External Mouthparts Research Articles

Comparative Morphology of the Mouthparts in Three Predatory Stink Bugs (Heteroptera: Asopinae) Reveals Feeding Specialization of Stylets and Sensilla.

Simple SummaryAs the only predatory group in the family Pentatomidae, Asopinae are a diverse group of specialized soft-bodied insect predators, which have the potential for use in controlling pests of orchards, forests, and field crops. However, the feeding behavior remains poorly known for Asopinae, especially how the mouthpart structures relate to various functions in feeding. The fine structure of the mouthparts, including distribution and abundance of receptor sensilla, was observed in three species of Asopinae using scanning electron microscopy and structural details are described for the first time. The morphology of the mouthparts is similar to those of other Heteroptera. The four-segmented labium and labrum in all studied species have fourteen types of sensilla. Unlike phytophagous pentatomids, two types of olfactory sensilla with nanopores (St1, Sb3) were observed in these three predatory insects, which probably function to locate prey by smell. In predatory stink bugs, each mandibular stylet tip has five irregular teeth and three long, pointed hooks; the apices of the right maxilla have small teeth and few short barbs along the edge of the food canal. The structure and function of the mouthparts are adapted for predatory feeding in the three studied species. The detailed structure of the predatory pentatomid’s mouthparts shown in this study can provide more data for the morphological differentiation of the mouthparts in the future.Mouthpart structures were observed in three species of Asopinae using scanning electron microscopy to investigate their morphological disparity. The examined species attack mainly slow-moving, soft-bodied insects, primarily larval forms of the Lepidoptera, and are the natural enemies of many pests. This is the first detailed description of their external mouthparts. The triangular and elongated labrum and four-segmented tube-like labium are longer in Picromerus species (Picromerus bidens (Linnaeus, 1758) and Picromerus lewisi Scott, 1874 than in Cazira bhoutanica Schouteden, 1907. The labrum of P. lewisi and C. bhoutanica appear to be equipped with olfactory sensilla basiconica Sb3, a special type of sensilla with nanopores. The labium surface in all studied species bears 14 types of sensilla (St1–St4, Sb1–7, Sst, Sca1–2). A new characteristic of sensilla trichodea is represented in sensillum St1; in both Picromerus species, it is classified as an olfactory sensillum with nanopores. The tripartite apex of the labium consists of two lateral lobes and a central membranous lobe having microtrichial extensions. Each lobe has one sensory field, including sensilla basiconica (Sb7), sensilla styloconica (Sst), and sensilla trichodea (St4). In the three studied predatory stink bugs, each mandibular stylet tip has five irregular teeth and three long, pointed hooks. The two opposing maxillae, which are held together by a tongue-and-groove system, form a food canal and a salivary canal. The apices of the right maxilla have small teeth and few short barbs along the edge of the food canal. In P. bidens and P. lewisi, there are 5 teeth, while in C. bhoutanica there are 2. Based on structural differences, we inferred that the hook-shaped mandibular teeth, right maxilla with small teeth, and few short barbs along edge of the food canal are more adapted for a predatory lifestyle. Predatory stink bugs use sharp recurved hooks and irregular teeth penetrating, tearing, or filing devices that aid in the mechanical disruption of host tissue. Stiff bristles in the food canal may indicate their possible adaptation to feeding on insect larvae. The evolution of mouthpart morphology and the putative functional significance of sensilla are discussed, providing insight into the sensory mechanism.

Morphological Disparity of the Mouthparts in Polyphagous Species of Largidae (Heteroptera: Pentatomomorpha: Pyrrhocoroidea) Reveals Feeding Specialization.

Mouthpart structures were observed in four species of Largidae using scanning electron microscopy to investigate their morphological disparity, and linked to changes in feeding specialization. The examined species are pests that feed mainly on seeds and plant sap of forbs, shrubs, and trees. Their external mouthparts are described in detail for the first time herein. The cone-like labrum and four-segmented tube-like labium are shorter in Physopelta species than in Macrocheraia grandis (Grey). The labium surface in all studied species bears nine types of sensilla (St1-St2, Sb1-3, Sch, Sca1-2, Sm). The distributions of sensilla on particular labial segments varies among the studied species. The tripartite apex of the labium consists of two lateral lobes and an apical plate that is partly divided in Physopelta species, and not divided in Macrocheraia. Each lateral lobe possesses a sensillar field with 10 thick-walled uniporous sensilla basiconica, one multiporous sensillum styloconicum, and one long non-porous hair sensillum. Each mandibular stylet tip in M. grandis has a central tooth placed anteriorly and pairs of teeth arranged dorso-laterally. In Physopelta, there are one or two central teeth placed anteriorly but two pairs of teeth dorso-laterally. In all studied species, the inner surfaces of the mandibular stylets have scale-like projections. A left–right asymmetry of the maxillary stylets is noticeable; the external end of the right maxillary stylet is smooth and slightly tapered in M. grandis and evidently wider (spoon–like) in the three species of Physopelta, while the left end of the stylets is straight and narrow in M. grandis in contrast to Physopelta, in which the end is straight and wide. No differences in the internal structure of the maxillary stylets were observed among the studied species. Based on structural differences, we inferred that the mandibles and maxillae are more adapted for seed-sucking in Physopelta species than in M. grandis. M. grandis has the ends of the maxillae more narrowed, a trait more adapted for sucking sap from phloem or parenchymal cells.

Development and functional morphology of the mouthparts and foregut in larvae and post-larvae of Macrobrachium jelskii (Decapoda: Palaemonidae)

The morphology of the mouthparts and foregut of the larvae and post-larvae of Macrobrachium jelskii was investigated to determine their functional roles in feeding, in order to understand the larval feeding behaviour and the changes that occur during its development. The mouthparts and foregut of the zoea I and II are morphologically similar, rudimentary and non-functional in feeding. Only in the final larval stage, zoea III, do the external mouthparts and foregut become structurally more complex and thus likely to play a potential role in feeding. Two behavioral trials (point of no return, point of reserve saturation) evaluated the resistance to starvation in zoea I, II, and III. The results indicate that they have sufficient nutritional reserves to permit them to complete metamorphosis without feeding. Overall, our results suggest that the zoea I and II of Macrobrachium jelskii engage in obligate lecithotrophy and zoea III in facultative lecithotrophy.

Functional morphology of mouthparts and digestive system during larval development of the cleaner shrimp Lysmata amboinensis (de Man, 1888)

Mouthpart and alimentary canal development was examined in Lysmata amboinensis larvae using scanning electron microscopy and histology. The gross morphological features of external mouthparts and internal digestive tract structures of larvae at different developmental stages indicate that ingestive and digestive capabilities are well developed from early on. With increasing age of the larvae the mouthpart appendages increased in size, the hepatopancreas in tubular density and the midgut in length. The density of setae and robustness of teeth and spines of individual structures increased. The most pronounced changes from early to late stage larvae involved formation of pores on the paragnaths and labrum, transformation of the mandibular spine-like teeth to molar cusps, development of the filter press in the proventriculus and of infoldings in the previously straight hindgut. The results suggest that early stage L. amboinensis larvae may benefit from soft, perhaps gelatinous prey, whereas later stages are better equipped to handle larger, muscular or more fibrous foods.

Motor Control in a Drosophila Taste Circuit

Tastes elicit innate behaviors critical for directing animals to ingest nutritious substances and reject toxic compounds, but the neural basis of these behaviors is not understood. Here, we use a neural silencing screen to identify neurons required for a simple Drosophila taste behavior and characterize a neural population that controls a specific subprogram of this behavior. By silencing and activating subsets of the defined cell population, we identify the neurons involved in the taste behavior as a pair of motor neurons located in the subesophageal ganglion (SOG). The motor neurons are activated by sugar stimulation of gustatory neurons and inhibited by bitter compounds; however, experiments utilizing split-GFP detect no direct connections between the motor neurons and primary sensory neurons, indicating that further study will be necessary to elucidate the circuitry bridging these populations. Combined, these results provide a general strategy and a valuable starting point for future taste circuit analysis.

Seasonal Prevalence and Transmission of Salivary Gland Hypertrophy Virus of House Flies (Diptera: Muscidae)

A survey (2005–2006) of house fly, Musca domestica L. (Diptera: Muscidae) populations on four Florida dairy farms demonstrated the presence of flies with acute symptoms of infection with salivary gland hypertrophy (SGH) virus on all farms. Disease incidence varied among farms (farm averages, 0.5–10.1%) throughout the year, and it showed a strong positive correlation with fly density. Infections were most common among flies that were collected in a feed barn on one of the farms, especially among flies feeding on wet brewers grains (maximum 34% SGH). No infections were observed among adult flies reared from larvae collected on the farms, nor among adults reared from larvae that had fed on macerated salivary glands from infected flies. Infected female flies produced either no or small numbers of progeny, none of which displayed SGH when they emerged as adults. Healthy flies became infected after they fed on solid food (a mixture of powdered milk, egg, and sugar) that had been contaminated by infected flies (42%) or after they were held in cages that had previously housed infected flies (38.6%). Healthy flies also became infected after they fed on samples of brewers grains (6.8%) or calf feed (2%) that were collected from areas of high fly visitation on the farms. Infection rates of field-collected flies increased from 6 to 40% when they fed exclusively on air-dried cloth strips soaked in a suspension of powdered egg and whole milk. Rates of virus deposition by infected flies on food were estimated by quantitative polymerase chain reaction at ≈100 million virus copies per fly per hour. Electron microscopy revealed the presence on enveloped virus particles in the lumen of salivary glands and on the external mouthparts of infected flies.

Seasonal Prevalence and Transmission of Salivary Gland Hypertrophy Virus of House Flies (Diptera: Muscidae)

A survey (2005-2006) of house fly, Musca dormestica L. (Diptera: Muscidae) populations on four Florida dairy farms demonstrated the presence of flies with acute symptoms of infection with salivary gland hypertrophy (SGH) virus on all farms. Disease incidence varied among farms (farm averages, 0.5-10.1%) throughout the year, and it showed a strong positive correlation with fly density. Infections were most common among flies that were collected in a feed barn on one of the farms, especially among flies feeding on wet brewers grains (maximum 34% SGH). No infections were observed among adult flies reared from larvae collected on the farms, nor among adults reared from larvae that had fed on macerated salivary glands from infected flies. Infected female flies produced either no or small numbers of progeny, none of which displayed SGH when they emerged as adults. Healthy flies became infected after they fed on solid food (a mixture of powdered milk, egg, and sugar) that had been contaminated by infected flies (42%) or after they were held in cages that had previously housed infected flies (38.6%). Healthy flies also became infected after they fed on samples of brewers grains (6.8%) or calf feed (2%) that were collected from areas of high fly visitation on the farms. Infection rates of field-collected flies increased from 6 to 40% when they fed exclusively on air-dried cloth strips soaked in a suspension of powdered egg and whole milk. Rates of virus deposition by infected flies on food were estimated by quantitative polymerase chain reaction at approximately 100 million virus copies per fly per hour. Electron microscopy revealed the presence on enveloped virus particles in the lumen of salivary glands and on the external mouthparts of infected flies.

Two Gr Genes Underlie Sugar Reception in Drosophila

We have analyzed the molecular basis of sugar reception in Drosophila. We define the response spectrum, concentration dependence, and temporal dynamics of sugar-sensing neurons. Using in situ hybridization and reporter gene expression, we identify members of the Gr5a-related taste receptor subfamily that are coexpressed in sugar neurons. Neurons expressing reporters of different Gr5a-related genes send overlapping but distinct projections to the brain and thoracic ganglia. Genetic analysis of receptor genes shows that Gr5a is required for response to one subset of sugars and Gr64a for response to a complementary subset. A Gr5a;Gr64a double mutant shows no physiological or behavioral responses to any tested sugar. The simplest interpretation of our results is that Gr5a and Gr64a are each capable of functioning independently of each other within individual sugar neurons and that they are the primary receptors used in the labellum to detect sugars.

Serotype Differences and Lack of Biofilm Formation Characterize Yersinia pseudotuberculosis Infection of the Xenopsylla cheopis Flea Vector of Yersinia pestis

Yersinia pestis, the agent of plague, is usually transmitted by fleas. To produce a transmissible infection, Y. pestis colonizes the flea midgut and forms a biofilm in the proventricular valve, which blocks normal blood feeding. The enteropathogen Yersinia pseudotuberculosis, from which Y. pestis recently evolved, is not transmitted by fleas. However, both Y. pestis and Y. pseudotuberculosis form biofilms that adhere to the external mouthparts and block feeding of Caenorhabditis elegans nematodes, which has been proposed as a model of Y. pestis-flea interactions. We compared the ability of Y. pestis and Y. pseudotuberculosis to infect the rat flea Xenopsylla cheopis and to produce biofilms in the flea and in vitro. Five of 18 Y. pseudotuberculosis strains, encompassing seven serotypes, including all three serotype O3 strains tested, were unable to stably colonize the flea midgut. The other strains persisted in the flea midgut for 4 weeks but did not increase in numbers, and none of the 18 strains colonized the proventriculus or produced a biofilm in the flea. Y. pseudotuberculosis strains also varied greatly in their ability to produce biofilms in vitro, but there was no correlation between biofilm phenotype in vitro or on the surface of C. elegans and the ability to colonize or block fleas. Our results support a model in which a genetic change in the Y. pseudotuberculosis progenitor of Y. pestis extended its pre-existing ex vivo biofilm-forming ability to the flea gut environment, thus enabling proventricular blockage and efficient flea-borne transmission.

Crustacean Hosts of the Pedunculate Barnacle Genus Octolasmis in the Northern Gulf of Mexico

A survey of live and preserved crustaceans from the northern portion of the Gulf of Mexico was conducted to investigate the colonization habits of the barnacle genus Octolasmis. In all, three crustacean orders (Decapoda, lsopoda, and Stomatopoda) comprising 43 families, 78 genera, and 122 species were surveyed. Octolasmis barnacles were observed to infest 14 families, 20 genera, and 27 species of the orders Decapoda and Isopoda. In order of decreasing frequency, the Octolasmis species encountered were O. lowei, O. forresti, O. hoehi, and O. aymonini geryonophila. The first two were found primarily in the gill chambers, the third was found mainly on external mouthparts, and the last was found exclusively on the external mouthparts, ventral pereonal and pleonal surfaces of the isopod, Bathynomus giganteus. The decapod families Pisidae and Portunidae had the highest rates of infestation, whereas the family Galatheidae (represented by six species) did not host Octolasmis. The order Stomatopoda, represented by two families (Lysiosquillidae and Squillidae), two genera, and seven species was also not infested with Octolasmis. Statistical tests confirm that octolasmids do not randomly occupy hosts, rather they appear to select a subset, generally the larger species of crustaceans.

Functional morphology of the mandibles of the larvae of Episyrphus balteatus (De Geer, 1776) (Diptera : Syrphidae)

Aphidophagous syrphid (Diptera : Syrphidae) larvae have no structures for seizing and killing such as prehensile legs and strongly sclerotized external mouthparts enabling them to capture and feed on their prey. Nevertheless they are considered to be efficient predators. In order to understand this paradox in Episyrphus balteatus, 2 complementary approaches were followed. These consisted of, first, a careful analysis of the morphology of mouthparts of the larvae, and second, an investigation of their feeding behaviour. The mouthparts were found to be composed of 2 groups of dental sclerites, corresponding to the 2 inner elements of the cephalopharyngeal skeleton. The exterior elements or triangular sclerites are absent in the first-instar larvae. These elements appeared close to the mouth in the second and the third-instar larvae, were oriented in the opposite direction to the other elements, and were positioned laterally. This structure probably serves to anchor the anterior part of the predator within the prey, thus preventing it from escaping. During the feeding activity, the seizing process occurred immediately after the recognition. The lifting-up behaviour of the first-instar larvae is probably due to the absence of the triangular sclerites. The suction was marked by an active movement of the cephalopharyngeal skeleton and a peristaltic movement of the abdomen. The feeding time was inversely proportional to the larval development.

Morphological changes in external and internal feeding structures during the transition phyllosoma-puerulus-juvenile in the Western Rock Lobster (Panulirus cygnus, Decapoda: Palinuridae).

External and internal feeding structures of the pelagic final phyllosoma, the transitional puerulus, and the benthic juvenile Western Rock Lobster, Panulirus cygnus, were studied by means of scanning electron microscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. The foregut, however, is not clearly divided into pyloric and cardiac regions and a gastric mill is absent, although a comb row and gland filter are present. Juveniles, on the other hand, have a well-developed gastric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juveniles are suitable for mastication of solid food particles and bear numerous setae. In contrast, external mouthparts of pueruli are largely non-setose. Furthermore, although the foregut is differentiated into pyloric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absence of such structures indicates that the puerulus may be a non-feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously proposed. © 1994 Wiley-Liss, Inc.

Cobalt filling of sensory projections from internal and external mouthparts in Drosophila.

Phase-contrast microscopy of 2.5 micron plastic sections reveals five different kinds of sense organs on the internal mouthparts of Drosophila melanogaster: a ventral group of sensilla on the epipharynx, three kinds of sense organs in the middle part of the sucking apparatus (the cibarium), one of them being described here for the first time, and an additional type of sensillum in the dorsal pharynx (Fig. 1). Three of these internal sense organs resembling each other structurally form similar projection patterns in the tritocerebrum, whereas external taste receptors on the labial palps show a different pattern in the suboesophageal ganglion (Fig. 12). The central projections of these internal and external sensilla were traced by applying an ethanolic solution of cobalt on the intact cuticle.

Drinking by Adult Cephenemyia (Diptera: Oestridae)1

Frequent citations in the literature indicate that all adult bot flies are aphagous and without functional mouthparts. This paper describes imbibing of free water by two species of adult Cephenemyia . While in the process of drinking, the functioning of the external mouthparts was viewed through a stereoscopic microscope. Intake of fluids was confirmed by vivisection of flies offered a 0.01% solution of aqueous neutral red dye. Amount of fluid imbibed was measured by weighing flies immediately before and after drinking. The longevity of flies drinking water was significantly longer than that of the controls. Possible intake of free fluids by these flies under natural conditions is discussed, and a description of the anatomy of the mouthparts is presented.