The geographic range of a species, whether measured as the area it occupies or the outermost boundary of its distribution, is not a fixed property. It expands, contracts and shifts as populations grow or collapse, as species interact, and as environmental conditions change. In a warming world, the classic expectation is poleward movement: as high latitudes become milder, temperate species follow the heat toward the poles. Most of the empirical evidence for this pattern comes from the Northern Hemisphere, where dense historical records and long-running ecological surveys make such shifts easier to detect. The Southern Hemisphere, and South America in particular, has been far less studied, despite mounting evidence of distributional changes and new outbreaks of both native and introduced insects in Chile.

The stakes of understanding these movements are considerable. Invasive insects are already among the most costly biological invaders on the planet, with global economic losses estimated at more than US$70 billion per year through damage to agriculture and forestry. As ectotherms, insects are exquisitely sensitive to temperature: their survival, growth rates, voltinism, the number of generations they produce per year, and even their size at maturity all respond to thermal conditions. For non-native species, climate change can do something even more insidious: it can weaken or dissolve the biotic and abiotic barriers that once held them in check, opening windows of opportunity for establishment and spread that did not exist before.

Chile presents an unusually instructive natural laboratory for studying these dynamics. The country is a long, narrow ribbon of land, ranging from 90 to 445 kilometers in width, stretched along the western edge of South America. To the north lies the Atacama Desert, an impassable barrier that effectively caps the northward spread of many species, which means that for beetles colonizing from the Northern Hemisphere, the only direction of meaningful range change is south. Since the 1950s, the arrival of non-native species in the region has intensified, driven by globalization, agricultural expansion and biological control programs. At the same time, central and southern Chile has endured a severe megadrought lasting at least fourteen years, reducing precipitation and water availability, weakening host plants and forests, and potentially rendering them more vulnerable to pest establishment.

To quantify these dynamics, the researchers drew on trap records from the National Plant Health System of Chile’s Agricultural and Livestock Service, known as SAG, which maintains a network of sampling sites in urban parks, forest plantations and natural or semi-natural areas. Sampling sites and effort were kept relatively constant through time, and all species detections were logged in a national database. The team focused on 25 exotic beetle species with long histories of establishment in Chile, each with more than 100 records, collected between 2007 and 2022. By restricting the analysis to species well past the initial expansion phase after introduction, the researchers aimed to separate genuine climate-driven range dynamics from the simple spreading that follows any new arrival.

The analytical approach centered on the latitude of each species’ southern range limit in each growing season, defined from July of one calendar year to June of the next to reflect the Southern Hemisphere’s seasonal cycle. To avoid noise from anecdotal detections, such as single individuals found in ports due to coastal shipping, the team used the 97.5 percent quantile of latitude as the operational definition of the southern limit. Environmental data came from the ERA5 global reanalysis, a high-resolution climate dataset providing monthly-averaged near-surface temperature and total precipitation. From these data the researchers calculated the positions of key isotherms, lines of constant temperature at 12 and 18 degrees Celsius in spring and summer, and isohyets, lines of constant rainfall at 300 and 500 millimeters. The temperature thresholds were chosen because they approximate the median and 90th percentile of lower thermal limits reported for beetles, while the rainfall thresholds bracket the annual precipitation typical of central Chile and serve as proxies for drought stress.

The statistical machinery was built around Generalized Additive Models, or GAMs, a flexible framework capable of capturing nonlinear relationships between the species’ southern limits and the climatic variables. Because GAMs are prone to overfitting, the researchers constrained each model to just three predictors, one spring isotherm, one summer isotherm and one precipitation variable, and employed cubic regression splines with shrinkage, a technique that adds an extra penalty capable of shrinking uninformative smooth terms to zero so they can be removed from the model. Restricted Maximum Likelihood was used to estimate the smoothing parameter instead of the default generalized cross-validation, and the best model for each species was selected using Bayesian Information Criterion weights and the proportion of deviance explained. The relative importance of each predictor was then assessed with the Average Shared Variance method, and range trends over time were tested with Spearman’s rank correlation, with negative correlations indicating southward expansion and positive correlations indicating contraction.

The results revealed a strikingly heterogeneous picture. For 11 of the 25 species, including the dried-fruit beetle Carpophilus lugubris, the ambrosia beetle Xyleborinus saxeseni, the eucalyptus borer Phoracantha semipunctata, the cigarette beetle Lasioderma serricorne and the pea weevil Bruchus pisorum, the best models explained more than half of the variation in southern range limit, with deviance explained values reaching as high as 0.985 for C. lugubris. Precipitation emerged as the single most important environmental variable, ranking first for five of the eleven well-explained species, followed by the spring 12-degree isotherm. Meanwhile, nine species showed statistically significant southward expansion between 2007 and 2021, with the gap between their minimum and maximum recorded southern limits ranging from 202 kilometers for C. lugubris to a remarkable 1,426 kilometers for the ladybird beetle Adalia bipunctata. The remaining 16 species showed no significant change, although ten displayed a tendency to expand and six to contract.

Perhaps the most puzzling finding is what did not predict these divergent outcomes. The researchers examined whether native range, feeding guild, host plants or time since establishment could explain why nine species expanded while sixteen did not, and no consistent pattern emerged. Among the aphid-eating ladybird beetles, Hippodamia variegata, Adalia bipunctata and Scymnus loewii expanded their ranges while their close relatives Hippodamia convergens and Olla v-nigrum did not. Both narrow specialists, such as Chrysolina hyperici confined to St. John’s wort, and generalists, such as S. loewii feeding on aphid colonies, appeared among the expanders. Establishment history offered no guidance either: C. lugubris, established in 1963, expanded while the closely related C. hemipterus, present since 1855, did not. The authors caution that for species with recent introductions, such as the bark beetle Hylastes linearis first recorded in 2006, human-assisted dispersal cannot be ruled out, and that the post-introduction spread phase may not be fully separable from climate-related change.

The implications for the austral ecosystems of Patagonia are sobering. If the documented associations between range limits and climate variables reflect genuine climatic constraints, then climate projections indicating decreased precipitation and rising temperatures across central Chile and northern Patagonia suggest that southward displacement may continue, with potentially significant consequences for some of the most intact ecosystems on the continent. Incoming insects could alter local species assemblages, shifting total biomass and richness, and even driving climate-induced hybridization between related native and exotic lineages. The authors note that for species unresponsive to macroclimate, biotic interactions such as competition and predation, or the latitudinal availability of host plants, may define their southern boundaries, and that integrating macro- and micro-environmental data will be essential for precise prediction. By identifying which species are moving, how fast, and under which climatic conditions, the study provides a foundation for designing containment strategies aimed at shielding the relatively pristine ecosystems of the far south from an invasion that, in at least nine cases, is already well underway.

Subject of Research: Climate-driven southward range expansion of non-native beetle species in Chile

Article Title: Divergent range dynamics among non-native Coleoptera: climate drivers and poleward expansion in multiple species

Article References: Januario, S. M., Silva, C. P., López, D. N., & Estay, S. A. (2026). Divergent range dynamics among non-native Coleoptera: climate drivers and poleward expansion in multiple species. Frontiers in Insect Science, 6, Article 1917683. https://doi.org/10.3389/finsc.2026.1917683

Image Credits: AI Generated

DOI: 10.3389/finsc.2026.1917683

Keywords: Coleoptera, invasive species, range shift, climate change, Chile, Patagonia, Generalized Additive Models, precipitation, temperature, biological invasion, ERA5 reanalysis, southern range limit