Land-use change in the past 40 years explains shifts in arthropod community traits.

Understanding how anthropogenic activities induce changes in the functional traits of arthropod communities is critical to assessing their ecological consequences. However, we largely lack comprehensive assessments of the long-term impact of global-change drivers on the trait composition of arthropod communities across a large number of species and sites. This knowledge gap critically hampers our ability to predict human-driven impacts on communities and ecosystems. Here, we use a dataset of 1.73 million individuals from 877 species to study how four functionally important traits of carabid beetles and spiders (i.e. body size, duration of activity period, tolerance to drought, and dispersal capacity) have changed at the community level across ~40 years in different types of land use and as a consequence of land use changes (that is, urbanisation and loss of woody vegetation) at the landscape scale in Switzerland. The results show that the mean body size in carabid communities declined in all types of land use, with particularly stronger declines in croplands compared to forests. Furthermore, the length of the activity period and the tolerance to drought of spider communities decreased in most land use types. The average body size of carabid communities in landscapes with increased urbanisation in the last ~40 years tended to decrease. However, the length of the activity period, the tolerance to drought, and the dispersal capacity did not change significantly. Furthermore, urbanisation promoted increases in the average dispersal capacities of spider communities. Additionally, urbanisation favoured spider communities with larger body sizes and longer activity periods. The loss of woody areas at the landscape level was associated with trait shifts to carabid communities with larger body sizes, shorter activity periods, higher drought tolerances and strongly decreased dispersal capacities. Decreases in activity periods and dispersal capacities were also found in spider communities. Our study demonstrates that human-induced changes in land use alter key functional traits of carabid and spider communities in the long term. The detected trait shifts in arthropod communities likely have important consequences for their functional roles in ecosystems.

Different roles of concurring climate and regional land-use changes in past 40 years' insect trends.

Climate and land-use changes are main drivers of insect declines, but their combined effects have not yet been quantified over large spatiotemporal scales. We analysed changes in the distribution (mean occupancy of squares) of 390 insect species (butterflies, grasshoppers, dragonflies), using 1.45 million records from across bioclimatic gradients of Switzerland between 1980 and 2020. We found no overall decline, but strong increases and decreases in the distributions of different species. For species that showed strongest increases (25% quantile), the average proportion of occupied squares increased in 40 years by 0.128 (95% credible interval: 0.123-0.132), which equals an average increase in mean occupancy of 71.3% (95% CI: 67.4-75.1%) relative to their 40-year mean occupancy. For species that showed strongest declines (25% quantile), the average proportion decreased by 0.0660 (95% CI: 0.0613-0.0709), equalling an average decrease in mean occupancy of 58.3% (95% CI: 52.2-64.4%). Decreases were strongest for narrow-ranged, specialised, and cold-adapted species. Short-term distribution changes were associated to both climate changes and regional land-use changes. Moreover, interactive effects between climate and regional land-use changes confirm that the various drivers of global change can have even greater impacts on biodiversity in combination than alone. In contrast, 40-year distribution changes were not clearly related to regional land-use changes, potentially reflecting mixed changes in local land use after 1980. Climate warming however was strongly linked to 40-year changes, indicating its key role in driving insect trends of temperate regions in recent decades.

Predation on Drosophila suzukii within Hedges in the Agricultural Landscape.

The invasive Drosophila suzukii feeds and reproduces on various cultivated and wild fruits and moves between agricultural and semi-natural habitats. Hedges in agricultural landscapes play a vital role in the population development of D. suzukii, but also harbor a diverse community of natural enemies. We investigated predation by repeatedly exposing cohorts of D. suzukii pupae between June and October in dry and humid hedges at five different locations in Switzerland. We sampled predator communities and analyzed their gut content for the presence of D. suzukii DNA based on the COI marker. On average, 44% of the exposed pupae were predated. Predation was higher in dry than humid hedges, but did not differ significantly between pupae exposed on the ground or on branches and among sampling periods. Earwigs, spiders, and ants were the dominant predators. Predator communities did not vary significantly between hedge types or sampling periods. DNA of D. suzukii was detected in 3.4% of the earwigs, 1.8% of the spiders, and in one predatory bug (1.6%). While the molecular gut content analysis detected only a small proportion of predators that had fed on D. suzukii, overall predation seemed sufficient to reduce D. suzukii populations, in particular in hedges that provide few host fruit resources.

Managing Floral Resources in Apple Orchards for Pest Control: Ideas, Experiences and Future Directions.

Functional biodiversity is of fundamental importance for pest control. Many natural enemies rely on floral resources to complete their life cycle. Farmers need to ensure the availability of suitable and sufficient floral biodiversity. This review summarizes 66 studies on the management of floral biodiversity in apple orchards, published since 1986. Approaches followed different degrees of intervention: short-term practices (mowing regime and weed maintenance, cover crops), establishment of durable ecological infrastructures (perennial flower strips, hedgerows) and re-design of the crop system (intercropping, agroforestry). Although short-term practices did not always target the nutrition of natural enemies by flowering plants, living conditions for them (alternative prey, provision of habitat) were often improved. Perennial flower strips reliably enhanced natural enemies and techniques for their introduction continuously developed. Resident natural enemies and their impact in pest control reacted positively to the introduction of a more diversified vegetation, whereas the response of very mobile organisms was often not directly linked to the measures taken. A careful selection and management of plants with particular traits exploitable by most natural enemies emerged as a key-point for success. Now the elaborated design of such measures needs to be adopted by stakeholders and policy makers to encourage farmers to implement these measures in their orchards.

The Distance Between Forests and Crops Affects the Abundance of Drosophila suzukii During Fruit Ripening, But Not During Harvest.

Drosophila suzukii (Matsumura; Diptera: Drosophilidae) is an invasive pest with the ability to reproduce not only in various soft fruit crops, but also in numerous wild hosts. Forests and forest edges harbor many wild hosts, provide suitable microclimatic conditions and are therefore thought to enhance the abundance of D. suzukii. Although the comprehension of pest activity based on specific landscape elements is important to implement efficient management strategies, knowledge of how forests affect the abundance of D. suzukii in nearby crops is very limited. We conducted a monitoring study with liquid baited traps across different crops at different distance from the forests. During fruit ripening, more flies were captured in crops closer to forests (22.21 % decrease per 500 m distance), whereas there was no significant relationship during harvest. Since color can affect the efficiency of D. suzukii traps, we have used traps either with a red or black lid. Acquired data suggest that traps with black lids capture significantly more flies than traps with red lids. We provide a quantitative estimation of how and when distance from adjacent forests affects the abundance of D. suzukii in crop fields. Our results can help consultants and farmers to estimate the pest pressure of D. suzukii in crop fields near forested, noncrop areas and to implement appropriate control strategies when D. suzukii populations increase and fruit becomes susceptible to infestation.

Divergent strategies in pre- and postzygotic reproductive isolation between two closely related Dianthus species.

Quantifying the relative contribution of multiple isolation barriers to gene flow between recently diverged species is essential for understanding speciation processes. In parapatric populations, local adaptation is thought to be a major contributor to the evolution of reproductive isolation. However, extrinsic postzygotic barriers assessed in reciprocal transplant experiments are often neglected in empirical assessments of multiple isolation barriers. We analyzed multiple isolation barriers between two closely related species of the plant genus Dianthus, a genus characterized by the most rapid species diversification in plants reported so far. Although D. carthusianorum L. and D. sylvestris Wulf. can easily be hybridized in crossing experiments, natural hybrids are rare. We found that in parapatry, pollinator-mediated prezygotic reproductive isolation barriers are important for both D. carthusianorum (0.761) and D. sylvestris (0.468). In contrast to D. carthusianorum, high hybrid viability in D. sylvestris (-0.491) was counteracted by strong extrinsic postzygotic isolation (0.900). Our study highlights the importance of including reciprocal transplant experiments for documenting extrinsic postzygotic isolation and demonstrates clearly divergent strategies and hence asymmetric pre- and postzygotic reproductive isolation between closely related species. It also suggests that pollinator-mediated and ecological isolation could have interacted in synergistic ways, further stimulating rapid speciation in Dianthus.

Female butterflies adapt and allocate their progeny to the host-plant quality of their own larval experience.

Recent studies with diverse taxa have shown that parents can utilize their experience of the environment to adapt their offspring's phenotype to the same environmental conditions. Thus, offspring would then perform best under environmental conditions experienced by their parents due to transgenerational phenotypic plasticity. Such an effect has been dubbed transgenerational acclimatization. However, evidence that parents can subsequently ensure the appropriate environmental conditions in order that offspring benefit from transgenerational acclimatization has never been demonstrated. We reared Pieris rapae larvae in the parental generation on high-nitrogen and low-nitrogen host plants, and reared the offspring (F1) of both treatments again on high- and low-nitrogen plants. Furthermore, we tested if females prefer to oviposit on high- or low-nitrogen host plants in two-way choice tests. We here show not only that females adapt their offspring's phenotype to the host-plant quality that they themselves experienced, but that females also mainly oviposit on the host quality to which they adapt their offspring. Moreover, effects of larval host plant on oviposition preference of females increased across two generations in F1-females acclimatized to low-nitrogen host plants, showing an adaptive host shift from one generation to the next. These findings may have profound implications for host-race formation and sympatric speciation.

Transgenerational acclimatization in an herbivore-host plant relationship.

Twenty years ago, scientists began to recognize that parental effects are one of the most important influences on progeny phenotype. Consequently, it was postulated that herbivorous insects could produce progeny that are acclimatized to the host plant experienced by the parents to improve progeny fitness, because host plants vary greatly in quality and quantity, and can thus provide important cues about the resources encountered by the next generation. However, despite the possible profound implications for our understanding of host-use evolution of herbivores, host-race formation and sympatric speciation, intense research has been unable to verify transgenerational acclimatization in herbivore-host plant relationships. We reared Coenonympha pamphilus larvae in the parental generation (P) on high- and low-quality host plants, and reared the offspring (F(1)) of both treatments again on high- and low-quality plants. We tested not only for maternal effects, as most previous studies, but also for paternal effects. Our results show that parents experiencing predictive cues on their host plant can indeed adjust progeny's phenotype to anticipated host plant quality. Maternal effects affected female and male offspring, whereas paternal effects affected only male progeny. We here verify, for the first time to our knowledge, the long postulated transgenerational acclimatization in an herbivore-host plant interaction.

Nectar amino acids enhance reproduction in male butterflies.

After over 30 years of research, it was recently shown that nectar amino acids increase female butterfly fecundity. However, little attention has been paid to the effect of nectar amino acids on male butterfly reproduction. Here, we show that larval food conditions (nitrogen-rich vs. nitrogen-poor host plants) and adult diet quality (nectar with or without amino acids) affected the amount of consumed nectar in Coenonympha pamphilus males. Furthermore, amino acids in the nectar diet of males increased progeny's larval hatching mass, irrespective of paternal larval reserves. Our study takes the whole reproductive cycle of male butterflies into account, and also considers the role of females in passing male nutrients to offspring, as males' realized reproduction was examined indirectly via nuptial gifts, by female performance. With this comprehensive approach, we demonstrate for the first time that nectar amino acids can improve male butterfly reproduction, supporting the old postulate that nectar amino acids generally enhance butterfly fitness.

Enhancing offspring quality or quantity? Different ways for using nectar amino acids in female butterflies.

Butterfly-pollinated flowers offer nectar with higher amino acid concentrations than most flowers pollinated by other animals, and female butterflies of some species prefer to consume amino acid-rich nectar. However, for over 30 years, there has been an ongoing discussion about whether nectar amino acids benefit butterfly fitness. A clear positive effect was only shown for the nectar-feeding Araschnia levana, and females of the fruit-feeding Bicyclus anynana also increased offspring quality when they were fed amino acids as adults. Thus, severe doubts remain about the general significance of these single positive results. We therefore tested a further species from a phylogenetically different butterfly subfamily, the small heath (Coenonympha pamphilus L., Satyrinae), taking into account feeding conditions over the whole life cycle of this species. C. pamphilus females receiving nectar amino acids as adults, irrespective of larval food quality, produced heavier larvae and also increased the hatching success of their eggs over the oviposition period. Furthermore, females raised under nitrogen-poor larval conditions tended to use nectar amino acids to increase the number of eggs laid. Thus, C. pamphilus females used nectar amino acids primarily to increase their offspring quality, and secondly tended to increase offspring quantity, if larval resources were scarce, showing a resource allocation pattern differing from both B. anynana and A. levana. Our study supports the old postulate that nectar amino acids generally enhance butterfly fitness.