Skipper Butterflies Research Articles

The compound eye of Parnara guttata (Insecta, Lepidoptera, Hesperiidae): Fine structure of the ommatidium

The fine structure of an ommatidium of a skipper butterfly, Parnara guttata, has been studied using the electron microscope. Each ommatidium has nine retinula cells, which were classified into three groups: two distal, six medial and one basal retinula cells. The rhabdomeres of the distal retinula cells are localized in the distal part of the rhabdom, while those of the six medial retinula cells appear throughout most of the rhabdom. The rhabdomere of the basal retinula cell occupies only the basal part of the rhabdom. The rhabdomeres of four medial cells are constructed of parallel microvilli, while fan-like microvilli form the rhabdomeres of other two medial retinula cells. The distal and basal retinula cells have rhabdomeres consisting of both parallel and fan-like microvilli. This is the first time the construction of the rhabdomeres of the distal and basal retinula cells has been described in such fine detail for a skipper butterfly. Nine retinula cell axons of each ommatidium extend to the first neuropile of the optic lobe, the lamina ganglionaris. No difference was found in the number of retinula cells of an ommatidium or the shape of the rhabdom between the dorsal and ventral regions of the compound eye.

Ecology and Declining Status of the Silver-Spotted Skipper Butterfly (Hesperia comma) in Britain

(1) A survey was made of all British colonies of Hesperia comma, which revealed that it had declined to about forty-nine populations, most of which were small. (2) Adult H. comma proved to be very particular when egg-laying. They preferred small Festuca ovina plants that were largely surrounded by bare ground or scree, and which also grew in sheltered sunspots. Most F. ovina growing on most sites were rejected as unsuitable, and the adult population density of H. comma was correlated with how closely the sward approached the ideal structure for egg-laying. (3) Most sites that had lost H. comma still contained abundant F. ovina, but were too overgrown to be suitable for breeding. Most extinctions of H. comma occurred during a twenty-year period, when many unfertilized downs in Britain became overgrown after rabbits were killed by myxomatosis. (4) The habitat on several former sites has improved for H. comma since the late 1970s, due to a recovery by rabbits and some sheep stocking on abandoned downs. To date, H. comma has only spread to re-occupy sites that were within 4 km of existing colonies. The natural recolonization of other sites may take decades or centuries. (5) Conservationists could dramatically improve the status of H. comma by making artificial introductions to unoccupied sites. A high proportion of the existing colonies are already on nature reserves, but one-quarter of 'protected' populations had become extinct by 1982, due to inadequate grazing.

Ultrastructural organization of the basal lamina in insect Malpighian tubules

Relatively little is known about the structure or function of the basal lamina in insect cells. I report here the ultrastructural organization of the basal lamina in Malpighian tubule yellow region primary cells of larval stage skipper butterflies (Calpodes ethlius). The Malpighian tubules selectively filter the blood and produce a primary urine which flows down the tubule lumen into the alimentary canal for excretion. The basal lamina provides the only barrier between the Malpighian tubule cells and the blood which freely circulates within the open body cavity and it may therefore regulate which molecules and ions gain access to the tubule cells. As a first step in these studies on the structure, composition and function of the basal lamina in insect cells the ultrastructure of the basal lamina in Calpodes Malpighian tubules after conventional TEM tissue processing and poststaining has been compared with that observed following en bloc staining with a variety of electron dense stains and probes with specificity for basal lamina components.

The resolving power of diurnal superposition eyes measured with an ophthalmoscope

1. The eyes of skipper butterflies and agaristid moths are of the superposition type, and they have fully open pupils in daylight. The quality of the images in these eyes was examined with an ophthalmoscopic technique. Images of objects shown to the eye in a plane at infinity could be photographed on the retina. 2. In the agaristid moths the retinal mosaic was clearly visible, using the eyes' own optics. In the skippers it was just visible (Fig. 4). 3. By projecting lines and gratings into the field of view of the eyes it was possible to measure the double-pass line-spread functions (Figs. 9 and 10) and the modulation transfer functions (Figs. 11–13) of the optics. Allowing for the effects of the retinal mosaic itself, these functions were used to obtain the point-spread functions for a single passage of light through the optical system. 4. The agaristidPhalanoides tristifica has an inter-rhabdom angle (Δϑ) of 1.90°, and the half-width of the point-spread function (Δϱgl) of the whole superposition pupil is 1.28°. This is only slightly wider than the half-width of the Airy disc produced by diffraction at a single 24 μm facet (1.19°). The acceptance angle of the single rhabdom (Δϱ) is 1.58° which is in agreement with the best values (1.6°) obtained electrophysiologically. In the skipperOcybadistes walkeri Δϑ is almost the same (1.95°), but the image is less well resolved.Δϱgl is 1.93°, andΔϱ is 2.18°. It is concluded that diffraction limited superposition eyes can and do exist. 5. In both species the point-spread functions have ‘tails’ of low amplitude, but with half-widths 2–3 times that of the central ‘image-forming’ Gaussian (Fig. 10). This ‘flare’ reduces the image contrast at the sampling frequency of the mosaic (1/2Δϑ) from 64% to 46% (Fig. 15). Stray light is a potentially serious problem in superposition eyes. 6. Although the resolution of apposition and superposition eyes in diurnal lepidopterans is similar, the superposition eyes are much more sensitive. When viewing an extended scene the skipper or agaristid rhabdoms should each capture about 100 times as many photons as a rhabdom in a butterfly eye. This increased sensitivity is partly the result of the lower F-number of the superposition eyes, and partly the wider diameter of the reflecting cylinders that trap light for the rhabdoms they enclose. 7. The poor resolving power of nocturnal superposition eyes is more likely to result from their unsheathed rhabdoms than from poor optics. There seems no obvious reason why sheathed rhabdoms should be confined to diurnal superposition eyes.

Retinular fine structure in compound eyes of diurnal and nocturnal sphingid moths

Retinular fine structure has been compared in the superposition compound eyes of three sphingid moths, one nocturnal, Cechenena, and two diurnal, Cephonodes and Macroglossum. Cechenena and Cephonodes have tiered retinas with three kinds of retinular cells: two distal, six regular and one basal. The distal retinular cells in Cechenena are special in having a complex partially intracellular rhabdomere not present in Cephonodes. Macroglossum lacks the distal retinular cell. In Cephonodes a unique rhabdom type, formed by the six regular retinular cells in the middle region of the retinula, is divided into three separate longitudinal plates arranged closely parallel to one another. Their constituent microvilli are consequently all nearly unidirectional. The ratio of rhabdom volume to retinular cell volume in the two diurnal sphingids is 10-27%; this is about the same as that (25%) of skipper butterflies, but significantly smaller than in the nocturnal Cechenena (60%). In the diurnal sphingids retinular cell membranes show elongate meandering profiles with septate junctions between adjacent retinular cells. From the comparative fine structure of their eyes the diurnal sphingids and the skippers would appear to be phylogenetically closely related.

Developmental changes in Malpighian tubule fluid transport

Developmental changes in Malpighian tubule fluid transport were studied using in vitro and in situ preparations from timed larval, pupal and adult skipper butterflies ( Calpodes ethlius). The ability to transport fluid and the rate of fluid secretion depend on the developmental stage and the physiological state. Larval tubules are permanently switched on, do not require a diuretic hormone and transport fluid at an increasing rate as the larvae feed and grow. Fluid transport continues at larval-larval moults but is switched off 24 hr before pupal ecdysis. No secretory activity occurs during the first half of the pupal stage when the tubules are remodelled for adult function. The resumption of fluid transport midway through the pupal stage is in preparation for a rapid diuresis at adult emergence. High rates of fluid secretion are associated with feeding or drinking in adults.

The organization of perpendicular fibre pathways in the insect optic lobe.

High resolution serial photomicrography has been used to plot the axonal projection patterns between retina, lamina and medulla in the optic lobes of various insects with differing ommatidial receptor arrangements. Observations are reported on the cabbage white and skipper butterflies, the bee, locust, fly, backswimmer and waterbug. The patterns of these fibre pathways have previously eluded non-rigorous analyses primarily because of their physical dimensions but are revealed in this study to have striking precision and uniformity between species when examined at the level of individually identifiable cells. Axon bundles of the tracts between retina and lamina or lamina and medulla project between a single ommatidium and its corresponding lamina cartridge or between corresponding lamina and medulla cartridges. Lateral interweaving of axons between adjacent bundles is absent. The bundles preserve the retinotopic order within their total array, so transferring the pattern of retinulae directly upon the lamina and thence after horizontal inversion in the chiasma upon the medulla. Within the lamina neuropile on the other hand the trajectories of the individual terminals from a bundle have patterns which are species-specific, sometimes involving lateral divergences. In species with open-rhabdomere ommatidia the terminals distribute to a group of lamina cartidges with a pattern which resembles the receptor pattern in the overlying ommatidium. In species with fused-rhabdome ommatidia the terminals of a single retinula behave less interestingly and all enter the same cartridge, within which, again, each occupies a position related to its cell body position within the retinula. Long visual fibres in both eye types penetrate the lamina and terminate in the particular medulla cartridge that connects with the lamina cartridge underlying their ommatidium. The perpendicular fibre pathways therefore project the visual field exactly upon the medulla in all species while the lack of interweaving between adjacent fibre bundles precludes their involvement in lateral interactions between pathways with differing visual axes. Uniformity of these projection patterns between cell layers and species differences in retinular terminal locations in the lamina can be correlated with different modes of axon growth between and within neuropile layers during optic lobe neurogenesis. Further discussion surrounds the question of which particular receptors give rise to which type of axon, for which no clear generalization has yet emerged.

Interference Competition Between a Hummingbird (Amazilia tzacatl) and Skipper Butterflies (Hesperiidae)

Observations of the hummingbird Amazilia tzacatl and skipper butterflies (Hesperiidae) at the flowering shrub Stachytarpheta jamaicensis showed that hummingbird foraging patterns reflected the distribution of flowers on the hedge while butterfly foraging patterns did not. The hummingbird was repeatedly observed to chase butterflies from middle and upper portions of the hedge. Removal of the hummingbird was followed by an immediate change in the distribution of the visits of the hesperid butterfly. Interference through interspecific aggression is suggested as the mechanism for vertical partitioning of this common food resource. INTERSPECIFIC COMPETITION has been difficult to demonstrate in nature in spite of its pervasive importance in theoretical discussions of community composition and stability. Miller (1967) defined interspecific as the active demand by members of two or more species at the same trophic level for a common resource requirement that is actually or potentially limiting. He further elaborated on two mechanisms of competition. In exploitative competition, success of one species is determined by the efficiency with which it utilizes the common resource once it has gained access to it. In competition, one species achieves success by limiting the access of competitors to the common resource. As part of this limitation of access, some form of space is substituted for a resource and is the proximate object of competition (Miller 1969). We believe that demonstration of should show (1) that two or more species use a common resource, (2) that distributions of competing species are mutually exclusive, (3) that removal of one species influences the distribution of the other species, and (4) what the mechanism is by which one species excludes the other. Experimental field demonstrations of interference in conformance with the above criteria are rare. While strong circumstantial evidence for the phenomenon exists in rodents (see Miller 1967, Grant 1972), diverse food sources and the secretive nature of the animals render criteria (1) and (4) difficult to assess outside of the laboratory. Connell (1961) showed that barnacles crush competing species and thereby usurp space on the substrate. Menge and Menge (1974) demonstrated interference through direct aggression in two starfish species. Unequivocal demonstrations of interference in terrestrial organisms include interspecific aggression at artificial baits in ants (Yasuno 1965, Carroll and Janzen 1973) and Trigoia bees (Johnson and Hubbell 1974). Kikuchi (1963) showed interspecific dominance at garden plants in several species of pollinators. In this paper we present an instance of interference between the rufous-tailed hummingbird (Amazilia tzacatl) and skipper butterflies (Hesperiidae) in a system uniquely valuable because of its potential for both observations of interactions between individuals and precise measurement of food resources. While hummingbird territoriality is well documented (Stiles and Wolf 1970, Cody 1968), experimental methods have not been used to determine the precise nature of this behavior.

The chromosomes of skipper butterflies from southwestern North America (Lepidoptera, Hesperiidae).

Chromosome numbers and karyotypic observations are reported for 22 species of Hesperiidae (Pyrginae and Hesperiinae) found in southwestern North America. Characteristic haploid numbers for certain genera are found: Amblyscirtes (N=29), Chiodes (N=31), Erynnis (N=30 or 31), Heliopetes (N=29 or 30), Panoquina (N=29), and Wallengrenia (N=28, 29, 30). Two genera with widely varying chromo-some numbers are Achalarus (N=16, 29) and Pyrgus (N=28, 32). The pheno-typically unusual Celotes nessus (Edwards) is shown to be cytogenetically distinct from all other Pyrginae with a haploid number of 13-14, the lowest number reported to date for the family Hesperiidae.

Evolution in Skipper Butterflies of the Genus Erynnis, by John M. Burns. University of California Publications in Entomology, Vol. 37, University of California Press, Berkeley and Los Angeles, Cal., 1964. pp. iv + 214, 22 figs., 1 pl. Price 5.00 U.S. dollars.

Evolution in Skipper Butterflies of the Genus Erynnis, by John M. Burns. University of California Publications in Entomology, Vol. 37, University of California Press, Berkeley and Los Angeles, Cal., 1964. pp. iv + 214, 22 figs., 1 pl. Price 5.00 U.S. dollars.

Evolution in Skipper Butterflies of the Genus Erynnis

Evolution in Skipper Butterflies of the Genus Erynnis

Book Notices

University of California Publications in Entomology. Vol. 3 1. Studies of fossiliferous amber arthropods of Chiapas, Mexico. By Alexander Petrunkevitch and others.University of California Publications in Entomology, Vol. 36. The Nearctic Parnopes with an analysis of the male genitalia in the genus. By Allan D. Telford.University of California Publications in Entomology, Vol. 37. Evolution in skipper butterflies of the genus Erynnis, by John M. Bums.University of California Publications in Entomology, Vol. 38. The North American sawflies of the genus Pamphilius (Hymenoptera: Pamphiliidae). By Woodrow W. Middlekauff.