Outsourced hearing in an orb-weaving spider that uses its web as an auditory sensor.

SignificanceThe sense of hearing in all known animals relies on possessing auditory organs that are made up of cellular tissues and constrained by body sizes. We show that hearing in the orb-weaving spider is functionally outsourced to its extended phenotype, the proteinaceous self-manufactured web, and hence processes behavioral controllability. This finding opens new perspectives on animal extended cognition and hearing-the outsourcing and supersizing of auditory function in spiders. This study calls for reinvestigation of the remarkable evolutionary ecology and sensory ecology in spiders-one of the oldest land animals. The sensory modality of outsourced hearing provides a unique model for studying extended and regenerative sensing and presents new design features for inspiring novel acoustic flow detectors.

Manduca sexta caterpillars parasitized by the wasp Cotesia congregata stop chewing despite an intact motor system.

The parasitic wasp Cotesia congregata suppresses feeding in its host, the caterpillar Manduca sexta, during specific periods of wasp development. We examined both feeding behaviour and the neurophysiology of the mandibular closer muscle in parasitized and unparasitized control M. sexta to determine how the wasp may accomplish this. To test whether the wasps activated a pre-existing host mechanism for feeding cessation, we examined the microstructure of feeding behaviour in caterpillars that stopped feeding due to illness-induced anorexia or an impending moult. These microstructures were compared with that shown by parasitized caterpillars. While there were overall differences between parasitized and unparasitized caterpillars, the groups showed similar progression in feeding microstructure as feeding ended, suggesting a common pattern for terminating a meal. Parasitized caterpillars also consumed less leaf area in 100 bites than control caterpillars at around the same time their feeding microstructure changed. The decline in food consumption was accompanied by fewer spikes per burst and shorter burst durations in chewing muscle electromyograms. Similar extracellular results were obtained from the motorneuron of the mandibular closer muscle. However, chewing was dramatically re-activated in non-feeding parasitized caterpillars if the connectives posterior to the suboesophageal ganglion were severed. The same result was observed in unparasitized caterpillars given the same treatment. Our results suggest that the reduced feeding in parasitized caterpillars is not due to damage to the central pattern generator (CPG) for chewing, motor nerves or chewing muscles, but is more likely to be due to a suppression of chewing CPG activity by ascending or descending inputs.

Motor and mechanical bases of the courtship call of the male treehopper Umbonia crassicornis.

This study is a physiological, anatomical and biophysical analysis of how plant-borne vibrational signals are produced by the treehopper Umbonia crassicornis During courtship, males and females engage in a vibrational duet, with each producing a characteristic call. For males, this consists of a frequency-modulated tonal signal which is accompanied by rhythmic broad-band clicks. Although previous studies have described these complex signals in detail, little is known about how they are produced. By combining video recordings, electromyograms, dissections and mechanical modeling, we describe the mechanism by which the male produces his courtship signal. High-speed videos show that the tonal portion of the call is produced by periodic dorso-ventral movements of the abdomen, with a relatively large amplitude oscillation alternating with a smaller oscillation. Electromyograms from the muscles we identified that produce this motion reveal that they fire at half the frequency of the abdominal oscillation, throughout the frequency modulation of the tonal signal. Adding weight to the abdomen of a calling male reduces the frequency of motion, demonstrating that the abdominal motion is strongly influenced by its mechanical resonance. A mathematical model accounting for this resonance provides excellent qualitative agreement with measurements of both the muscle firing rate recorded electrophysiologically and the oscillatory motion of the abdomen as recorded in the high-speed video. The model, electromyograms and analysis of video recordings further suggest that the frequency modulation of the abdominal response is due to a simultaneous modulation in the muscle firing rate and a fluctuation in stiffness of the abdominal attachment.

The parasitic wasp Cotesia congregata uses multiple mechanisms to control host (Manduca sexta) behaviour.

Some parasites alter the behaviour of their hosts. The larvae of the parasitic wasp Cotesia congregata develop within the body of the caterpillar Manduca sexta During the initial phase of wasp development, the host's behaviour remains unchanged. However, once the wasps begin to scrape their way out of the caterpillar, the caterpillar host stops feeding and moving spontaneously. We found that the caterpillar also temporarily lost sensation around the exit hole created by each emerging wasp. However, the caterpillars regained responsiveness to nociception in those areas within 1 day. The temporary reduction in skin sensitivity is probably important for wasp survival because it prevents the caterpillar from attacking the emerging wasp larvae with a defensive strike. We also found that expression of plasmatocyte spreading peptide (PSP) and spätzle genes increased in the fat body of the host during wasp emergence. This result supports the hypothesis that the exiting wasps induce a cytokine storm in their host. Injections of PSP suppressed feeding, suggesting that an augmented immune response may play a role in the suppression of host feeding. Injection of wasp larvae culture media into non-parasitized caterpillars reduced feeding, suggesting that substances secreted by the wasp larvae may help alter host behaviour.

Biodegradable plastic agricultural mulches and key features of microbial degradation.

The development of biodegradable plastic mulch films for use in agriculture has been ongoing for decades. These films consist of mixtures of polymers with various additives. As a result, their physical and chemical properties differ from those of the pure polymers often used for in vitro enzymatic and microbial degradation studies, raising questions about the biodegradation capability of mulch films. Currently, standards exist for the biodegradation of plastics in composting conditions but not in soil. Biodegradation in soil or compost depends on a complex synergy of biological and abiotic degradative processes. This review discusses the physicochemical and structural properties of biodegradable plastic mulches, examines their potential for on-site decomposition in light of site-to-site variance due to environmental and biological conditions, and considers the potential for long-term effects on agroecosystem sustainability and functionality.

Native soil fungi associated with compostable plastics in three contrasting agricultural settings.

Plastics are used widely as agricultural mulches to suppress weeds and retain soil moisture. Disposal of conventional plastic mulches requires physical removal for disposal in a landfill or incineration. Biodegradable plastic mulches that could be tilled into the soil at the end of a growing season represent an attractive alternative to conventional plastic mulches. In this study, three commercially available mulches labeled as "biodegradable" and one experimental, potentially biodegradable mulch were used during a tomato growing season, and then buried in field soil at three locations for approximately 6 months, as would occur typically in an agricultural setting. Degradation after 6 months in soil was minimal for all but the cellulosic mulch. After removal of mulches from soil, fungi were isolated from the mulch surfaces and tested for their ability to colonize and degrade the same mulches in pure culture. The majority of culturable soil fungi that colonized biodegradable mulches were within the family Trichocomaceae (which includes beneficial, pathogenic, and mycotoxigenic species of Aspergillus and Penicillium). These isolates were phylogenetically similar to fungi previously reported to degrade both conventional and biodegradable plastics. Under pure culture conditions, only a subset of fungal isolates achieved detectable mulch degradation. No isolate substantially degraded any mulch. Additionally, DNA was extracted from bulk soil surrounding buried mulches and ribosomal DNA was used to assess the soil microbial community. Soil microbial community structure was significantly affected by geographical location, but not by mulch treatments.

Biodegradable mulch performed comparably to polyethylene in high tunnel tomato (Solanum lycopersicum L.) production.

BACKGROUND: High tunnels in the cool climate of north western Washington state improve the growing environment for crops otherwise suited to warmer climates. Biodegradable mulch may improve the sustainability of high tunnel vegetable production if it performs comparably to polyethylene. Four biodegradable mulch treatments (BioAgri, BioTelo, WeedGuardPlus and SB-PLA-10/11/12) were compared to black polyethylene and bare ground in high tunnels and open field settings to assess the impact of production system and mulch treatment on weed control, tomato yield, and fruit quality. RESULTS: Fewer weeds grew in high tunnels than in the open field. High tunnels increased total and marketable fruit yields and increased individual fruit weight. High tunnel production increased juice content and pH of tomato fruit, but decreased total soluble solids, titratable acidity, and total phenolics compared to the open field. All mulch treatments except SB-PLA-10 controlled weeds. BioAgri, BioTelo and polyethylene increased total yields by 20%, though marketability was reduced 14% compared to bare ground and WeedGuardPlus treatments. CONCLUSION: High tunnels can improve tomato yield and affect fruit quality in north western Washington. Biodegradable plastic mulches performed comparably to polyethylene in weed control, tomato yield, and fruit quality and may, therefore, improve the sustainability of high tunnel vegetable production.

Evaluation of real-time nutrient analysis of fertilized raspberry using petiole sap.

The time delay in receiving conventional tissue nutrient analysis results caused red raspberry (Rubus idaeus L.) growers to be interested in rapid sap tests to provide real-time results to guide immediate nutrient management practices. However, sap analysis has never been conducted in raspberry. The present work aimed to evaluate the relationship of petiole sap nitrate (NO3 -), potassium (K+), and calcium (Ca2+) concentrations measured using compact ion meters and leaf tissue total nitrogen (TN), potassium (K), and calcium (Ca) concentrations measured using conventional tissue nutrient analysis. The relationship of petiole sap NO3 - and leaf tissue TN concentrations with plant growth and production variables was also explored. Fertilizer treatments of urea were surface applied to raised beds of established "Meeker" floricane red raspberry plots at control, low, medium, and high rates (0, 34, 67, and 101 kg N ha-1, respectively) in 2019 and 2020. The experiment was arranged in a randomized complete block design with three replications. Whole leaves were collected from representative primocanes in mid- and late- July and August 2019 and 2020 (i.e., four sampling time points per year). At each sampling time point, a subsample of leaves was used for petiole sap analyses of NO3 -, K+, and Ca2+ concentrations using compact ion meters, and conventional tissue testing of leaf tissue TN, K, and Ca concentrations, respectively. There were no interactions between N fertilizer rate and year nor between N fertilizer rate and sampling time. No significant differences were found due to N fertilizer rate for petiole sap NO3 -, K+, Ca2+ nor leaf tissue TN, K, Ca concentrations. However, significant year and sampling time effects occurred in measured petiole sap and leaf tissue nutrient concentrations. Overall, the correlations between petiole sap NO3 - and leaf tissue TN, petiole sap Ca2+ and leaf tissue Ca, petiole sap K+ and leaf tissue K concentrations were non-strong and inconsistent. Future research is warranted as the interpretation of correlations between raspberry petiole sap and leaf tissue nutrient concentrations were inconclusive.

Micrographic View of Graft Union Formation Between Watermelon Scion and Squash Rootstock.

Grafting has become a common practice for watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] production in many parts of the world, due to its efficacy against biotic and abiotic stressors. However, grafting success for watermelon is challenging in part due to the complex anatomy of the cucurbit vascular system. The survival of grafted transplants depends on compatibility between the scion and rootstock, which in turn depends on anatomical, physiological, and genetic variables. A better understanding of cucurbit anatomy and graft union formation would inform grafting approaches and transplant management. An anatomical study was conducted by scanning electron microscopy (SEM) at 11 and 25 days after grafting (DAG) with seedless watermelon cultivar 'Secretariat' grafted onto compatible rootstock cultivars 'Pelop' (Lagenaria siceraria) and 'Tetsukabuto' (Cucurbita maxima × Cucurbita moschata) in comparison to non-grafted watermelon and rootstock seedlings. At 11 DAG, the parenchymatic cells of the central pith of grafted plants were dead and a necrotic layer was observed, representing the beginning of callus formation. New xylem strands were formed in the vascular system, connecting the rootstock with the scion. At 25 DAG, fully developed vascular bundles at the graft interface were observed with both scion-rootstock combinations. Although more studies are necessary to characterize the sequence of physiological events after grafting in Cucurbit species, this is one of the first studies to describe the complex anatomical changes that occur during watermelon graft healing.

In-field degradation of soil-biodegradable plastic mulch films in a Mediterranean climate.

Soil-biodegradable plastic mulch films are a promising alternative to polyethylene mulches, but adoption has been slow, in part because of uncertainties about in-field degradation. The international biodegradability standard EN-17033 requires 90% degradation within 2 years in an aerobic incubation at constant temperature (20-28 °C). However, in-laboratory biodegradability does not guarantee in-field degradation will follow the same timeframe. Field test protocols are needed to assess biodegradable mulches under a range of environmental conditions and collate site-specific information to predict degradation. Our objectives were to (1) monitor in-field degradation of soil-biodegradable plastic mulches following successive applications and incorporations, (2) quantify mulch recovery 2 years after the final incorporation, and (3) compare in-field degradation with the laboratory standard in terms of calendar and thermal times based on a zeroth-order kinetics model. A field experiment was established in spring 2015 in Mount Vernon, WA testing five biodegradable mulches laid each spring and incorporated each fall until 2018. Mulch recovery was quantified every 6 months until fall 2020, 2 years after the final incorporation. While mulches were incorporated annually, recovery of visible fragments (>2.36 mm) was constant or decreasing over time, indicating mulch deterioration kept pace with new additions. In fall 2020, mulch recovery was 4-16% of total mulch mass incorporated. A zeroth-order kinetics model was used to analyze mulch degradation after the final application. Model extrapolations indicate it would take 21 to 58 months to reach 10% recovery (90% degradation), exceeding the laboratory standard's 24-month benchmark by up to a factor of 2.4. However, when the analysis is done with thermal time, better agreement between in-field and laboratory degradation rates is observed. While other factors, including soil type, soil moisture, and mulch fragment size are also at play, thermal time, rather than calendar time, will be more applicable for assessing site-specific, in-field mulch degradation.

Sampling and degradation of biodegradable plastic and paper mulches in field after tillage incorporation.

Plastic biodegradable mulch (plastic BDM) is tilled after use, but there is concern about incomplete degradation and potential impact on subsequent crops, and we lack a reliable method to measure mulch degradation post soil-incorporation. We conducted two field experiments to (i) develop a sampling method to estimate the amount of mulch (fragments size >2.36 mm) in the field post soil-incorporation, and (ii) assess the amount of BDM in the soil after four consecutive years of mulch incorporation. In Expt. 1, we used the quartering method to reduce soil from a 1 m2 field sample area to a representative 19 L sample. In Expt. 2, we applied and tilled four plastic BDMs: BioAgri, Naturecycle, Organix AG, and an experimental mulch; and one paper mulch, WeedGuardPlus, in their respective plots for four consecutive years. Starting in year 2, we sampled soil with the quartering method each spring and fall to determine mulch recovery. With respect to the total amount of mulch applied, average mulch recovery in the fall for the three commercial plastic BDMs was 71%, 50%, and 35% after second, third and fourth applications, respectively. For the experimental mulch, the average recovery was 80%, 69%, and 54% in the fall after second, third, and fourth applications, respectively. Recovery was slightly lower in spring than in preceding fall all years. For WeedGuardPlus, average recovery was 14%-20% in each fall, and no recovery in any spring (complete degradation). The results show that the quartering method reliably estimates the amount of mulch in a field and BDMs degrade over time in the field even with repeated applications, but complete degradation takes >1 year. While a few standards (e.g., ASTM D5988) specify how to determine biodegradation of plastics in soil under controlled laboratory conditions, our sampling method assesses plastic degradation under diverse field conditions.

In situ degradation of biodegradable plastic mulch films in compost and agricultural soils.

The global use of agricultural plastic films, which provide multiple benefits for food production, is expected to grow by 59% from 2018 to 2026. Disposal options for agricultural plastics are limited and a major global concern, as plastic fragments from all sources ultimately accumulate in the sea. Biodegradable plastic mulches could potentially alleviate the disposal problem, but little is known about how well they degrade under different environmental conditions. We quantified the degradation of biodegradable plastic mulches in compost and in soil at warm and cool climates (Tennessee and Washington). Mulch degradation was assessed by Fourier-transformed infrared (FTIR) spectroscopy, molecular weight analysis, thermogravimetric analysis (TGA), nuclear-magnetic resonance (NMR), and mulch surface-area quantification. Biodegradable plastic mulches degraded faster in compost than in soil: degradation, as assessed by surface-area reduction, in compost ranged from 85 to 99% after 18 weeks, and in soil from 61 to 83% in Knoxville and 26 to 63% in Mount Vernon after 36 months. FTIR analyses indicate that hydrolytic degradation of ester bonds occurred, and a significant reduction of molecular weight was observed. TGA and NMR confirmed degradation of biodegradable polymers. Our results indicate that biodegradable plastic mulches degrade in soil, but at different rates in different climates and that degradation occurs over several years. Faster degradation occurred in compost, making composting a viable disposal method, especially in cool climates, where mulch fragments in soil may persist for many years.

Greenhouse Evaluation of Seed and Drench Treatments for Organic Management of Soilborne Pathogens of Spinach.

The efficacy of 14 seed and drench treatments for control of soilborne damping-off pathogens in organic production of spinach was evaluated in a greenhouse study. The efficacy of each treatment was compared with nontreated seed and seed treated with a conventional fungicide for control of Fusarium oxysporum f. sp. spinaciae, Pythium ultimum, and Rhizoctonia solani. Two experimental seed treatments, GTG I and GTG II (each comprised of a proprietary organic disinfectant and the latter also containing Trichoderma harzianum T22), provided equivalent control to the conventional fungicide, mefenoxam, against P. ultimum in one trial and significant reduction of damping-off in the second trial. Natural II and Natural X (Streptomycete products), and Subtilex (Bacillus subtilis) seed treatments each suppressed damping-off significantly in one of the two trials. For R. solani, GTG I and Natural II seed treatments reduced damping-off as effectively as a drench with the fungicide Terraclor (pentachloronitrobenzene). A soil drench with Prestop (Gliocladium catenulatum) suppressed postemergence wilt caused by F. oxysporum in both trials; a compost tea drench and seed treatment with Yield Shield (Bacillus pumilis) each suppressed postemergence wilt in only one of two trials. GTG I and GTG II significantly increased seed germination compared to nontreated seed. No treatment was effective against all three pathogens, and some treatments exacerbated damping-off.

Release of micro- and nanoparticles from biodegradable plastic during in situ composting.

Plastic is ubiquitous in modern life, but most conventional plastic is non-biodegradable and accumulates as waste after use. Biodegradable plastic is a promising alternative to conventional plastic. However, biodegradable plastics must be thoroughly evaluated to ensure that they undergo complete degradation and have no adverse impact on the environment. We evaluated the degradation of biodegradable plastics during 18-week full-scale composting, and determined whether additives from the plastics are released upon degradation. Two biodegradable plastic films-one containing polybutylene co-adipate co-terephthalate (PBAT) and the other containing polylactic acid/poly-hydroxy-alkanoate (PLA/PHA)-were placed into meshbags and buried in the compost. Degradation was assessed by image analysis, scanning electron microscopy, Fourier-transformed infrared spectroscopy, electrophoretic mobility, δ13C isotope analyses, and single particle mass spectrometry of mulch fragments. The results showed >99% macroscopic degradation of PLA/PHA and 97% for PBAT film. Polymers in the biodegradable films degraded; however, micro- and nanoparticles, most likely carbon black, were observed on the meshbags. Overall, biodegradable plastics hold promise, but the release of micro- and nanoparticles from biodegradable plastic upon degradation warrants additional investigation and calls for longer field testing to ensure that either complete biodegradation occurs or that no long-term harm to the environment is caused.

Isolation of native soil microorganisms with potential for breaking down biodegradable plastic mulch films used in agriculture.

Fungi native to agricultural soils that colonized commercially available biodegradable mulch (BDM) films were isolated and assessed for potential to degrade plastics. Typically, when formulations of plastics are known and a source of the feedstock is available, powdered plastic can be suspended in agar-based media and degradation determined by visualization of clearing zones. However, this approach poorly mimics in situ degradation of BDMs. First, BDMs are not dispersed as small particles throughout the soil matrix. Secondly, BDMs are not sold commercially as pure polymers, but rather as films containing additives (e.g. fillers, plasticizers and dyes) that may affect microbial growth. The procedures described herein were used for isolates acquired from soil-buried mulch films. Fungal isolates acquired from excavated BDMs were tested individually for growth on pieces of new, disinfested BDMs laid atop defined medium containing no carbon source except agar. Isolates that grew on BDMs were further tested in liquid medium where BDMs were the sole added carbon source. After approximately ten weeks, fungal colonization and BDM degradation were assessed by scanning electron microscopy. Isolates were identified via analysis of ribosomal RNA gene sequences. This report describes methods for fungal isolation, but bacteria also were isolated using these methods by substituting media appropriate for bacteria. Our methodology should prove useful for studies investigating breakdown of intact plastic films or products for which plastic feedstocks are either unknown or not available. However our approach does not provide a quantitative method for comparing rates of BDM degradation.

Behavioral and chemosensory responses to a host recognition cue by larvae of Pieris rapae.

Larvae of the cabbage white Pieris rapae are specialists on plants belonging to the family Brassicaceae (Cruciferae). Adult females have been shown to use the glucosinolate gluconasturtiin (phenylethylglucosinolate) as a recognition cue for cruciferous plants, so they can identify an appropriate host for oviposition (Huang and Renwick in J Chem Ecol 20:1025-1037, 1994). Here, we report our results from a study of the role of this glucosinolate in feeding preferences of P. rapae larvae. The larvae were allowed to choose between leaf disks from the non-host cowpea Vigna sinensis (Fabaceae) that were treated with pure gluconasturtiin in solvent, or solvent alone. Our results showed that gluconasturtiin is a feeding stimulant for P. rapae larvae. A series of chemosensory ablations revealed that this response is mediated by one set of taste sensilla, the sensilla styloconica. Electrophysiological tip recordings revealed two neurons in the lateral sensillum styloconicum that are sensitive to gluconasturtiin. These neurons show significantly higher firing frequencies with 4 mM gluconasturtiin added to the recording pipette than for recording solution alone. We propose that the sensitivity to gluconasturtiin shown by these two taste neurons is an important contributor to the animals' behavioral preference for this compound.

Chemosensory tuning to a host recognition cue in the facultative specialist larvae of the moth Manduca sexta.

Larvae of Manduca sexta are facultative specialists on plants in the family Solanaceae. Larvae reared on solanaceous foliage develop a strong preference for their host; otherwise, they remain polyphagous. The host-specific recognition cue in potato foliage for Manduca larvae is the steroidal glycoside, indioside D. Two pairs of galeal taste sensilla, the lateral and medial sensilla styloconica, are both necessary and sufficient for the feeding preferences of host-restricted larvae. We conducted electrophysiological tip recordings from sensilla of solanaceous or wheat germ diet-reared larvae. For each animal, recordings of the responses to indioside D, glucose, tomatine and KCl were compared. All responses included both phasic and tonic portions. The sensilla styloconica of solanaceous-reared larvae were tuned to indioside D, defined as maintaining a high sensitivity to indioside D, while showing lower sensitivity to other plant compounds. Half of the sensillar neurons of solanaceous-reared larvae were 'tuned' to indioside D, whereas those of wheat germ diet-reared larvae were not. The different responses between the two types of animals were a result of changes of individual receptor cells' responses in the sensilla. Feeding on solanaceous foliage therefore appears to result in a modification of the physiological responses of individual taste receptor cells that causes them to be tuned to the host-recognition cue indioside D. We propose that this tuning is the basis for the host-restricted larvae's strong behavioral preferences for solanaceous foliage.

Hypokalemic thyrotoxic periodic paralysis: a case report and review.

Hypokalemic thyrotoxic periodic paralysis (HTPP) is a rare disorder affecting primarily men of Asian descent. Males are 20 times more likely to be affected than females. The following case describes a young Native American female with HTPP.