Semiochemical Release and Ontogenetic Changes in a Primary Scent Gland of Podisus maculiventris

The spined shoulder bug, Podisus maculiventris, is a generalist predator studied for its biocontrol potential. Despite our growing understanding of gland development, the conditions that elicit releases are largely unknown. To determine if male age or gland development affects the chemical composition and release behavior, we dissected adult male bugs and profiled the chemical composition of the male DAG 1, 7, and 14 d post-eclosion. To determine if gland development is related to sexual maturity, we counted the number of sperm present in the seminal vesicles at the same time points. Finally, we measured the diurnal release patterns of different aged males and in various male-female combinations. We observed that newly eclosed adults have under-developed glands and male seminal vesicles contained few sperm. One week post-eclosion the DAG contained previously reported semiochemical compounds and males contained many sperm. Mirroring the trend in reproductive maturation and gland development, the number of semiochemical releases increased with age and the majority of releases followed a scotophase pattern unaffected by sexual composition. These findings link male age to 1) dorsal abdominal gland development 2) release behavior and 3) sexual maturity, which will help our understanding of when these olfactory cues are present for other organisms, like prey, to perceive. Given the results, releasing adults that are at least 1 week post eclosion will maximize the non-consumptive effects of this biocontrol agent.

Microrheology of hemolymph plasma of the bumblebee Bombus terrestris

Viscosity, which impacts the rate of hemolymph circulation and heat transfer, is one of the transport properties that affects the performance of an insect . Measuring the viscosity of insect fluids is challenging due to the small amount available per specimen. Using particle tracking microrheology, which is well suited to characterise the rheology of the fluid part of the hemolymph, we study the plasma viscosity in the bumblebee Bombus terrestris. In a sealed geometry, the viscosity exhibits an Arrhenius dependence with temperature, with an activation energy compared to that of hornworm larvae estimated in Kenny et al., 2018. In an open to air geometry, it increases by 4 to 5 orders of magnitude during evaporation. Evaporation times are temperature dependent and longer than typical insect hemolymph coagulation times. Unlike standard bulk rheology, microrheology can be applied to even smaller insects, paving the way to characterise biological fluids such as pheromones, pad secretions or cuticular layers.

Effects of diesel exhaust particles on the health and survival of the buff-tailed bumblebee Bombus terrestris after acute and chronic oral exposure

The diesel-powered transportation sector is a major producer of environmental pollution in the form of micro- and nanoscale diesel exhaust particles (DEP). Pollinators, such as wild bees, may inhale DEP or ingest it orally through plant nectar. However, if these insects are adversely affected by DEP is largely unknown. To investigate potential health threats of DEP to pollinators, we exposed individuals of Bombus terrestris to different concentrations of DEP. We analysed the polycyclic aromatic hydrocarbons (PAH) content of DEP since these are known to elicit adverse effects on invertebrates. We investigated the dose-dependent effects of those well-characterized DEP on survival and fat body content, as a proxy for the insects' health condition, in acute and chronic oral exposure experiments. Acute oral exposure to DEP showed no dose-dependent effects on survival or fat body content of B. terrestris. However, we could show dose-dependent effects after chronic oral exposure with high doses of DEP where significantly increased mortality was observed. Further, there was no dose-dependent effect of DEP on the fat body content after exposure. Our results give insights into how the accumulation of high concentrations of DEP e.g., near heavily trafficked sites, can influence insect pollinators' health and survival.

Gene expression differences consistent with water loss reduction underlie desiccation tolerance of natural Drosophila populations

BACKGROUND

Climate change is one of the main factors shaping the distribution and biodiversity of organisms, among others by greatly altering water availability, thus exposing species and ecosystems to harsh desiccation conditions. However, most of the studies so far have focused on the effects of increased temperature. Integrating transcriptomics and physiology is key to advancing our knowledge on how species cope with desiccation stress, and these studies are still best accomplished in model organisms.

RESULTS

Here, we characterized the natural variation of European D. melanogaster populations across climate zones and found that strains from arid regions were similar or more tolerant to desiccation compared with strains from temperate regions. Tolerant and sensitive strains differed not only in their transcriptomic response to stress but also in their basal expression levels. We further showed that gene expression changes in tolerant strains correlated with their physiological response to desiccation stress and with their cuticular hydrocarbon composition, and functionally validated three of the candidate genes identified. Transposable elements, which are known to influence stress response across organisms, were not found to be enriched nearby differentially expressed genes. Finally, we identified several tRNA-derived small RNA fragments that differentially targeted genes in response to desiccation stress.

CONCLUSIONS

Overall, our results showed that basal gene expression differences across individuals should be analyzed if we are to understand the genetic basis of differential stress survival. Moreover, tRNA-derived small RNA fragments appear to be relevant across stress responses and allow for the identification of stress-response genes not detected at the transcriptional level.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Sub-critical limits are viable alternatives to critical thermal limits

Thermal traits are frequently used to explain variation in species distributions, abundance, and sensitivity to climate change. Due to their utility and ease of measurement, critical thermal limits in particular have proliferated across the ecophysiological literature. Critical limit assays can, however, have deleterious or even lethal effects on individuals and there is growing recognition that intermediate metrics of performance can provide a further, nuanced understanding of how species interact with their environments. Meanwhile, the scarcity of data describing sub-critical or voluntary limits, which have been proposed as alternatives to critical limits and can be collected under less extreme conditions, reduces their value in comparative analyses and broad-scale syntheses. To overcome these limitations and determine if sub-critical limits are viable proxies for upper and lower critical thermal limits we measured and compared the critical and sub-critical thermal limits of 2023 ants representing 51 species. Sub-critical limits in isolation were a satisfactory linear predictor for both individual and species critical limits and when species identity was also considered there were substantial gains in variance explained. These gains indicate that a species-specific conversion factor can further improve estimates of critical traits using sub-critical proxies. Sub-critical limits can, therefore, be integrated into broader syntheses of critical limits and confidently used to calculate common ecological metrics, such as warming tolerance, so long as uncertainty in estimates is explicitly acknowledged. Although lower thermal traits exhibited more variation than their upper counterparts, the stronger phylogenetic signal of lower thermal traits indicates that appropriate conversions for lower thermal traits can be inferred from congenerics or other closely related taxa.

Histological, histochemical and energy disorders caused by R-limonene on Aedes aegypti L. larvae (Diptera: Culicidae)

The study evaluated the effects of R-limonene, in sublethal concentration, on the histology, histochemistry, biochemistry, and carbohydrates and proteins levels in the third instar Aedes aegypti larvae. The R-limonene (LC50 of 27 ppm) and control groups were analyzed 12 and 24 h after the beginning of treatments. The midgut of the control larvae was composed of cylindrical and elongated cells with a spherical and central nucleus and regenerative cells with a pyramidal shape. After 12 h of treatment, columnar cells, protuberances, and cytoplasmic vacuolization were found. However, 24 h after treatment, complete disorganization of the epithelium was observed. There was a positive reaction in all treatments for the presence of glycogen. However, the midgut of larvae treated with R-limonene showed higher levels. For the total protein, positive marking occurred in all groups evaluated, with higher levels in treatments and the lowest in control 12 h. The levels of total protein and glycogen increased in the treated larvae compared to the 12 h control. Besides, a reduction in total sugar levels was observed in the treated larvae compared to controls 12 and 24 h, being more evident in the last one. Therefore, these results demonstrate that R-Limonene caused pathological changes in the epithelium of the A. aegypti midgut at histophysiological and biochemical levels.

Neuropeptide and microRNA regulators of juvenile hormone production

The sesquiterpenoid juvenile hormone(s) (JHs) of insects are the primary regulators of growth, metamorphosis, and reproduction in most insect species. As a consequence, it is essential that JH production be precisely regulated so that it is present only during appropriate periods necessary for the control of these processes. The presence of JH at inappropriate times results in disruption to metamorphosis and development and, in some cases, to disturbances in female reproduction. Neuropeptides regulate the timing and production of JH by the corpora allata. Allatostatin and allatotropin were the names coined for neuropeptides that serve as inhibitors or stimulators of JH biosynthesis, respectively. Three different allatostatin neuropeptide families are capable of inhibiting juvenile hormone but only one family is utilized for that purpose dependent on the insect studied. The function of allatotropin also varies in different insects. These neuropeptides are pleiotropic in function acting on diverse physiological processes in different insects such as muscle contraction, sleep and neuromodulation. Genome projects and expression studies have assigned individual neuropeptide families to their respective receptors. An understanding of the localization of these receptors is providing clues as to how numerous peptide families might be integrated in regulating physiological functions. In recent years microRNAs have been identified that down-regulate enzymes and transcription factors that are involved in the biosynthesis and action of juvenile hormone.

A fitness cost resulting from Hamiltonella defensa infection is associated with altered probing and feeding behaviour in Rhopalosiphum padi

Many herbivorous arthropods, including aphids, frequently associate with facultative endosymbiotic bacteria, which influence arthropod physiology and fitness. In aphids, endosymbionts can increase resistance against natural enemies, enhance aphid virulence and alter aphid fitness. Here, we used the electrical penetration graph technique to uncover physiological processes at the insect-plant interface affected by endosymbiont infection. We monitored the feeding and probing behaviour of four independent clonal lines of the cereal-feeding aphid Rhopalosiphum padi derived from the same multilocus genotype containing differential infection (+/-) with a common facultative endosymbiont, Hamiltonella defensa Aphid feeding was examined on a partially resistant wild relative of barley known to impair aphid fitness and a susceptible commercial barley cultivar. Compared with uninfected aphids, endosymbiont-infected aphids on both plant species exhibited a twofold increase in the number of plant cell punctures, a 50% reduction in the duration of each cellular puncture and a twofold higher probability of achieving sustained phloem ingestion. Feeding behaviour was also altered by host plant identity: endosymbiont-infected aphids spent less time probing plant tissue, required twice as many probes to reach the phloem and showed a 44% reduction in phloem ingestion when feeding on the wild barley relative compared with the susceptible commercial cultivar. Reduced feeding success could explain the 22% reduction in growth of H. defensa-infected aphids measured on the wild barley relative. This study provides the first demonstration of mechanisms at the aphid-plant interface contributing to physiological effects of endosymbiont infection on aphid fitness, through altered feeding processes on different quality host plants.

Observation of an anisotropic texture inside the wax layer of insect cuticle

The outermost part of insect cuticles is very often covered with wax, which prevents desiccation and serves for chemical communication in many species. Earlier studies on cuticular waxes have mainly focused on their chemical composition revealing complex mixtures of lipids. In the absence of information on their physical organization, cuticular waxes have been considered isotropic. Here we report the presence of parallel stripes in the wax layer of the carapace of the scarab beetle, Chrysina gloriosa, with a textural periodicity of ca. 28 nm, as revealed by electron microscopy of transverse sections. Observations at oblique incidence argue for a layered organization of the wax, which might be related to a layer-by-layer deposition of excreted wax. Our findings may lay the foundation for further studies on the internal structure of cuticular waxes for other insects.

Characterization of gut bacterial flora of Apis mellifera from north-west Pakistan

Gut microbiota has been recognized to play a beneficial role in honey bees (Apis mellifera). Present study was designed to characterize the gut bacterial flora of honey bees in north-west Pakistan. Total 150 aerobic and facultative anaerobic bacteria from guts of 45 worker bees were characterized using biochemical assays and 16S rDNA sequencing followed by bioinformatics analysis. The gut isolates were classified into three bacterial phyla of Firmicutes (60%), Proteobacteria (26%) and Actinobacteria (14%). Most of the isolates belonged to genera and families of Staphylococcus, Bacillus, Enterococcus, Ochrobactrum, Sphingomonas, Ralstonia, Enterobacteriaceae, Corynebacterium and Micrococcineae. Many of these bacteria were tolerant to acidic environments and fermented sugars, hence considered beneficial gut inhabitants and involved the maintenance of a healthy microbiota. However, several opportunistic commensals that proliferate in the hive environment including members Staphylococcus haemolyticus group and Sphingomonas paucimobilis were also identified. This is the first report on bee gut microbiota from north-west Pakistan geographically situated at the crossroads of Indian subcontinent and central Asia.

Lipid metabolism in Rhodnius prolixus: Lessons from the genome

The kissing bug Rhodnius prolixus is both an important vector of Chagas' disease and an interesting model for investigation into the field of physiology, including lipid metabolism. The publication of this insect genome will bring a huge amount of new molecular biology data to be used in future experiments. Although this work represents a promising scenario, a preliminary analysis of the sequence data is necessary to identify and annotate the genes involved in lipid metabolism. Here, we used bioinformatics tools and gene expression analysis to explore genes from different genes families and pathways, including genes for fat breakdown, as lipases and phospholipases, and enzymes from β-oxidation, fatty acid metabolism, and acyl-CoA and glycerolipid synthesis. The R. prolixus genome encodes 31 putative lipase genes, including 21 neutral lipases and 5 acid lipases. The expression profiles of some of these genes were analyzed. We were able to identify nine phospholipase A2 genes. A variety of gene families that participate in fatty acid synthesis and modification were studied, including fatty acid synthase, elongase, desaturase and reductase. Concerning the synthesis of glycerolipids, we found a second isoform of glycerol-3-phosphate acyltransferase that was ubiquitously expressed throughout the organs. Finally, all genes involved in fatty acid β-oxidation were identified, but not a long-chain acyl-CoA dehydrogenase. These results provide fundamental data to be used in future research on insect lipid metabolism and its possible relevance to Chagas' disease transmission.