Toxicity of the insecticide sulfoxaflor alone and in combination with the fungicide fluxapyroxad in three bee species.

The sulfoximine insecticide sulfoxaflor is regarded as a potential substitute for neonicotinoids that were recently banned in the EU due to their side effects on bees. Like neonicotinoids, sulfoxaflor acts as a competitive modulator of nicotinic acetylcholine receptors. In agricultural environments, bees are commonly exposed to combinations of pesticides, and neonicotinoids are known to interact synergistically with fungicides. The objective of our study is to assess the acute oral toxicity of sulfoxaflor alone and in combination with a single dose of fluxapyroxad, a succinate dehydrogenase inhibitor (SDHI) fungicide, in three bee species: Apis mellifera, Bombus terrestris and Osmia bicornis. Because synergism may be dose-dependent, we tested a range of sulfoxaflor doses. Synergistic effects were assessed using three different approaches: Bliss criterion of drugs independence, ratio test comparing LD50s and model deviation ratio. Osmia bicornis was the most sensitive species to sulfoxaflor and both O. bicornis and A. mellifera showed significant synergism between the insecticide and the fungicide. For the most part, these synergistic effects were weak and only occurred at early assessment times and intermediate sulfoxaflor doses. The potential ecological relevance of these effects should be confirmed in field and/or cage studies. Overall, our laboratory results demonstrate that sulfoxaflor is somewhat less toxic than the recently banned neonicotinoids imidacloprid, thiamethoxam and clothianidin, but much more toxic than other neonicotinoids (acetamiprid, thiacloprid) still in use in the EU at the time this study was conducted.

Stream chemistry response to changing nitrogen and sulfur deposition in two mountain areas in the Iberian Peninsula.

Sulfur (S) and nitrogen (N) increasing anthropogenic emissions in the last century has arisen wide concern on the ecological effects of S and N deposition. In this paper, we use bulk deposition and stream water measurements in the central Pyrenees (PYR-C and PYR-AT sites) and Montseny (MSY-TM0) covering different time lengths in the period 1983-2017 to investigate how these mountain environments respond to ongoing changes of regional emissions to the atmosphere. PYR-C, in spite of its position far away from urban and industrial areas, presented higher SO4-S, NO3-N and NH4-N bulk deposition than the Montseny site closer to Barcelona and the inclusion of dry deposition only reversed this pattern for NO3-N. This indicates that distance to pollution sources does not protect these mountain sites from a considerable impact of pollution. Time-trends in SO42- and NO3- concentrations in bulk deposition were similar between sites: SO42- monotonically decreased, while NO3- increased until the mid-2000 s and decreased thereafter. In the period 1983 to 2017, SO2 emissions in Europe (EU-28) decreased by 95%, while in the SO42- concentrations in bulk deposition declined by 35-50% in Pyrenees and Montseny respectively and SO42- concentrations in the streams by 25-35%, respectively. Other sources of SO42- (e.g. episodic African dust) may explain the different reduction rate between anthropogenic emissions and bulk deposition. Net S budget was positive for MSY-TM0 (indicating flushing from the catchment) and negative for the PYR-C site (indicating retention), while it was close to zero for the other Pyrenean site, but in the PYR-C site net retention showed a significant increasing trend tending to lower retention in recent years. Bulk N deposition in the Pyrenees was lower but stream concentrations and export was higher than at Montseny, this leading to less N retention in the Pyrenean sites. However, the MSY-TM0 site showed a trend towards less N retention in recent years. This was driven by higher exports during the wet months, which would correspond to a first stage of N saturation according Stoddard's classification.

Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks.

The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects.

Global patterns of phosphatase activity in natural soils.

Soil phosphatase levels strongly control the biotic pathways of phosphorus (P), an essential element for life, which is often limiting in terrestrial ecosystems. We investigated the influence of climatic and soil traits on phosphatase activity in terrestrial systems using metadata analysis from published studies. This is the first analysis of global measurements of phosphatase in natural soils. Our results suggest that organic P (Porg), rather than available P, is the most important P fraction in predicting phosphatase activity. Structural equation modeling using soil total nitrogen (TN), mean annual precipitation, mean annual temperature, thermal amplitude and total soil carbon as most available predictor variables explained up to 50% of the spatial variance in phosphatase activity. In this analysis, Porg could not be tested and among the rest of available variables, TN was the most important factor explaining the observed spatial gradients in phosphatase activity. On the other hand, phosphatase activity was also found to be associated with climatic conditions and soil type across different biomes worldwide. The close association among different predictors like Porg, TN and precipitation suggest that P recycling is driven by a broad scale pattern of ecosystem productivity capacity.

Ant-mediated expansion of an obligate seeder species during the first years after fire.

Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade-intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate-seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant-mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population.

Effect of temperature regime on diapause intensity in an adult-wintering Hymenopteran with obligate diapause.

Osmia lignaria is a solitary bee that over-winters as a fully eclosed, cocooned, unfed adult. Our objective is to understand the effect of wintering temperature on diapause maintenance and termination in this species. We measure respiration rates and weight loss in individuals exposed to various wintering temperatures (0, 4, 7, 22 degrees C, outdoors) and durations (28, 84, 140, 196, 252 days). We use time to emerge and respiration response (respiration rate measured at 22 degrees C) as indicators of diapause intensity. Adults spontaneously lower their respiration rates to approximately 0.1 ml/gh within 1 month after adult eclosion, indicating obligatory diapause. Non-wintered individuals maintain low respiration rates, but lose weight rapidly and die by mid-winter. In wintered adults, two phases can be distinguished. First, respiration response undergoes a rapid increase and then reaches a plateau. This phase is similar in bees wintered at 0, 4 and 7 degrees C. In the second phase, respiration response undergoes an exponential increase, which is more pronounced at the warmer temperatures. Composite exponential functions provide a good fit to the observed respiration patterns. Adults whose respiration response has reached 0.45 ml/gh emerge promptly when exposed to 20 degrees C, indicating diapause completion. Individuals wintered for short periods do not reach such respiration levels. When exposed to 20 degrees C these individuals lower their metabolic rate, and their emergence time is extended. The relationship between respiration rates and emergence time follows a negative exponential function. We propose two alternative models of diapause termination to interpret these results.