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Changes to the fire regime in boreal Alaska are shifting the ratio of coniferous to deciduous dominance on the landscape. The increase in aspen and birch may have important effects on predatory hymenopteran assemblages by providing a source of extrafloral nectar and increasing prey availability. Furthermore, fire-induced changes in successional age alter habitat structure and microclimate in ways that may favor ants. This study is the first to characterize the influence of fire-related vegetation changes on boreal predatory hymenopteran assemblages. We compare the abundance, species richness, and composition of predatory hymenopteran assemblages among forests at different stages of succession and of varying post-fire tree species compositions. Ant assemblages were weakly related to forest composition, but ants were significantly more abundant and speciose in early-successional forests than in mid-late successional forests. In contrast, macropterous wasp morphospecies richness and abundance, and micropterous wasp abundance, were positively related to the basal area of aspen, but were not related to successional stage. The results suggest that shifts in boreal vegetation related to climate warming will result in changes to the predaceous insect community, with ants responding positively to disturbance and wasps responding positively to an increase in the representation of aspen on the landscape.

Ant–plant interactions often are mediated by extrafloral nectar (EFN) composition that may influence plant visitation by ants. Over a 300 km range in the Indian Western Ghats, we investigated the correlation between the EFN composition of the myrmecophytic ant-plant Humboldtia brunonis (Fabaceae) and the number and species of ants visiting EFN. EFN composition varied among H. brunonis populations and between plant organs (floral bud vs. young leaf EFN). In general, EFN was rich in sugars with small quantities of amino acids, especially essential amino acids, and had moderate invertase activity. In experiments at the study sites with sugar and amino acid solutions and with leaf or floral bud EFN mimics, dominant EFN-feeding ants differentiated between solutions as well as between mimics. The castration parasite Crematogaster dohrni (northern study site) was the least selective and did not exhibit any clear feeding preferences, while the largely trophobiont-tending non-protective Myrmicaria brunnea (middle study site) preferred higher sucrose concentrations and certain essential/non-essential amino acid mixtures. The mutualistic Technomyrmex albipes (southern study site) preferred sucrose over glucose or fructose solutions and consumed the leaf EFN mimic to a greater extent than the floral bud EFN mimic. This young leaf EFN mimic had low sugar concentrations, the lowest viscosity and sugar:amino acid ratio, was rich in essential amino acids, and appeared ideally suited to the digestive physiology of T. albipes . This preference for young leaf EFN may explain the greater protection afforded to young leaves than to floral buds by T. albipes , and may also help to resolve ant–pollinator conflicts. The differential response of dominant ants to sugar, amino acids, or solution viscosity suggests that plants can fine-tune their interactions with local ants via EFN composition. Thus, EFN can mediate local partner-choice mechanisms in ant–plant interactions.

Extrafloral nectar mediates food-for-protection mutualisms between plants and ants. Ant—plant mutualisms are keystone associations, occurring within a complex web of biotic interactions. As such, these interactions may affect plant fitness in a number of ways, both positive and negative. In Senna mexicana var. chapmanii (Isely) H. S. Irwin & Barneby (Fabaceae), the presence of ants has been shown to reduce herbivory and increase fruit and seed set. These effects, however, are not the result of only one interaction but the balance of many. We conducted a field study to determine the processes by which ants affect reproductive fitness in S. chapmanii. Thirty plants were established in a semi-natural area adjacent to native pine rockland habitat in southern Florida. Ants were excluded from half of the plants by painting a sticky resin (Tanglefoot™) around the base of each stem. Over the course of a single flowering season (Oct–May), we observed the effects of ants on the activity of herbivores, predators, pollinators, and pre-dispersal seed predators. We also observed the overall effects of ants on plant size and reproductive output. Plants with ants were quicker to establish, grew larger, and produced floral displays that attracted more pollinators. Contrary to our expectations, relative pollinator efficiency and rates of pre-dispersal seed predation were unaffected by ants. In S. chapmanii, ants did not appear to affect the outcome of other plant—insect associations, but they affected the scale at which they occurred. Ants facilitated plant growth and establishment in S. chapmanii, with subsequent effects on reproductive investment.

The effect of access to buckwheat flowers (Fagopyrum esculentum Moench; Polygonales: Polygonaceae) or vetch extrafloral nectaries (Vicia sativa L. cv. ‘cahaba white’; Fabales: Fabaceae) on the fitness of Anagyrus pseudococci (Girault) (Hymenotpera: Encyrtidae) (a parasitoid of the vine mealybug, Planococcus ficus [Signoret]) (Hemiptera: Pseudococcidae) was determined in the laboratory. Female A. pseudococci provided with vetch survived 4 days longer compared with water only. Buckwheat had no effect on the average longevity of A. pseudococci. Anagyrus pseudococci offspring production increased by 132% and 152% when females were provided either vetch or buckwheat, respectively, when compared with water. There was no significant difference in parasitoid longevity or fecundity between plant species. Buckwheat increased the percentage of female A. pseudococci offspring by 15% and 19% when compared with water and vetch, respectively.

Plants produce a wide array of secretions both above and below ground. Known as mucilages or exudates, they are secreted by seeds, roots, leaves and stems and fulfil a variety of functions including adhesion, protection, nutrient acquisition and infection. Mucilages are generally polysaccharide‐rich and often occur in the form of viscoelastic gels and in many cases have adhesive properties. In some cases, progress is being made in understanding the structure–function relationships of mucilages such as for the secretions that allow growing ivy to attach to substrates and the biosynthesis and secretion of the mucilage compounds of the Arabidopsis seed coat. Work is just beginning towards understanding root mucilage and the proposed adhesive polymers involved in the formation of rhizosheaths at root surfaces and for the secretions involved in host plant infection by parasitic plants. In this article, we summarise knowledge on plant exudates and mucilages within the concept of their functions in microenvironmental design, focusing in particular on their bioadhesive functions and the molecules responsible for them. We draw attention to areas of future knowledge need, including the microstructure of mucilages and their compositional and regulatory dynamics.

In modern agricultural landscapes, many organisms providing ecosystem services such as pollination and natural pest control are likely constrained by shortage of nectar and/or pollen required for adult nutrition. More and more flower‐rich field margin strips and other habitats are created to eliminate these constraints. For most target organisms, however, it is not well known which (types of) flowers are effective in providing suitable pollen and nectar. We studied the suitability of a wide range of flowers as a food source for zoophagous hoverflies (hoverflies with predatory larvae) at five different levels: nectar accessibility (based on flower morphology), realized adult fitness, flower choice (both based on cage experiments), flower visitation and hoverfly abundance in mixed vegetation (both based on field observations). Realized survival of Episyrphus balteatus is related to effective flower depth by a sigmoid function. The critical flower depth is 1·6 mm, which is less than the proboscis size of the hoverfly. For Asteraceae, the critical floret depth is even less than 1·0 mm, which – in contrast to common knowledge – rules out most species within this family. Both flower choice in the laboratory and flower visitation rates in the field are well correlated with nectar accessibility and realized adult survival. In mixed floral vegetation, the number of zoophagous hoverflies is highly correlated with the abundance of only those flowers that have accessible nectar for these hoverflies. Synthesis and applications. This comparative study demonstrates that nectar (and not pollen) accessibility is the main driver determining flower resource suitability, flower choice and abundance of zoophagous hoverflies in arable field margins. The study identifies the limited range of plant species that can effectively support these beneficial insects. Preserving the right flowers in and around agricultural fields could enhance local populations and the pest control and pollination services they provide.

The effects of feeding Spodoptera littoralis(Boisd.) (Lepidoptera: Noctuidae) larvae on the quantity and distribution of extrafloral nectar production by leaves of castor (Ricinus communis) and cotton (Gossypium herbaceum) were investigated. Following larval feeding, the total volume of nectar secreted by foliar nectaries increased 2.5- and 12-fold, respectively. As HPLC-analysis showed no difference in sugar composition between extrafloral nectar from insect-damaged and control plants, it can be concluded that the plants increased the secretion of carbohydrates in response to herbivory. In damaged castor leaves, the amount of sugar excreted through extrafloral nectaries represented approx. 1‰ of the leaf's daily assimilate production. Induction of nectar production was mainly restricted to the damaged leaf, although a weaker systemic response was found in adjacent younger leaves. Spatial and temporal patterns of induced nectar production could help plants to optimize indirect defence by concentrating the recruitment of predators and parasitoids on the site, and at the time, of attack.

• The evolution of plant defenses has traditionally been studied at single plant ontogenetic stages, overlooking the fact that natural selection acts continuously on organisms along their development, and that the adaptive value of phenotypes can change along ontogeny. • We exposed 20 replicated genotypes of Turnera velutina to field conditions to evaluate whether the targets of natural selection on different defenses and their adaptative value change across plant development. • We found that low chemical defense was favored in seedlings, which seems to be explained by the assimilation efficiency and the ability of the specialist herbivore to sequester cyanogenic glycosides. Whereas trichome density was unfavored in juvenile plants, it increased relative plant fitness in reproductive plants. At this stage we also found a positive correlative gradient between cyanogenic potential and sugar content in extrafloral nectar. • We visualize this complex multi-trait combination as an ontogenetic defensive strategy. The inclusion of whole-plant ontogeny as a key source of variation in plant defense revealed that the targets and intensity of selection change along the development of plants, indicating that the influence of natural selection cannot be inferred without the assessment of ontogenetic strategies in the expression of multiple defenses.

1. Extrafloral nectar (EFN) provides plants with indirect defence against herbivores by attracting predatory insects, predominantly ants. Decades of research have supported the role of EFN as an effective plant defence, dating back to Thomas Belt's description of ants on acacia in 1874. 2. Despite this extensive body of literature, knowledge of the ecological role of EFN has rarely been applied in the field of pest management. We review the existing literature on the use of EFN in agriculture and consider the obstacles that have hindered this transition. 3. Chief among these obstacles is the influence of ecological context on the outcome of EFN-mediated interactions. As such, we consider the options for various agricultural systems in the light of the growth habit of EFN-producing species, focusing first on orchard species and then on herbaceous crops. In each case, we highlight the benefits and difficulties of utilizing EFN as a pest management tool and of measuring its efficacy. 4. Synthesis and applications. We argue that it is time for a shift in extrafloral nectar (EFN) research towards applied settings and seek to address the question: How can a context-dependent and often inducible plant trait be utilized as a reliable tool in agricultural pest management? Breeding crops for increased EFN production, and intercropping with EFN-producing plants, can enhance assemblages of beneficial insects in many agricultural settings. Orchard systems, in particular, provide an ecological context in which the attraction of ants can contribute to cost-effective and sustainable pest management programmes over a broad geographic range.

Chronic anthropogenic disturbance (CAD) and climate change represent two of the major threats to biodiversity globally, but their combined effects are not well understood. Here we investigate the individual and interactive effects of increasing CAD and decreasing rainfall on the composition and taxonomic (TD), functional (FD) and phylogenetic diversity (PD) of plants possessing extrafloral nectaries (EFNs) in semi-arid Brazilian Caatinga. EFNs attract ants that protect plants against insect herbivore attack and are extremely prevalent in the Caatinga flora. EFN-bearing plants were censused along gradients of disturbance and rainfall in Catimbau National Park in north-eastern Brazil. We recorded a total of 2243 individuals belonging to 21 species. Taxonomic and functional composition varied along the rainfall gradient, but not along the disturbance gradient. There was a significant interaction between increasing disturbance and decreasing rainfall, with CAD leading to decreased TD, FD and PD in the most arid areas, and to increased TD, FD and PD in the wettest areas. We found a strong phylogenetic signal in the EFN traits we analysed, which explains the strong matching between patterns of FD and PD along the environmental gradients. The interactive effects of disturbance and rainfall revealed by our study indicate that the decreased rainfall forecast for Caatinga under climate change will increase the sensitivity of EFN-bearing plants to anthropogenic disturbance. This has important implications for the availability of a key food resource, which would likely have cascading effects on higher trophic levels.