Function of the heater: the dead horse arum revisited.

The dead horse arum, Helicodiceros muscivorus, is a conspicuous, foul smelling and thermogenic plant of the Araceae family. This Mediterranean arum lily copies several aspects of a carcass in order to attract carrion blowflies, which are subsequently exploited as unrewarded pollinators. We have previously shown that this plant exhibits a highly accurate olfactory carrion mimicry, which serves to attract the blowflies. In this study, we have investigated the role of thermogeny in the arum. We show that the thermogeny has a direct effect on the pollinators, altering their behaviour. By manipulating heat and odour release of the plant, we can show that the heat, produced along the appendix, is important to lure the flies to this structure, which is vital as the flies from the appendix are more prone to enter the trap chamber that houses the female and male florets. This study provides rare evidence for a direct functional role of thermogeny.

Effects of octopaminergic substances on the labellar lobe spreading response in the blowfly Protophormia terraenovae.

The effectiveness of labellar taste input in evoking the feeding response of labellar lobe spreading in Protophormia was greatly increased by injecting flies with clonidine or DL-octopamine. This effect was suppressed when either drug was administered together with yohimbine; when injected alone, the latter determined a strong decrease in the feeding responses. Drug treatment did not determine variations in labellar taste input or evoke spontaneous activity in the denervated muscle. These results suggest that the injected substances lower the feeding-related reflex threshold at the CNS level.

Reflex cardiac response to various olfactory stimuli in the blowfly, Protophormia terraenovae.

In the present investigation it is shown that a reflex change in the heart activity of Protophormia flies is evoked by olfactory stimulation with several volatile substances, and particularly with those which are repellent for blowflies. Among these, i-pentanal and hexanal vapours evoked a fast, highly persistent cardiac response, whereas in the case of hexanol and ammonia vapours the response resulted slower and could be suppressed as a function of repeated stimulation.

Electrophysiological recordings from the taste chemosensilla of Tabanus nigrovittatus (Diptera: Tabanidae) and determination of behavioral tarsal acceptance thresholds.

A modified behavioral test for determining the median tarsal acceptance thresholds of field-collected, female Tabanus nigrovittatus Macquart to sugars showed that flies were sensitive to the three major nectar sugars (fructose, sucrose, and glucose, in that order of decreasing sensitivity) whereas galactose, a nonnectar sugar, was not comparably stimulating. Comparisons of various treatment effects on the median tarsal acceptance thresholds showed that for future studies, flies should be fed 10% sucrose before testing, should be starved for 24 h before testing, and they do not have to be pretested for a water response. Electrophysiological recordings showed that gustatory chemosensilla were located on the labellum, tip of labrum, labral food canal, foretarsi, tibia, and antennae. All chemosensilla responded to sugar and salt, whereas only those chemosensilla at the tip of the labrum and those lining the food canal, which normally contact the blood meal, responded to sera and plasma.

Neuropeptide F peptides act through unique signaling pathways to affect cardiac activity.

Elucidating how neuropeptides affect physiology may result in delineating peptidergic mechanisms and identifying antagonists for application in basic and translational science. Human neuropeptide Y (NPY) regulates cardiac activity; frequently invertebrates contain orthologs of vertebrate peptides. We report invertebrate NPY-like neuropeptide F (NPF) arrested the signal frequency of the slow phase of the cardiac cycle (EC50 = 1 pM); however, signal frequency of the fast phase was affected only minimally. Neuropeptide F decreased the duration of the slow phase by ~70% (EC50 = 0.6 pM), but increased the duration of the fast phase by ~57% (EC50 = 10nM). Short NPF-1 (sNPF-1) decreased the signal frequency of the slow phase by ~70% (EC50 = 9 nM); yet, signal frequency of the fast phase was unaffected. Short NPF-1 decreased the duration of the slow phase ~55% (EC50 ~50 nM), but increased the duration of the fast phase ~20% without dose dependency. Neuropeptide F and sNPF-1 increased isoelectric period duration. This novel report demonstrated NPY-like peptides are cardioactive but functionally unique. These data contribute to understanding how invertebrate orthologs affect cardiovascular activity. Dipteran fast and slow phases may be generated from separate pacemakers in the abdominal heart and in the anterior thoracocephalic aorta, respectively. Thus, our research suggests NPF and sNPF-1 act through different mechanisms to regulate cardiac activity. Invertebrate NPY-like peptides act in olfaction and feeding yet mechanisms which are associated with their cardioactive effects remain unknown; our work may provide evidence linking their roles in sensory response and cardiac activity.

The presence of acid mucopolysaccharides in viscous extrusions from the labellar and tarsal chemosensilla of Phormia regina (Meig.).

Mucopolysaccharide substances are present in the shafts of both tarsal and labellar chemosensilla of Phormia. These substances are extruded at the tip of the chemosensilla. A certain amount of mucopolysaccharides can also be observed on the outer surface of the tarsal hair wall at various points along the hair shaft. The influence of mucopolysaccharide substances on hair responsiveness to external stimuli is discussed.

Electrical resistance of labellar taste hairs in the blowfly, Phormia regina M., as a function of age and sex.

The electrical resistance of the labellar taste hairs of Phormia regina M. is enhanced by aging in both males and females; this increase is greater in males. Resistance variations, related to changes in response of stimulated chemoreceptors, may explain, at least in part, the reduction in reflex food intake, O2 consumption, weight increase and, on the whole, survival capabilities of males vis-à-vis female insects.

Functional morphology of the dorsal vessel in the adult fly Protophormia terraenovae (diptera, calliphoridae).

The morphology and ultrastructure of the contractile tubular vessel acting as the cardiac pump in Protophormia terraenovae flies were analyzed by means of light microscopy, SEM and TEM. The results provide a novel anatomical picture of the two vessel portions, the abdominal heart and the aorta, and lay the foundations for an interpretation of the cardiocirculatory function in the fly. In the thorax, the thin and unchambered aorta is without apertures, while the abdominal heart presents a very small caudal aperture and pairs of lateral ostia, one in each of the five chambers of which it is composed. The ostia of the four more distal chambers are of the incurrent type, which is to say that they act as valves ensuring that hemolymph flows only into the heart. Conversely, the ostia in the most proximal chamber allow hemolymph to flow both into and out of the heart. The entire vessel is composed of a single layer of myofibers that are oriented circularly around the lumen in the abdominal heart and longitudinally in the thoracic aorta. The abdominal heart has a thicker wall, a far more diffused and thick distribution of tracheoles, and a far greater number of mitochondria with respect to the aorta. This arrangement ensures a greater availability of oxygen and energy in the abdominal heart compared to the aorta and leads one to suppose that the high- and low-frequency contractions of the cardiac cycle (Thon, [1982] J. Insect Physiol. 28:411-416) can be attributed to the abdominal heart and the aorta, respectively. J. Morphol. 240:15-31, 1999. © 1999 Wiley-Liss, Inc.

Chronic electrode for long-term electrophysiological recording from insect chemosensilla.

Insertion of a chronic, non-damaging Pt electrode for electrophysiological recording from chemosensilla in Phormia is described. The experimental procedure did not modify in a significant way the survival capabilities or the general behaviour of the operated insects as compared to control, untreated ones. This method, which allows the performance of subsequent tests on the same specimen up to its full lifespan with fairly constant results, proved to be suitable in long-term experiments on the chemosensory function of insects.

Mechanism of JH influence on the function of labellar chemosensilla in Phormia: experimental suggestions.

The aim of this research study was to determine at which level the JH effect of increasing chemosensillar sensitivity in Phormia could take place. Two-day-old adult female Phormia regina (Meigen) flies were used. Variations in electrical resistance and spike firing frequency of labellar chemosensilla stimulated with NaCl solutions were measured before and after topical application of a JH analogue (JHA). Variations in the above two parameters were also determined in a group of control flies. Results showed that an inverse linear relationship exists between electrical resistance and spike firing frequency in both JHA-treated and control flies. On this basis, we conclude that the above sensitivity variations depend on a mechanism common to both groups of flies. As regards the mode of action of this mechanism, we suggest that JH may influence the mucopolysaccharide secretory function of the accessory cells, the activity of which seems to account for changes in electrical resistance and therefore in sensitivity of the labellar chemosensilla.

Electrophysiological activity of labellar and tarsal chemosensilla of Hybomitra lasiophtalma (Macquart) to stimulation with NaCl and various sugars.

The responses from labellar and tarsal chemosensilla of Hybomitra lasiophtalma to stimulation with NaCl or sugars (sucrose, glucose, fructose, galactose) were recorded. Results showed that 4 chemosensory units were located in each chemosensillum. Among these, a water-, a salt-, and a sugar-sensitive unit were detectable. NaCl (higher than 50 mM) as well as sucrose (higher than 100 mM) sensitivity thresholds were determined; sucrose and galactose proved to be more active as stimuli than fructose and glucose.

Ovipositor chemosensilla in Tabanus nigrovittatus (Macq.) Chrysops fuliginosus (Wied.), and Rhagoletis pomonella (Walsh).

The possible presence of chemosensilla in the ovipositor region has been investigated in three different pest insect species by means of the standard tip-recording electrophysiological technique. Results showed that hair-like structures responding to chemical stimulation were located at the lower-inner edge of the anal leaflets in Tabanus nigro Macq. as well as in Chrysops fuliginosus Wied, whereas peg-like chemosensilla proved to be located in two longitudinal grooves at the apical portion of the ovipositor in Rhagoletis pomonella Walsh.. At least 3 chemosensory units could be detected in each chemosensillum tested. No hair-or peg-like structure on the ovipositor region other than that we described showed any chemosensory responsiveness.

The labellar and tarsal chemosensilla in Anopheles maculipennis atroparvus Van Thiel: electrophysiological and morphological observation.

The presence of chemosensilla on labella and tarsi of Anopheles m.a. has been demonstrated by means of morphological (S.E.M.) and electro physiological (tip-recording) techniques. Results have shown that: 1) at least 3 chemosensory units are located in both types of chemosensilla; 2) stimulation with NaCl evoked various response patterns depending on NaCl concentration in the labellar chemosensilla and just a single pattern in the tarsal ones.