Control of invasive hosts by generalist parasitoids

This article was motivated by the invasion of leaf-mining microlepidopteron attacking horse chestnut trees in Europe and the need for a biological control. Following Owen & Lewis (2001, Bull. Math. Biol., 63, 655-684), we consider predation of leafminers by a generalist parasitoid with a Holling Type II functional response. We first identified six equilibrium points and discussed their stabilities in the non-spatial model. The model always predicts persistence of the parasitoid. Depending on the parameter values, the model may predict that the host persists and goes extinct or there is something like an Allee effect where the outcome depends on the initial host density. Special cases were also studied for small carrying capacities leading to complex dynamical behaviours. Then, numerical simulations of the spatial reaction--diffusion model enabled us to identify the conditions for which the leafminer's advance can be stopped and reversed by parasitoids. Compared to the ordinary differential equation model, the incorporation of space, combined with the polyphagy of the parasitoid, leads to a decrease of the parameter domain of coexistence. This is in stark to several other models in which space promotes coexistence by enabling hosts to escape.

Dispersive and non-dispersive waves through plants: implications for arthropod vibratory communication

Vibratory communication in arthropods is a widespread phenomenon. Arthropods living on plants have been reported to use only dispersive bending waves in the context of prey-predator, competition, social and sexual interactions. Differences in signal structure have also been postulated to work as species recognition mechanisms and speciation agents. Using two identical laser Doppler vibrometers and a wavelet analysis, we quantified the wave propagation modes in rush stems (Juncus effusus) over the whole range of frequencies used by arthropods. A non-dimensionalized analysis shows that mechanical waves propagate not only as dispersive bending waves, but also as non-dispersive waves. Our analysis implies that an arthropod can communicate through non-dispersive bending waves by either producing signals of high frequencies or by choosing large stems, two widely different options tapping into the physiological and the behavioural repertoires, respectively. Non-dispersive waves, unreported so far in insect vibratory communication in plants, present serious advantages over dispersive bending waves in terms of signal integrity and may well be much more widely used than anticipated, in particular for species recognition.

Ontogeny of air-motion sensing in cricket

Juvenile crickets suffer high rates of mortality by natural predators that they can detect using extremely sensitive air-sensing filiform hairs located on their cerci. Although a huge amount of knowledge has accumulated on the physiology, the neurobiology and the biomechanics of this sensory system in adults, the morphological and functional aspects of air sensing have not been as well studied in earlier life history stages. Using scanning electronic microscopy, we performed a survey of all cercal filiform hairs in seven instars of the wood cricket (Nemobius sylvestris). Statistical analyses allowed us to quantify profound changes in the number, the length and the distribution of cercal hairs during development. Of particular importance,we found a fivefold increase in hair number and the development of a bimodal length-frequency distribution of cercal hairs from the second instar onwards. Based on theoretical estimations of filiform hair population coding, we found that the cercal system is functional for a wide range of frequencies of biologically relevant oscillatory flows, even from the first instar. As the cricket develops, the overall sensitivity of the cercal system increases as a result of the appearance of new hairs, but the value of the best tuned frequency remains fixed between 150 and 180 Hz after the second instar. These frequencies nicely match those emitted by natural flying predators, suggesting that the development of the cercal array of hairs may have evolved in response to such signals.

Hair canopy of cricket sensory system tuned to predator signals

Filiform hairs located on the cerci of crickets are among the most sensitive sensors in the animal world and enable crickets to sense the faintest air movements generated by approaching predators. While the neurophysiological and biomechanical aspects of this sensory system have been studied independently for several decades, their integration into a coherent framework was wanting. In order to evaluate the hair canopy tuning to predator signals, we built a model of cercal population coding of oscillating air flows by the hundreds of hairs on the cerci of the sand cricket Gryllus bimaculatus (Insecta: Orthoptera). A complete survey of all hairs covering the cerci was done on intact cerci using scanning electronic microscopy. An additive population coding of sinusoid signals of varying frequencies and velocities taking into account hair directionality delivered the cercal canopy tuning curve. We show that the range of frequencies and velocities at which the cricket sensory system is best tuned corresponds to the values of signals produced by approaching predators. The relative frequencies of short (< 0.5 x 10(-3) m) and long hairs and their differing responses to oscillating air flows therefore enable crickets to detect predators in a time-frequency-intensity space both as far as possible and at close range.

Variation in morphology and performance of predator-sensing system in wild cricket populations

Even though variation in morphology is known to translate into variation in performance, studies looking at structural variability of a sensor to predict its consequences on the performance of animals are exceedingly rare. We investigated the morphological variability of air-flow-sensing receptors in wild populations of wood crickets (Nemobius sylvestris) sampled in a wide variety of habitats differing in latitude, litter structure, vegetation and predator communities. These hair receptors act as predator sensors. The observed levels of hair morphological variation were then incorporated into a biomechanical model of the hair canopy response to air flow to predict their influence on cricket predator perception. Cricket populations differ from each other, often strongly so, in the total number of hairs and in the number of hairs longer than 1 mm, which are the hairs most sensitive for the perception of approaching predators. The hair canopy response, the output of the biomechanical model, sums up over the entire canopy the angles of deflection at which a neurophysiological response is triggered and represents the sensitivity of the cercal system. It is 35% higher in the most sensitive population, compared with the least sensitive population. These large differences in perception sensitivity for a given predator signal translate into larger distances at which predators could be perceived. Thus, differences in morphology at the sensor level seem to be translated both at the perception level and subsequently at the performance level of crickets.

Matching host reactions to parasitoid wasp vibrations

The sensory ecology of predator detection by prey has been little studied for any arthropod prey predator system, in contrast to the sensory ecology of prey finding by predators. The aim of this study was to quantify the foraging signals produced by the parasitoid Sympiesis sericeicornis (Hymenoptera: Eulophidae) and the sensory ecology of enemy detection and the avoidance behaviour of the leaf-mining host, Phyllonorycter spp. (Lepidoptera: Gracillariidae). We used synthetic vibrations approximating the signals generated by ovipositor insertions to stimulate the host in its mine. Tothe authors' knowledge, this is the first manipulative study to describe a match in the frequency range between a parasitoid foraging stimulus and a host behavioural response. We discuss our findings in relation to other predator-prey systems for which a coevolution between prey sensitivity and predator signal has been described.

The role of leaf structure in vibration propagation

The leaf and its structural components play a key role in the propagation of short transient signals produced by insects. In this paper, it is shown how the complex structure of an apple leaf could be modeled by a much simpler one for the analysis of vibratory signal propagation. Waves were produced by impacts of small spheres and the propagation studied using two laser vibrometers, followed by a wavelets analysis. Three components of the leaf were investigated: the midvein, minor veins, and the interspaced homogeneous regions making up the leaf lamina. The loss of signal energy over the leaf lamina and across minor veins and midvein was studied. For the midvein, the loss of energy decreased from 80% at the leaf base to 40% at the apex. For minor veins, the loss of energy decreased from 70% at the leaf base to 31% at the apex. The loss in homogeneous regions was 40%. A signal decomposition into two frequency ranges, above and below 1.7 kHz, showed that the midvein acted as a low-pass filter. As energy loss was mainly a function of vein diameter and not vein type, veins smaller or equal to 0.2 mm were considered as equivalent to homogeneous regions. Hence, a model leaf reduced to the leaf lamina and veins with a diameter >0.2 mm is retained for the study of signal propagation in a leaf.

Occlusive effect of metallic stents on canine ureters

A three-part study, with successive modifications based on preceding results, was conducted to evaluate ureteral placement of metallic stents. Gianturco self-expanding (10 mm and 4 mm diameter) and balloon-expanded (4 mm diameter) metallic stents were placed in normal and stenotic canine ureters. No migration or ureteral perforation occurred during the follow-up of 10 mm stents. Varying degrees of hydronephrosis and hydroureter were found on all 1-week pyelograms. At 4 weeks, complete occlusion of the stented ureter was noted in all cases because of mucosal hyperplasia around the stent wires. To prevent this reaction, 4 mm self-expanding stents constructed of smaller wire that was uncoated or coated with either Teflon or poly-urethane were tested in five dogs. In all cases, results were similar to those obtained with the larger prostheses. Finally, 4 mm balloon-expanded stents were placed in a normal ureter of three dogs. In one dog, the stent migrated out of the ureter. No migration or ureteral perforation occurred in the two remaining dogs. In these animals, mucosal hyperplasia and complete ureteral occlusion occurred 6 and 8 weeks after placement. Therefore, ureteral placement of Gianturco self-expanding as well as balloon-expanded metallic stents leads to occlusion of the ureter instead of maintaining its patency. Stents, therefore, may be useful as ureteral occlusion devices.

A new device for transcatheter closure of the patent ductus arteriosus. A feasibility study in dogs

A new device for transcatheter closure of the patent ductus arteriosus was developed and initially evaluated in the vasculature of adult mongrel dogs. The device consists of a nylon sack that can be made in various sizes and shapes. A small flexible crossbar attached to the distal end maintains the position of the sack while it is filled with a segment of modified guide wire. The device is delivered coaxially through a 10-Fr Teflon catheter and is easily repositioned or retrieved before release. The expansile force of the sack against the vessel wall can be varied, and its stability is easily checked prior to detachment. The device produced immediate and permanent vascular occlusion without inflammation or erosion. Over time, the entire unit became incorporated into the vessel wall by neointimal encasement. Nylon sacks offer a simple, unique method of closing virtually any ductus arteriosus without general anesthesia and major surgery.

The superior mesenteric artery fat plane: is obliteration pathognomonic of pancreatic carcinoma?

Obliteration of the fat plane surrounding the superior mesenteric artery has been described as characteristic of pancreatic carcinoma. To determine the specificity of this and other computed tomography findings in the pancreas and peripancreatic region, scans of 86 patients were reviewed without clinical history. Diagnoses included pancreatitis (26 patients); pancreatic adenocarcinoma (14 patients); lymphoma (17 patients); metastatic nonpancreatic carcinoma (14 patients); and normal findings (15 patients). Confluent adenopathy could not be reliably differentiated from a pancreatic mass except when adenopathy separated the common bile duct from the duodenum. Retrocrural adenopathy was unusual with pancreatic carcinoma. The fat plane surrounding the superior mesenteric artery was obliterated with pancreatic carcinoma (36%), nonpancreatic carcinoma (29%), and lymphoma (24%), but not with pancreatitis, although perivascular edema was seen in 19%. Evaluation of the celiac axis was less rewarding. Obliteration of the superior mesenteric artery fat plane is a sign of malignancy, but it is not specific for pancreatic carcinoma. We propose that the superior mesenteric artery origin be considered within a paraaortic space, separate from the anterior pararenal space. This explains its characteristic lack of involvement by pancreatitis.