Eric F. Erbe

Effects of snow crystal shape on the scattering of passive microwave radiation

A discrete dipole scattering model is used to measure the passive microwave radiation scattered by snow particles having different shapes and sizes. The model results demonstrate that the shape of the snow crystal is insignificant in scattering microwave energy in the 37-GHz region of the spectrum.

Morphological observations on Brevipalpus phoenicis (Acari: Tenuipalpidae) including comparisons with B. californicus and B. obovatus

The genus Brevipalpus has over 300 species worldwide. The three most important agricultural pest species in the genus, Brevipalpus californicus (Banks), B. obovatus Donnadieu, and B. phoenicis (Geijskes), have been consistently confused and misidentified for more than 50 years. The present study provides a discussion of the characters and character states used to separate these mites. Low-temperature scanning electron microscopy and traditional light microscopy techniques were used to illustrate the subtle morphological differences between these three species. Morphology of the dorsal propodosoma, opisthosoma, and leg chaetotaxy of all three species was examined and compared. The number of dorsal setae, the number of solenidia (omega) on tarsus II, and dorsal cuticular patterns were the most important characters in the identification of Brevipalpus species. B. phoenicis is similar to B. californicus in having two omega on tarsus leg II and different from B. obovatus which has only one omega on tarsus leg II and similar to B. obovatus in having only one pair of F setae (f3), but differing from B. californicus which has two pairs of F setae (f2–3). The dorsal opisthosomal and propodisomal cuticular patterns frequently used to distinguish between these three species are useful but one must be aware that age, feeding, and mounting techniques can affect the appearance of these characters.

Structural organization of the sex pheromone gland in Helicoverpa zea in relation to pheromone production and release

Morphological location of the sex pheromone producing area in the ovipositor of the female corn earworm Helicoverpa zea, was correlated with gas chromatographic analysis of the extracted pheromone. Histological studies showed that the pheromone gland occupied an almost complete ring of specialized columnar cells between the 8th and 9th abdominal segments. Ultrastructure of the pheromone gland cells revealed distinct features such as microvilli, pockets of granular material, intercellular canals with abundant desmosomes. Apparent changes in some of these features are associated with phases of pheromone production and non-production. Examination of the tissue with low temperature scanning electron microscopy showed the presence of excreted droplets at the tips of cuticular hairs in the glandular area during the period of pheromone production.

Semiochemistry of the Goldeneyed Lacewing Chrysopa oculata: Attraction of Males to a Male-Produced Pheromone

Gas chromatographic-electroantennographic detection (GC-EAD) experiments showed that antennae of males and females of the goldeneyed lacewing, Chrysopa oculata Say (Co. = Chrysopa), consistently responded to four compounds extracted from the abdominal cuticle of males: nonanal, nonanol, nonanoic acid, and (1R*,2S*,5R*,8R*)-iridodial. These compounds were not detected from abdominal cuticle of females. Thoracic extracts of both sexes contained antennal-stimulatory 1-tridecene and EAD-inactive skatole. Chrysopa oculata adults were most sensitive to (1R,2S,5R,8R)-iridodial standard at an EAD-response threshold between 0.1 and 1 pg, which was 10–100 times lower than thresholds for nonanal and nonanoic acid, and up to 10,000 times lower than thresholds for other compounds tested. A similar EAD response pattern was also found in another Chrysopa sp. (Co. quadripunctata Burmeister). In field-trapping experiments, (1R,2S,5R,8R)-iridodial was the only male-specific compound that attracted Co. oculata males. Males also were weakly attracted to (1R,4aS,7S,7aR)-nepetalactol (an aphid sex pheromone component), probably due to the 5% (1R,2S,5R,8R)-iridodial present in the synthetic sample as an impurity. A herbivore-induced plant volatile, methyl salicylate, increased attraction of males to (1R,2S,5R,8R)-iridodial, whereas 1-tridecene was antagonistic. No females were caught in the entire study. Scanning electron micrographs revealed numerous male-specific, elliptical epidermal glands on the 3rd–8th abdominal sternites of Co. oculata, which are likely the pheromone glands. Another lacewing species, Chrysoperla rufilabris (Burmeister) (Cl. = Chrysoperla), did not produce male-specific volatiles or possess the type of gland presumed to produce pheromone in Co. oculata males, but (Z)-4-tridecene was identified as a major antennal-stimulatory compound from thoracic extracts of both sexes of Cl. rufilabris. Thus, (1R,2S,5R,8R)-iridodial (or its enantiomer) is now identified as a male-produced male aggregation pheromone for Co. oculata, the first pheromone identified for lacewings.

Circadian rhythm of sperm release in the gypsy moth, Lymantria dispar: ultrastructural study of transepithelial penetration of sperm bundles

Release of mature bundles of spermatozoa from the testis into the vas deferens is a critical but poorly understood step in male insect reproduction. In moths, the release of sperm bundles is controlled by a circadian clock which imposes a temporal gate on the daily exit of bundles through the terminal epithelium-a layer of specialized epithelial cells separating testis follicles from the vas deferens. The sequence of cellular events associated with the daily cycle of sperm release was investigated by scanning and transmission electron microscopy. In the hours preceding sperm release, there is a solid barrier between the testis and the vas deferens formed by the interdigitation of cytoplasmic processes of adjacent terminal epithelial cells. At the beginning of the sperm release cycle, sperm bundles protrude through this barrier while the terminal epithelial cells change their shape and position relative to the bundles. Subsequently, the cyst cells enveloping the sperm bundles break down and spermatozoa move out of the testis through the exit channels formed between the epithelial cells. Afterwards, cyst cell remnants and other cellular debris are released into the vas deferens lumen, and the epithelial barrier is reconstructed due to phagocytic activity of its cells. These data provide a foundation on which to build an understanding of the cellular mechanisms of clock-controlled sperm release in insects.

Seasonal variation in the structure and red reflectance of leaves from yellow poplar, Red Oak, and Red Maple

Abstract A laboratory goniometer was used to measure the light scattered from leaves as a function of view angle in the principal plane for yellow poplar (Liriodendron tulipifera L.), red oak (Quercus rubra L.), and red maple (Acer rubrum L.). The source was a parallel-polarized helium-neon laser (632.8 nm). Yellow poplar leaves had the highest reflectance of the three species, which may have been due to its shorter palisade cells and more extensive spongy mesophyll. Prior to senescence, there was a significant decrease, but not total extinction, in the reflectance of the beam incident at 60° from nadir on the adaxial (upper) side of the leaves of all three species. This was interpreted as a Brewster angle effect. The reflectance increased as the leaves senesced. The abaxial (lower) side of the leaf did not exhibit the reflectance decrease at the Brewster angle, indicating that multiple reflections were obscuring the effect. The multiple reflections could have been from either the spongy mesophyll or from the abaxial surface (which was rougher than the adaxial). Low-temperature scanning electron microscope (SEM) observations showed differences in the surface wax patterns among the three species but did not indicate a cause of the reflectance changes other than possibly the accumulation and aging of the wax. SEM observations confirmed the greater roughness of the abaxial side of the leaf. This type of information on leaf bidirectional scattering should be useful for linking remote sensing observations with leaf optical properties.

Snow crystal imaging using scanning electron microscopy: I. Precipitated snow

Abstract Low-temperature scanning electron microscopy (SEM) was used to observe precipitated snow crystals. The newly-fallen snow crystals were obtained in storms at Beltsville, Maryland, and at Bearden Mountain near Davis, West Virginia, USA. The snow samples were mounted on modified SEM stubs, frozen in liquid nitrogen, sputter coated with platinum, and imaged with an electron beam. Many types of precipitated snow crystals were observed including hexagonal plates, columns, needles, stellar dendrites, bullets, graupel, and rimed crystals. The SEM techniques that were developed can be used for quantitative measurements of size, shape and structure of crystals. SEM of precipitated snow appears to have direct application for the inference of atmospheric and cloud conditions where the snow crystals formed and travelled to the ground and for the development of a relationship between snow crystal type and snowfall intensity and amount. The SEM technique provides a new procedure to record permanently snow cryst...

Snow crystal imaging using scanning electron microscopy: II. Metamorphosed snow

Abstract Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow crystals and grains obtained in the field. Metamorphosed snow was obtained from seasonal snowpacks in the Colorado Rocky Mountains and in Alaska. The snow samples obtained in snowpits were mounted on modified SEM stubs, frozen in liquid nitrogen, transported in Dewar flasks to the SEM facility, sputter coated with platinum, and imaged with an electron beam. Analysis of a representative set of snow samples revealed examples of metamorphosed stellar crystals, fine snow grains with sintering, rounded and faceted crystals, several types of depth hoar, rounded grains of melt metamorphism, and an ice lens. Some of the crystals exhibiting both rounding and facets indicated that both equitemperature and temperature gradient metamorphism influenced the snowpack. The SEM methods developed are operable in the field and can be used to quantify three-dimensionally size, shape and bonding characteristics of crystals. SEM ...

Raoiella indica (Acari: Tenuipalpidae): an exploding mite pest in the neotropics

Major infestations of the flat mite species Raoiella indica Hirst affecting bananas, palms and other ornamental plants have been reported from the Caribbean islands, Mexico, FL (USA), Venezuela, Colombia and Brazil. Specimens from these localities were examined using traditional light microscopy and low-temperature scanning electron microscopy techniques. While little is known about the biology of this mite, its recent appearance in the Americas in both commercial coconut and banana plantations has raised concerns about its economic impact as an invasive pest.

Relative advantages of low temperature versus ambient temperature scanning electron microscopy in the study of mite morphology

Abstract Low temperature scanning electron microscopy (LTSEM) is an effective technique for studying the morphology of Acari. This study evaluates results from two approaches: ambient temperature scanning electron microscopy (ATSEM) and LTSEM. Four preparation techniques for ATSEM were evaluated. The advantages and disadvantages of the preparation procedures of ATSEM and LTSEM are discussed. In general, LTSEM was found to be superior to ATSEM in the study of mites.