Charles E. Beard

Hydrophobic–hydrophilic dichotomy of the butterfly proboscis

Mouthparts of fluid-feeding insects have unique material properties with no human-engineered analogue: the feeding devices acquire sticky and viscous liquids while remaining clean. We discovered that the external surface of the butterfly proboscis has a sharp boundary separating a hydrophilic drinking region and a hydrophobic non-drinking region. The structural arrangement of the proboscis provides the basis for the wetting dichotomy. Theoretical and experimental analyses show that fluid uptake is associated with enlargement of hydrophilic cuticular structures, the legulae, which link the two halves of the proboscis together. We also show that an elliptical proboscis produces a higher external meniscus than does a cylindrical proboscis of the same circumference. Fluid uptake is additionally facilitated in sap-feeding butterflies that have a proboscis with enlarged chemosensory structures forming a brush near the tip. This structural modification of the proboscis enables sap feeders to exploit films of liquid more efficiently. Structural changes along the proboscis, including increased legular width and presence of a brush-like tip, occur in a wide range of species, suggesting that a wetting dichotomy is widespread in the Lepidoptera.

Butterfly proboscis: combining a drinking straw with a nanosponge facilitated diversification of feeding habits

The ability of Lepidoptera, or butterflies and moths, to drink liquids from rotting fruit and wet soil, as well as nectar from floral tubes, raises the question of whether the conventional view of the proboscis as a drinking straw can account for the withdrawal of fluids from porous substrates or of films and droplets from floral tubes. We discovered that the proboscis promotes capillary pull of liquids from diverse sources owing to a hierarchical pore structure spanning nano- and microscales. X-ray phase-contrast imaging reveals that Plateau instability causes liquid bridges to form in the food canal, which are transported to the gut by the muscular sucking pump in the head. The dual functionality of the proboscis represents a key innovation for exploiting a vast range of nutritional sources. We suggest that future studies of the adaptive radiation of the Lepidoptera take into account the role played by the structural organization of the proboscis. A transformative two-step model of capillary intake and suctioning can be applied not only to butterflies and moths but also potentially to vast numbers of other insects such as bees and flies.

Seasonality of trichomycetes in larval black flies from South Carolina, USA

Trichomycete fungi are common endobionts of aquatic insect larvae, but little is known of their ecology. In this study, the seasonality of trichomycete colonization of larval black flies (Diptera: Simuliidae) was investigated in three streams in northwestern South Carolina. At least eight species of trichomycetes were found in two species of black flies, and 93.8% of 1819 larval black flies examined contained trichomycetes. Significant differences were found in the seasonal prevalence of Harpella melusinae, Simuliomyces microsporus, and Paramoebidium spp. at one of three sites. At this site, the lowest mean prevalence for H. melusinae occurred in winter (67%) versus the other seasons (96–100%), whereas mean prevalence was lowest in summer for Simuliomyces microsporus (1%) versus the other seasons (2–21%) and lowest in summer for P. spp. (9%) versus the other seasons (45–67%). Significant differences in levels of colonization among seasons were not detected. Conjugations of H. melusinae (representing early stages of sexual reproduction) occurred most frequently in the spring and winter (up to 14% of larvae). Sexual reproduction (represented by zygospores) of Legeriomycetaceae occurred most frequently in the spring and fall (up to 17% of larvae).

Prevalence of the trichomycete fungus Harpella melusinae (Harpellales: Harpellaceae) in larval black flies (Diptera: Simuliidae) across a heterogeneous environment.

A total of 2063 mid- to late-instar larval black flies were collected from 64 stream sites in South Carolina and screened for the presence of the trichomycete fungus Harpella melusinae. Sixteen of 18 host species were colonized by H. melusinae on at least one occasion. Prevalence of H. melusinae in larvae of Simulium tuberosum cytospecies “A” was highest in acidic streams with low conductivity, whereas H. melusinae colonized larvae of Simulium verecundum most frequently in slower-moving streams. Ecological conditions, therefore, can serve as predictors of the prevalence of H. melusinae. Prevalence in host larvae was significantly lower in the Piedmont ecoregion than in the Mountain ecoregion. Prevalence did not differ in the host species S. verecundum across ecoregions, suggesting that different prevalences among host species might indicate some host preference. The prevalence of H. melusinae differed significantly between two univoltine host species (Simulium venustum and Prosimulium magnum) at the same site but not between two multivoltine host species (S. tuberosum cytospecies “FG” and S. tuberosum cytospecies “CDE”), suggesting that host life history could be important in determining fungal prevalence.

The microdistribution of the trichomycete Smittium culisetae in the hindgut of the black fly host Simulium vittatum

We examined the distribution of hyphae of the trichomycete fungus Smittium culisetae (Harpellales: Legeriomycetaceae) in the hindgut of a larval black fly (Simulium vittatum, cytospecies IS-7) by analyzing its prevalence and relative abundance. Hyphal prevalence was highest in the posterior colon (93.1%) and rectum (86.3%), with low prevalence (12.0%) in the anterior colon. Relative abundance of hyphae was highest in the posterior colon, followed by the rectum; relative abundance of hyphae in the anterior colon was lower. Hyphae of S. culisetae were not observed in the pylorus. We used a novel method of quantifying the relative abundance of S. culisetae in the host hindgut. The hindgut was observed with an ocular grid, and abundance was expressed as the ratio of grids occupied by hyphae to the number of grids occupied by hindgut.

Paradox of the drinking-straw model of the butterfly proboscis

Fluid-feeding Lepidoptera use an elongated proboscis, conventionally modeled as a drinking straw, to feed from pools and films of liquid. Using the monarch butterfly, Danaus plexippus (Linnaeus), we show that the inherent structural features of the lepidopteran proboscis contradict the basic assumptions of the drinking-straw model. By experimentally characterizing permeability and flow in the proboscis, we show that tapering of the food canal in the drinking region increases resistance, significantly hindering the flow of fluid. The calculated pressure differential required for a suction pump to support flow along the entire proboscis is greater than 1 atm (~101 kPa) when the butterfly feeds from a pool of liquid. We suggest that behavioral strategies employed by butterflies and moths can resolve this paradoxical pressure anomaly. Butterflies can alter the taper, the interlegular spacing and the terminal opening of the food canal, thereby controlling fluid entry and flow, by splaying the galeal tips apart, sliding the galeae along one another, pulsing hemolymph into each galeal lumen, and pressing the proboscis against a substrate. Thus, although physical construction of the proboscis limits its mechanical capabilities, its functionality can be modified and enhanced by behavioral strategies.

Ecology of Symbiotes of Larval Black Flies (Diptera: Simuliidae): Distribution, Diversity, and Scale

ABSTRACT Symbioses are major drivers in ecology and evolution. Although nearly omnipresent in flowing waters, they remain poorly studied in these systems. To examine fundamental aspects of the ecology of symbioses in flowing-water systems, we use larval black flies as hosts and various fungi, nematodes, and protists as symbiotes, focusing on aspects of distribution, diversity, and scale. Most symbiotes of larval black flies are considered parasitic, although the dynamic nature of the relationship is becoming apparent for some systems in which it shifts along a continuum involving commensalism, mutualism, and parasitism. Perspective also is moving from a pairwise view of symbiotic associations to a multispecies network of interactions. Distributions of symbiotes are related to scale-dependent processes that influence the hosts and the stream habitats of the hosts; thus, characteristics of streams, as well as hosts, can be useful in predicting spatial patterns of symbiotes. As the taxonomy of symbiotes improves, so too does the understanding of ecological relationships of symbiosis, such as host specificity and patterns of diversity along spatial and temporal scales.

Structure of the lepidopteran proboscis in relation to feeding guild.

Most butterflies and moths (Lepidoptera) use modified mouthparts, the proboscis, to acquire fluids. We quantified the proboscis architecture of five butterfly species in three families to test the hypothesis that proboscis structure relates to feeding guild. We used scanning electron microscopy to elucidate the fine structure of the proboscis of both sexes and to quantify dimensions, cuticular patterns, and the shapes and sizes of sensilla and dorsal legulae. Sexual dimorphism was not detected in the proboscis structure of any species. A hierarchical clustering analysis of overall proboscis architecture reflected lepidopteran phylogeny, but did not produce a distinct group of flower visitors or of puddle visitors within the flower visitors. Specific characters of the proboscis, nonetheless, can indicate flower and nonflower visitors, such as the configuration of sensilla styloconica, width of the lower branches of dorsal legulae, presence or absence of dorsal legulae at the extreme apex, and degree of proboscis tapering. We suggest that the overall proboscis architecture of Lepidoptera reflects a universal structural organization that promotes fluid uptake from droplets and films. On top of this fundamental structural organization, we suggest that the diversity of floral structure has selected for structural adaptations that facilitate entry of the proboscis into floral tubes. J. Morphol. 277:167–182, 2016.

Bionomics, axenic culture, and substrate-related variation in trichospores of Smittium megazygosporum

Smittium megazygosporum, previously known only from southern France, was collected in South Carolina, USA, indicating a Holarctic distri- bution. An axenic culture was obtained from a black fly (Diptera, Simuliidae) that was probably a spurious host. The holdfast, with a refractive secreted-material base, is described for the first time, and verticillate branching in vegetative growth is confirmed. Zygo- spores, the largest known for the genus, were found in chironomids co-occurring with the black fly host. Trichospore sizes varied significantly depending on the host and medium in which they grew. This host- related size variation could have consequences for species diagnoses of Smittium that often are based on

Zygospores of selected Trichomycetes in larval Diptera of the families Chironomidae and Simuliidae

The midgut-inhabiting fungi (Harpellaceae) Harpella melusinae and Stachylina pedifer were induced to form zygospores, using an application of a pH 10 potassium hydroxide solution with culture media. The previously unknown zygospores of S. pedifer are borne perpendicular to the zygosporophore, as in Harpella melusinae. The zygospores of the hindgut-inhabiting species Smittium coloradense, borne obliquely to the zygosporophore (in vivo), are described for the first time.