Comparison of Predatory Performance among Three Ladybird Species, Harmonia axyridis, Coccinella septempunctata and Hippodamia variegata, Feeding on Goji Berry Psyllid, Bactericera gobica

The psyllid Bactericera gobica is a serious pest in goji berry orchards. The current primary psyllid control methods involve chemical pesticides, which pose potential risks to human health and the environment. The implementation and promotion of biological control agents should receive increased attention as an alternative approach to safeguarding goji berry orchards. To compare the predatory performance of three potential biocontrol agents of psyllids, including Harmonia axyridis, Coccinella septempunctata and Hippodamia variegata, the functional response and intraspecific interactions of adult ladybirds were studied under laboratory conditions. We observed a significantly higher searching efficiency (0.84 ± 0.09) in H. axyridis when preying on psyllids compared to H. variegata (0.55 ± 0.05), whereas the handling time for psyllids was considerably longer in H. axyridis (7.33 ± 0.83 min) than in H. variegata (5.67 ± 0.97 min). The impact of intraspecific interactions on H. variegata (0.44 ± 0.04) was significantly greater than that on C. septempunctata (0.29 ± 0.03), whereas the maximum consumption by C. septempunctata (223.35 ± 41.3) significantly exceeded that of H. variegata (133.4 ± 26.9). Our study suggests that each of these three ladybird species possesses distinct advantages as a potential predator of psyllids. However, further field studies are required to determine the most promising ladybird species for rapid impact through inundative biological control, taking into consideration the specific environmental adaptability of each ladybird species. The present study is expected to provide evidence that supports the potential of incorporating promising ladybird species as an effective biological control agent in goji berry orchard management programs.

Physiological Differences Between Seasonal Dimorphs of Agonoscena pistaciae (Hemiptera: Aphalaridae) Elicit Distinct Host Plant Responses, Informing Novel Pest Management Insights

We examined differences in the physiology and life history between dimorphs of the common pistachio psyllid, Agonoscena pistaciae (Burckhardt and Lauterer) (Hemiptera: Aphalaridae), and how they differ in elicitating host plant production of key metabolites and volatile compounds involved in the recruitment of herbivores and natural enemies. Summer morphs had higher activities of glutathione S-transferase, carboxylesterase, acetylcholinesterase, and cytochrome P450 monooxygenase, superoxide dismutase, catalase, peroxidase, phenoloxidase, and a higher total protein content compared to winter morphs, whereas the latter had higher amounts of lipid, carbohydrate, and glycogen. Winter morphs were heavier, with a higher chitin content and longer preoviposition period, but greater fecundity and longevity than summer morphs. A lower LC50 to thiamethoxam for winter morphs resulted in higher mortality following exposure to the recommended rate of this insecticide in a greenhouse trial. Feeding by winter morphs elicited more strongly the release of volatile compounds known to be attractive to other herbivores, whereas feeding by summer morphs elicited more strongly the release of volatiles implicated in the attraction of natural enemies. Feeding by psyllids increased the concentrations of nitrogenous compounds, carbohydrates, vitamins, and amino acids in plants, the winter morph eliciting larger changes and more improved host plant quality. We conclude that winter morphs are more vulnerable targets for chemical control in early spring, whereas management of summer morphs could rely more on conservation biological control.

Understanding nutritive need in Harmonia axyridis larvae: Insights from nutritional geometry

The multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an important natural enemy in agricultural ecosystems. In spite of being a carnivore consuming protein-rich preys, the lady beetles often consume carbohydrate-rich food like nectar or honeydew. However, most studies on nutrition regulation of carnivores mainly focus on protein and lipid, two major macronutrients in preys. In this study, nutrition regulation of protein and carbohydrate has been investigated in the 4th instar larvae of H. axyridis using Geometric Framework. We provided the insects two pairs of foods, one a protein-biased one and the second carbohydrate-biased, to determine the intake target. We then confined them to nutritionally imbalanced foods to examine how they regulated food intake to achieve maximal performance. The larvae performed well on the 2 foods that containing the closest P : C ratios to the intake target, but, surprisingly, the lipid content was much lower than that in the choice experiment. The lady beetles seemed to maintain the optimal lipid content by consuming carbohydrate-rich food. Moreover, consuming the carbohydrate-rich food was less metabolically expensive than the protein-rich food. Therefore, switching behavior between plant and animal foods actually reflects their nutritive needs. These findings extended our understanding of predator forage behavior and its influence on food web in ecosystems, and shed light on the role of agri-environment schemes in meeting the nutritional need of predators in field.

Seed choice in ground beetles is driven by surface-derived hydrocarbons

Ground beetles (Coleoptera: Carabidae) are among the most prevalent biological agents in temperate agroecosystems. Numerous species function as omnivorous predators, feeding on both pests and weed seeds, yet the sensory ecology of seed perception in omnivorous carabids remains poorly understood. Here, we explore the sensory mechanisms of seed detection and discrimination in four species of omnivorous carabids: Poecilus corvus, Pterostichus melanarius, Harpalus amputatus, and Amara littoralis. Sensory manipulations and multiple-choice seed feeding bioassays showed olfactory perception of seed volatiles as the primary mechanism used by omnivorous carabids to detect and distinguish among seeds of Brassica napus, Sinapis arvensis, and Thlaspi arvense (Brassicaceae). Seed preferences differed among carabid species tested, but the choice of desirable seed species was generally guided by the olfactory perception of long chain hydrocarbons derived from the seed coat surface. These olfactory seed cues were essential for seed detection and discrimination processes to unfold. Disabling the olfactory appendages (antennae and palps) of carabid beetles by ablation left them unable to make accurate seed choices compared to intact beetles.

Ground beetles are generalist predators of various arable weed seeds. Sensory manipulations and multiple-choice feeding bioassays show that seed choice is stimulated by volatile chemicals derived from the epicuticular lipids on the seed coat.

Vegetation shapes aboveground invertebrate communities more than soil properties and pollution: a preliminary investigation on a metal-contaminated site

Pollution with trace metals (TM) has been shown to affect diversity and/or composition of plant and animal communities. While ecotoxicological studies have estimated the impact of TM contamination on plant and animal communities separately, ecological studies have widely demonstrated that vegetation is an important factor shaping invertebrate communities. It is supposed that changes in invertebrate communities under TM contamination would be explained by both direct impact of TM on invertebrate organisms and indirect effects due to changes in plant communities. However, no study has clearly investigated which would more importantly shape invertebrate communities under TM contamination. Here, we hypothesized that invertebrate communities under TM contamination would be affected more importantly by plant communities which constitute their habitat and/or food than by direct impact of TM. Our analysis showed that diversity and community identity of flying invertebrates were explained only by plant diversity which was not affected by TM contamination. Diversity of ground-dwelling (GD) invertebrates in spring was explained more importantly by plant diversity (27% of variation) than by soil characteristics including TM concentrations (8%), whereas their community identity was evenly explained by plant diversity and soil characteristics (2-7%). In autumn, diversity of GD invertebrates was only explained by plant diversity (12%), and their identity was only explained by soil characteristics (8%). We conclude that vegetation shapes invertebrate communities more importantly than direct effects of TM on invertebrates. Vegetation should be taken into account when addressing the impacts of environmental contamination on animal communities.

The biology of seed discrimination and its role in shaping the foraging ecology of carabids: A review

Species of carabid (ground) beetles are among the most important postdispersal weed seed predators in temperate arable lands. Field studies have shown that carabid beetles can remove upwards of 65%-90% of specific weed seeds shed in arable fields each year. Such data do not explain how and why carabid predators go after weed seeds, however. It remains to be proven that weed seed predation by carabids is a genuine ecological interaction driven by certain ecological factors or functional traits that determine interaction strength and power predation dynamics, bringing about therefore a natural regulation of weed populations. Along these lines, this review ties together the lines of evidence around weed seed predation by carabid predators. Chemoperception rather than vision seems to be the primary sensory mechanism guiding seed detection and seed selection decisions in carabid weed seed predators. Selection of weed seeds by carabid seed predators appears directed rather than random. Yet, the nature of the chemical cues mediating detection of different seed species and identification of the suitable seed type among them remains unknown. Selection of certain types of weed seeds cannot be predicted based on seed chemistry per se in all cases, however. Rather, seed selection decisions are ruled by sophisticated behavioral mechanisms comprising the assessment of both chemical and physical characteristics of the seed. The ultimate selection of certain weed seed types is determined by how the chemical and physical properties of the seed match with the functional traits of the predator in terms of seed handling ability. Seed density, in addition to chemical and physical seed traits, is also an important factor that is likely to shape seed selection decisions in carabid weed seed predators. Carabid responses to seed density are rather complex as they are influenced not only by seed numbers but also by trait-based suitability ranks of the different seed types available in the environment.

On the evolution of trophic position

The trophic structure of food webs is primarily determined by the variation in trophic position among species and individuals. Temporal dynamics of food web structure are central to our understanding of energy and nutrient fluxes in changing environments, but little is known about how evolutionary processes shape trophic position variation in natural populations. We propose that trophic position, whose expression depends on both environmental and genetic determinants of the diet variation in individual consumers, is a quantitative trait that can evolve via natural selection. Such evolution can occur either when trophic position is correlated with other heritable morphological and behavioural traits under selection, or when trophic position is a target of selection, which is possible if the fitness effects of prey items are heterogeneously distributed along food chains. Recognising trophic position as an evolving trait, whose expression depends on the food web context, provides an important conceptual link between behavioural foraging theory and food web dynamics, and a useful starting point for the integration of ecological and evolutionary studies of trophic position.

Cannibalism and Necrophagy Promote a Resource Loop and Benefit Larval Development in Insects of Temporary Waters

Temporary aquatic habitats are contingent on the allochthonous inputs of plant and animal detritus, whose quality and availability can significantly affect the species developing in these habitats. Although animal detritus (i.e., invertebrate carcasses) is a high-quality food, it is an unpredictable and variable resource. On the contrary, conspecific individuals (dead or alive) are a nutritionally high-quality food source that is always available. In this context, conspecifics consumption, by cannibalism or necrophagy, can be a good strategy to overcome nutrient limitation and allow individual maintenance and development. Here, we tested this hypothesis by using the tiger mosquito Aedes albopictus. By carrying out laboratory and semi-field experiments, we first estimated the relative rate of cannibalism and necrophagy, under different larval densities. Then, we analyzed the effects of cannibalism and necrophagy on larval survival and adult yield. Consistent with our hypothesis, we found that cannibalism and necrophagy occurred under all experimental conditions, and that conspecific consumption had positive effects on individual development, as it significantly increased the rate of adult emergence and larval survival. Interestingly, about 50% of the initial cohort was consumed by conspecifics, suggesting that cannibalism and necrophagy can drive an important resources loop in temporary aquatic habitats.

Effect of body lipid content is linked to nutritional adaptation in the acclimation responses of mesic-adapted Paederus to seasonal variations in desiccation stress

Desiccation stress causes mesic-adapted arthropods to lose their body water content. However, mesic-adapted Paederus beetles can survive over prolonged periods under dry field conditions, suggesting that these beetles adopt an array of water conservation mechanisms. We investigated the water balance mechanisms of field-collected Paederus adults over a 14-month sampling period. We also assessed their nutritional adaptations by performing a stable isotope analysis to examine their diet. The water loss rate (WLR) of the beetles was significantly associated with the rice crop cycle and saturation deficit. The cuticular permeability (CP) of adult beetles was maintained at < 30 µg cm^-2h^-1 mmHg^-1; however, CP increased significantly with the WLR. This result indicates that CP might play a minor role in reducing excessive water loss in beetles. The beetles' body water content and percentage total body water content increased when the WLR was high. Trehalose, glucose, and glycogen did not appear to play a central role in enhancing the water reserves in the insects. The body lipid content ranged from 0.22 ± 0.06 to 0.87 ± 0.07 mg and was negatively associated with the WLR. This association indicates that the increase in internal metabolic water was mediated by lipid catabolism. Stable isotope analysis results revealed that the Paederus beetles shifted their diet to carbohydrate-rich plants when the saturation deficit increased and the associated WLR reached its peak; otherwise, they consumed a high amount of staple carbohydrate-poor herbivore prey. The accumulation of energy reserves in the form of lipids through seasonal dietary shifts may exert major effects on the survival and population success of mesic-adapted Paederus beetles.

Asymmetric foraging lowers the trophic level and omnivory in natural food webs

Food webs capture the trophic relationships and energy fluxes between species, which has fundamental impacts on ecosystem functioning and stability. Within a food web, the energy flux distribution between a predator and its prey species is shaped by food quantity-quality trade-offs and the contiguity of foraging. But the distribution of energy fluxes among prey species as well as its drivers and implications remain unclear. Here we used 157 aquatic food webs, which contain explicit energy flux information, to examine whether a predator's foraging is asymmetric and biased towards lower or higher trophic levels, and how these patterns may change with trophic level. We also evaluate how traditional topology-based approaches may over- or under-estimate a predator's trophic level and omnivory by ignoring the asymmetric foraging patterns. Our results demonstrated the prevalence of asymmetric foraging in natural aquatic food webs. Although predators prefer prey at higher trophic levels with potentially higher food quality, they obtain their energy mostly from lower trophic levels with a higher food quantity. Both tendencies, that is, stronger feeding preference for prey at higher trophic levels and stronger energetic reliance on prey at lower trophic levels are alleviated for predators at higher trophic levels. The asymmetric foraging lowers trophic levels and omnivory at both species and food web levels, compared to estimates from traditional topology-based approaches. Such overestimations by topology-based approaches are most pronounced for predators at lower trophic levels and communities with higher number of trophic species. Our study highlights the importance of energy flux information in understanding the foraging behaviour of predators as well as the structural complexity of natural food webs. The increasing availability of flux-based food web data will thus provide new opportunities to reconcile food web structure, functioning and stability.

The food web in a subterranean ecosystem is driven by intraguild predation

Trophic interactions of cave arthropods have been understudied. We used molecular methods (NGS) to decipher the food web in the subterranean ecosystem of the Ardovská Cave (Western Carpathians, Slovakia). We collected five arthropod predators of the species Parasitus loricatus (gamasid mites), Eukoenenia spelaea (palpigrades), Quedius mesomelinus (beetles), and Porrhomma profundum and Centromerus cavernarum (both spiders) and prey belonging to several orders. Various arthropod orders were exploited as prey, and trophic interactions differed among the predators. Linear models were used to compare absolute and relative prey body sizes among the predators. Quedius exploited relatively small prey, while Eukoenenia and Parasitus fed on relatively large prey. Exploitation of eggs or cadavers is discussed. In contrast to previous studies, Eukoenenia was found to be carnivorous. A high proportion of intraguild predation was found in all predators. Intraspecific consumption (most likely cannibalism) was detected only in mites and beetles. Using Pianka's index, the highest trophic niche overlaps were found between Porrhomma and Parasitus and between Centromerus and Eukoenenia, while the lowest niche overlap was found between Parasitus and Quedius. Contrary to what we expected, the high availability of Diptera and Isopoda as a potential prey in the studied system was not corroborated. Our work demonstrates that intraguild diet plays an important role in predators occupying subterranean ecosystems.

Prey identity but not prey quality affects spider performance

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Prey identity affected the survival and body mass of a generalist spider predator.

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Trophic level of the prey did not affect spider survival and body mass.

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Prey identity and cordgrass quality had an interactive effect on spider body mass.

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Greater spider body mass led to greater egg production.

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In a literature review, female spider fitness increased with greater body size.

Increasing host plant quality affects higher trophic level predators, but whether such changes are simply a result of prey density or are also affected by changes in prey quality remain uncertain. Moreover, whether changes in prey quality affect measures of predator performance is understudied. Using a combination of field and greenhouse mesocosm experiments, we demonstrate that the survival and body size of a hunting spider (Pardosa littoralis Araneae: Lycosidae) is affected more by prey species identity than the trophic level of the prey. Furthermore, increasing host plant quality does not necessarily propagate through the food web by altering prey quality. While changes in plant quality affected spider body mass, they did so in opposite ways for spiders feeding on Prokelisia (Hemiptera: Delphacodes) herbivores relative to Tytthus (Hemiptera: Miridae) egg predators, and had no impact on spider body mass for two additional species of intraguild prey. These changes in body mass were important because greater body mass increased spider egg production. To examine the generality of this pattern, we reviewed the literature and found a consistent positive relationship between female body size and egg production for Pardosa species, indicating that body size is a reliable proxy for fitness. While many studies emphasize the importance of nitrogen to arthropod diets, this focus may be driven largely by our understanding of herbivore diets rather than predator diets. Thus, the positive impact of host plant quality on higher trophic level predators appears to be driven more by altering prey composition, density, and availability rather than simply providing predators with more nutritious prey.

Bottom-up Effects on Tri-trophic Interactions: Plant Fertilization Enhances the Fitness of a Primary Parasitoid Mediated by Its Herbivore Host

Plants play a pivotal role in interactions involving herbivores and their natural enemies. Variation in plant primary and secondary metabolites not only affects herbivores but, directly and indirectly, also their natural enemies. Here, we used a commercial NPK fertilizer to test the impact of three fertilizer, namely 50, 100, and 200 ppm nitrogen, and one control (i.e., water) treatments, on the weight of the nymphs of the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Subsequently, the whitefly parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) was reared on the different groups of whitefly nymphs and upon parasitoid emergence, the number of oocytes was determined as a measure of reproductive capacity. Trials were done on tomato and tobacco plants. The level of nitrogen concentration in tobacco leaves was directly correlated with the fertilizer applications, thus confirming the effect of our fertilizer treatments. Both in tomato and tobacco plants, healthy as well as parasitized whitefly nymphs, were heaviest in the 200 ppm nitrogen treatment. The highest number of oocytes per female parasitoid was recorded in the 200 ppm nitrogen treatment in tomato (31% more oocytes as compared with the control) and in the 100 and 200 ppm nitrogen treatments in tobacco (200% more oocytes). We suggest that the increase in oocytes was the result of the enhanced size (food quantity) and/or nutritional quality of the whitefly host. The practical implications of these results for the mass rearing of whitefly parasitoids and for biological pest control are discussed.

Effects of mummy consumption on fitness and oviposition site selection on Harmonia axyridis

Intraguild predation (IGP) has been commonly reported between predators and parasitoids used as biological control agents as predators consuming parasitoids within their hosts. However, the effect of parasitoid-mummy consumption on the fitness of the predator and subsequent oviposition site selection have not been well studied. In our study, we conducted two laboratory experiments to examine the influence of Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) mummies as prey on fitness and subsequently oviposition site selection of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Results indicate that when H. axyridis was reared on A. gifuensis mummies only, its larval development was prolonged, and body weight of the 4th instar larvae and newly emerged adults, and fecundity decreased. Moreover, H. axyridis did not exhibit oviposition preference on plants infested with unparasitized aphids or aphids parasitized for shorter than 9 days. However, compared with plants with mummies (parasitized ≥9 days), H. axyridis laid more eggs on plants with unparasitized aphids. In contrast, H. axyridis previously fed with A. gifuensis mummies did not show a significant oviposition preference between plants with unparasitized aphids and those with mummies (parasitized ≥9 days). Overall, our results suggest that mummy consumption reduced the fitness of H. axyridis. Although H. axyridis avoided laying eggs on plants with A. gifuensis mummies, prior feeding experience on A. gifuensis mummies could alter the oviposition site preference. Thus, in biological control practice, prior feeding experience of H. axyridis should be carefully considered for reduction of IGP and increase of fitness of H. axyridis on A. gifuensis.

Sexual Dimorphism in the Multielemental Stoichiometric Phenotypes and Stoichiometric Niches of Spiders

Nutritional limitations may shape populations and communities of organisms. This phenomenon is often studied by treating populations and communities as pools of homogenous individuals with average nutritional optima and experiencing average constraints and trade-offs that influence their fitness in a standardized way. However, populations and communities consist of individuals belonging to different sexes, each with specific nutritional demands and limitations. Taking this into account, we used the ecological stoichiometry framework to study sexual differences in the stoichiometric phenotypes, reflecting stoichiometric niches, of four spider taxa differing in the hunting mode. The species and sexes differed fundamentally in their elemental phenotypes, including elements beyond those most commonly studied (C, N and P). Both species and sexes were distinguished by the C:N ratio and concentrations of Cu, K and Zn. Species additionally differed in concentrations of Na, Mg and Mn. Phosphorous was not involved in this differentiation. Sexual dimorphism in spiders' elemental phenotypes, related to differences in their stoichiometric niches, suggests different nutritional optima and differences in nutritional limitation experienced by different sexes and species. This may influence the structure and functioning of spider populations and communities.

High-quality alternative food reduces cannibalism in the predatory mite Amblyseius herbicolus (Acari: Phytoseiidae)

Predatory mites of the Phytoseiidae family are important biological control agents. Many species of this family are omnivores, i.e., besides on prey, they can feed on plant resources such as nectar and pollen. It has been shown that the addition of alternative food for predators to a crop enhances biological control. However, factors such as food availability and quality can also affect interactions such as cannibalism, and thus influence biological control. We investigated the role of quality of the alternative food in the tendency of Amblyseius herbicolus to engage in cannibalism, a common ecological interaction in many phytoseiid mite species. Cannibalism on eggs by A. herbicolus was significantly reduced in the presence of high-quality food (cattail pollen) compared to egg cannibalism without alternative food, whereas this was not the case in the presence of low-quality food (cotton pollen). This suggests that cattail pollen is a high-quality alternative food, not only because it results in increased development and reproduction of predators, but also because it can minimize cannibalism.

Allochthonous aquatic subsidies alleviate predation pressure in terrestrial ecosystems

The input of external energy and matter in recipient ecosystems can act as a bottom-up force that subsidizes consumers, with subsequent cascading effects throughout the food web. Depending on the amount of input, dietary preference, and the strength of trophic links, allochthonous resources generally play a stabilizing role on food webs. In this study, we investigated the stabilizing role of allochthonous aquatic resources on intraguild predation (IGP) and their consequences on shared prey in a terrestrial ecosystem. To this end, we manipulated the input of emergent aquatic insects (the allochthonous resources) from streams to land, and predation pressure by bats and birds (the top predators), in a multitrophic food web using an orthogonal exclusion experiment. Using stable isotope metrics, we found that bats, birds, and spiders (the mesopredators), were highly subsidized by emergent aquatic insects. Moreover, among terrestrial prey, top predators fed more on spiders than insects. As predicted, spiders were strongly affected by the presence of top predators when allochthonous resources were excluded. Consequently, in this scenario terrestrial insects were two times more abundant. Because spiders showed a higher preference for consuming aquatic resources, we suggest that nonconsumptive effects of spiders upon terrestrial insects could be mediating the strong response of those shared prey. We demonstrate that the input of allochthonous aquatic resources can play a fundamental role in stabilizing terrestrial trophic interactions and trophic cascades in riparian zones via decreasing predation pressure.

Experimental N and P additions relieve stoichiometric constraints on organic matter flows through five stream food webs

Human activities have dramatically altered global patterns of nitrogen (N) and phosphorus (P) availability. This pervasive nutrient pollution is changing basal resource quality in food webs, thereby affecting rates of biological productivity and the pathways of energy and material flow to higher trophic levels. Here, we investigate how the stoichiometric quality of basal resources modulates patterns of material flow through food webs by characterizing the effects of experimental N and P enrichment on the trophic basis of macroinvertebrate production and flows of dominant food resources to consumers in five detritus-based stream food webs. After a pre-treatment year, each stream received N and P at different concentrations for 2 years, resulting in a unique dissolved N:P ratio (target range from 128:1 to 2:1) for each stream. We combined estimates of secondary production and gut contents analysis to calculate rates of material flow from basal resources to macroinvertebrate consumers in all five streams, during all 3 years of study. Nutrient enrichment resulted in a 1.5× increase in basal resource flows to primary consumers, with the greatest increases from biofilms and wood. Flows of most basal resources were negatively related to resource C:P, indicating widespread P limitation in these detritus-based food webs. Nutrient enrichment resulted in a greater proportion of leaf litter, the dominant resource flow-pathway, being consumed by macroinvertebrates, with that proportion increasing with decreasing leaf litter C:P. However, the increase in efficiency with which basal resources were channelled into metazoan food webs was not propagated to macroinvertebrate predators, as flows of prey did not systematically increase following enrichment and were unrelated to basal resource flows. This study suggests that ongoing global increases in N and P supply will increase organic matter flows to metazoan food webs in detritus-based ecosystems by reducing stoichiometric constraints at basal trophic levels. However, the extent to which those flows are propagated to the highest trophic levels likely depends on responses of individual prey taxa and their relative susceptibility to predation.

Ecophysiological and life-history adaptations of Gammarus balcanicus (Schäferna, 1922) in a sinking-cave stream from Western Carpathians (Romania)

Freshwater gammarids are known to colonise occasionally sinking-cave streams, providing contrasting morphological, life-history and ecophysiological adaptations compared to their surface conspecifics. In this study, a subterranean and a surface population of the species Gammarus balcanicus was surveyed for one year in a sinking-cave stream from the Western Carpathians (Romania). The results showed that the cave-dwelling population comprised individuals that were significantly larger compared to their surface conspecifics, had larger body-size at sexual maturity and that the females produced fewer, but larger eggs, compared to the population situated outside the cave. The trophic position and the omnivory were significantly higher for the cave-dwelling compared to surface population and the elemental imbalance for C:P molar ratios lower, but similar for C:N. However, the subterranean population did not present troglomorphic characters or longer lifespan as known for other cave-surface paired crustaceans. This, together with the rather extensive hydrological connection of the habitats, suggests active gene-flow between populations and similar response to seasonality for body-size distributions, indicating that the observed ecophysiological and life-history differences are rather the consequence of phenotypic plasticity than the result of genetic adaptation.

The role of omnivory in mediating metacommunity robustness to habitat destruction

Omnivores have long been known to play an important role in determining the stability of ecological communities. Recent theoretical studies have suggested that they may also increase the resilience of their communities to habitat destruction, one of the major drivers of species extinctions globally. However, these outcomes were obtained for minimal food webs consisting of only a single omnivore and its prey species, while much more complex communities can be anticipated in nature. In this study, we undertake a systematic comparative analysis of the robustness of metacommunities containing various omnivory structures to habitat loss and fragmentation using a mathematical model. We observe that, in general, omnivores are better able to survive facing habitat destruction than specialist predators of similar trophic level. However, the community as a whole does not always benefit from the presence of omnivores, as they may drive their intraguild prey to extinction. We also analyze the frequency with which these modules occur in a set of empirical food webs, and demonstrate that variation in their rate of occurrence is consistent with our model predictions. Our findings demonstrate the importance of considering the complete food web in which an omnivore is embedded, suggesting that future study should focus on more holistic community analysis.

Different predation capacities and mechanisms of Harmonia axyridis (Coleoptera: Coccinellidae) on two morphotypes of pear psylla Cacopsylla chinensis (Hemiptera: Psyllidae)

Pear psylla, Cacopsylla chinensis (Yang & Li) are present as two seasonal morphotypes in pear orchards where they, suck phloem sap, defoliate pear trees, and cause fruit russet. Despite the importance of natural enemies in psyllid control, the interactions between predators and the two seasonal morphotypes of psyllids remain poorly documented. Here we determined the predation efficiencies of the Asian lady beetle, Harmonia axyridis (Pallas) on the two psyllid morphotypes. Predation of H. axyridis on both morphotypes conformed to a Type II functional response: the proportion of consumed psyllids decreased with increasing prey densities. Predation efficiency of H. axyridis against the winterforms increased with temperature when measured from 8 to 25°C. Predation rate on the summerforms was significantly higher than that of the winterforms. This was linked to smaller body size, higher soluble protein level, thinner cuticle, and lower chitin content of summerform psyllids compared to winterform psyllids. Predation capacities of H. axyridis on both morphotypes indicated its potential as a biocontrol agent in psyllids management. Predation efficiency was higher on summerforms, likely due to the difference in body size, exoskeleton fragility, and nutritional value between the two morphotypes. Due to the Type II functional response of H. axyridis to both morphotypes of pear psylla, application of H. axyridis in pear orchards under suitable temperatures could be taken into consideration for suppression of C. chinensis, although further experiments conducted in field conditions are needed to validate our findings.

Does prey encounter and nutrient content affect prey selection in wolf spiders inhabiting Bt cotton fields?

Wolf spiders are abundant and voracious predators at the soil-plant interface in cotton crops. Among other prey, they attack late-instar larvae of the cotton bollworm Helicoverpa spp., an economically important pest. Consequently, wolf spiders in transgenic Bt cotton could provide significant biological control of Bt-resistant Helicoverpa larvae that descend to the soil to pupate. The predator-prey interactions between wolf spiders and Helicoverpa could, however, be constrained by the presence of alternative prey and intraguild predators. This study used laboratory enclosures to analyse the effect of alternative prey on predatory selection of the wolf spider Tasmanicosa leuckartii Thorell. The prey included another wolf spider Hogna crispipes Koch (potential intraguild predator), the ground cricket Teleogryllus commodus Walker (minor pest), and Helicoverpa armigera larvae (major pest). We tested if encounter rates, prey vulnerability, and prey nutritional content influenced the likelihood that a prey was attacked. In three-way food webs, Tasmanicosa encountered and attacked Teleogryllus and Helicoverpa in similar frequencies. However, in the presence of a competing intraguild predator and potential prey (Hogna) in a four-way food web, Tasmanicosa did not always attack Teleogryllus at first encounter, but still attacked Helicoverpa at each encounter. Helicoverpa (protein-poor) and Hogna (protein-rich) were consumed by Tasmanicosa in similar proportions, suggesting that Tasmanicosa might benefit from nutrient balance as an outcome of diverse prey in this food web. As Teleogryllus (protein rich) escapes quicker than Helicoverpa and Hogna, Hogna may be an easier protein-rich option than Teleogryllus. Field surveys showed that while Teleogryllus was the most common prey, wolf spiders feed on diverse insect taxa, as well as other spiders. That Tasmanicosa readily attacked Helicoverpa larvae in the presence of alternative prey is an encouraging result that supports the potential of Tasmanicosa predation to assist in the control of Bt-resistant Helicoverpa larvae and thereby inhibit the proliferation and spread of resistance.

We Are What We Eat: A Stoichiometric and Ecometabolomic Study of Caterpillars Feeding on Two Pine Subspecies of Pinus sylvestris

Many studies have addressed several plant-insect interaction topics at nutritional, molecular, physiological, and evolutionary levels. However, it is still unknown how flexible the metabolism and the nutritional content of specialist insect herbivores feeding on different closely related plants can be. We performed elemental, stoichiometric, and metabolomics analyses on leaves of two coexisting Pinus sylvestris subspecies and on their main insect herbivore; the caterpillar of the processionary moth (Thaumetopoea pityocampa). Caterpillars feeding on different pine subspecies had distinct overall metabolome structure, accounting for over 10% of the total variability. Although plants and insects have very divergent metabolomes, caterpillars showed certain resemblance to their plant-host metabolome. In addition, few plant-related secondary metabolites were found accumulated in caterpillar tissues which could potentially be used for self-defense. Caterpillars feeding on N and P richer needles had lower N and P tissue concentration and higher C:N and C:P ratios, suggesting that nutrient transfer is not necessarily linear through trophic levels and other plant-metabolic factors could be interfering. This exploratory study showed that little chemical differences between plant food sources can impact the overall metabolome of specialist insect herbivores. Significant nutritional shifts in herbivore tissues could lead to larger changes of the trophic web structure.

Prey nutrient content creates omnivores out of predators

The proximate forces that create omnivores out of herbivores and predators have long fascinated ecologists, but the causal reasons for a shift to omnivory are poorly understood. Determining what factors influence changes in trophic position are essential as omnivory plays a central role in theoretical and applied ecology. We used sevenspotted lady beetles (Coccinella septempunctata) to test how prey nutrient content affects beetles' propensity to engage in herbivory. We show that beetles consuming an all-prey diet demonstrate normal growth and development, but suffer a complete loss of fitness (spermatogenic failure) that is restored via herbivory and supplementation with phytosterols and cholesterol. Furthermore, we show that lady beetles possess a state-dependent sterol-specific appetite and redressed their sterol deficit by feeding on foliage. These results demonstrate that predators balance their nutrient intake via herbivory when prey quality is low, and reveal a selective force (sterol nutrition) that drives predatory taxa to omnivory.

Biogeochemistry and forest composition shape nesting patterns of a dominant canopy ant

Humans are increasing nutrient deposition across the globe, and we know little about how these changes influence consumer populations in tropical rainforests. We used a long-term fertilization experiment conducted in a Panamanian forest to explore how nutrient availability and tree traits affect abundance of a higher-level consumer. We added nitrogen, phosphorus and potassium in a factorial design for 18 years. Given that phosphorus often limits ecosystem processes in lowland tropical forests, and added nitrogen reduces insect abundance in our experiment, we first hypothesized that phosphorus addition would increase nest density and nest size of Azteca chartifex ants while nitrogen addition would have the opposite effects. We found 48% lower nest density in the canopy of nitrogen addition plots relative to plots that did not receive nitrogen. Phosphorus addition did not affect nest density or size. These nutrient effects were not diminished by the selectivity of host trees. In general, larger trees held more nests, despite their low frequencies across the forest, while some abundant species (e.g., palms) were rarely used. We further predicted higher nest frequency on trees with extrafloral nectaries, because this ant fuels its large colonies with extrafloral nectar. Despite the non-random distribution of A. chartifex nests, across tree species and nutrient treatments, trees with extrafloral nectaries did not host more nests. Our study suggests that areas of a tropical lowland forest which are not oversaturated with nitrogen, and contain large trees, have higher nest density. This could enable A. chartifex in similar areas to outcompete other ants due to high abundance.

Connectivity increases trophic subsidies in fragmented landscapes

Landscape corridors mitigate the negative effects of habitat fragmentation by increasing dispersal. Corridors also increase biodiversity in connected habitat fragments, suggestive of metacommunity dynamics. What is unknown in this case is the mechanisms through which metacommunity dynamics act. Working in a large-scale fragmentation experiment, we tested the effect of corridors on the movement of prey species and subsequent effects on predator nutrition (which we call trophic subsidies). We enriched plants of central patches with ¹⁵ N, then measured δ¹⁵ N in green lynx spiders, the most abundant insect predator, in patches that were either connected to or isolated from the enriched patch. We found that corridors increased prey movement, as they increased spider δ¹⁵ N by 40% in connected patches. Corridors also improved spider body condition, increasing nitrogen relative to carbon. We suggest a novel mechanism, trophic subsidies, through which corridors may increase the stability or size of populations in connected landscapes.

A Better Understanding of Bee Nutritional Ecology Is Needed to Optimize Conservation Strategies for Wild Bees-The Application of Ecological Stoichiometry

The observed decline in wild bees may be connected to the decreasing diversity of flowering plants. Changes in floral composition shape nutrient availability in inhabited areas, and bee larvae need food rich in body-building nutrients to develop into adults. Adult food, mainly composed of energy-rich nectar, differs from larval food, mainly composed of pollen, and adult bees forage on different plant species for nectar and pollen. Defining bee-friendly plants based on the quantities of food produced, and on the visitation rates of adult pollinating insects leads to the planting of bee habitats with poor-quality food for larvae, which limits their growth and development, and negatively affects the population. Consequently, failing to understand the nutritional needs of wild bees may lead to unintended negative effects of conservation efforts. Ecological stoichiometry was developed to elucidate the nutritional constraints of organisms and their colonies, populations, and communities. Here, I discuss how applying ecological stoichiometry to the study of the nutritional ecology of wild bees would help fill the gaps in our understanding of bee biology. I present questions that should be answered in future studies to improve our knowledge of the nutritional ecology of wild bees, which could result in better conservation strategies.

Short-term tissue decomposition alters stable isotope values and C:N ratio, but does not change relationships between lipid content, C:N ratio, and Δδ13C in marine animals

Measures (e.g. δ15N, δ13C, %C, %N and C:N) derived from animal tissues are commonly used to estimate diets and trophic interactions. Since tissue samples are often exposed to air or kept chilled in ice over a short-term during sample preparation, they may degrade. Herein, we hypothesize that tissue decomposition will cause changes in these measures. In this study, we kept marine fish, crustacean and mollusc tissues in air or ice over 120 h (5 days). We found that tissue decomposition in air enriched δ15N (range 0.6‰ to 1.3‰) and δ13C (0.2‰ to 0.4‰), decreased %N (0.47 to 3.43 percentage points from staring values of ~13%) and %C (4.53 to 8.29 percentage points from starting values of ~43%), and subsequently increased C:N ratio (0.14 to 0.75). In air, while such changes to δ13C were relatively minor and therefore likely tolerable, changes in δ15N, %N, %C and C:N ratio should be interpreted with caution. Ice effectively reduced the extent to which decomposition enriched δ15N (≤ 0.4‰) and δ13C (≤ 0.2‰), and eliminated decomposition in C:N ratio, %N and %C. In our second experiment, for fish tissues in either air or ice over 120 h, we observed no effects of decomposition on relationships between lipid content, C:N ratio, and Δδ13C (change in δ13C after lipid removal), which are employed to correct δ13C for samples containing lipid. We also confirmed that lipid in tissues caused large errors when estimating δ13C (mean ± standard error = -1.8‰ ± 0.1‰, range -0.6‰ to -3.8‰), and showed both lipid extraction and mathematical correction performed equally well to correct for lipids when estimating δ13C. We, therefore, recommend that specimens of marine animals should be kept in ice during sample preparation for a short-term, as it is an effective means for minimizing changes of the stable isotope measures in their tissue.

Caught in the web: Spider web architecture affects prey specialization and spider-prey stoichiometric relationships

Quantitative approaches to predator-prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator-prey interactions. Here, we used spider-prey interactions as a model system to investigate whether different spider web architectures-orb, tangle, and sheet-tangle-affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle-web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet-tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle-web spiders than for orb and sheet-tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator-prey interactions.

Diet selectivity in a terrestrial forest invertebrate, the Auckland tree wētā, across three habitat zones

Insects are important but overlooked components of forest ecosystems in New Zealand. For many insect species, information on foraging patterns and trophic relationships is lacking. We examined diet composition and selectivity in a large-bodied insect, the Auckland tree wētā Hemideina thoracica, in three habitat zones in a lowland New Zealand forest. We asked whether H. thoracica selectively forage from available plant food sources, and whether these choices were lipid-rich compared to nonpreferred available plants. We also identified the proportion of invertebrates in their frass as a proxy for omnivory. From reconnaissance plot sampling, together with fecal fragment analysis, we report that more than 93% of individual tree wētā had eaten invertebrates before capture. Additionally, wētā in the highest elevation hillslope habitat zone consumed significantly fewer species of plants on average than wētā on the low-elevation terrace habitat. Upper hillslope wētā also had the highest average number of invertebrate fragments in their frass, significantly more than wētā in the low-elevation terrace habitat zone. Wētā showed high variability in the consumption of fruit and seeds across all habitat zones. Generally, we did not observe diet differences between the sexes (although it appears that male wētā in the mid-hillslope habitat ate fruits and seeds more voraciously than females), suggesting that the sexes have similar niche breadths and display similar degrees of omnivorous behavior. Extraction of leaf lipids demonstrated a range of lipid content values in available plants, and Ivlev's Electivity Index indicated that plant species which demonstrated high electivity tended to have higher concentrations of lipids in their leaves. Our findings indicate that H. thoracica forage omnivorously and selectively, and hence play multiple roles in native ecosystems and food webs.

The Quality of Nonprey Food Affects Cannibalism, Intraguild Predation, and Hyperpredation in Two Species of Phytoseiid Mites

Generalist arthropod predators not only prey on herbivores but also may engage in competitive interactions by attacking and consuming conspecifics (cannibalism) or other predators (intraguild predation [IGP] and hyperpredation). These types of interactions are quite common among predators used in biological control. Although there is evidence that nonprey food relaxes cannibalism and IGP, there is little information regarding the impact of the quality of the nonprey food. Herein, we examined how pollen of different nutritional quality (pine, narrow-leaf cattail, or apple) impacted 1) the cannibalism by females of Euseius stipulatus (Athias-Henriot) (Acari: Phytoseiidae) on conspecific larvae, 2) the reciprocal predation between gravid females of E. stipulatus or Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) and heterospecific larvae, and 3) the predation of E. stipulatus on the eggs of the aphid predator Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). E. stipulatus cannibalism was significantly reduced in the cattail pollen treatment, whereas in the pine pollen it did not significantly differ from control (no food). Predation between I. degenerans and E. stipulatus was significantly reduced in the cattail pollen treatment as compared to the control treatment. Finally, predation of E. stipulatus on A. aphidimyza eggs was significantly reduced when cattail or apple pollen was provided compared to the pine pollen or control treatments. These results suggest that cattail or apple pollen is suitable for mitigating negative interactions among generalist predatory mites used in biological control.

Implications of animal water balance for terrestrial food webs

Recent research has documented shifts in per capita trophic interactions and food webs in response to changes in environmental moisture, from the top-down (consumers to plants), rather than solely bottom-up (plants to consumers). These responses may be predictable from effects of physiological, behavioral, and ecological traits on animal water balance, although predictions could be modified by energy or nutrient requirements, the risk of predation, population-level responses, and bottom-up effects. Relatively little work has explicitly explored food web effects of changes in animal water balance, despite the likelihood of widespread relevance, including during periodic droughts in mesic locations, where taxa may lack adaptations for water conservation. More research is needed, particularly in light of climate change and hydrological alteration.

Ecological stoichiometry of the honeybee: Pollen diversity and adequate species composition are needed to mitigate limitations imposed on the growth and development of bees by pollen quality

The least understood aspects of the nutritional needs of bees are the elemental composition of pollen and the bees' need for a stoichiometrically balanced diet containing the required proportions of nutrients. Reduced plant diversity has been proposed as an indirect factor responsible for the pollinator crisis. We suggest stoichiometric mismatch resulting from a nutritionally unbalanced diet as a potential direct factor. The concentrations and stoichiometric ratios of C, N, S, P, K, Na, Ca, Mg, Fe, Zn, Mn, and Cu were studied in the bodies of honeybees of various castes and sexes and in the nectar and pollen of various plant species. A literature review of the elemental composition of pollen was performed. We identified possible co-limitations of bee growth and development resulting mainly from the scarcity of Na, S, Cu, P and K, and possibly Zn and N, in pollen. Particular castes and sexes face specific limitations. Concentrations of potentially limiting elements in pollen revealed high taxonomic diversity. High floral diversity may be necessary to maintain populations of pollen eaters. Single-species crop plantations, even if these species are rich in nectar and pollen, might limit bee growth and development, not allowing for gathering nutrients in adequate proportions. However, particular plant species may play greater roles than others in balancing honeybee diets. Therefore, we suggest specific plant species that may (1) ensure optimal growth and production of individuals by producing pollen that is exceptionally well balanced stoichiometrically (e.g., clover) or (2) prevent growth and development of honeybees by producing pollen that is extremely unbalanced for bees (e.g., sunflower). Since pollen is generally poor in Na, this element must be supplemented using "dirty water". Nectar cannot supplement the diet with limiting elements. Stoichiometric mismatch should be considered in intervention strategies aimed at improving the nutritional base for bees.

Variation in the web-based chemical cues of Argiope keyserlingi

Pheromones are chemical compounds used to transmit information between individuals of the same species. Pheromone composition is influenced by both genetic and environmental factors. Numerous studies, predominately of insects, have demonstrated a role for diet in pheromone expression. The chemical composition of spider web-silk varies with diet and in many species these chemicals are crucial to mate choice processes. Here, we investigated individual variation in the chemical compounds found on the surface of web-silk of female Argiope keyserlingi, and further explored the degree to which they are influenced by diet, investment in egg sac production and site of collection. We observed variation in the web-based chemical cues both between and within individuals. Additionally, we found that some of this variation could be explained by diet and gravid status but not by collection site. We discuss our findings in relation to mate choice processes and the costs and benefits of the observed variation in these web-based chemicals.

A Stoichioproteomic Analysis of Samples from the Human Microbiome Project

Ecological stoichiometry (ES) uses organism-specific elemental content to explain differences in species life histories, species interactions, community organization, environmental constraints and even ecosystem function. Although ES has been successfully applied to a range of different organisms, most emphasis on microbial ecological stoichiometry focuses on lake, ocean, and soil communities. With the recent advances in human microbiome research, however, large amounts of data are being generated that describe differences in community composition across body sites and individuals. We suggest that ES may provide a framework for beginning to understand the structure, organization, and function of human microbial communities, including why certain organisms exist at certain locations, and how they interact with both the other microbes in their environment and their human host. As a first step, we undertake a stoichioproteomic analysis of microbial communities from different body sites. Specifically, we compare and contrast the elemental composition of microbial protein samples using annotated sequencing data from 690 gut, vaginal, oral, nares, and skin samples currently available through the Human Microbiome Project. Our results suggest significant differences in both the median and variance of the carbon, oxygen, nitrogen, and sulfur contents of microbial protein samples from different locations. For example, whereas proteins from vaginal sites are high in carbon, proteins from skin and nasal sites are high in nitrogen and oxygen. Meanwhile, proteins from stool (the gut) are particularly high in sulfur content. We interpret these differences in terms of the local environments at different human body sites, including atmospheric exposure and food intake rates.