Defense of Milkweed Bugs (Heteroptera: Lygaeinae) against Predatory Lacewing Larvae Depends on Structural Differences of Sequestered Cardenolides

Predators and parasitoids regulate insect populations and select defense mechanisms such as the sequestration of plant toxins. Sequestration is common among herbivorous insects, yet how the structural variation of plant toxins affects defenses against predators remains largely unknown. The palearctic milkweed bug Lygaeus equestris (Heteroptera: Lygaeinae) was recently shown to sequester cardenolides from Adonis vernalis (Ranunculaceae), while its relative Horvathiolus superbus also obtains cardenolides but from Digitalis purpurea (Plantaginaceae). Remarkably, toxin sequestration protects both species against insectivorous birds, but only H. superbus gains protection against predatory lacewing larvae. Here, we used a full factorial design to test whether this difference was mediated by the differences in plant chemistry or by the insect species. We raised both species of milkweed bugs on seeds from both species of host plants and carried out predation assays using the larvae of the lacewing Chrysoperla carnea. In addition, we analyzed the toxins sequestered by the bugs via liquid chromatography (HPLC). We found that both insect species gained protection by sequestering cardenolides from D. purpurea but not from A. vernalis. Since the total amount of toxins stored was not different between the plant species in H. superbus and even lower in L. equestris from D. purpurea compared to A. vernalis, the effect is most likely mediated by structural differences of the sequestered toxins. Our findings indicate that predator-prey interactions are highly context-specific and that the host plant choice can affect the levels of protection to various predator types based on structural differences within the same class of chemical compounds.

Tracheal Rupture After Endotracheal Intubation: Experience with Management in 13 Cases

BACKGROUND

Tracheal rupture is a rare complication of endotracheal intubation. Potential causes, diagnosis, management, and outcome of cases treated at an university hospital are analysed.

PATIENTS AND METHODS

This is a retrospective report on thirteen cases of tracheal rupture related to tracheal intubation, treated at our institution from February 1989 to May 2002. In all patients, the tracheal rupture was confirmed by fiberoptic bronchoscopy.

RESULTS

Eleven patients underwent primary repair through a right thoracotomy. Three postoperative deaths unrelated to the tracheal lesion occurred. All remaining cases showed an uneventful recovery after surgical therapy. Two lacerations of the cervical part of the trachea were treated nonsurgically with a satisfactory outcome.

CONCLUSIONS

Prognosis of tracheal ruptures depends both on the underlying disease and general condition of the patient and on the rapidity of diagnosis and treatment. Surgical therapy is preferred as it allows reconstruction of the trachea and drainage of the mediastinum. Conservative management appears to be justified for small ruptures in the upper third of the trachea without mediastinitis.

[Persistent perineal sinus closure after rectal extirpation-an alternative using bulbocavernosus fat flaps]

We present a 78-year-old female who had undergone rectal excision due to Crohn's disease of the rectum with loss of fecal continence. This led to a chronic perineal sinus and vaginal fistula which was closed with a Martius procedure using a bulbocavernosus fat flap. The sinus healed uneventfully after 4 weeks. In our opinion, the gracilis muscle was too large for this defect. We suggest use of this flap in female patients with small persistent perineal sinuses.

Morbidity and validity of the hemiclamshell approach for thoracic surgery

OBJECTIVE

This is a prospective study to evaluate the indications and outcome of the hemiclamshell incision (longitudinal partial sternotomy combined with an antero-lateral thoracotomy) as used for a consecutive series of patients requiring surgery for various thoracic pathologies not ideally approached by postero-lateral thoracotomy, sternotomy or thoracoscopy.

METHODS

All patients with a hemiclamshell incision performed between 1994 and 1998 were prospectively analyzed regarding indications, postoperative morbidity and outcome (clinical examination and pulmonary function testing) in order to validate this incision for thoracic surgery.

RESULTS

25 patients (15 men, 10 women) with an age ranging from 16 to 73 years (mean 43 years) underwent a hemiclamshell incision. The indications for the hemiclamshell approach were (1) chest trauma with massive hemorrhage requiring urgent access to the mediastinum and the ipsilateral pleural space (40%), (2) tumors of the anterior cervico-thoracic junction with suspicion of vascular involvement (28%) and (3) lesions involving both one chest cavity and the mediastinum (32%). The 30-day mortality was 8%. One patient suffered a sternal wound infection, mediastinitis and pleural empyema after a gun shot wound, whereas wound healing was uneventful in all other patients. Analgesic requirements for postoperative pain relief were not increased as compared to those following a standard thoracotomy. At 3 months normal sensitivity of the entire chest wall and intact shoulder girdle function was noted in 90% of the patients. Pulmonary function testing showed no restriction due to the hemiclamshell incision.

CONCLUSIONS

The hemiclamshell incision is a useful approach in selected patients and does not cause more morbidity or long-term sequelae than a standard thoracotomy.

Mechanics of the transduction of sound in the tympanal organ of adults and larvae of locusts

The mechanical transmission of sound in the tympanal organ of adults and 5th instar larvae of Locusta migratoria and Schistocerca gregaria has been investigated by means of stroboscopic measurements within a frequency range from 1-20 kHz. Frequency dependent spatial distributions of amplitudes and phases of oscillation on the tympanal membrane and the Müller's organ could be demonstrated. Cuticular structures on the membrane may act as a lever arm (e.g. elevated process) and cause a transformation of the (unidimensional) membrane motion into components of displacements in the Müller's organ perpendicular, as well as even parallel, to the membrane. Sites of maximum relative displacements at distinct frequencies are found to be correlated to the course of the dendrites of the acoustic receptor cells. Differences in morphology of the tympanal organ between the two species as well as between adults and larvae always correspond to differences in the mechanical properties (resonances etc.). Consequently, differences or changes in the neurophysiological response characteristics of the different receptor cells have been found. Based upon these findings a correlation between the anatomical and physiological classification of the receptor cell groups is presented.

Problems of recordings of nervous activity with glass microelectrodes in the CNS of insects

Extracellular single unit recordings with glass microelectrodes in the central nervous system of insects display action potentials of variable amplitude, polarity and time course. This phenomenon is due to capacitive influences at the electrode in contact with the tissue. This is demonstrated by an electrical model circuit simulating extracellular recording conditions. Extracellularly recorded potentials often are very similar to intracellularly recorded ones. Criteria for the decision whether the electrode is intracellularly or not are discussed. Action potentials and slow potentials were recorded simultaneously in the acoustic neuropiles of Locusta. Since slow potentials may not only be distorted by capacitive properties of both the tissue and the electrode, but also are influenced by the anatomical organization of the nervous tissue, their interpretation is ambiguous.