Pollinator enhancement in agriculture: comparing sown flower strips, hedges and sown hedge herb layers in apple orchards

In intensive agricultural landscapes semi-natural habitats for pollinators are often limited, although willingness to establish pollinator habitat is increasing among farmers. A common pollinator enhancement measure is to provide flower strips, but existent or improved hedgerows might be more effective. In this study, we compare the effectiveness of three pollinator enhancement measures at edges of conventional apple orchards: (i) perennial flower strips, (ii) existent hedgerows, and (iii) existent hedgerows complemented with a sown herb layer. We used orchard edges without any enhancement as control. The study took place over three consecutive years in Southern Germany. Wild bee abundance and species richness were highest in flower strips followed by improved hedges. Hoverflies were also most abundant in flower strips, but not more species rich than at control sites. Wild bee but not hoverfly community composition differed between control and enhancement sites. The overall pollinator community included only few threatened or specialized species. Flower abundance was the main driver for wild bee diversity, whereas hoverflies were largely unaffected by floral resources. Pollinator enhancement had neither an effect on the abundance or species richness within the orchards nor on apple flower visitation. Perennial flower strips seem most effective to enhance wild bees in intensive agricultural landscapes. Additionally, flower-rich hedgerows should be promoted to complement flower strips by extending the flowering period and to increase connectivity of pollinator habitat in agricultural landscapes.

Bees increase seed set of wild plants while the proportion of arable land has a variable effect on pollination in European agricultural landscapes

Background and aims – Agricultural intensification and loss of farmland heterogeneity have contributed to population declines of wild bees and other pollinators, which may have caused subsequent declines in insect-pollinated wild plants. Material and methods – Using data from 37 studies on 22 pollinator-dependent wild plant species across Europe, we investigated whether flower visitation and seed set of insect-pollinated plants decline with an increasing proportion of arable land within 1 km. Key results – Seed set increased with increasing flower visitation by bees, most of which were wild bees, but not with increasing flower visitation by other insects. Increasing proportion of arable land had a strongly variable effect on seed set and flower visitation by bees across studies. Conclusion – Factors such as landscape configuration, local habitat quality, and temporally changing resource availability (e.g. due to mass-flowering crops or honey bee hives) could have modified the effect of arable land on pollination. While our results highlight that the persistence of wild bees is crucial to maintain plant diversity, we also show that pollen limitation due to declining bee populations in homogenized agricultural landscapes is not a universal driver causing parallel losses of bees and insect-pollinated plants.

IPM reduces insecticide applications by 95% while maintaining or enhancing crop yields through wild pollinator conservation

Pest management practices in modern industrial agriculture have increasingly relied on insurance-based insecticides such as seed treatments that are poorly correlated with pest density or crop damage. This approach, combined with high invertebrate toxicity for newer products like neonicotinoids, makes it challenging to conserve beneficial insects and the services that they provide. We used a 4-y experiment using commercial-scale fields replicated across multiple sites in the midwestern United States to evaluate the consequences of adopting integrated pest management (IPM) using pest thresholds compared with standard conventional management (CM). To do so, we employed a systems approach that integrated coproduction of a regionally dominant row crop (corn) with a pollinator-dependent specialty crop (watermelon). Pest populations, pollination rates, crop yields, and system profitability were measured. Despite higher pest densities and/or damage in both crops, IPM-managed pests rarely reached economic thresholds, resulting in 95% lower insecticide use (97 versus 4 treatments in CM and IPM, respectively, across all sites, crops, and years). In IPM corn, the absence of a neonicotinoid seed treatment had no impact on yields, whereas IPM watermelon experienced a 129% increase in flower visitation rate by pollinators, resulting in 26% higher yields. The pollinator-enhancement effect under IPM management was mediated entirely by wild bees; foraging by managed honey bees was unaffected by treatments and, overall, did not correlate with crop yield. This proof-of-concept experiment mimicking on-farm practices illustrates that cropping systems in major agricultural commodities can be redesigned via IPM to exploit ecosystem services without compromising, and in some cases increasing, yields.

Low Pollinator Sharing Between Coexisting Native and Non-native Plant Pairs: The Effect of Corolla Length and Flower Abundance

Understanding the mechanisms by which non-native plants can attract pollinators in their new geographical zones is important because such species infiltrate native communities and can disrupt native ecological interactions. Despite the large number of studies assessing how invasive plants impact plant–pollinator interactions, the specific comparison of pollination interactions between native and non-native plant pairs has received much less attention. Here we focused on four coexisting co-flowering pairs of common native and non-native species, both with abundant flowers but different floral traits, and asked: (1) to what extent native and non-native plants share pollinator species, and whether the non-native plants attract a different set of pollinators, (2) whether the most shared pollinators are the most frequent floral visitors and the most generalized in their interactions, and (3) how much of the variation in the diversity and frequency of pollinator species between native and non-native plant species can be explained by floral trait dissimilarity and flower abundance. Direct pollinator observations revealed that the plant pairs shared a low fraction (0–33%) of insect species, i.e., non-native plants tended to acquire a different set of pollinators than their native counterparts. The most shared pollinators in each plant pair were the most common but not the most generalized species, and non-native species attracted both generalized and specialized pollinators. Corolla length at opening and flower abundance showed to be important in determining the differences in flower visitation rate between natives and non-natives. Our findings support the general pattern that non-native species have no barriers at the pollination stage to integrate into native communities and that they may attract a different assemblage of pollinators relative to those that visit native plants with which they coexist.

First records of Meromacrus cactorum (Diptera: Syrphidae) from Chile, with new biological data

The syrphid genus Meromacrus is widespread in the Neotropics, but its presence in Chile has been confirmed just recently. Adults pollinate, and larvae are saprophagous of vegetal materials. In this note, we report Meromacrus cactorum Ricarte et al. for the first time from Chile. New data on adult habitats and flower visitation are also provided for this Meromacrus. Adults were observed on flowers of the cacti Opuntia ficus-indica, Cumulopuntia sphaerica, and the vulnerable Browningia candelaris. Species distribution and pollinator potential are discussed for M. cactorum.

Plant phylogeny as a major predictor of flower visitation by nitidulid beetles, a lineage of ancestral angiosperm pollinators

Plant phylogeny sometimes predicts interspecific variation in pollinator composition better than floral features, and its predictive value seems to differ among major groups of insect pollinators. Earlier findings suggesting that pollination by Plant phylogeny sometimes predicts interspecific variation in pollinator composition better than gross floral features, and its predictive value seems to differ among major groups of insect pollinators. Pollination by beetles exhibits the strongest phylogenetic signal and the strongest phylogenetic conservatism, which is particularly intriguing given that beetles were probably the pollinators of early angiosperms. We examine in this paper the relationship between plant phylogeny and flower visitation by nitidulid beetles (Coleoptera: Nitidulidae), an old monophyletic group of flower specialists and pollinators of gymnosperms and angiosperms. Using quantitative data on pollinator composition for 251 plant species (belonging to 167 genera in 46 families) from well-preserved Mediterranean montane habitats from southeastern Spain, the following questions were addressed: Is pollination by nitidulids correlated with plant phylogeny in the large species sample studied, and if it does, which are the relative importances of plant phylogeny, floral characteristics, and environmental features as predictors of nitidulid pollination in the plant assemblage studied ? Nitidulids were recorded in flowers of 25% of the plant species considered. Their distribution was significantly related to plant phylogeny, being clustered on certain lineages (Ranunculales, Malvales, Rosales, Asterales) and remarkably absent from others (e.g., Fabales, Lamiales). None of the environmental (habitat type, elevation) or macroscopic floral features considered (perianth type and color, flower mass) predicted nitidulid visitation after statistically accounting for the effect of plant phylogeny. We theorize that nitidulid beetles use characters of plants that track plant phylogeny at least as deep as the early radiation of the eudicots, imaginably characters such as the chemical signatures of pollen.

Elevated CO2 Impacts on Plant–Pollinator Interactions: A Systematic Review and Free Air Carbon Enrichment Field Study

The impact of elevated CO2 (eCO2) on plant–pollinator interactions is poorly understood. This study provides the first systematic review of this topic and identifies important knowledge gaps. In addition, we present field data assessing the impact of eCO2 (150 ppm above ambient) on bluebell (Hyacinthoides non-scripta)–pollinator interactions within a mature, deciduous woodland system. Since 1956, only 71 primary papers have investigated eCO2 effects on flowering time, floral traits and pollination, with a mere 3 studies measuring the impact on pollination interactions. Our field experiment documented flowering phenology, flower visitation and seed production, as well as the abundance and phenology of dominant insect pollinators. We show that first and mid-point flowering occurred 6 days earlier under eCO2, but with no change in flowering duration. Syrphid flies and bumble bees were the dominant flower visitors, with peak activity recorded during mid- and late-flowering periods. Whilst no significant difference was recorded in total visitation or seed set between eCO2 and ambient treatments, there were clear patterns of earlier flowering under eCO2 accompanied by lower pollinator activity during this period. This has implications for potential loss of synchrony in pollination systems under future climate scenarios, with associated long-term impacts on abundance and diversity.