Antennal chemoreceptors in the European ectoparasitoid Sclerodermus cereicollis (Hymenoptera: Bethylidae).

Sclerodermus cereicollis is a European flat wasp ectoparasitoid of some longhorn beetle species. This species is important as a suitable biological control agent against xylophagous pests. To better understand its chemical ecology, the ultrastructure of the antennal sensilla of the adult was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The sensilla are located mainly in the ventro-medial side of the antennae. We report a clearly sexual dimorphism with respect to antennae length, and to types, number, and distribution of chemosensilla. The antennae in males are significantly longer than those of females. We describe in detail the external and internal structure of different chemoreceptors represented by sensilla placodea, long sensilla basiconica, multiporous sensilla chaetica, grooved sensilla ampullacea, uniporous grooved sensilla chaetica. The potential involvement of the different kinds of chemoreceptors in inter- (mainly sexual recognition and social behavior-kin recognition) or intra-specific communication (mainly host selection) is discussed on the basis of behavioral and electrophysiological investigations performed on other parasitoid species belonging to the same family. Other sensilla with morphology that is not consistent with that of chemoreceptors are represented by grooved pegs, coeloconic pegs, trichoid sensilla. Such detailed ultrastructural investigation of the flagellar chemoreceptors of S. cereicollis, clarifying the number of chemosensory neurons innervating the different sensilla, is crucial for further electrophysiological investigations on this important species. RESEARCH HIGHLIGHTS: Evident sexual dimorphism concerning antennae length, type, number, and distribution of chemosensilla. Long sensilla basiconica (LSB) present only in females could play a role in host location and/or maternal care. Multiporous sensilla chaetica (MSC), significantly longer and mostly represented in males, could play a role in the perception of sexual pheromones. Detailed ultrastructural study is crucial for electrophysiological investigations on this important species.

Reproductive performance effects of rearing the quasi-social parasitoid, Sclerodermus brevicornis (Hymenoptera: Bethylidae), on a factitious host.

Wasps in the genus Sclerodermus are ectoparasitoids that typically attack the larvae of woodboring coleopterans. Interest in these species is increasing as they are used in programs to control longhorn beetle pests of economic importance in China and have invasive pest control potential in Europe. Wasps may be mass reared for field release, but using the target host species can be time consuming and physically demanding. There is thus a need for factitious hosts with lower production costs and that are easier to rear. The present research focuses on Sclerodermus brevicornis, which was found in Italy in association with the invasive longhorn beetle, Psacothea hilaris hilaris, and can be laboratory reared on this longhorn beetle and on a factitious lepidopteran host, Corcyra cephalonica. As it is known that the biology of natural enemies can be influenced by the host they emerge from and that the behavior of S. brevicornis is relatively complex due to its degree of sociality (multiple foundress females cooperate to paralyze the host and produce offspring communally), we explored whether, and how, performance and behavioral traits of adult females are influenced by the host species on which they were reared, both when no choice or a choice of current host species was offered. We evaluated the survival of foundresses and their movements between offered hosts and their tendency to form groups with other foundresses according to kinship and host characteristics. We also evaluated the production of offspring and the timing of their development. We found that S. brevicornis reared from C. cephalonica do have some disadvantages compared with those that have developed on P. h. hilaris but also that they recognize, prefer, and can reproduce on P. h. hilaris. We conclude that the use of the more convenient factitious host for mass-rearing is unlikely to greatly compromise the potential of S. brevicornis to suppress longhorn beetle pests in the field.

Insect Biodiversity in a Prealpine Suburban Hilly Area in Italy.

Human activities and habitat fragmentation are known to greatly influence biodiversity. The aim of this study was to update an entomological checklist of a prealpine area in Italy, and also to evaluate the influence of different habitats and the proximity to cities on the entomological fauna. This study included different areas of a local park in Northern Italy, covering about 4000 ha, and situated at altitudes between 190 and 960 m asl. The surveys were carried out between 2010 and 2013 using different monitoring techniques (pitfall traps, car mounted nets, light traps, direct catches on soil and vegetation, visual sampling, gall collection). Furthermore, to assess the effect of habitat and locality on the composition of epigeic beetles, pitfall traps were set and inspected from April to September. All captured specimens were classified to species level. A total of 409 species were recorded, belonging to 7 orders and 78 families. A total of 76.1% were represented by Coleoptera, 13% Lepidoptera, 9.4% Hymenoptera, followed by other orders. In particular, some species with peculiar characteristics, or whose presence in the area had not been previously reported, were detected, such as Atheta pseudoelongatula, Ocypus rhaeticus, Tasgius tricinctus, Euplagia quadripunctaria, Scotopteryx angularia, Elachista constitella, Parornix bifurca, Oegoconia huemeri, and Lasius (Lasius) alienus. It seems possible that the habitat affected the community more than the locality. The woods showed a reduced biodiversity, and a simplified community structure. The comparison of the same habitats in different localities did not show significant differences.

Thermal Shift Assay as a Tool to Evaluate the Release of Breakdown Peptides from Cowpea ß-Vignin during Seed Germination.

The present work aimed to characterize the molecular relationships between structure and function of the seed storage protein ß-vignin, the vicilin storage protein of cowpea (Vigna unguiculata, l. Walp) seeds. The molecular characterization of ß-vignin was carried out firstly by assessing its thermal stability, under different conditions of pH and ionic strength, by thermal shift assay (TSA) using SYPRO Orange fluorescent dye. Secondly, its aggregation propensity was evaluated using a combination of chromatographic and electrophoretic techniques. Two forms of ß-vignin were considered: the native form purified from mature quiescent seeds, and a stable breakdown intermediate of 27 kDa produced while seeds germinate. TSA is a useful tool for determining and following over time the structural changes that occur to the protein during germination. The main result was the molecular characterization of the 27 kDa intermediate breakdown polypeptide, which, to the best of our knowledge, has never been described before. ß-vignin seems to retain its trimeric conformation despite the evident degradation of its polypeptides.

Combined Effects of Pesticides and Electromagnetic-Fields on Honeybees: Multi-Stress Exposure.

Honeybee and general pollinator decline is extensively reported in many countries, adding new concern to the general biodiversity loss. Many studies were addressed to assess the causes of pollinator decline, concluding that in most cases multi-stress effects were the most probable ones. In this research, the combined effects of two possible stress sources for bees, pesticides and electromagnetic fields (multi-stress conditions), were analyzed in the field. Three experimental sites were chosen: a control one far from direct anthropogenic stress sources, a pesticide-stress site and multi-stress one, adding to the same exposure to pesticides the presence of an electromagnetic field, coming from a high-voltage electric line. Experimental apiaries were monitored weekly for one year (from April 2017 to April 2018) by means of colony survival, queen activity, storage and brood amount, parasites and pathogens, and several biomarkers in young workers and pupae. Both exposure and effect biomarkers were analysed: among the first, acetylcholinesterase (AChE), catalase (CAT), glutathione S-transferase (GST) and alkaline phosphatase (ALP) and Reactive Oxygen Species (ROS); and among the last, DNA fragmentation (DNAFRAGM) and lipid peroxidation (LPO). Results showed that bee health conditions were the worst in the multi-stress site with only one colony alive out of the four ones present at the beginning. In this site, a complex picture of adverse effects was observed, such as disease appearance (American foulbrood), higher mortality in the underbaskets (common to pesticide-stress site), behavioral alterations (queen changes, excess of honey storage) and biochemical anomalies (higher ALP activity at the end of the season). The overall results clearly indicate that the multi-stress conditions were able to induce biochemical, physiological and behavioral alterations which severely threatened bee colony survival.

Mechanical Processing of Hermetia illucens Larvae and Bombyx mori Pupae Produces Oils with Antimicrobial Activity.

The aim of this work was to develop processing methods that safeguard the quality and antimicrobial properties of H. illucens and B. mori oils. We adopted a vegetable diet for both insects: leftover vegetables and fruit for H. illucens and mulberry leaves for B. mori. First, alternative techniques to obtain a good oil extraction yield from the dried biomass of H. illucens larvae were tested. Traditional pressing resulted to be the best system to maximize the oil yield and it was successfully applied to B. mori pupae. Oil quality resulted comparable to that obtained with other extraction methods described in the literature. In the case of B. mori pupae, different treatments and preservation periods were investigated to evaluate their influence on the oil composition and quality. Interestingly, agar diffusion assays demonstrated the sensitivity of Gram-positive Bacillus subtilis and Staphylococcus aureus to H. illucens and B. mori derived oils, whereas the growth of Gram-negative Pseudomonas aeruginosa and Escherichia coli was not affected. This study confirms that fat and other active compounds of the oil extracted by hot pressing could represent effective antimicrobials against bacteria, a relevant result if we consider that they are by-products of the protein extraction process in the feed industry.

Impact of Agro-industrial Byproducts on Bioconversion, Chemical Composition, in vitro Digestibility, and Microbiota of the Black Soldier Fly (Diptera: Stratiomyidae) Larvae.

The interest in using byproducts from agro-food industries as a rearing substrate for insects is increasing rapidly. We investigated the influence of byproducts of vegetal origin (okara-a byproduct of soy milk production, maize distillers with solubles, brewer's grains), used as rearing diet for black soldier fly larvae (BSFL), on the following parameters: biomass production, substrate reduction (SR), nutritional profile and in vitro digestibility, and larval gut microbiota. Hen diet was used as a control substrate. The highest larval biomass was collected on maize distillers, whereas the highest SR was observed on okara. The rearing substrate affected ash, ether extract, and chitin larval content. The BSFL reared on okara were characterized by a lower lauric acid content (17.6% of total fatty acids). Diets also influenced in vitro crude protein digestibility (%) for monogastrics, with the highest values for BSFL reared on maize distillers (87.8), intermediate for brewer's grains and okara BSFL, and the lowest for hen BSFL (82.7). The nutritive value for ruminants showed a lower Net Energy for lactation for BSFL reared on hen diet than okara and dried maize distillers BSFL. The different byproducts showed an influence on the larval gut microbiota, with a major bacterial complexity observed on larvae fed with the hen diet. The neutral detergent fiber concentration of dietary substrate was negatively correlated with Firmicutes and Actinobacteria relative abundance. Insects valorized byproducts converting them into high-value larval biomass to be used for feed production. The results evidenced the effects of the tested byproducts on the measured parameters, underling the chemical composition importance on the final insect meal quality.

Survival rate and changes in foraging performances of solitary bees exposed to a novel insecticide.

Solitary bees are among the most important pollinators worldwide however population declines especially in croplands has been noticed. The novel pesticide sulfoxaflor is a competitive modulator of nicotinic acetylcholine receptors (nAChR) in insects. While there is evidence of a negative impact of neonicotinoids on bees of several social organization levels, our overall knowledge on the impact of sulfoxaflor on bees is poor. Here we present for the first time a study showing effects of field realistic doses of sulfoxaflor on solitary bees. Bees submitted to long term exposure of field realistic doses of sulfoxaflor (5 µg dm-3, 10 µg dm-3, 50 µg dm-3) and control were observed regarding their survival rate. Moreover, we recorded metrics related to flower visitation and flight performance. We discover that the highest field realistic dose is lethal to Osmia bicornis along five days of exposure. The effect of sulfoxaflor reduces the outcome of foraging, important features for fruit and seed production of cross-pollinated plant species. Bees exposed to pesticide visited flowers mostly walking rather than flying. Flight performance was also impaired by the pesticide.

Tools to Tie: Flower Characteristics, VOC Emission Profile, and Glandular Trichomes of Two Mexican Salvia Species to Attract Bees.

A plant can combine physical and chemical tools to interact with other organisms. Some are designed for pollinator attraction (i.e., colors and volatile organic compounds-VOCs); others can act to discourage herbivores (i.e., non-glandular trichomes). Few studies fully address available tools in a single species; notwithstanding, this information can be pivotal in understanding new interactions out of the home range. We characterized flower traits, emission profiles of constitutive compounds from flowers and leaves, micro-morphology of the glandular trichomes, and listed flower visitors of two Mexican bird-pollinated Salvia species (S. blepharophylla and S. greggii), growing in an Italian botanical garden. Flowers were highly variable in their morphometric characteristics. In both species, four trichome morphotypes with similar histochemistry and distribution were documented for leaves and flowers except the calyx abaxial side. The vegetative emission profiles were qualitatively more complex than the floral ones; however, common compounds occurring in high relative percentages were ß-caryophyllene and germacrene D. Floral bouquets were dominated by limonene and ß-pinene in S. greggii and by 1,8-cineole in S. blepharophylla. Two potential (non-bird) pollinators were especially abundant: small bees belonging to the genus Lasioglossum and large bees belonging to the species Xylocopa violacea. Our study highlights the plasticity of these plants, as well as tools that can be conveniently used to establish novel interactions.

Factors Affecting the Reproduction and Mass-Rearing of Sclerodermus brevicornis (Hymenoptera: Bethylidae), a Natural Enemy of Exotic Flat-Faced Longhorn Beetles (Coleoptera: Cerambycidae: Lamiinae).

Many species of long-horned beetles are invasive pests causing significant economic damage in agro-forestry systems. They spend the majority of their life-cycle concealed inside natural wood or wooden packaging materials and are largely protected from adverse environmental conditions and pesticide sprays. Biological control via parasitoid natural enemies including members of the bethylid genus Sclerodermus, has proven effective against some long-horned beetles that are invasive in China. In Europe, the biocontrol potential of native Sclerodermus species is being evaluated with a view to developing efficient mass-rearing techniques and then actively deploying them against invasive Asian beetles. Here, we continue evaluations of S. brevicornis by establishing that groups of females that have already reared offspring to emergence are capable of reproducing subsequent hosts and by evaluating the lifetime reproductive capacity of individual females provided with successive hosts. Additionally, we assess the laboratory shelf-life of adult females stored for different times at different temperatures including cold storage, and then assess the post-storage reproductive performance of groups of females provided with a single host. We found that adult female longevity declines with increasing storage temperature and that most aspects of subsequent performance are negatively affected by high temperatures. The adaptability to low temperature storage enhances the suitability of S. brevicornis to mass-rearing programs and thus biocontrol deployment.

Environmental Display Can Buffer the Effect of Pesticides on Solitary Bees.

Environmental quality (e.g., diversity of resource availability, nesting sites, environmental display) plays an important role in an animal's life. While homogeneous environments can restrict organisms from developing activities such as food seeking (behavioral impairment), more complex environments allow animals to perform activities with learning and behavioral perfecting outcomes. Pesticides are known to affect the learning and foraging behaviors of bees; however, little is known about the counterbalance displayed by the environment. Herein, we conducted two experiments that simulated distinct environmental displays, in which the effects of a fungicide (IndarTM 5EW-febunconazole) on solitary bee foraging activities were tested. We found that the fungicide only impaired the activities of bees in one of the studied environments. The difference in visitation rates and flower exploitation of bees between the two different environmental displays led to changes in metrics of bee-flower networks across environments. Linkage density, a metric associated with pollination efficiency that is known to be impacted by different environments, differed across environments. Our results showed that ecological interaction network metrics can differ regarding the different environmental displays. This study indicates that environmental complexity helps balance the negative effects of pesticides on solitary bees and highlights the potential use of solitary bees as model organisms for experimental simulations of environmental change.

Co-foundress confinement elicits kinship effects in a naturally sub-social parasitoid.

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub-social, with single foundress females exhibiting post-ovipositional maternal care via short-term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female-biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi-foundress reproduction on some hosts. Here, we screen for further life-history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1-8 Goniozus nephantidis females together with a host for 5+ days. Multi-foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female-biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female-biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi-foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi-foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi-foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.

A botanic garden as a tool to combine public perception of nature and life-science investigations on native/exotic plants interactions with local pollinators.

Life-sciences are pointing towards an alarming worldwide pollinator decline. This decline proceeds along with overall biodiversity losses, even in the context of urban landscapes and human welfare. At the same time, social-sciences are arguing an increased distance from nature, experienced by citizens. The strong connection between the public good and pollinator sustainability, even in urban areas, is well-documented. However, usually basic and applied life-sciences tend to underestimate public perception of nature, which is better tackled by the fields of social-sciences. Therefore, more efforts are needed to link scientific questions and public 'perception' of nature. We designed a transversal project where research questions directly confront public concerns: i.e., even while addressing scientific knowledge gaps, our questions directly arise from public concerns. Social studies highlighted that appreciation of (exotic) plants is related to the impact they may have on the surrounding natural environment: therefore, we investigated links of native and exotic flowers to local pollinators. Other studies highlighted that scientific results need to link to everyday individual experience: therefore, we investigated pollination modes of the renown Salvia, native and exotic, largely used in cuisine and gardening. The botanic garden was the promoter of scientific questions addressed by the public, and also collated the results in a travelling exhibition. The exhibition, together with a dedicated catalogue, were especially designed to enlighten the wide public on the relationships that plants, native and exotic alike, establish with the surrounding world.

Rearing of Hermetia Illucens on Different Organic By-Products: Influence on Growth, Waste Reduction, and Environmental Impact.

The aim of the study was to evaluate the use of three by-products as growing substrates for Hermetia illucens (Black Soldier Fly (BSF)) larvae: okara, maize distiller, brewer's grains, and a control hen diet. The study focused on larval growth and bioconversion performance, production of methane by larvae and environmental burden of larvae production, using Life Cycle Assessment (LCA) on a lab scale. Chemical composition of substrates differed: okara had the highest crude protein and ether extract contents, while brewer's grains showed the highest fiber content. Larvae fed on a hen diet and maize distiller exhibited the highest final weights (2.29 and 1.97 g, respectively). Larvae grown on okara showed the highest indexes for waste reduction and efficiency of conversion of the ingested feed. The BSF larvae did not produce any detectable traces of CH4. LCA evaluation showed that larvae production on a hen diet resulted in the most impact for most of environmental categories, for the inclusion of soybean meal in the diet (for climate change, 5.79 kg CO2 eq/kg dry larvae). Feed production activities resulted in the main contributions to environmental impact. In order to compare the larvae production obtained on all substrates, an environmental impact was attributed to okara and brewer's grain through a substitution method, and, by this approach, the best sustainable product resulted from the larvae grown on the maize distiller.

Salvia verticillata: Linking glandular trichomes, volatiles and pollinators.

Plants have developed a plethora of signals to interact with other organisms, finally building up a sophisticate language for communication. In this context, we investigated Salvia verticillata L. (Lamiaceae), with the primary goal to link secondary metabolites and actual biotic relationships. We specifically analysed the volatile organic compounds (VOC) spontaneously emitted by leaves and flowers and determined the composition of the essential oils obtained from the aerial parts across 2015 and 2016. We merged information of chemical analyses to a micromorphological investigation on the glandular indumentum and to focal observations on the pollinator assemblage. The VOC profiles were highly variable, with the floral bouquet being the most complex. Flowers and leaves showed 37 and 20 exclusive compounds, dominated by 1,8-cineole (10.4%) and germacrene D (38.4%), respectively. Sesquiterpene hydrocarbons prevailed (83.3% leaves; 73.7% flowers) and 19 common compounds were detected. The oil profiles proved to be consistent across the two years: sesquiterpene hydrocarbons invariably dominated, with germacrene D, bicyclogermacrene and ß-caryophyllene as main compounds. The whole plant epidermis is thickly covered by two types of glandular hairs: peltates and small capitates, both responsible for the synthesis of terpenes, finally resulting in the VOC emission and in the essential oil production. S. verticillata attracted mainly bees belonging to two functional groups: medium-sized and large bees, notwithstanding the small size of its flowers. At the site, Apis mellifera and different Bombus species were recorded, mainly interested in feeding on nectar. The literature survey on the isolated volatile compounds confirmed the hypotheses on the seduction strategies towards Apoidea.

Assessment of Vegetable and Fruit Substrates as Potential Rearing Media for Hermetia illucens (Diptera: Stratiomyidae) Larvae.

Hermetia illucens (L.) (Diptera: Stratiomyidae) is able to consume a wide range of organic matter and is of particular interest for waste management. The nutritional value of preimaginal stages, in particular the protein content, makes this species a valid candidate for use as feed for other organisms. Vegetables and fruits are promising rearing substrates for insects produced for this purpose according to the EU regulation. In order to examine the effects of diets on insect performance and chemical composition, larvae were reared on the following substrates: 1) fruit (apple, pear, and orange); 2) vegetable (lettuce, green beans, and cabbage); and 3) mixed fruits and vegetables. High percentages of survival were observed on all diets, but there were differences among weights of larvae, pupae, and adults, with weights of larvae reared on mixed fruits and vegetables lower than on other diets. Pupae reared on the mixed diet were heaviest, and also morphometric measurements of adults were highest. Larvae reared on fruit diets had the highest fat content, comprising mostly saturated fatty acids; the highest content of essential n-3 fatty acids was found in vegetable reared larvae and that of n-6 in mixed reared larvae. Larvae reared on the mixed diet had the highest protein content. Calcium contents were high and moderate amounts of iron and zinc were found. H. illucens showed the capability to develop on vegetable and fruits diets displaying different nutrient profiles and biological performances. The best-performing rearing strategy should vary in relation to the final use of H. illucens.

First record of Rhoptrocentruspiceus Marshall (Hymenoptera, Braconidae, Doryctinae) as parasitoid of Psacotheahilarishilaris (Pascoe) (Coleoptera, Cerambycidae).

The species Rhoptrocentruspiceus Marshall (Hymenoptera: Braconidae) was reared from the larvae of the xylophagous beetle Psacotheahilarishilaris (Pascoe) (Coleoptera: Cerambycidae), an exotic pest of Ficus and Morus species native to eastern Asia. It was recorded in the north of Italy in September 2005. This discovery is the first report of this species as parasitoids of the yellow spotted longicorn beetle all over the world.

Characterization of the bacterial community associated with larvae and adults of Anoplophora chinensis collected in Italy by culture and culture-independent methods.

The wood-boring beetle Anoplophora chinensis Forster, native to China, has recently spread to North America and Europe causing serious damage to ornamental and forest trees. The gut microbial community associated with these xylophagous beetles is of interest for potential biotechnological applications in lignocellulose degradation and development of pest-control measures. In this study the gut bacterial community of larvae and adults of A. chinensis, collected from different host trees in North Italy, was investigated by both culture and culture-independent methods. Larvae and adults harboured a moderately diverse bacterial community, dominated by Proteobacteria, Actinobacteria, and Firmicutes. The gammaproteobacterial family Enterobacteriaceae (genera Gibbsiella, Enterobacter, Raoultella, and Klebsiella) was the best represented. The abundance of such bacteria in the insect gut is likely due to the various metabolic abilities of Enterobacteriaceae, including fermentation of carbohydrates derived from lignocellulose degradation and contribution to nitrogen intake by nitrogen-fixing activity. In addition, bacteria previously shown to have some lignocellulose-degrading activity were detected at a relatively low level in the gut. These bacteria possibly act synergistically with endogenous and fungal enzymes in lignocellulose breakdown. The detection of actinobacterial symbionts could be explained by a possible role in the detoxification of secondary plant metabolites and/or protection against pathogens.

Impact of age and retinal degeneration on the light input to circadian brain structures.

Aging causes anatomical and functional changes in visual and circadian systems. In wild type mice rods, cones, and photosensitive retinal ganglion cells (pRGCs) decline with age. In rd/rd cl mice, the early loss of rods and cones is followed by protracted transneuronal loss of inner retinal neurons as well as the pRGCs. Here we use Fos induction to study the light input pathway to the suprachiasmatic nuclei (SCN), the intergeniculate leaflets (IGL) and ventral lateral geniculate nuclei (vLGN) of old (∼700 days) and young (∼150 days) wild type and rd/rd cl mice. Cholera toxin tracing was used in parallel to study the anatomy of this pathway. We find that aging rather than retinal degeneration is a more important factor in reducing light input to the SCN, causing both a reduction in Fos expression and retinal afferents. Furthermore, we show light-induced Fos within the vLGN and IGL is predominantly subserved by rods and cones, and once again aging reduces the amplitude of this response.

The effects of rod and cone loss on the photic regulation of locomotor activity and heart rate.

Behavioral responses to light indirectly affect cardiovascular output, but in anesthetized rodents a direct effect of light on heart rate has also been described. Both the basis for this response and the contribution of rods, cones and melanopsin-based photosensitive retinal ganglion cells (pRGCs) remains unknown. To understand how light acutely regulates heart rate we studied responses to light in mice lacking all rod and cone photoreceptors (rd/rd cl ) along with wild-type controls. Our initial experiments delivered light to anesthetized mice at Zeitgeber time (ZT)16 (4 h after lights off, mid-activity phase) and produced an increase in heart rate in wild-type mice, but not in rd/rd cl animals. By contrast, parallel experiments in freely-moving mice demonstrated that light exposure at this time suppressed heart rate and activity in both genotypes. Because of the effects of anesthesia, all subsequent studies were conducted in freely-moving animals. The effects of light were also assessed at ZT6 (mid-rest phase). At this timepoint, wild-type mice showed an irradiance-dependent increase in heart rate and activity. By contrast, rd/rd cl mice failed to show any modulation of heart rate or activity, even at very high irradiances. Increases in heart rate preceded increases in locomotor activity and remained elevated when locomotor activity ceased, suggesting that these two responses are at least partially uncoupled. Collectively, our results show an acute and phase-dependent effect of light on cardiovascular output in mice. Surprisingly, this irradiance detection response is dependent upon rod and cone photoreceptors, with no apparent contribution from melanopsin pRGCs.