Aim Urbanization is one of the most significant anthropogenic alterations of the surface of the Earth and constitutes a major threat to biodiversity at the global level. Arthropods are a very diverse group of organisms, with many species that provide essential ecosystem services. However, their response to urbanization is still unclear. Here, we describe the first meta‐analysis to evaluate the overall effects of urbanization on terrestrial arthropod communities and driving factors related to cities, arthropods and methods. Location Global. Time period 1979–2019. Major taxa studied Arthropods. Methods We compiled a dataset of 162 publications that have evaluated the effects of urbanization along rural–urban gradients, which yielded 196 observations for diversity and 148 for abundance of arthropods. Moderator variables related to cities (climatic region, size, age, air pollution level and vegetation cover), arthropods (taxonomic and functional group and mobility level) and methods (study duration and type of gradient) were considered. We analysed the data through a hierarchical meta‐analysis that allowed us to take into account the dependence of multiple effect sizes obtained from one study. Results Overall, urbanization had a negative effect on the diversity and abundance of terrestrial arthropods. The magnitude of the changes in diversity and abundance along the urban gradient depended on the arthropod taxonomic group. Coleoptera and Lepidoptera were the most affected groups, suggesting that not all species respond in the same way to urbanization. In addition, the age of the cities had a slightly negative influence, but only on abundance. Main conclusions Our results indicate that terrestrial arthropod communities are less diverse and abundant in more urbanized landscapes. Considering the current biodiversity crisis and the fact that urbanization is one of the most extreme forms of global environmental change, the evidence presented here could be useful to support and direct new conservation efforts in urban habitats.

Abstract. Local habitat size has been shown to influence colonization and extinction processes of species in patchy environments. However, species differ in body size, mobility, and trophic level, and may not respond in the same way to habitat size. Thus far, we have a limited understanding of how habitat size influences the structure of multitrophic communities and to what extent the effects may be generalizable over a broad geographic range. Here, we used water-filled bromeliads of different sizes as a natural model system to examine the effects of habitat size on the trophic structure of their inhabiting invertebrate communities. We collected composition and biomass data from 651 bromeliad communities from eight sites across Central and South America differing in environmental conditions, species pools, and the presence of large-bodied odonate predators. We found that trophic structure in the communities changed dramatically with changes in habitat (bromeliad) size. Detritivore : resource ratios showed a consistent negative relationship with habitat size across sites. In contrast, changes in predator : detritivore (prey) ratios depended on the presence of odonates as dominant predators in the regional pool. At sites without odonates, predator : detritivore biomass ratios decreased with increasing habitat size. At sites with odonates, we found odonates to be more frequently present in large than in small bromeliads, and predator : detritivore biomass ratios increased with increasing habitat size to the point where some trophic pyramids became inverted. Our results show that the distribution of biomass amongst food-web levels depends strongly on habitat size, largely irrespective of geographic differences in environmental conditions or detritivore species compositions. However, the presence of largebodied predators in the regional species pool may fundamentally alter this relationship between habitat size and trophic structure. We conclude that taking into account the response and multitrophic effects of dominant, mobile species may be critical when predicting changes in community structure along a habitat-size gradient.

1. Urbanisation is one of the main land-use changes behind global insect collapse. Despite that previous studies have described the negative effects of urbanisation on insect communities, so far there is no synthesis that considers multiple urban drivers, their combined effects, and the role of species traits altogether.2. Here we developed an integrative framework of the underlying mechanisms behind terrestrial insect species loss in cities by exploring five leading drivers: impervious surfaces, habitat fragmentation, urban heat island, pollution, and exotic plants. For each driver, we identified the main direct and indirect (mediated through species interactions or changes in resources) effects on insect populations and communities, emphasising the role of species traits as moderators of such effects.3. Body size, mobility, and oviposition/nesting requirements were the traits that frequently defined insect vulnerability to urban drivers. Urban heat island and pollution deserve further research from a community-level approach. Direct effects of drivers dominated the literature, while most indirect paths were mediated by changes in resources rather than species interactions.4. In conclusion, our review showed the challenges of recognising particular effects and mechanisms for each urban driver and their combined effects. By doing so, we intended to encourage researchers to address some of the gaps we noticed in order to fully understand how urbanisation is affecting insect communities. Finally, we outlined the main recent urban planning strategies and future challenges in order to successfully conserve urban insect biodiversity.

The optimal oviposition theory predicts that oviposition preferences of phytophagous insects should correlate with host suitability for their offspring. As plant host suitability depends not only on its quality as food, but also on its provision of enemy‐free space, we examined the relationship between adult host preference and offspring performance for the leafminer Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) on various host plants, considering also the interaction with natural enemies. Preference and offspring performance were assessed through observational field data and laboratory experiments in central Argentina. Field data suggested a positive host preference – performance linkage, as the leafminer attained larger body size on the crops where it was more abundant. Laboratory trials supported these results: Vicia faba L. (Fabaceae) was the preferred host in the laboratory as well as in the field, performance of L. huidobrensis being also best on this host, with highest survival rates and shortest development time. The actively feeding larval stage showed the largest plant‐related effects. Higher overall parasitism rates were found on plants from which smaller leafminers were reared, reinforcing the preference–performance linkage. On the other hand, the main parasitoid Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) reached larger body size, and caused higher mortality rates on crops where the leafminer was larger. Changes in abundance of particular parasitoid species could thus modify overall parasitism trends.

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1. The spatial structure of plant patches has been shown to affect host–parasitoid interactions, but its influence on parasitoid diversity remains largely ignored. Here we tested the prediction that parasitoid species richness of the specialist leafminer Liriomyza commelinae increases in larger and less isolated patches of its host plant Commelina erecta. We also explored whether parasitoid abundance and body size affected the occurrence of parasitoid species in local assemblages.2. A total of 893 naturally established C. erecta patches were sampled on 18 sites around Córdoba city (Argentina). Also, two experiments were performed by creating patches differing in the number of plants and the distance from a parasitoid source. For these tests, plants were infected with the miner in the laboratory prior to placement in the field.3. Plant patch size, independently of host abundance, positively affected the number of parasitoid species in both survey observations and experimental data. However, plant patch isolation did not influence parasitoid species richness.4. The probability of finding rare parasitoid species increased with patch size, whereas occupation of isolated patches was independent of dispersal abilities (body size) of parasitoid species.5. Overall, the results highlight the importance of considering spatial aspects such as the size of plant patches in the study of parasitoid communities.

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Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-free space. Female leafminers preferred laying their eggs on Vicia faba (Fabaceae) over Beta vulgaris var. cicla (Chenopodiaceae), in both laboratory and field choice experiments, although no oviposition preference was observed in no-choice tests. Females fed more often on B. v. var. cicla (no-choice test) or showed no feeding preference (choice test), even when their realized fecundity was remarkably higher on V. faba. Offspring developed faster, tended to survive better, and attained bigger adult size on the preferred host plant. Also, a field experiment showed higher overall parasitism rates for leafminers developing on B. v. var. cicla, with a nonsignificant similar tendency in field surveys. According to these results, host plant selection by L. huidobrensis appears to be driven mainly by variation in host quality. Moreover, the consistent oviposition choices for the best host and the labile feeding preferences observed here, suggest that host plant selection might be driven by maximization of offspring fitness even without a conflict of interest between parents and offspring. Overall, these results highlight the complexity of decisions performed by phytophagous insects regarding their host plants, and the importance of simultaneous evaluation of the various driving forces involved, in order to unravel the adaptive significance of female choices.