Changed host plant volatile emissions induced by chemical interaction between unattacked plants reduce aphid plant acceptance with intermorph variation

Olfactory orientation by aphids is guided by specific volatile blends released from their hosts. Host plants that co-exist with other plants may be less attractive for aphids due to volatile interactions between neighboring plants which can lead to changes in their volatile emissions. These changes in host plant volatile profiles induced by interactions between undamaged plants could be used to manage aphid populations in crops. When potato plants are exposed to volatiles from onion plants, the volatile profile of potato changes in relation to that of unexposed plants with consistently greater quantities of two terpenoids released. We examined the host plant searching behavior of aphids and showed that induced changes in plant volatile emissions affect aphid behavior. We assessed olfactory responses of winged and wingless aphids, Myzus persicae Sulzer (Hemiptera: Aphididae) to the changed volatile emissions. Both morphs were significantly less attracted to odors of potato plants that had been exposed to volatiles from onion than to odors of unexposed potato plants. Further, both morphs were significantly less attracted to synthetic blends mimicking volatiles emitted by onion-exposed potato plants than to blends mimicking non-exposed controls, and to single compounds emitted in greater quantities by exposed potato. Aphid morphs were repelled differently depending on the concentration of odor sources; winged aphids responded to higher doses than did wingless aphids. The aphid responses to changes in plant volatile profiles induced by neighboring plants may facilitate refinement of habitat manipulation strategies (e.g., intercropping) for integrated pest management to reduce aphid occurrence in crops

Volatile mediated plant-plant communication in cultivar mixtures

Modern agriculture is characterized by simplified cropping systems, associated with negative effects on environment, biodiversity and biological control potential. Cultivar mixtures are often presented as a more efficient and sustainable alternative due to additive effects of cultivar properties and pest reduction, but previous studies have provided equivocal results for this claim. Therefore, a better understanding of the processes underlying the effects of crop genotypic diversity on plant and herbivore responses is needed. Our review of published studies on volatile interactions between plants demonstrates that plant communication is a general event not limited to damaged plants, and that it is more a phenomenon of volatile eavesdropping rather than signalling. Empirical studies in this thesis show that barley plants perceive the growth pattern of their neighbours via volatiles and adapt their own growth strategy accordingly, which can be seen as a preparation for future competition. Field experiments show different trait responses of cultivars grown in mixtures, and that these responses depend on the neighbouring cultivar identity. Plants responded to their neighbours with adaptive and maladaptive growth responses, with increased nitrogen accumulation efficiency, biomass production and grain yield as a result. Aphid populations were generally supressed in these cultivar mixtures; not due to aphid colonization pattern or natural enemy abundance, but possibly induced by volatile interactions between neighbouring plants of different cultivars. Aphid responses to one cultivar in a mixture were neighbour specific and pest suppression was most pronounced when both cultivars in a mixture showed a reduced aphid-plant acceptance after reciprocal volatile exposure in the laboratory. Such individual neighbour responses mediated by volatiles can explain the inconsistent effects of cultivar mixtures in previous research. The findings of this thesis establish a better understanding of volatile communication between plants adding a new dimension to plant behaviour and community processes. Combining cultivars in mixtures based on how they interact with each other is a promising strategy for productive and sustainable agriculture

Decoding neighbour volatiles in preparation for future competition and implications for tritrophic interactions

Plant volatile signals can provide important information about the physiological status and genetic identity of the emitter, and nearby plants can use this information to detect competitive neighbours. The novelty of these signals is that plants eavesdropping to volatiles of undamaged neighbours respond with typical competition responses, even before competition takes place, initiating specific growth responses that can increase their competitive capacity. This preparing for future competition mechanism affects the behaviour and abundance of herbivore pests and their natural enemies. Previously, such responses were only known to occur in response to volatiles released by damaged plants. However, volatile interactions occur only in specific combination of species/genotypes, indicating that plants use volatile signals in the detection and adaption only to substantial competitive neighbours. (C) 2016 The Author(s). Published by Elsevier GmbH

Pest suppression in cultivar mixtures is influenced by neighbor-specific plant-plant communication

Increased plant genotypic diversity in crop fields can promote ecosystem services including pest control, but understanding of mechanisms behind herbivore population responses to cultivar mixtures is limited. We studied aphid settling on barley plants exposed to volatiles from different cultivars, aphid population development in monocultures and two-cultivar mixtures, and differences in volatile composition between studied cultivars. Aphid responses to one cultivar in a mixture were neighbor-specific and this was more important for pest suppression than the overall mixture effect, aphid colonization patterns, or natural enemy abundance. Aphid populations decreased most in a mixture where both cultivars showed a reduced aphid-plant acceptance after reciprocal volatile exposure in the laboratory, and reduced population growth compared to monocultures in the field. Our findings suggest that herbivore population responses to crop genotypic diversity can depend on plant-plant volatile interactions, which can lead to changes in herbivore response to individual cultivars in a mixture, resulting in slower population growth. The impact of plant-plant interaction through volatiles on associated herbivore species is rarely considered, but improved understanding of these mechanisms would advance our understanding of the ecological consequences of biodiversity and guide development of sustainable agricultural practices. Combining cultivars in mixtures based on how they interact with each other is a promising strategy for sustainable pest management

Catches, bycatches and stock indicators of fisheries targeting cyprinids along the Swedish Baltic Sea coast

Decreasing abundance of many traditionally exploited fish stocks in the Baltic Sea force small-scale fisheries to find new ways to make a living. In line with Swedish national strategies on food supply there is an interest to develop commercial cyprinid fisheries. In the Bothnian Bay in the northern part of the Baltic Sea, annual catches have increased from zero-catches 2018-30 tonnes 2021. To aid a sustainable development of these cyprinid fisheries that target mainly bream (Abramis brama) and ide (Leuciscus idus), we study catch efficiency of target species and bycatch in different gears and seasons using logbook data from the Bothnian Bay. Using cameras, we also assessed bycatch rates. To assist the sustainability of the fishery we develop potential stock indicators. Our results suggests that larger gear (pound-nets) are more effective in catching bream, and that the proportion of bycatch decreased with gear size, being < 10% in the largest gear, which is similar or lower than many other Baltic Sea fisheries. By-catches of salmon is of concern in the Bothnian Bay, but the camera study indicates that salmon bycatches are sporadic. Catch per unit effort (CPUE) of bream was highest in spring and fall, and we conclude that site specific median CPUE is the most suitable stock abundance indicator. The size indicator L90, the 90th percentile of the length distribution, was similar among areas and we propose it as a suitable indicator of the demographic structure of the targeted bream stocks. Our results provide reference points for relatively unfished conditions, but as the study was based on mainly fishery dependent data, it is important to also include fishery independent data to assess ecosystem effects of a future and intensified cyprinid fishery

Samodla kornsorter - och minska bladlusangreppen

Samodling av specifika sortkombinationer mobiliserar kornets försvar mot bladlöss, vilket kan vara en viktig del av ett förebyggandeväxtskydd i ekologisk produktion. Men vilka sorter ska mansamodla? Ett pågående SLU- och Formasprojekt kommer ge svar

Fishing cyprinids for food - Evaluation of ecosystem effects and contaminants in cyprinid fish

We conclude that a coastal cyprinid fishery may have positive effects on the ecosystem and with regard to levels of toxic contaminants, the fish is safe for humans to eat. There is, however, a need to scale up the targeted cyprinid fishery in order to evaluate and quantify the effects on the ecosystem. Scaling up from the pilot scale fisheries requires a change in consumer’s attitude and product development, so that larger quantities of cyprinid fish can be harvested and sold. Several wild fish stocks in the Baltic Sea are in poor condition and today the supply of fish for human consumption in Sweden heavily relies on farmed and imported fish. At the same time, eutrophication and climate change has led to increasing populations of cyprinid fish (e.g. bream, roach, ide) in many coastal areas of the Baltic Sea, which threatens to violate Swedish and international environmental goals. During recent years, there has been an increased interest to fish cyprinids for human consumption in Finland and Sweden. This report evaluates potential ecosystem effects resulting from an increased cyprinid fishery, and how to monitor and assess these effects in the Baltic Sea. We also assess potential barriers to increased cyprinid fisheries for human consumption due to food safety issues resulting from environmental contaminants and market incentives for fishers. In a literature review on biomanipulation targeting cyprinids in lakes, we show that removing cyprinids as a measure to improve water quality has been successful in around 60% of the cases where it has been tested. In the Baltic Sea, however, there have only been a few pilot projects of biomanipulation of cyprinids. Differences between coastal areas and lakes makes it unlikely that the same success rate as in lakes would also apply to coastal areas, especially when considering lowering of nutrient concentrations. Still, we think that a sustainable fishery targeting cyprinids may promote at least positive effects on water transparency and macrophytes in the Baltic Sea on a longer time-scale. In line with results from our literature review, we suggest a monitoring program for evaluation of a targeted cyprinid fishery in coastal areas. Based on the potential ecosystem effects of a cyprinid fishery we suggest that monitoring should prioritize fish community composition, water transparency, chlorofyll α, and submerged macrophytes. For more thorough scientific evaluations, the monitoring program should also include abundance of phyto- and zooplankton, as well as and nutrient and oxygen levels. An increased use of cyprinids from the Baltic Sea as human food will also have societal impacts. To examine if human consumption of cyprinid fish entails any increased risk of exposure to contaminants, we analysed concentration levels of several toxins (mercury, cadmium, dioxins, PCBs, PFAS and PBDE) in bream, ide and roach from five sites along the Swedish coast of the northern Baltic Sea. Our results show that, based on the regulations in Sweden today, cyprinids meet all health regulations for human food. Based on recommendations of weekly intake there are no apparent health risks of consuming cyprinid fish from the Baltic Sea at least weekly. However, since knowledge and regulations of certain environmental toxins are poor or non-existent, we believe it is important to conduct a more comprehensive study, especially for PFAS. An increased fishery targeting cyprinids would diversify the small-scale coastal fishery in Sweden, but the currently low demand makes it risky for fishers to invest in equipment and distribution becomes relatively expensive

Plasticity of barley in response to plant neighbors in cultivar mixtures

Aims Cultivar mixtures can increase productivity through complementarity in resource use, but reported results are often conflicting and the role of plasticity in shaping plant-plant interactions is poorly understood. We aim to determine if individual cultivars show different phenotypic responses when grown in a mixture, whether these responses depend on the neighboring cultivar identity, and how they contribute to variations in productivity and nitrogen (N) use. Methods Five spring barley cultivars were field-grown in pure stands and in mixtures during 2 years. Plant traits related to development, growth, N use, and reproduction were measured to identify temporal patterns of plastic responses to neighboring plants. Results Plants in mixtures were shorter and developed slower early in the season, but later on they grew faster and produced more grain than the corresponding pure stands. Some cultivars showed complementary N accumulation only when grown together with specific neighbors. Mechanisms of improved productivity differed between the individual mixtures. Conclusions Plastic plant-plant interaction between cultivars is an important driver behind the variability in mixing effects. Results contribute to a better understanding of how productivity in cultivar mixtures is affected by plastic adaptation and differentiation of plant traits, depending on the environment created by neighboring genotypes

Data supporting the results

Data supporting the result