Behavioural function and development of body-to-limb proportions and active movement ranges in three stick insect species

Overall body proportions and relative limb length are highly characteristic for most insect taxa. In case of the legs, limb length has mostly been discussed with regard to parameters of locomotor performance and, in particular cases, as an adaptation to environmental factors or to the mating system. Here, we compare three species of stick and leaf insects (Phasmatodea) that differ strongly in the length ratio between antennae and walking legs, with the antennae of Medauroidea extradentata being much shorter than its legs, nearly equal length of antennae and legs in Carausius morosus, and considerably longer antennae than front legs in Aretaon asperrimus. We show that that relative limb length is directly related to the near-range exploration effort, with complementary function of the antennae and front legs irrespective of their length ratio. Assuming that these inter-species differences hold for both sexes and all developmental stages, we further explore how relative limb length differs between sexes and how it changes throughout postembryonic development. We show that the pattern of limb-to-body proportions is species-characteristic despite sexual dimorphism, and find that the change in sexual dimorphism is strongest during the last two moults. Finally, we show that antennal growth rate is consistently higher than that of front legs, but differs categorically between the species investigated. Whereas antennal growth rate is constant in Carausius, the antennae grow exponentially in Medauroidea and with a sudden boost during the last moult in Aretaon.

Increasing temperatures reduce invertebrate abundance and slow decomposition

Decomposition is an essential ecosystem service driven by interacting biotic and abiotic factors. Increasing temperatures due to climate change can affect soil moisture, soil fauna, and subsequently, decomposition. Understanding how projected climate change scenarios will affect decomposition is of vital importance for predicting nutrient cycling and ecosystem health. In this study, we experimentally addressed the question of how the early stages of decomposition would vary along a gradient of projected climate change scenarios. Given the importance of biodiversity for ecosystem service provisioning, we measured the effect of invertebrate exclusion on red maple (Acer rubrum) leaf litter breakdown along a temperature gradient using litterbags in warming chambers over a period of five weeks. Leaf litter decomposed more slowly in the warmer chambers and in the litterbag treatment that minimized invertebrate access. Moreover, increasing air temperature reduced invertebrate abundance and richness, and altered the community composition, independent of exclusion treatment. Using structural equation models, we were able to disentangle the effects of average air temperature on leaf litter loss, finding a direct negative effect of warming on the early stages of decomposition, independent of invertebrate abundance. This result indicates that not only can climate change affect the invertebrate community, but may also directly influence how the remaining organisms interact with their environment and their effectiveness at provisioning ecosystem services. Overall, our study highlights the role of biodiversity in maintaining ecosystem services and contributes to our understanding of how climate change could disrupt nutrient cycling.

Estimating densities of larval Salmonflies (Pteronarcys californica) through multiple pass removal of post-emergent exuvia in Colorado rivers

Traditional methods of collecting, sorting, and identifying benthic macroinvertebrate samples are useful for stream biomonitoring and ecological studies, however, these methods are time consuming, expensive, and require taxonomic expertise. Estimating larval densities through collection of post-emergent exuvia can be a practical and time efficient alternative. We evaluated the use of multiple pass depletion techniques of the post-emergent exuvia of Pteronarcys californica to estimate larval densities at ten sites in three Colorado rivers. Exuvia density was highly correlated with both final-instar larval density (R2 = 0.90) and total larval density (R2 = 0.88) and the multiple pass removal technique performed well. Exuvia surveys found P. californica at three low density sites where benthic sampling failed to detect it. At moderate and high density sites the exuvia surveys always produced lower density estimates than benthic surveys. Multiple pass depletion estimates of exuvia proved to be an accurate and efficient technique at estimating larval densities and provided an effective alternative for traditional benthic sampling when objectives are detecting and monitoring P. californica, especially at low density sites.

Geographical origin determines responses to salinity of Mediterranean caddisflies

Many freshwater ecosystems worldwide, and particularly Mediterranean ones, show increasing levels of salinity. These changes in water conditions could affect abundance and distribution of inhabiting species as well as the provision of ecosystem services. In this study we conduct laboratory experiments using the macroinvertebrate Smicridea annulicornis as a model organism. Our factorial experiments were designed to evaluate the effects of geographical origin of organisms and salinity levels on survival and behavioral responses of caddisflies. The experimental organisms were captured from rivers belonging to three hydrological basins along a 450 Km latitudinal gradient in the Mediterranean region of Chile. Animals were exposed to three conductivity levels, from 180 to 1400 μS/cm, close to the historical averages of the source rivers. We measured the behavioral responses to experimental stimuli and the survival time. Our results showed that geographical origin shaped the behavioral and survival responses to salinity. In particular, survival and activity decreased more strongly with increasing salinity in organisms coming from more dilute waters. This suggests local adaptation to be determinant for salinity responses in this benthic invertebrate species. In the current scenario of fast temporal and spatial changes in water levels and salt concentration, the conservation of geographic intra-specific variation of aquatic species is crucial for lowering the risk of salinity-driven biodiversity loss.

The genetic mechanism of selfishness and altruism in parent-offspring coadaptation

The social bond between parents and offspring is characterized by coadaptation and balance between altruistic and selfish tendencies. However, its underlying genetic mechanism remains poorly understood. Using transcriptomic screens in the subsocial European earwig, Forficula auricularia, we found the expression of more than 1600 genes associated with experimentally manipulated parenting. We identified two genes, Th and PebIII, each showing evidence of differential coexpression between treatments in mothers and their offspring. In vivo RNAi experiments confirmed direct and indirect genetic effects of Th and PebIII on behavior and fitness, including maternal food provisioning and reproduction, and offspring development and survival. The direction of the effects consistently indicated a reciprocally altruistic function for Th and a reciprocally selfish function for PebIII. Further metabolic pathway analyses suggested roles for Th-restricted endogenous dopaminergic reward, PebIII-mediated chemical communication and a link to insulin signaling, juvenile hormone, and vitellogenin in parent-offspring coadaptation and social evolution.

Pressure-induced silk spinning mechanism in webspinners (Insecta: Embioptera)

The articulated appendages of arthropods are highly adaptable and potentially multifunctional, used for walking, swimming, feeding, prey capture, or other functions. Webspinners (Order Embioptera) are a paragon in this context. In contrast to other arthropods producing silk, they utilize their front feet for silk production. However, employing the same leg for alternative functions rather than for pure locomotion potentially imposes constraints and compromises. We here present morphological and experimental evidence for a "passive" pressure-induced silk spinning mechanism induced by external mechanical stimuli. Furthermore, we demonstrate that, as a consequence of the conflicting functions for their front feet, webspinners have evolved a unique style of walking that reduces the potentially problematic contact between silk ejectors and the substrate. Here we answer for the first time a long-term question within this enigmatic group of insects-how webspinners can use their front feet to spin their nanoscale silk. This knowledge may open the door for experimental studies on an artificial spinning process and for future utilization in applied fields of robotics or chemistry.

Pest and natural enemy: how the fat bodies of both the southern armyworm Spodoptera eridania and the predator Ceraeochrysa claveri react to azadirachtin exposure

The effects of biopesticides on insects can be demonstrated by morphological and ultrastructural tools in ecotoxicological analysis. Azadirachtin-based products are widely used as biopesticides, affecting numerous insect populations. Through morphological biomarkers, this study aimed to characterize the fat bodies of both the southern armyworm Spodoptera eridania and the predator Ceraeochrysa claveri after chronic exposure to azadirachtin. Larvae of S. eridania and C. claveri were fed with fresh purple lettuce leaves (Lactuca sativa) and egg clusters of Diatraea saccharalis treated with azadirachtin solution of 6 mg active ingredient (a.i.)/L and 18 mg a.i./L for 7 days, respectively. The biological data showed a significant reduction in survival and body mass in S. eridania and cytotoxic effects in the parietal and perivisceral fat bodies in both species. Ultrastructural cell damage was observed in the trophocytes of both species such as dilated cisternae of the rough endoplasmic reticulum and swollen mitochondria. Trophocytes of S. eridania and C. claveri of the parietal and perivisceral layers responded to those injuries by different cytoprotective and detoxification means such as an increase in the amount of cytoplasmic granules containing calcium, expression of heat shock protein (HSP)70/HSP90, and development of the smooth endoplasmic reticulum. Despite all the different means of cytoprotection and detoxification, they were not sufficient to recover from all the cellular damages. Azadirachtin exhibited an excellent performance for the control of S. eridania and a moderate selectivity for the predator C. claveri, which presents better biological and cytoprotective responses to chronic exposure to azadirachtin.

Evolutionary history of Polyneoptera and its implications for our understanding of early winged insects

Polyneoptera represents one of the major lineages of winged insects, comprising around 40,000 extant species in 10 traditional orders, including grasshoppers, roaches, and stoneflies. Many important aspects of polyneopteran evolution, such as their phylogenetic relationships, changes in their external appearance, their habitat preferences, and social behavior, are unresolved and are a major enigma in entomology. These ambiguities also have direct consequences for our understanding of the evolution of winged insects in general; for example, with respect to the ancestral habitats of adults and juveniles. We addressed these issues with a large-scale phylogenomic analysis and used the reconstructed phylogenetic relationships to trace the evolution of 112 characters associated with the external appearance and the lifestyle of winged insects. Our inferences suggest that the last common ancestors of Polyneoptera and of the winged insects were terrestrial throughout their lives, implying that wings did not evolve in an aquatic environment. The appearance of the first polyneopteran insect was mainly characterized by ancestral traits such as long segmented abdominal appendages and biting mouthparts held below the head capsule. This ancestor lived in association with the ground, which led to various specializations including hardened forewings and unique tarsal attachment structures. However, within Polyneoptera, several groups switched separately to a life on plants. In contrast to a previous hypothesis, we found that social behavior was not part of the polyneopteran ground plan. In other traits, such as the biting mouthparts, Polyneoptera shows a high degree of evolutionary conservatism unique among the major lineages of winged insects.

Potential Effects of Future Climate Changes on Brazilian Cool-Adapted Stoneflies (Insecta: Plecoptera)

The continuous pursuit of welfare and economic development through the exploitation of natural resources by human societies consequently resulted in the ongoing process of climate change. Changes in the distribution of species towards the planet's poles and mountain tops are some of the expected to biological consequences of this process. Here, we assessed the potential effects of future climate change on four cool-adapted Gripopterygidae (Insecta: Plecoptera) species [Gripopteryx garbei Navás 1936, G. cancellata (Pictet 1841), Tupiperla gracilis (Burmeister 1839), and T. tessellata (Brauer 1866)] from Southeastern Brazilian Atlantic forest. As species adapted to cold conditions, in the future scenarios of climate change, we expected these organisms to shrink/change their distributions ranges towards areas with suitable climatic conditions in Southern Brazilian regions, when compared with their predicted distributions in present climatic conditions. We used seven principal components derived from 19 environmental variables from Worldclim database for the present scenario and also seven principal components obtained from 17 different Atmosphere-Ocean Global Circulation Models (AOGCMs), considering the most severe emission scenario for green-house gases to predict the species' distributions. Depending on the climatic scenario considered, there were polewards distribution range changes of the species. Additionally, we also observed an important decrease in the amount of protected modeled range for the species in the future scenarios. Considering that this Brazilian region may become hotter in the future and have its precipitation regime changed, as observed in the severe 2013-2014 drought, we believe these species adapted to high altitudes will be severely threatened in the future.

Excretion in the mother's body: modifications of the larval excretory system in the viviparous dermapteran, Arixenia esau

The vast majority of Dermaptera are free-living and oviparous, i.e., females lay eggs within which embryonic development occurs until the larva hatches. In contrast, in the epizoic dermapteran Arixenia esau, eggs are retained within mother's body and the embryos and first instar larvae develop inside her reproductive system. Such a reproductive strategy poses many physiological challenges for a mother, one of which is the removal of metabolic waste generated by the developing offspring. Here, we examine how the Arixenia females cope with this challenge by analyzing features of the developing larval excretory system. Our comparative analyses of the early and late first instar larvae revealed characteristic modifications in the cellular architecture of the Malpighian tubules, indicating that these organs are functional. The results of the electron probe microanalyses suggest additionally that the larval Malpighian tubules are mainly involved in maintaining ion homeostasis. We also found that the lumen of the larval alimentary track is occluded by a cellular diaphragm at the midgut-hindgut junction and that cells of the diaphragm accumulate metabolic compounds. Such an organization of the larval gut apparently prevents fouling of the mother's organism with the offspring metabolic waste and therefore can be regarded as an adaptation for viviparity.

Proprioceptive input to a descending pathway conveying antennal postural information: Terminal organisation of antennal hair field afferents

Like several other arthropod species, stick insects use their antennae for tactile exploration of the near-range environment and for spatial localisation of touched objects. More specifically, Carausius morosus continuously moves its antennae during locomotion and reliably responds to antennal contact events with directed movements of a front leg. Here we investigate the afferent projection patterns of antennal hair fields (aHF), proprioceptors known to encode antennal posture and movement, and to be involved in antennal movement control. We show that afferents of all seven aHF of C. morosus have terminal arborisations in the dorsal lobe (DL) of the cerebral (=supraoesophageal) ganglion, and descending collaterals that terminate in a characteristic part of the gnathal (=suboesophageal) ganglion. Despite differences of functional roles among aHF, terminal arborisation patterns show no topological arrangement according to segment specificity or direction of movement. In the DL, antennal motoneuron neurites show arborizations in proximity to aHF afferent terminals. Despite the morphological similarity of single mechanoreceptors of aHF and adjacent tactile hairs on the pedicel and flagellum, we find a clear separation of proprioceptive and exteroceptive mechanosensory neuropils in the cerebral ganglion. Moreover, we also find this functional separation in the gnathal ganglion.

Pollen Ingestion by Chrysoperla externa (Hagen) Adults in a Diversified Organic Agroecosystem

Chrysoperla externa (Hagen) larvae prey on pest insects and mites in agroecosystems, and adults mainly feed on pollen, nectar, and honeydew. Therefore, preserving this lacewing in crop systems depends on having plants that provide these resources. The objectives of this research were to identify pollen grains ingested by Ch. externa adults collected in a diversified organic agroecosystem and to evaluate whether there is a difference in the amount of ingested pollen grains between males and females. The adults of Ch. externa were collected in four different crops during 13 months in Seropédica, state of Rio de Janeiro, Brazil, using a collecting net. The adults were killed and underwent acetolysis, in order to recover the pollen in the gut. A total of 37,441 pollen grains from 19 Angiospermae families were found, besides 16 Pteridophyte spores. Among the recognized pollen grains, those of Poaceae were the majority, both in frequency of occurrence (87.5%) and in quantity (33496), and were found and recovered in every month of collection. Females and males ingested, respectively, 71.9 and 28.1% of the total number of Angiospermae pollen grains consumed by both sexes. The highest number of Poaceae pollens was obtained from the females (72.1% of the total number of Poaceae pollen, recovered from females + males). Taken as a whole, this study showed that adults of Ch. externa find possibilities to maintain throughout the year, in different crops, but the main source of pollen to males and females was Poaceae plants.