two biological mechanisms by which ectotherms can adjust their phenology in the face of climate change to maintain correct timing: (1) organisms undergo evolution of the development thermal reaction norm and (2) organisms have a plastic response in their development to multiple environmental cues. Here, we use high‐resolution records of densities of the smaller tea tortrix (Adoxophyes honmai) over multiple decades across nine locations in Japan to infer temperature‐dependent changes in development rates over both time and space. The pest insect displays regular single‐generation limit cycles, which provides a unique opportunity to infer changes in developmental rates directly from historical records of natural populations. The last half century has seen a temperature increase of about 1°C across Japan, and our analyses show that populations slowed development on average by 16% to maintain the correct timing of the overwintering stage. Development rates measured from common garden experiments reveal that the change is not due to evolution. Our results build on recent laboratory studies to suggest that there is substantial plasticity in developmental thermal reaction norms that may explain how the phenology of ectotherms could respond to climate warming in natural systems.

The majority of non-native animal species globally are insects, though some insect species are more successful invaders than others. These differences can be attributed, in part, to differences among dominant trophic groups. Previous analyses indicate that insect herbivores are generally over-represented among non-native species while other groups, such as predators, are under-represented. Here we explore how invasion success varies among insect taxa and trophic groups. We quantify over-representation in species grouped by taxon (order or family) and larval trophic group (herbivore, detritivore, predator, parasite, brood carer); over- and under-representation is computed by comparing proportional representation of groups among non-native species in 12 world regions with total numbers in these same groups globally. Although herbivores are generally the most successful group among non-natives, we found their invasion success to vary among their taxonomic groups: herbivores are over-represented among Hemiptera, Diptera, Thysanoptera and Hymenoptera, but under-represented among Lepidoptera and Orthoptera; similar patterns are seen at the family-level within orders. Even after accounting for trophic group, some orders were still over-represented. Within trophic groups, this pattern appeared strongest for herbivores, where predominantly parthenogenetic families belonging to the Hemiptera and Thysanoptera were over-represented in non-native assemblages, while families in the Lepidoptera and Polyneoptera were under-represented. Over time (1850s to 2000s), fractions of non-native species numbers in certain orders and trophic groups have varied, such as among parasites, where a considerable turnover took place from mostly bird-lice (Psocodea) in the 19^th century to parasitic wasps (Hymenoptera) in the 20^th century. It is thus likely that factors other than trophic group, such as associations with invasion pathways (e.g., plants, wood packaging), cause the observed differences in the over-representation of families belonging to different orders.

Propagule pressure is one of the key drivers of establishment success of non-native species, including insects. However, border interception data, which have the potential to act as a proxy for true arrival rates (i.e., propagule pressure) of insects into a country, are seldom used to predict invasions. This can be due to the limited amount of interception data in some countries, difficulties accessing such data, and when these data are available, difficulties in addressing biases caused by variation in interception probability for different taxa due to policy changes, and operational influences of import inspections. The type of interception data required to reliably estimate arrival rates is rarely available. To improve the use of interception data as a proxy for propagule pressure, we investigated the fraction of established species which had interceptions and vice versa by taxonomic group and by biological characteristics (development type and feeding group), using several national datasets from five continents. We identified higher fractions of established species that were intercepted for plant feeding insect groups compared to fractions of non-plant feeding groups, even in countries with more general import inspection strategies. This is likely to reflect greater search effort for and recording of plant-feeding insect groups during inspections. To address this variation in interception probability and improve establishment predictions based on interception frequency, we developed a methodology to account for such taxonomic variation. We apply this to three hazard lists of insects, containing potential pests for an industry or potential pests for a country, to assess its effectiveness.

Aim: The Hemiptera is the fifth‐largest insect order but among non‐native insect species is approximately tied with the Coleoptera as the most species‐rich insect order (Hemiptera comprise 20% more species than in world fauna). This over‐representation may result from high propagule pressure or from high species invasiveness. Here, we assess the reasons for over‐representation in this group by analysing geographical, temporal and taxonomic variation in numbers of historical invasions.Location: Global.Method: We assembled lists of historical Hemiptera invasions in 12 world regions, countries or islands (Australia, Chile, Europe, New Zealand, North America, South Africa, South Korea, Japan and the Galapagos, Hawaiian, Okinawa and Ogasawara Islands) and border interception data from nine countries (Australia, Canada, European Union, United Kingdom, Hawaii, Japan, New Zealand, South Korea, USA mainland and South Africa). Using these data, we identified hemipteran superfamilies that are historically over‐represented among established non‐native species, and superfamilies that are over‐represented among arrivals (proxied by interceptions). We also compared temporal patterns of establishments among hemipteran suborders and among regions.Results: Across all regions, patterns of over‐ and under‐representation were similar. The Aphidoidea, Coccoidea, Aleyrodoidea, Cimicoidea and Phylloxeroida were over‐represented among non‐native species. These same superfamilies were not consistently over‐represented among intercepted species indicating that propagule pressure does not completely explain the tendency of some Hemiptera to be over‐represented among invasions. Asexual reproduction is common in most over‐represented superfamilies and this trait may be key to explaining high invasion success in these superfamilies.Conclusions: We conclude that both propagule pressure and species invasiveness are drivers of high invasion success in the Sternorrhyncha suborder (aphids, scales, whiteflies) and this group plays a major role in the exceptional invasion success of Hemiptera in general. The high historical rates of invasion by Sternorrhyncha species provide justification for biosecurity measure focusing on exclusion of this group.

Aim: Invasions of non‐native insects can have substantial impacts on agriculture, forestry, human health and biodiversity with considerable economic and environmental consequences. To understand the causes of these invasions, it is important to quantify the relative influence of principal drivers such as international imports and climatic effects.Location: North America, Chile, Europe, Australia, New Zealand and Japan.Time Period: 1881–2020.Methods: To evaluate the relative contributions of various factors in explaining global variation in numbers of non‐native insect establishments in different world regions, we conducted two multivariate regression analyses to quantify temporal changes in family‐level composition and native ranges of established non‐native species in several world regions.Results: There were temporal changes in the family‐level composition of non‐native species assemblages. Prior to 1900, invasions were dominated by scale insects, subsequently shifting to a more diverse set of species, except in North America, which had relatively small compositional change over time compared to other regions. Spatial and temporal variation in the composition of established species was associated with differences in the origin of imports and climatic factors, each explaining 26.3% and 27.4% of the total variation, respectively. The analysis of native ranges of non‐native species indicated that there was no consistent temporal variation across all regions. Established species in New Zealand were predominantly native to Australasia and species in North America and Chile were mainly from Europe. Non‐native species in Europe mainly originated from the Nearctic region while those in Japan and Australia generally originated from multiple regions. Climatic factors in the destination regions had a primary effect (66.3%) on variation in the native range of established species, although imports also had substantial effects (45.4%).Main Conclusions: Geographical variation in climate and imports act together as drivers of establishment success for non‐native insects in all six regions.