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Agricultural yield is the result of multiple factors and ecological processes (e.g., pollination, fertilization, pest control). Understanding how the different factors interact is fundamental to designing management practices aimed to increase these yields, which are environmental friendly and sustainable over time. In this study, we focus on insect pollination and plant nutrition status, since they are two key factors that influence crop yield. The study was carried out in Northwest Patagonia Argentina, which is an area of intensive production of pears and apples of global importance, during the harvest seasons 2018 and 2019. The plant nutrition was estimated from leaf chlorophyll content. Biotic pollination benefits were evaluated by comparing fruit quantity (fruit to flower ratio) and quality (weight, size, and sugar concentration) from approximately 25 flowers exposed to pollinators and 25 flowers excluded to them per tree (a total of 160 apple trees and 130 pear trees). In addition, we estimated the visitation rate of pollinators to flowers and related it to fruit quality in apple. Despite different floral characteristics, we found in both crops a positive effect of insect pollination in both the quantity and the quality of the fruits. Interestingly, the nutrition of the trees, although variable, did not affect either the quantity or the quality of the fruits. Despite the weak effect of nutrition, we found no interaction between pollination and plant nutrition (i.e., additive effects). These results highlight the importance of agricultural practices that promote pollinators on farms.

Invasive social bees can alter plant-pollinator interactions with detrimental effects on both partners. However, most studies have focused on one invasive bee species, while the interactions among two or more species remain poorly understood. Also, many study sites had a history of invasive bees, being hard to find sites with historical low abundances. In Patagonia, Bombus ruderatus (F.) invasion begun in 1993 and B. terrestris (L.) in 2006. Though honey bees (Apis mellifera L.) introduction started in 1859, their density is still low in some parts. By experimentally increasing honey bee densities, we evaluated the effect of honey bees and bumblebees floral visitation on native pollinator floral visitation, pollen deposition, and reproductive success of three plant species in mixed Nothofagus antarctica forests of northern Patagonia: Oxalis valdiviensis, Mutisia spinosa and Cirsium vulgare. Our results show that exotic bees became the main floral visitors. No negative association was found between invasive bee and native pollinator visitation rates, but there was evidence of potential competition between honey bees and bumblebees. Floral neighborhood diversity played an important role in pollinator behavior. Conspecific pollen deposition was high for all species, while deposition of heterospecific pollen was very high in M. spinosa and C. vulgare. Not as expected, honey bees visitation rate had a negative effect on heterospecific pollen deposition in C. vulgare. For O. valdiviensis, exotic visitation rates increased conspecific pollen deposition, which was positively related to reproductive success. Although exotic bees became main floral visitors, their contribution to reproductive success was only clear for one species.

Cool-season grasses establish symbioses with vertically transmitted Neotyphodium endophytes widespread in nature. The frequency of endophyte-infected plants in closed populations (i.e., without migrations) depends on both the differential fitness between infected and non-infected plants, and the endophyte-transmission efficiency. Most studies have been focused on the first mechanism ignoring the second. Infection frequency and endophyte transmission from vegetative tissues to seeds were surveyed in two grasses growing in vegetation units that differ in flood and grazing regimes, and soil salinity. Transmission efficiency and infection frequency for tall fescue did not vary significantly and were 0.98 and 1.00, respectively. For Italian ryegrass, transmission efficiency and infection frequency were 0.88 and 0.57 in humid prairies, and 0.96 and 0.96 in the other vegetation units. Only in humid mesophytic meadows, the observed pattern was irrespective of the presence or absence of grazers. Our results suggest that selection forces for endophyte infection are different for both species. Imperfect transmission was only compensated in tall fescue through an increased fitness of infected plants. Interpreting variations of infection frequency only in terms of differential fitness can be misleading, considering that endophyte transmission can be imperfect and variable in nature. Therefore, this study highlights the importance of measuring transmission efficiency.