Terrestrial Insects Research Articles

Entomopathogen-based biopesticides: insights into unraveling their potential in insect pest management.

Global food security is a critical challenge to fulfill the demands of an exponentially growing population. To date, growers rely on chemicals; the broad-spectrum application of synthetic molecules leads to environmental contamination, resistance development, residual toxicity, pest resurgence, and a detrimental effect on human health and cattle. Crop production needs to be improved considering environmental and human health concerns to ensure food security. Furthermore, economically important crops are prone to attack by insect pests, causing considerable yield losses. Microbes are an eco-friendly, versatile alternative, and a potential candidate for combatting destructive pests below the economic injury level and improving the plant's health and productivity. Several microbial pathogens, including parasites, predators, parasitoids, pollinators, and many beneficial microorganisms, possess toxic properties against target organisms but do not cause harm to the non-target organisms. Entomopathogens (ENMs) have great potential for pest suppression due to their remarkable properties. Bacteria are host-specific, but fungi have a broader host range and can be significantly affected by both soil-dwelling and terrestrial insect pests. Virulent pathogens cause mortality in target insect pests known as ENMs and can penetrate through natural openings, ingestions, and integuments to cause a possible effect on target insect pests. The objective of using ENMs is to sustain productivity, improve environmental health, reduce pesticides, and conserve natural resources. Moreover, research is ongoing to discover other possible aspects, especially exploring potential ENMs. Therefore, there is a need for identification, isolation, and bioformulation to overcome the existing issues. This study is mainly focused on the status of bio-formulations, pathogenicity, their mode of action, and the potential application of different types of microbial formulations for sustainable pest management.

Decomposition in an artificial lentic environment: approaches to post-mortem interval estimation

ABSTRACT While terrestrial decomposition has been extensively researched to produce reliable methods of estimating the post-mortem interval of remains, there is limited literature documenting aquatic decomposition. Consequently, the ability to reliably estimate the post-mortem submersion interval for remains in water bodies is poor, despite markedly varying insect succession between aquatic and terrestrial decomposition This study was conducted to compare decomposition on Sus domesticus carcases in terrestrial and artificial lentic environments, aiming to provide more detailed characterization of aquatic decomposition and document the role of terrestrial organisms in the accompanying insect succession. Three trials consisting of six stillborn piglets in lentic environments and three in terrestrial environments were observed daily over a period of 12 months. Decomposition stage and morphological changes between terrestrial and lentic piglets were noted. Insects were sampled from remains and reared to adulthood for identification. Lentic decomposition was prolonged relative to terrestrial decomposition, reflecting aquatic decomposition characteristics accompanied by terrestrial insect colonization. Diptera were more prevalent on terrestrial remains, and Coleoptera in the lentic environments, with few dipteran taxa common between environments. Results show the variability of decomposition stages, characteristics and insects between terrestrial and lentic remains, and are discussed with regard to implications for aquatic forensic casework.

DNA metabarcoding reveals rangewide variation in aquatic diet of a riparian avian insectivore, the Prothonotary Warbler

Abstract Riparian avian insectivores not only depend on terrestrial insect prey but also benefit from the inclusion of aquatic prey during critical life-history periods. Diets identified herein show that Prothonotary Warbler (Protonotaria citrea) nestlings were provisioned with aquatic prey throughout the breeding season across their range, but with variation in prey frequency of occurrence and taxonomy. Anthropogenic activity and climate change may impact the trophic link especially between aquatic and riparian habitats by altering the presence, abundance, and timing of prey availability. Thus, we used DNA metabarcoding of fecal samples to quantify the frequency of occurrence of nestling diet items at 9 sites across their breeding range that differed in expected aquatic prey consumption. We analyzed spatial and temporal differences in the occurrence and multivariate diet assemblages of each prey source. Lepidoptera was the predominant terrestrial prey occurring in diets across space and time, whereas emergent aquatic insects and freshwater mollusks in aquatic diet exhibited greater variation. The frequency of emergent aquatic prey occurrence in nestling diets ranged from 61% to 100% across sites and was greater for early-season nestlings. The seasonal decrease in aquatic prey consumption indicates a potential temporal shift in the nutritional landscape from aquatic to terrestrial prey sources and a possible nutritional phenological mismatch for early nestlings as climate change advances the timing of insect emergence. Our findings also suggest that Prothonotary Warblers respond to environmental variability by consuming alternative prey and argue for future research investigating the extent to which shifting diets have nutritional consequences for riparian nestlings.

Year-Round Bat Activity and Species Richness Near Temporary Ponds in the Mediterranean Region.

Mediterranean temporary ponds are recognized as conservation priority habitats that face anthropogenic threats and are important habitats for a number of aquatic and terrestrial animals and plants. Bats are a diverse group of animals that use ponds for drinking and feeding on emerging aquatic insects and terrestrial insects in the riparian zone. We investigated the importance of temporary ponds for bats in Greece by acoustically sampling bat community structures and activity at temporary ponds throughout the year. We sampled monthly, from 3 to 13 months in 2019-2020, at sites at the pond edge and approximately 150-300 m away from the edge, at four temporary ponds in northern and southern Greece. Our results confirm the importance of temporary ponds for bats as activity was recorded year-round and was high in all but the winter months. In general, the distance to the edge of the pond and the presence of water in the pond explained bat activity together with air temperature. Importantly, whether dry or not, all ponds supported bat activity, independent of their particular characteristics. This study highlights the urgent need for the conservation of temporary ponds, especially in areas with limited water availability.

Effects of phthalate and bisphenol plasticizers on the activity of glycolytic enzymes of the moth Spodoptera littoralis

Environmental plastic pollution has significantly increased in the recent decades, and severely impacts economies, human and biodiversity health. Plastics are made of several chemical additives, including bisphenol and phthalate plasticizers such as bisphenol A (BPA) and Di(2-ethylhexyl)phthalate (DEHP). In some animal species, both BPA and DEHP are known as endocrine disruptor compounds, and can alter physiological and metabolic homeostasis, reproduction, development and/or behavior. To date, the impacts of BPA and DEHP have mainly focused on vertebrates, and to a lesser extent, on aquatic invertebrates. Yet, the few studies which examined the effects of DEHP on terrestrial insects also revealed the impacts this pollutant can have on development, hormone titrations, and metabolic profiles. In particular, it has been hypothesized in the Egyptian cotton leafworm Spodoptera littoralis that the observed metabolic alterations could result from the energetic costs necessary for DEHP detoxification or to the dysregulation of hormonally-controlled enzymatic activities. To get additional insights into the physiological effects of bisphenol and phthalate plasticizers on the moth S. littoralis, larvae were fed with food contaminated by BPA, DEHP, or the mixture of both compounds. Then, activities of four glycolytic enzymes, hexokinase, phosphoglucose isomerase, phosphofructokinase, and pyruvate kinase were measured. BPA and/or DEHP had no effects on the activities of phosphofructokinase and pyruvate kinase. Conversely, BPA-contaminated larvae were characterized by a 1.9-fold increase in phosphoglucose isomerase activity, and BPA + DEHP-fed larvae had highly variable hexokinase activity. Overall, since no disruption of glycolytic enzyme was observed in DEHP-contaminated larvae, our work tended to demonstrate that exposure to bisphenol and DEHP increased the amount of oxidative stress experienced.

Terrestrial insect fauna of the herbaceous stratum of reservoir embankment slopes, Korea

Herbaceous strata with a dominant plant community 50 m in size were selected from 10 reservoir embankment areas in Shinan-gun, a southwestern island region of South Korea. Terrestrial insects were sampled 100 times with quantitative sweep sampling to investigate the insect fauna and their association with flora. The survey areas were mainly dominated either by Phragmites japonica or Miscanthus sinensis plant species. A total of 1,948 individual insects representing 173 species from 64 families within 9 orders were collected. The number of species was the highest at Jaeundo while the Shannon-Wiener diversity index was the highest at Saokdo. Similarity analysis showed that the insect species composition tended to be similar among survey sites with plant communities comprising the same dominant plant species. Species diversity was the highest in April while the number of individual insects was the highest in September. Petaphora maritima and Ochetellus glaber were the dominant and subdominant insect species, with a high frequency of occurrence at these sites. The results of this study could be applied towards biodiversity conservation and monitoring of reservoir embankment areas in the future.

Suboptimal host tree benefits the overwintering of a destructive forest insect pest

Winter represents a stressful period for many organisms, and terrestrial insects are particularly susceptible to adverse thermal conditions. However, exposure to thermal stress and its effects on insect survival and performance can be modulated by various external factors. In forest systems, the overwintering microsite, stand structure, and regional climatic conditions may play a role in overwintering survival and performance at the individual microsite, local stand, and landscape level, respectively. To better understand the effects of these potential influences, rarely examined simultaneously, we deployed wild and lab-reared diapausing spruce budworm in a series of field experiments established across a range of spatial scales.Overwintering survival was higher on black spruce than balsam fir, likely owing to differences in substrate structure (and hence microsite quality/availability) between these two hosts. At the stand level, neither tree species nor age had an impact on insect survival; however, we observed a positive carryover effect of overwintering in a black spruce stand, enhancing performance in post-diapause development, possibly owing to buffering against warm spells during winter. Lastly, despite exposure to a broad range of winter temperatures across an extensive latitudinal gradient, overwintering survival was high (>80%) and did not vary at the landscape level.Our results indicate that insect overwintering was influenced by environmental factors at multiple spatial scales. Interestingly, despite it being considered a poor host for larval feeding, overwintering on black spruce clearly benefited spruce budworm survival and post-diapause performance. Secondly, microsite and stand-level factors had a greater impact than did regional climate variation. Collectively, these findings highlight the importance of finer-scale environmental factors on larval overwintering at both the lethal and sub-lethal level, with implications for basic and applied ecology of this iconic forest insect pest.

Food web structure in the Xingu River rapids prior to operation of the Amazon’s largest hydropower plant

The results of recent theoretical studies suggest that food webs are size-structured, with top predators coupling across different energy sources. However, evidence supporting this hypothesis is still scarce, especially in highly diverse tropical rivers. In the present study, we explored the association between body size, trophic position, and the use of allochthonous and autochthonous basal production sources in the Volta Grande rapids of the Xingu River, a major clearwater tributary of the Amazon River, during the period prior to operation of the Belo Monte Hydropower Plant (BMHP). This section of the river contains a maze of channels with rocky shoals that support dozens of endemic fishes, mollusks and other aquatic taxa that may be impacted by flow regulation by the Pimental Dam located upstream. During the low-water season, we surveyed fish, crustaceans, mollusks, sponges, aquatic and terrestrial insects, zooplankton, and basal production sources to obtain tissue samples for analysis of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N). The results indicated that the biomass of most aquatic organisms appears to be largely supported by riparian vegetation, highlighting the importance of the lateral connectivity between aquatic and terrestrial habitats. In contrast to expectation, we did not observe a gradual increase in the coupling of energy pathways with increasing body size and trophic position. These findings provide a baseline for the trophic ecology of this river under the natural flow regime that can be used for future impact assessments, and they also indicate that more complex food web models, potentially including additional functional traits (e.g., gut length) are needed to describe resource and habitat use in highly diverse tropical ecosystems.

Microplastics in terrestrial insects, long-horned beetles (Coleoptera: Cerambycidae), from China

Despite studies have proposed that microplastics (MPs) could exert adverse effects on terrestrial ecosystems and biota, the occurrence of MPs in wild terrestrial insects has been rarely investigated. This study examined MPs in 261 long-horned beetle (Coleoptera: Cerambycidae) samples collected from four different Chinese cities. Detection frequency of MPs in long-horned beetles from different cities was 68–88 %. Long-horned beetles from Hangzhou (4.0 items/individual) had the highest mean abundance of MPs, followed by that from Wuhan (2.9 items/individual), Kunming (2.5 items/individual), and Chengdu (2.3 items/individual). The mean size of MPs in long-horned beetles from four Chinese cities was 381–690 μm. Fiber consistently represented the major shape of MPs in long-horned beetles from different Chinese cities, contributing 60, 54, 50, and 49 % of total items of MPs in Kunming, Chengdu, Hangzhou, and Wuhan, respectively. Polypropylene was the major polymer composition of MPs in long-horned beetles from Chengdu (68 % of total items of MPs) and Kunming (40 %). However, polyethylene and polyester were the major types of polymer compositions of MPs in long-horned beetles from Wuhan (39 % of total MP items) and Hangzhou (56 %), respectively. To our knowledge, this is the first study investigating the occurrence of MPs in wild terrestrial insects. These data are important for evaluating the risks of exposure to MPs for long-horned beetles.

Microhabitat conditions remedy heat stress effects on insect activity.

Anthropogenic global warming has major implications for mobile terrestrial insects, including long-term effects from constant warming, for example, on species distribution patterns, and short-term effects from heat extremes that induce immediate physiological responses. To cope with heat extremes, they either have to reduce their activity or move to preferable microhabitats. The availability of favorable microhabitat conditions is strongly promoted by the spatial heterogeneity of habitats, which is often reduced by anthropogenic land transformation. Thus, it is decisive to understand the combined effects of these global change drivers on insect activity. Here, we assessed the movement activity of six insect species (from three orders) in response to heat stress using a unique tracking approach via radio frequency identification. We tracked 465 individuals at the iDiv Ecotron across a temperature gradient up to 38.7°C. In addition, we varied microhabitat conditions by adding leaf litter from four different tree species to the experimental units, either spatially separated or well mixed. Our results show opposing effects of heat extremes on insect activity depending on the microhabitat conditions. The insect community significantly decreased its activity in the mixed litter scenario, while we found a strong positive effect on activity in the separated litter scenario. We hypothesize that the simultaneous availability of thermal refugia as well as resources provided by the mixed litter scenario allows animals to reduce their activity and save energy in response to heat stress. Contrary, the spatial separation of beneficial microclimatic conditions and resources forces animals to increase their activity to fulfill their energetic needs. Thus, our study highlights the importance of habitat heterogeneity on smaller scales, because it may buffer the consequences of extreme temperatures of insect performance and survival under global change.

Variety among physical landscape features in natural grassland-plantation forestry mosaics promotes diverse butterfly assemblages

Various physical landscape features across local and regional spatial scales contribute to heterogeneity. This means that ostensible maintenance of physical landscape features as representatives of heterogeneity (i.e., a meso-filter conservation approach) can contribute to conservation of insect assemblages. Using butterflies as model organisms, we investigate the conservation value of specific physical landscape feature types (rocky areas, wetlands, and gullies) relative to open grasslands, across 32 study sites in a natural grassland-plantation forestry mosaic in South Africa. We found that all considered landscape feature types had equal species richness and diversity levels compared to open grasslands. Yet, β-diversity (mostly accounted for by species turnover) was overall high between rocky areas, wetlands, and open grasslands, resulting from associations between some butterfly species and certain landscape feature types. Gullies were occupied by nested assemblages of rocky areas and open grasslands, suggesting that gullies have lower conservation importance, and should be targets for restoration. Topography and butterfly food plant availability further influenced β-diversity patterns and should also be considered when adopting a meso-filter conservation approach. β-diversity was also high among similar feature types, suggesting that a variety of landscape features that encapsulates environmental variation at a landscape scale can best conserve regional butterfly assemblages. While our focus was on butterflies, we anticipate these findings to be relevant to other insect groups, given that butterflies have successfully been used as conservation surrogates for other terrestrial insect taxa (e.g., grasshoppers) in the same area.

Insectivorous bat foraging tracks the availability of aquatic flies (Diptera)

AbstractRivers and their adjacent riparian zones are model ecosystems for observing cross‐ecosystem energy transfers. Aquatic insects emerging from streams, for example, are resource subsidies that support riparian consumers such as birds, spiders, lizards, and bats. We collaborated with recreational river runners in Grand Canyon, Arizona, USA, to record acoustic bat activity and sample riparian insects using light traps at dusk from April through October 2017–2020. River runners collected these data on 1,428 events over 611 sampling nights at 410 sites throughout a 470‐km segment of the Colorado River. We documented 71 insect taxa in light traps and recorded 19 bat species with acoustic detectors. We hypothesized that bat activity along this highly regulated river segment would be influenced primarily by variation in prey availability, as compared to other habitat descriptors. We predicted that bat activity would be positively related to aquatic insect catch rates and unrelated to terrestrial insect abundance. We fit Bayesian regression models to test these hypotheses and to quantify the relationship between bat activity and a suite of environmental variables: time of year, time of day, distance from perennial tributaries, distance from rapids, channel width, geomorphic reach, tall vegetation cover, air temperature, and lunar phase. Bat activity was positively related to the abundance of aquatic flies (Diptera), which outcompeted all other prey categories and structural habitat descriptors in our models. Within our dusk sampling period, activity of small myotis (California myotis [Myotis californicus] and Yuma myotis [M. yumanensis]) was high late in the evening and canyon bats (Parastrellus hesperus), conversely, were more active early in the evening. Activity of canyon bats varied seasonally, with peak activity in August. Our results support the hypothesis that aquatic prey, specifically aquatic flies, are key predictors of bat activity along a large, regulated river corridor and demonstrate the power of community science as a tool for ecosystem monitoring.

A Possible Biomass Contribution to Fauna of Finike Seamounts by Terrestrial Insects

A Possible Biomass Contribution to Fauna of Finike Seamounts by Terrestrial Insects

Collation of a century of soil invertebrate abundance data suggests long-term declines in earthworms but not tipulids.

Large-scale declines in terrestrial insects have been reported over much of Europe and across the world, however, population change assessments of other key invertebrate groups, such as soil invertebrates, have been largely neglected through a lack of available monitoring data. This study collates historic data from previously published studies to assess whether it is possible to infer previously undocumented long-term changes in soil invertebrate abundance. Earthworm and tipulid data were collated from over 100 studies across the UK, spanning almost 100 years. Analyses suggested long-term declines in earthworm abundance of between 1.6 to 2.1% per annum, equivalent to a 33% to 41% decline over 25 years. These appeared greatest in broadleaved woodlands and farmland habitats, and were greater in pasture than arable farmland. Significant differences in earthworm abundance between habitats varied between models but appeared to be highest in urban greenspaces and agricultural pasture. More limited data were available on tipulid abundance, which showed no significant change over time or variation between enclosed farmland and unenclosed habitats. Declines in earthworm populations could be contributing to overall declines in ecosystem function and biodiversity as they are vital for a range of ecosystem services and are keystone prey for many vertebrate species. If robust, our results identify a previously undetected biodiversity decline that would be a significant conservation and economic issue in the UK, and if replicated elsewhere, internationally. We highlight the need for long-term and large-scale soil invertebrate monitoring, which potentially could be carried out by citizen/community scientists.

Insects within bushes assemble and forage closer to artificial light at night

AbstractArtificial light at night (ALAN) has been implicated in the global decline of insect populations. Causal mechanisms contributing to declines remain unclear, however. Here we examine causal factors which could link some declining terrestrial insect populations with ALAN. To do so, we defined the closest and furthest halves of individual bushes according to the nearest source of artificial light. We sampled leaves and invertebrates from both sides to determine herbivory and abundance. First, we observed that, within bushes, leaves were significantly more likely to display herbivory at closer distances to established streetlighting. This may be due to the phenomenon of positive phototaxis in insects (flight to light). Further, insects within bushes were significantly more abundant on the side closest to streetlighting at midnight, but not at midday, when lights are unilluminated. Consequently, we argue that ALAN creates bottom‐up trophic effects, driven by insect light attraction behaviours even at the scale of single plants.

Different environmental conditions in lowlands and uplands highlight challenges for butterfly conservation in Central Europe

Studies from all over the world have recently reported severe declines in insect diversity and abundance. Due to their high sensitivity to environmental changes, butterflies are well-suited indicators for assessing the overall state of the terrestrial insect fauna. Though they rank among the best-studied insect groups, Europe's butterfly populations are still declining in many places, especially in landscapes under intensive land use. In this study, we investigated the response of butterfly assemblages to environmental conditions in 169 plots in the wider countryside of North Rhine-Westphalia (NW Germany, Central Europe). Our study revealed a strong relationship between butterfly species richness and density and the environmental conditions in the study area. Due to the maintenance of low-intensity land use, the uplands were characterised by more favourable conditions for butterflies and consistently had a higher species richness and density of species overall and of threatened species than the intensively used lowlands. In addition to elevation, landscape diversity in particular fostered butterfly diversity. By contrast, butterfly assemblages exhibited a negative response to urban areas and arable land, which were among the most dominant habitat types in the lowlands. Moreover, our study highlighted the importance of nutrient-poor grasslands for butterflies, which is mainly a result of their high habitat quality. According to the findings of our study, it is especially important to promote heterogeneous landscapes with a large extent of semi-natural, nutrient-poor habitats. Therefore, the key issue for butterfly conservation is to change the current farming policies to increase the amount of low-intensity farmland.

An Eocene fossil scarab beetle (Coleoptera: Scarabaeoidea) from Tanzania

A fossil scarabaeoid (Coleoptera: Scarabaeoidea) Mahengea mckayi new genus, new species – the only well-preserved insect fossil and one of only a few insects found at the site – is described from an otherwise rich Eocene (~ 45.6 mya) maar Lagerstätte at Mahenge in central northern Tanzania. Numerous fossil fishes and plants have been recovered from this site and described. The dearth of insect fossils is surprising considering their richness in other deposits of similar origin and age. We suggest that the rich fish fauna present in the oxygen-rich parts of the water in the former volcanic crater lake may have scavenged most of the terrestrial insects that fell into the water. Although the fossil described here is undoubtedly that of a member of the Scarabaeoidea, the family placement remains unsure. Significance: We describe the first Eocene fossil scarab from Africa. It is one of only a few scarab fossils from the continent and one of the best-preserved insect (invertebrate) fossils from the deposit.

Investigation of presence and impact of radiation-induced bystander effect in Acheta domesticus

Purpose Radiation-induced bystander effect (RIBE), a non-targeted effect of ionizing radiation in which non-irradiated individuals behave as if they have been irradiated after interactions with irradiated individuals, has been well documented in vertebrates. However, little research has been done investigating RIBE in terrestrial insects, this paucity of invertebrate RIBE leads to lack of knowledge on invertebrates living in fallout and exclusion zones. This paper aims to better understand the impacts of RIBE on terrestrial insects. Methods and materials: House crickets who have interacted with irradiated crickets were examined to investigate population effects of ionizing radiation exposure to better understand RIBE in insects. Results The results demonstrated RIBE in crickets and found that cohabitated males had higher growth rate (mg/day) when compared to non-cohabitated males. Further, cohabitated males and females matured significantly faster with no significant difference in maturation weight than non-cohabitated populations. Experiment with adult irradiated crickets found saturability of bystander signals and similar shifts in maturation parameters. These results highlight that bystander signals can impacted development and maturation in crickets. Conclusion Given long-term impacts of RIBE in insects, these results may have significant implications for interactions between insects inhabiting fringe nuclear exclusion zones and those outside of it.

Habitat–trait interactions that control response to climate change: North American ground beetles (Carabidae)

AbstractAimAs one of the most diverse and economically important families on Earth, ground beetles (Carabidae) are viewed as a key barometer of climate change. Recent meta‐analyses provide equivocal evidence on abundance changes of terrestrial insects. Generalizations from traits (e.g., body size, diets, flights) provide insights into understanding community responses, but syntheses for the diverse Carabidae have not yet emerged. We aim to determine how habitat and trait syndromes mediate risks from contemporary and future climate change on the Carabidae community.LocationNorth America.Time period2012–2100.Major taxa studiedGround beetles (Carabidae).MethodsWe synthesized the abundance and trait data for 136 species from the National Ecological Observatory Network (NEON) and additional raw data from studies across North America with remotely sensed habitat characteristics in a generalized joint attribute model. Combined Light Detection and RAnging (LiDAR) and hyperspectral imagery were used to derive habitat at a continental scale. We evaluated climate risks on the joint response of species and traits by expanding climate velocity to response velocity given habitat change.ResultsHabitat contributes more variations in species abundance and community‐weighted mean traits compared to climate. Across North America, grassland fliers benefit from open habitats in hot, dry climates. By contrast, large‐bodied, burrowing omnivores prefer warm‐wet climates beneath closed canopies. Species‐specific abundance changes predicted by the fitted model under future shared socioeconomic pathways (SSP) scenarios are controlled by climate interactions with habitat heterogeneity. For example, the mid‐size, non‐flier is projected to decline across much of the continent, but the magnitudes of declines are reduced or even reversed where canopies are open. Conversely, temperature dominates the response of the small, frequent flier Agonoleptus conjunctus, causing projected change to be more closely linked to regional temperature changes.Main conclusionsCarabidae community reorganization under climate change is being governed by climate–habitat interactions (CHI). Species‐specific responses to CHI are explained by trait syndromes. The fact that habitat mediates warming impacts has immediate application to critical habitat designation for carabid conservation.

Trophic transfer of polyunsaturated fatty acids across the aquatic-terrestrial interface: An experimental tritrophic food chain approach.

Aquatic and their adjacent terrestrial ecosystems are linked via the flux of organic and inorganic matter. Emergent aquatic insects are recognized as high-quality food for terrestrial predators, because they provide more physiologically relevant long-chain polyunsaturated fatty acids (PUFA) than terrestrial insects. The effects of dietary PUFA on terrestrial predators have been explored mainly in feeding trials conducted under controlled laboratory conditions, hampering the assessment of the ecological relevance of dietary PUFA deficiencies under field conditions. We assessed the PUFA transfer across the aquatic-terrestrial interface and the consequences for terrestrial riparian predators in two outdoor microcosm experiments. We established simplified tritrophic food chains, consisting of one of four basic food sources, an intermediary collector gatherer (Chironomus riparius, Chironomidae), and a riparian web-building spider (Tetragnatha sp.). The four basic food sources (algae, conditioned leaves, oatmeal, and fish food) differed in PUFA profiles and were used to track the trophic transfer of single PUFA along the food chain and to assess their potential effects on spiders, that is, on fresh weight, body condition (size-controlled measurement of nutritional status), and immune response. The PUFA profiles of the basic food sources, C.riparius and spiders differed between treatments, except for spiders in the second experiment. The PUFA α-linolenic acid (ALA, 18:3n-3) and ɣ-linolenic acid (GLA, 18:3n-6) were major contributors to the differences between treatments. PUFA profiles of the basic food sources influenced the fresh weight and body condition of spiders in the first experiment, but not in the second experiment, and did not affect the immune response, growth rate, and dry weight in both experiments. Furthermore, our results indicate that the examined responses are dependent on temperature. Future studies including anthropogenic stressors would deepen our understanding of the transfer and role of PUFA in ecosystems.