Diverse material properties and morphology of moth proboscises relates to the feeding habits of some macromoth and other lepidopteran lineages

Insects have evolved unique structures that host a diversity of material and mechanical properties, and the mouthparts (proboscis) of butterflies and moths (Lepidoptera) are no exception. Here, we examined proboscis morphology and material properties from several previously unstudied moth lineages to determine if they relate to flower visiting and non-flower visiting feeding habits. Scanning electron microscopy and three-dimensional imaging were used to study proboscis morphology and assess surface roughness patterns on the galeal surface, respectively. Confocal laser scanning microscopy was used to study patterns of cuticular autofluorescence, which was quantified with colour analysis software. We found that moth proboscises display similar autofluorescent signals and morphological patterns in relation to feeding habits to those previously described for flower and non-flower visiting butterflies. The distal region of proboscises of non-flower visitors is brush-like for augmented capillarity and exhibited blue autofluorescence, indicating the possible presence of resilin and increased flexibility. Flower visitors have smoother proboscises and show red autofluorescence, an indicator of high sclerotization, which is adaptive for floral tube entry. We propose the lepidopteran proboscis as a model structure for understanding how insects have evolved a suite of morphological and material adaptations to overcome the challenges of acquiring fluids from diverse sources.

Adaptations for gas exchange enabled the elongation of lepidopteran proboscises

The extensive biodiversification of butterflies and moths (Lepidoptera) is partly attributed to their unique mouthparts (proboscis [Pr]) that can span in length from less than 1 mm to over 280 mm in Darwin's sphinx moths. Lepidoptera, similar to other insects, are believed to inhale and exhale respiratory gases only through valve-like spiracles on their thorax and abdomen, making gas exchange through the narrow tracheae (Tr) challenging for the elongated Pr. How Lepidoptera overcome distance effects for gas transport to the Pr is an open question that is important to understanding how the Pr elongated over evolutionary time. Here, we show with scanning electron microscopy and X-ray imaging that distance effects on gas exchange are overcome by previously unreported micropores on the Pr surface and by superhydrophobic Tr that prevent water loss and entry. We find that the density of micropores decreases monotonically along the Pr length with the maxima proportional to the Pr length and that micropore diameters produce a Knudsen number at the boundary between the slip and transition flow regimes. By numerical estimation, we further show that the respiratory gas exchange for the Pr predominantly occurs via diffusion through the micropores. These adaptations are key innovations vital to Pr elongation, which likely facilitated lepidopteran biodiversification and the radiation of angiosperms by coevolutionary processes.

Comparative Material and Mechanical Properties among Cicada Mouthparts: Cuticle Enhanced with Inorganic Elements Facilitates Piercing through Woody Stems for Feeding

Adult cicadas pierce woody stems with their mouthparts to feed on xylem, suggesting the presence of cuticular adaptations that could increase hardness and elastic modulus. We tested the following hypotheses: (a) the mouthpart cuticle includes inorganic elements, which augment the mechanical properties; (b) these elements are abundant in specific mouthpart structures and regions responsible for piercing wood; (c) there are correlations among elements, which could provide insights into patterns of element colocalization. We used scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to investigate mouthpart morphology and quantify the elemental composition of the cuticle among four cicada species, including periodical cicadas (Magicicada sp.). Nanoindentation was used to quantify hardness and elastic modulus of the mandibles. We found 12 inorganic elements, including colocalized manganese and zinc in the distal regions of the mandible, the structure most responsible for piercing through wood; nanoindentation determined that these regions were also significantly harder and had higher elastic modulus than other regions. Manganese and zinc abundance relates to increased hardness and stiffness as in the cuticle of other invertebrates; however, this is one of the first reports of cuticular metals among insects with piercing-sucking mouthparts (>100,000 described species). The present investigation provides insight into the feeding mechanism of cicadas, an important but understudied component of their life traits.

Mouthpart adaptations of antlion larvae facilitate prey handling and fluid feeding in sandy habitats

Antlion larvae are fluid-feeding ambush predators that feed on arthropods trapped in their funnel-shaped pits built in sandy habitats; however, details are lacking about their feeding mechanism. Here we tested the hypothesis that the antlion, Myrmeleon crudelis, has adaptations that facilitate fluid feeding in sandy habitats. We measured contact angles of water droplets and used the capillary-rise technique to assess mouthpart wettability. A structural organization was discovered that provides a hydrophobic-hydrophilic wetting dichotomy that would simultaneously support self-cleaning and fluid uptake and is enabled by antiparallel movements of the maxillae. The mouthparts also are augmented by their mechanical properties, including maxillae and mandible tips that might be heavily sclerotized, as determined by confocal microscopy, which likely facilitate piercing prey. Our findings provide insight on how antlion larvae have overcome the challenges of fluid feeding in sandy habitats, which likely contributed to their success and widespread distribution.

Feeding behavior of honey bees on dry sugar

The feeding habits of insects can be influenced by food abundance, nutrition, physical forces, and many other variables, which is why this topic is multidisciplinary and perennially fascinating. Although honey bees primarily feed on liquid nectar, they also can feed on dry sugar; however, the feeding mechanism for feeding on dry substances by a primarily fluid-feeding insect remains unexplored. We observed that, when honey bees are accessible to both dry sugar and liquid nectar, they prefer to feed on the latter. To elucidate the diet preference, we conducted a comparative study between feeding on dry-sugar and drawing up liquid-nectar, from the tongue kinematics and dynamic configuration, friction force, glossal durability, and feeding efficiency. Using a high-speed camera, we discovered that the hairy tongue of the honey bee uses back-and-forth movements to furrow a groove on pieces of dry sugar, with saliva simultaneously dissolving the sugar. We found that the lapping frequency of the tongue on dry sugar reduces from 4.5 Hz to 1.6 Hz when compared to feeding on the liquid diet; a 64% decrease in average tongue speed. Through tribological tests, we revealed that the friction forces when feeding on dry sugar is approximately 5 times that of dipping nectar, and the glossal hairs wear 4 times faster when feeding on dry sugar compared to the sucrose solution. We built a mathematical model to bridge the gap between energy intake rate and tongue dynamics of these two feeding modes. The theoretical net energy intake rate of feeding on dry sugar is 50% lower than when feeding on sucrose solutions. Both experimental and theoretical discoveries revealed that although honey bees can feed on dry substances, natural selection has forged their tongue structures primarily for a liquid diet. This study combined behavioral and mechanical tests with mathematical modeling, which highlights the advantages of using multidisciplinary approaches for uncovering the feeding physiology of insects.

An augmented wood-penetrating structure: Cicada ovipositors enhanced with metals and other inorganic elements

Few insect species are as popular as periodical cicadas (Magicicada spp.). Despite representing an enormous biomass and numbers that exceed 370/m² during mass emergences, the extended time period of the underground nymphal stages (up to 17 years) complicates investigations of their life history traits and ecology. Upon emergence, female cicadas mate and then use their ovipositors to cut through wood to lay their eggs. Given the ability to penetrate into wood, we hypothesized that the ovipositor cuticle is augmented with inorganic elements, which could increase hardness and reduce ovipositor fracturing. We used scanning electron microscopy and energy dispersive x-ray spectroscopy to evaluate the material properties of ovipositors of four cicada species, including three species of periodical cicadas. We found 14 inorganic elements of the cuticle, of which P, Ca, Si, Mg, Na, Fe, Zn, Mn, Cl, K, and S show the highest concentrations (%wt) near the apex of the ovipositor, where other structural modifications for penetrating wood are present. To the best of our knowledge, this is the first report of metal deposits in the cuticle of true bugs (Hemiptera, >80,000 described species).

A quick tongue: older honey bees dip nectar faster to compensate for mouthpart structure degradation

The western honey bee, Apis mellifera L. (Hymenoptera), is arguably the most important pollinator worldwide. While feeding, A. mellifera uses a rapid back-and-forth motion with its brush-like mouthparts to probe pools and films of nectar. Due to the physical forces experienced by the mouthparts during the feeding process, we hypothesized that the mouthparts acquire wear or damage over time, which is paradoxical, because it is the older worker bees that are tasked with foraging for nectar and pollen. Here, we show that the average length of the setae (brush-like structures) on the glossa decreases with honey bee age, particularly when feeding on high-viscosity sucrose solutions. The nectar intake rate, however, remains nearly constant regardless of age or setae length (0.39±0.03 µg/s for honey bees fed a 45% sucrose solution and 0.48±0.05 µg/s for those fed a 35% sucrose solution). Observations of the feeding process with high-speed video recording revealed that the older honey bees with shorter setae dip nectar at a higher frequency. We propose a liquid transport model to calculate the nectar intake rate, energy intake rate and the power to overcome viscous drag. Theoretical analysis indicates that A. mellifera with shorter glossal setae can compensate both nectar and energy intake rates by increasing dipping frequency. The altered feeding behavior provides insight into how A. mellifera, and perhaps other insects with similar feeding mechanisms, can maintain a consistent fluid uptake rate, despite having damaged mouthparts.

The Ingestion of Fluorescent, Magnetic Nanoparticles for Determining Fluid-uptake Abilities in Insects

Fluid-feeding insects ingest a variety of liquids, which are present in the environment as pools, films, or confined to small pores. Studies of liquid acquisition require assessing mouthpart structure and function relationships; however, fluid uptake mechanisms are historically inferred from observations of structural architecture, sometimes unaccompanied with experimental evidence. Here, we report a novel method for assessing fluid-uptake abilities with butterflies (Lepidoptera) and flies (Diptera) using small amounts of liquids. Insects are fed with a 20% sucrose solution mixed with fluorescent, magnetic nanoparticles from filter papers of specific pore sizes. The crop (internal structure used for storing fluids) is removed from the insect and placed on a confocal microscope. A magnet is waved by the crop to determine the presence of nanoparticles, which indicate if the insects are able to ingest fluids. This methodology is used to reveal a widespread feeding mechanism (capillary action and liquid bridge formation) that is potentially shared among Lepidoptera and Diptera when feeding from porous surfaces. In addition, this method can be used for studies of feeding mechanisms among a variety of fluid-feeding insects, including those important in disease transmission and biomimetics, and potentially other studies that involve nano- or micro-sized conduits where liquid transport requires verification.

Jamaica's Critically Endangered Butterfly: A Review of the Biology and Conservation Status of the Homerus Swallowtail (Papilio (Pterourus) homerus Fabricius)

The Homerus swallowtail, Papilio (Pterourus) homerus Fabricius, is listed as an endangered species and is endemic to the Caribbean island of Jamaica. The largest butterfly in the Western Hemisphere, P. homerus once inhabited seven of Jamaica's 14 parishes and consisted of at least three populations; however, now only two stronghold populations remain, a western population in the rugged Cockpit Country and an eastern population in the Blue and John Crow Mountains. Despite numerous studies of its life history, much about the population biology, including estimates of total numbers of individuals in each population, remains unknown. In addition, a breeding program is needed to establish an experimental population, which could be used to augment wild populations and ensure the continued survival of the species. Here, we present a review of the biology of P. homerus and recommendations for a conservation plan.

Mouthpart conduit sizes of fluid-feeding insects determine the ability to feed from pores

Fluid-feeding insects, such as butterflies, moths and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here, we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle. In addition, the ability to feed on the liquids collected from pores depends on a relationship between the diameter of the mouthpart conduits and substrate pore size diameter; insects with mouthpart conduit diameters larger than the pores cannot successfully feed, thus there is a limiting substrate pore size from which each species can acquire liquids for fluid uptake. Given that natural selection independently favoured mouthpart architectures that support these methods of fluid uptake (Diptera and Lepidoptera share a common ancestor 280 Ma that had chewing mouthparts), we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling trace amounts of fluids from porous surfaces.

Mouthpart separation does not impede butterfly feeding

The functionality of butterfly mouthparts (proboscis) plays an important role in pollination systems, which is driven by the reward of nectar. Proboscis functionality has been assumed to require action of the sucking pump in the butterfly's head coupled with the straw-like structure. Proper proboscis functionality, however, also is dependent on capillarity and wettability dynamics that facilitate acquisition of liquid films from porous substrates. Due to the importance of wettability dynamics in proboscis functionality, we hypothesized that proboscides of eastern black swallowtail (Papilio polyxenes asterius Stoll) (Papilionidae) and cabbage butterflies (Pieris rapae Linnaeus) (Pieridae) that were experimentally split (i.e., proboscides no longer resembling a sealed straw-like tube) would retain the ability to feed. Proboscides were split either in the drinking region (distal 6-10% of proboscis length) or approximately 50% of the proboscis length 24 h before feeding trials when butterflies were fed a red food-coloring solution. Approximately 67% of the butterflies with proboscides split reassembled prior to the feeding trials and all of these butterflies displayed evidence of proboscis functionality. Butterflies with proboscides that did not reassemble also demonstrated fluid uptake capabilities, thus suggesting that wild butterflies might retain fluid uptake capabilities, even when the proboscis is partially injured.

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.

Control of Cimex lectularius using heat combined with dichlorvos resin strips

Successful management of the bed bug, Cimex lectularius L. (Hemiptera: Cimicidae), is difficult because of its pesticide resistance, which can allow a reduction in population, but not elimination. We evaluated the effect of heat and/or air circulation on the efficacy of dichlorvos resin strips in the control of bed bugs. Treatments were performed in unoccupied dormitory rooms and consisted of dichlorvos resin strips containing 18.6% active ingredient, the same strips + fan, and strips + fan + heat. The mortality of recently fed bed bugs and weight loss of the dichlorvos strips were evaluated over 7 days. Dichlorvos resin strips killed bed bugs and eggs in just over 7 days. The addition of a fan or a fan + heat decreased time to 100% mortality to 3 days and 36 h, respectively. Eggs located in treated rooms did not hatch. Resin strips in the strips + fan treatment and the strips + fan + heat treatment volatilized 10 and 70 times, respectively, faster than strips in the strips-only treatment. The addition of heat in treatments with dichlorvos resin strips enhances the overall efficacy of the volatile insecticide and reduces the time required to eliminate live bed bugs and eggs.

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.

A case study of Megaselia scalaris (Diptera: Phoridae) causing ocular myiasis in a western hognose snake

Late instar larvae of the scuttle fly, Megaselia scalaris Loew, were found near the right eye of a live captive-reared western hognose snake, Heterodon nasicus Baird and Girard. Dissection and removal of the snake's dorsal cranial bones revealed tissue degradation of the infected eye, the optic nerve, and the brain case; we suggest that these factors contributed to the death of this snake. This case study further demonstrates the opportunistic behavior of M. scalaris.

Expression of a unique helios isoform in human leukemia cells

The purpose of the present study was to characterize the human Helios gene products expressed in leukemia cells. A 3.5 kb human Helios cDNA clone was isolated from a human T-cell cDNA library derived from the human T-acute lymphoblastic leukemia (ALL) cell line JURKAT. This cDNA clone had a unique open reading frame (ORF) encoding a novel 304 amino acid (AA) peptide, which was designated as Helios 3. The sequence of the 289 AA C-terminal portion of Helios 3 downstream of V-16 is identical to the corresponding sequence found in Helios 1 and 2 and contains two zinc fingers. By contrast, the 15 AA N-terminal portion of Helios 3 is unique and does not contain the N-terminal zinc finger motifs that are conserved in Helios 1 and 2 as well as other previously identified members of the Ikaros family. Southern blot analysis of genomic DNA fragments of the human Helios gene locus showed that Helios 3 is encoded by the same genomic locus as Helios 1 and 2. The expression of Helios 3 mRNA was not restricted to T-lineage ALL cells or another immunophenotypically distinct subset of leukemias. Helios 3 mRNA was expressed in freshly obtained primary leukemic cells from six of 15 children with newly diagnosed ALL. Helios 3 exhibited a unique protein interaction profile via its N-terminal portion, which may have biological significance in pathogenesis of human leukemias.