Cold tolerance of field-collected and laboratory reared larvae of Sesamia nonagrioides (Lepidoptera: Noctuidae)

Sesamia nonagrioides Lefébvre (Lepidoptera: Noctuidae) is considered one of the most destructive pests of corn in the Mediterranean region. The purpose of the present study was to investigate some aspects of the cold tolerance of non-diapausing and diapausing laboratory reared larvae of S. nonagrioides, as well as of field-collected larvae, taking into consideration various parameters, such as supercooling ability, mean lethal temperature and accumulation of cryoprotectant substances, in relation to diapause. Our results provide evidence that S. nonagrioides has limited cold tolerance as it displays a low ability of supercooling. This is strongly supported by the fact that mortality of the individuals occurred after extended exposure to subzero temperatures, equivalent or slightly lower to their mean supercooling point. However, lethal temperatures of diapausing larvae were significantly lower in relation to that of non-diapausing larvae, indicating the existence of a direct link between diapause and cold tolerance. Regarding the role of cryoprotectant substances, accumulation of glycerol seems to be closely related to diapause, in contrast to accumulation of trehalose, which is more related to exposure to low temperatures slightly higher than 0 degree C. Finally, non-diapausing larvae of different instars displayed a similar ability of supercooling and tolerance to low temperatures as well as accumulation of cryoprotectant substances. The ecological significance of our findings on cold tolerance of this species is being discussed with particular reference to the microclimate observed in northern Greece.     

Cryopreservation of the late stage embryos of Spodoptera exigua (Lepidoptera: Noctuidae)

Genetic devolution, genetic drift and contamination are all threats to maintain germplasm stability during mass rearing of many insects. Cryopreservation of beet armworm (Spodoptera exigua) embryos was studied to provide information to improve mass rearing. A series of experiments was conducted on late-stage embryos (45-48 h at 27 degree C) of the beet armyworm, which included evaluation of cryoprotectants (CPAs), their toxicity and glass-forming tendency and optimization of experimental procedures. The results showed that ethylene glycol (EG) was the best CPA with comparatively low toxicity compared to the other six CPAs tested (methanol, 1,3-propanediol, glycerol, 2-amino-1-ethanol, 3-amino-1-propanol 3-methoxy-1 and 2-propanediol). The highest hatching rate of 8.8 degree was attained after freezing with a 3-step loading procedure and a 1-step unloading procedure, but the hatched larvae from frozen-thawed embryos did not actively feed and could not develop to a later stage. This was attributed to injuries from freezing in late stage embryos of S. exigua which had formed midguts.     

Ultrastructure of the Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) midgut

The insect midgut has ultimately been the focus of researches tempting to control insect pests because alterations in the insect gut may affect not only its development, but also physiological events such as nutrient absorption and transformation. The objective of the present work was to describe morphologically, histochemically, and ultrastructurally the larva midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), a cotton key pest in Brazil. Light and electronic transmission microscopy was used to obtain images from midgut sections of late fourth-instar larvae of A. argillacea. In general, the morphology, histochemistry, and ultrastructure characteristics of A. argillacea midgut follow that described in the literature for other lepidopteran species. However, the results showed a mitochondrial polymorphism and branched microvilli, which suggest an ultrastrucutural and physiological modification possibly associated with a high absorption and secretion activity by the columnar cells of this species. This intense activity may favor a faster response related to the action of ingested microbial agents and/or toxins, and can explain the high susceptibility of A. argillacea to the agents of control such as the toxin of Bacillus thuringiensis.     

Ultrastructural analysis of midgut cells from Culex quinquefasciatus (Diptera: Culicidae) larvae resistant to Bacillus sphaericus

The larvicidal action of the entomopathogen Bacillus sphaericus towards Culex quinquefasciatus is due to the binary (Bin) toxin present in crystals, which are produced during bacterial sporulation. The Bin toxin needs to recognize and bind specifically to a single class of receptors, named Cqm1, which are 60-kDa α-glucosidases attached to the apical membrane of midgut cells by a glycosylphosphatidylinositol anchor. C. quinquefasciatus resistance to B. sphaericus has been often associated with the absence of the α-glucosidase Cqm1 in larvae midgut microvilli. In this work, we aimed to investigate, at the ultrastructural level, the midgut cells from C. quinquefasciatus larvae whose resistance relies on the lack of the Cqm1 receptor. The morphological analysis showed that midgut columnar cells from the resistant larvae are characterized by a pronounced production of lipid inclusions, throughout the 4th instar. At the end of this stage, resistant larvae had an increased size and number of these inclusions in the midgut cells, while only a small number were observed in the cells from susceptible larvae. The morphological differences in the midgut cells of resistant larvae found in this work suggested that the lack of the Cqm1 receptor, which also has a physiological role as being an α-glucosidase, can be related to changes in the cell metabolism. The ultrastructural effects of Bin toxin on midgut epithelial cells from susceptible and resistant larvae were also investigated. The cytopathological alterations observed in susceptible larvae treated with a lethal concentration of toxin included breakdown of the endoplasmic reticulum, mitochondrial swelling, microvillar disruption and vacuolization. Some effects were observed in cells from resistant larvae, although those alterations did not lead to larval death, indicating that the receptor Cqm1 is essential to mediate the larvicidal action of the toxin.This is the first ultrastructural study to show differences in the cell morphology of resistant larvae and further investigation is needed to understand the impact of the lack of expression of midgut enzymes on the physiology of resistant insects.     

Effect of sweet flag rhizome oil (Acorus calamus) on hemogram and ultrastructure of hemocytes of the tobacco armyworm, Spodoptera litura (Lepidoptera: Noctuidae)

Effect of the essential oil of Acorus calamus L. rhizomes, was studied on hemocytes of the tobacco armyworm, Spodoptera litura. The oil was administered in oral application at concentration of 500 and 1000 ppm to last instar larvae of S. litura and its effect on ultrastructure of hemocytes and hemogram was evaluated. The oil was administered in topical application at 250 microg dose to pupae to ascertain its effect on total and differential hemocyte counts. At both scanning (SEM) and transmission electron microscopic (TEM) levels, the major effect of oil treatment was observed on plasmatocytes (PLs) and granular hemocytes (GRs). SEM study revealed that the cytoplasmic projections of granular hemocytes were reduced, while the filopods of plasmatocytes remained unaffected. The vacuolization in the cytoplasm and degeneration of the organelles in both plasmatocytes and granular hemocytes was observed by TEM. However, no such deformities were observed in prohemocytes (PRs), spherulocytes (SPs), and oenocytoids (OEs). A concentration-dependent decrease has been observed in the larval body weight and hemolymph volume (HV), 24-72 h after treatment. In comparison to the controls, the maximum percentage growth inhibition (GI) was recorded to be 58.28 and 66.48, respectively at 500 and 1000 ppm after 72 h treatment. Similarly after 72 h treatment, the percentage reduction in hemolymph volume was 61.38 and 69.05, respectively at 500 and 1000 ppm. Total hemocyte count (THC), in larvae computed from five recorded hemocyte types viz. PRs, PLs, GRs, SPs and OEs, decreased only after 48-72 h of treatment. The maximum decrease in THC was recorded to be 29.15 and 49.05% at 500 and 1000 ppm, respectively, after 72 h of treatment. There was continuous decline in THC in pupae after 24-72 h treatment. DHC study revealed that both the concentrations of oil in 6th instar larvae of S. litura caused a decrease in PRs, PLs and SPs and increase in GRs and OEs after 24-72 h of treatment. Since A. calamus oil treatment causes the injury to both PLs and GRs and also affects the hemogram, it can be inferred that cellular defence reactions of S. litura are impaired.     

Cytopathology of the trachea of Bombyx mori (Lepidoptera: Bombycidae) to Bombyx mori nucleopolyhedrovirus

Bombyx mori is a holometabolous insect found only in germplasm banks and morphological data related of resistance and susceptibility to diseases is important when selecting hybrids for commercial and scientific interest. This study analyzed the cytopathology of B. mori trachea to BmNPV, isolated geographically in Paraná state, Brazil. Fifth instar larvae were divided into two groups, control and inoculated; the viral suspension used was 2.4 × 10⁷ polyhedral occlusion bodies/mL. From the second to the ninth day post-inoculation, segments of silkworm organs, containing the trachea, were processed for transmission electron microscopy. Analyses of fresh hemolymph were also performed to verify the susceptibility of the hemocytes. Signs of infection were initially detected in the hemocytes and in the tracheal cells on the second and fourth post-inoculation days, respectively. The cytopathology of the trachea showed all stages of the viral cycle, which was the same as in other tissues. Virions were detected in the basal lamina, which showed structural disorganization. So, the infection time of the hemocytes prior to trachea and the presence of virus in basal lamina, suggests that the trachea was a secondary target, infected by budded virus coming from the hemolymph.     

Atypical mechanoreceptors in larvae of biting midges Forcipomyia nigra (Diptera: Ceratopogonidae)

The dorsolateral setae of Forcipomyia nigra have been investigated. They are mechanoreceptors, sensilla trichoidea, innerved by a single neuron. The tubular body is located at the base of the hair shaft. Although the fine structure of the dorsolateral setae is similar to dorsal setae that perform a double function: secretion of a hygroscopic viscous substance through the pores and mechanoreception dorsolateral setae, they do not secrete any fluid. In both types of setae, trichogen cells (hair forming cells) produce the hair shafts and thereafter do not retract from the cavity of the setae. They contain a large polyploid nucleus and expanded bundles of microtubules. In dorsolateral mechanoreceptors, the microtubules form a network around the nucleus of the trichogen cell and are especially numerous in the cytoplasm invading the interior of the seta, which is evidenced by immunofluorescence light microscopy. No tormogen cell, responsible for the production of the setal socket, was found. Our observations indicate that the dorsolateral setae are solely mechanoreceptors but their trichogen cells reveal some glandular activity.     

Changes in entrance surface dose in relation to the location of shielding material in chest computed tomography

This study examined the effects of entrance surface dose (ESD) on the abdomen and pelvis of the patient when undergoing chest computed tomography (CT) procedure, and evaluated the effects of ESD reduction depending on the location of radiation shield. For CT scanner, the 64-slice multi-detector computed tomography was used. The alderson radiation therapy phantom and optically stimulated luminescence dosimeter (OSLD), which enabled measurement from low to high dose, were also used. For measurement of radiation dose, the slice number from 9 to 21 of the phantom was set as the test range, which included apex up to both costophrenic angles. A total of 10 OSLD nanoDots were attached for measurement of the front and rear ESD. Cyclic tests were performed using the low-dose chest CT and high-resolution CT (HRCT) protocol on the following set-ups: without shielding; shielding only on the front side; shielding only on the rear side; and shielding for both front and rear sides. According to the test results, ESD for both front and rear sides was higher in HRCT than low-dose CT when radiation shielding was not used. It was also determined that, compared to the set-up that did not use the radiation shield, locating the radiation shield on the front side was effective in reducing front ESD, while locating the radiation shield on the rear side reduced rear ESD level. Shielding both the front and rear sides resulted in ESD reduction. In conclusion, it was confirmed that shielding the front and rear sides was the most effective method to reduce the ESD effect caused by scatter ray during radiography.     

Localized vibrations ofH andD in Ta and their relation to theH(D) potential

The localized vibrations ofH(D) in and TaH(D) _x have been studied by high resolution inelastic neutron scattering. The frequencies of the fundamentals have been determined with very high accuracy. The corresponding line widths are extremely narrow in contrast to literature data. The slight broadening of the higher fundamental in the phase could be related to the orthorhombic distortion of this phase. For the first time higher harmonics of localizedH(D) vibrations in Ta could be observed. Their frequency shift relative to the harmonic value and the deviation of the fundamental frequencies from the harmonic isotope effect could consistently be described by one anharmonicity parameter for theH(D) potential.     

Ultrastructure of the sensilla on larval antennae and mouthparts in the peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae)

The ultrastructure of the sensilla on the larval antennae and mouthparts of the peach fruit moth, Carposina sasakii Matsumura, were investigated using scanning electron microscopy. On each three-segmented antenna, the basal scape is devoid of sensilla, the pedicel possesses two sensilla chaetica and three sensilla basiconica, and the terminal flagellum carries distally one sensillum styloconicum and three sensilla basiconica. The labrum bears six pairs of sensilla chaetica; the epipharynx carries two pairs of small epipharyngeal sensilla, three pairs of flattened sensilla chaetica, and a pair of broad sensillum digitiformium. Each dentate mandible carries two sensilla chaetica basally on its outer face. On the maxillae, the cardo and stipes each carry a sensillum chaeticum distally; each galea has three elongate flattened sensilla basiconica, two short sensilla chaetica, and two large sensilla styloconica. The distal segment of the maxillary palp possesses distally seven sensilla basiconica and one sensillum styloconicum, and laterally one sensillum digitiformium and one sensillum placodeum. Each labial palp bears distally a short cone-shaped sensillum chaeticum and an elongate slender sensillum styloconicum. The possible functions of these sensilla in the feeding process are briefly discussed.     

Eyes of male and female Orgyia antiqua (Lepidoptera; Lymantriidae) react differently to an exposure with UV-A

The structural organization of the eyes belonging to 12 winged male and 12 wingless female Orgyia antiqua moths, exposed for 1 h to UV-radiation (lambda(max)=351 nm) of 1.4 kW/m2, was compared with that of 12 male and 12 female non-irradiated control specimens. Following the UV-exposure, the screening pigments were found in a position indicative of extreme light-adaptation. Extensive formations of vesicles along the perimeter of the cones as well as disintegrating ER in the cone cytoplasm were noticeable, especially in the eye of the female. On the retinal side of the clearzone, the microvilli of the rhabdoms had become affected by the UV in characteristic ways: in the male eye, retinal cell damage in the form of microvillar swellings and disintegrations were largely confined to just two cells per ommatidium, placed opposite to each other. The female eye, once again, exhibited greater vulnerability and more widespread microvillar disruptions that affected all of the ommatidial retinula cells. The greater resistance of the eye of the male to an exposure with UV makes sense, if we consider the consequences of the retinal damage, which would clearly be a more severe handicap for an actively flying individual than for an almost sedentary one like the wingless female.     

The 0(6) limit of the interacting boson model and its relation to triaxial nuclear models

It is shown that the 0(6) limit of the interacting boson model (IBA) corresponds to the γ-unstable model of Jean and Wilets, if one considers an infinite number of bosons in IBA (N → ∞). The rigid triaxial rotor model with γ = 30° satisfies the same selection rules, but differs considerably with respect to B(E2) values and energies.     

On the relation of periodic acoustic emission pulses to slow solitary elastic waves (SSEW): Experiments with radiation-damaged glass in liquids

The periodicity (to 20 hours) of acoustic emission signals from radiation-damaged glass placed into liquid is detected. It is assumed that this periodicity is caused by slow solitary elastic waves (SSEW) with discrete velocities, which arise under experimental conditions. (SSEW were discovered and studied at the Lebedev Physical Institute since 1992.)     

Photoemission investigation on the oxidation of Si(111)Ag interfaces and its relation to the interface structure

We give the first photoemission results on the enhancement of Si reactivity to oxygen when a noble metal (Ag) is present. The tunability of synchrotron radiation (SR) has been used to get high surface sensitivity and to take advantage of cross section energy dependence. We show that when one monolayer of Ag is deposited onto Si(111), the exposure to oxygen (30 × 10⁶L) originates the overgrowth of an oxide phase which is basically SiO₂. This indicates that Ag breaks the sp³ configuration of Si atoms with a consequent dramatic increase in the Si reactivity. This behaviour rules out the model of Ag adsorbed on top of Si with an atomically abrupt interface.