Natacha P. Chacoff

Wild bees are parasitized by a variety of organisms, including those that attack brood cells within nests. Brood parasitism reduces reproductive output by increasing offspring mortality, with potential impacts on the persistence of bee populations. Understanding the biotic and abiotic drivers of parasitism in solitary bees becomes crucial under current anthropogenic environmental changes. We evaluated how nest and brood cell abundance, climate, and latitude drive brood parasitism in cavity-nesting solitary bee communities across a broad environmental gradient in the Monte Desert of Argentina. Parasitism rates at the community level increased with decreasing total nest and brood cell abundance and temperature. Across the gradient, parasitism decreased with increasing latitude. The overall parasitism rate was mainly determined by the prevalence of parasitized nests rather than by parasitism intensity within those nests, suggesting that parasitism pressure depends more on the likelihood of hosts being parasitized than on the extent of infestation within each parasitized nest.

Soybean (Glycine max) is a predominantly self-pollinating crop; however, its flowers exhibit traits associated with insect pollination. While several studies report yield benefits from floral visitation, others suggest little or no effect, and few have assessed pollen limitation through direct hand-pollination experiments. Here, we assess pollinator contribution and pollen limitation through two manipulative common garden experiments using different soybean cultivars. First, we assessed the contribution of pollinators by comparing reproductive variables between caged (pollinator excluded) and open-pollinated plants over two growing seasons. Second, we supplemented flowers with cross-pollen to test for pollen limitation, evaluating pollen-tube growth, pod set, seed number per pod, and seed weight. Pollinator exclusion did not significantly reduce total pod or seed production per plant, but open pollination increased seed set (seeds per flower) by ~16%. In contrast, hand supplementation substantially improved reproductive success at the flower level, tripling pod set probability and increasing seed number per pod by 40%. Additionally, both open-pollinated and hand-pollinated flowers exhibited higher pollen-tube growth relative to autonomous selfing. These findings highlight that even in largely self-compatible crops like soybean, additional pollen input can enhance reproductive success and help bridge the gap between the ecological and agronomic dimensions of pollination.

The reproductive performance of wild bees is a key determinant of their population persistence. However, few studies have directly examined the environmental drivers of demographic processes using a geographically broad approach. In this study, we explored how biotic and abiotic factors influence the reproduction of solitary, cavity-nesting bees across the Monte Desert ecoregion in Argentina. Using artificial nests and a standardized sampling spanning 2000 km and 20° of latitude, we related key reproductive metrics—nest establishment, offspring production and offspring survival—to latitude, climate and biotic factors (flower abundance, vegetation cover and brood parasitism). Climate was the strongest predictor of bee reproductive performance: warm, humid conditions during the nesting period were associated with reduced nest establishment and offspring survival. Brood parasitism further reduced offspring survival. Across the Monte Desert’s latitudinal gradient, nest establishment peaked at mid-latitudes, while offspring production and survival increased towards higher latitudes. These general patterns matched those of M. leucografa, the most abundant bee species. These findings highlight the sensitivity of wild bee reproduction to climatic conditions, particularly during the nesting period. Our study advances our understanding of the potential impacts of climate change on Neotropical wild bees, where extensive areas are experiencing dramatic land-use changes.

Blueberry cultivation requires insect‐mediated pollination for optimal fruit formation. Studies have shown that improving the efficiency of pollen exchange during flowering increases both the quantity and quality of fruit. Blueberry flowers have a unique anther structure that facilitates pollen release through a specialised interaction called ‘buzz pollination’, which is performed by wild bee species rather than Apis mellifera. The study aims to assess the effects of pollination management, weed management, and landscape heterogeneity on pollinator communities, and their interaction with the crop and blueberry fruit set. Nine blueberry plots were studied to investigate the influence of including Bombus pauloensis hives, the presence of inter‐row vegetation, and landscape heterogeneity on pollinator abundance, richness, visitation rate, and fruit production. Generalised linear mixed models (GLMM) were used to analyse the relationship between these factors. No significant differences in fruit formation were found between plots receiving pollination services from Apis mellifera and those with a combination of A. mellifera + B. pauloensis hives. However, inter‐row vegetation had a positive effect on pollinator abundance and visitation rate to blueberry flowers. The increase in cultivated areas had a negative effect on the visitation rate of both managed and native pollinators. Conversely, more diverse landscapes had a negative and significant effect on A. mellifera abundance within the plots. These findings suggest the importance of implementing wild pollinator‐friendly management practices, carefully assessing honeybee densities, and managing resources at both local and landscape scales to enhance bee visitation and blueberry fruit production.

Honey bees (Apis mellifera) are important pollinators for natural and cultivated species. Due to their high sensitivity to stressors, they are also valuable indicators of environmental changes and agricultural management practices. In this study, we compared the performance and incidence of pesticides over sentinel hives within forest remnants with those within linear forest fragments (LFF) surrounded by soybean fields under conventional management. Sentinel hives in LFF showed some signs of deterioration, such as colony collapse, low numbers of brood frames, and pesticide occurrences, but honey production and the number of adult bees were similar to hives in the forest. Soybean pollen was scarce in honey and absent in bee bread, suggesting that bees may be relying more on wild plant species. We detected 5 pesticides (azoxystrobin, carbendazim, chlorpyrifos, imidacloprid, and coumaphos) in hives both at forests and LFF in pollen, bee bodies, and wax; pesticides in honey were detected in old sentinel hives (2 yr of exposition to agricultural conventional management). Only 2 of the 5 pesticides were applied in one of the farms under study, highlighting the importance of considering landscape-scale agricultural management. Our results indicate that conventional agriculture of soybean/maize primarily affected the performance of beehives, and pesticides were detected in honey only after long exposure to hives. Beekeeping in soybean fields in the Chaco could be feasible if cautions were followed, such as the conservation of forest fragments and key plant species, appropriate pesticide schedules, coordinated applications among farms, and linear forest remnants improvements.

Low diversity of pollinators and the modified composition of functional groups of bees have been proposed as the causes of pollination deficiency in cultivated Cucurbitaceae species. Functional groups of bees are determined by traits, such as body size, nesting site, and social behavior. The presence of bees with specific traits can be differentially affected by agricultural management practices. This work aimed to assess how management types (agroecological and conventional) in Cucurbita maxima var. zapallito crops affect the abundance of bees with different biological traits. The study was conducted on four farms located in horticultural areas of central-eastern Santa Fe province, Argentina. A total of 108 10-min censuses were conducted to record bee species abundance in flowers. The species were assigned to categories for each of the three biological traits. A total of 552 individuals, belonging to 16 bee species, were recorded. Honey bees were more abundant under conventional management, whereas the native bees Eucera fervens and other species were more abundant under agroecological management. Species of the categories analyzed (body size: small, medium, and large; nesting site: above-ground cavities or ground-nesting; and social behavior: solitary or social) were present on farms under both management types. We found that management type affected bees, and their effects differed among bees with specific biological traits. Medium-sized and small bees, ground-nesting bees, and solitary bees were found in greater abundance on agroecological farms than on conventional farms. Our data allowed us to explain the diversity and abundance of bees relative to the management type and biological traits of the species. Implications for insect conservation: This study suggests that incorporating biodiversity-based management strategies might increase abundance and richness of native bees with different biological traits, ensuring the free pollination service they provide and a taxonomically and functionally diverse assemblage.

Pollination services are affected by landscape context, farming management and pollinator community structure, all of which impact flower visitation rates, pollen deposition and final production. We studied these processes in Argentina for highbush blueberry crops, which depend on pollinators to produce marketable yields. We studied how land cover and honeybee stocking influence the abundance of wild and managed pollinators in blueberry crops, using structural equation modelling to disentangle the cascading effects through which pollinators contribute to blueberry fruit number, size, nutritional content and overall yield. All pollinator functional groups responded to landscape changes at a spatial scale under 1000 m, and the significance or direction of the effects were modulated by the field‐level deployment of honeybee hives. Fruit diameter increased with pollen deposited, but decreased with honeybee abundance, which, had indirect effects on fruit acidity. Honeybees had a positive effect on the number of fruit produced by the plants and also benefited the overall yield (kg plant⁻¹) through independent effects on both the quality and quantity components of fruit production. Synthesis and applications. Deployment of beehives in blueberry fields can buffer, but not compensate for the negative effects on honeybee abundance produced by surrounding large scale none‐flowering crops. Such compensation would require high‐quality beehives by monitoring their health and strength. The contribution of honeybees to crop production is not equal across production metrics. That is, higher abundance of honeybees increases the number of berries produced but at the cost of smaller and more acidic fruits, potentially reducing their market value. Growers must consider this trade‐off between fruit quantity and quality when actively managing honeybee abundance.