Feeding behaviour of female Aedes aegypti: effects of diet temperature, bicarbonate and feeding technique on the response to ATP

Abstract. The effects of variation in diet temperature, mouthpart deployment and the addition of bicarbonate to a saline-ATP diet were investigated for their effects on amount ingested and diet destination in female Aedes aegypti (L.). Mouthpart deployment was achieved by having the insects feed through a membrane, or from a free-liquid surface with mouthparts intact, or with the fascicle separated from the labial groove.
Under the 'feeding through membrane' protocol, a 6-fold increase in the percentage of Aedes feeding on ATP-diets was recorded at 37C compared with 21C. Bicarbonate (9.5 or 19 mM) induced a 3-fold increase in numbers feeding at both 21C and 37C. Neither diet temperature nor bicarbonate content appeared to affect meal size. The pH of all diets was adjusted to 7.0. Diet was directed primarily to the midgut for all diets tested under this regimen, with the exception of the saline-ATP-19 mM NaHC0₃ at 37C which caused the diet to be directed primarily to the crop.
Under the 'feeding without membrane through feeding tube' protocol, females showed little control over diet destination. Female Aedes aegypti exhibited no strong response to ATP when the mouthparts were immersed in 21C diets in feeding tubes and few of these insects ingested large meals. The addition of bicarbonate to the ATP diets did not enhance feeding under these test conditions.     

Ingestion and diet destination in Culiseta inornata: responses to water, sucrose and cellobiose

ABSTRACT. At ambient temperature, contact with free liquids containing sugar induces Culiseta inornata Williston (Diptera: Culicidae) females to adopt the nectar-feeding mode of behaviour. While in this mode, two distinct control mechanisms appear to operate: one controlling the amount of ingestion, the other diet destination. Mosquitoes were exposed to water and various concentrations of sucrose and cellobiose in water. Only small or taste amounts of water were imbibed, and it was directed to the midgut. Cellobiose solutions of less than 0.1M were treated as water. Cellobiose was phagostimulatory; as the concentration increased from 0.1 to 0.5 M the percentage of insects ingesting large amounts rose from 11% to 68%. Cellobiose diets were directed primarily to the midgut. Sucrose was also phagostimulatory. As the concentration increased from 0.025 to 0.2 M, the percentage of insects ingesting large amounts increased from 20 to 92. At lower sucrose levels, insects ingesting large amounts put it mainly into the crop, while insects ingesting smaller amounts put the diet into the midgut or both the crop and midgut. At sucrose concentrations of 0.4 M or more, most insects took large amounts and directed it to the crop. Different combinations of sucrose and cellobiose with a total concentration of 0.5 M all caused insects to take mainly large meals. At sucrose concentrations of 0.2M and above, the insects responded as they would to sucrose alone, directing the diet to the crop. At sucrose concentrations of 0.1M or less, diet destination patterns were more complex, with individual animals depositing the diet in the crop, the midgut, or in both. A behavioural model is presented which postulates different receptors for sucrose and cellobiose, control of diet destination via differential control of midgut and crop valves, and variation of threshold values according to endogenous factors.     

Feeding behaviour,midgut distension and ovarian development in Phlebotomus papatasi (Diptera: Psychodidae)

Phlebotomus papatasi females were fed through membranes or from cotton wool soaked in blood, water, sucrose or sodium chloride solutions. In membrane-fed flies, all diets were routed to the midgut and not to the crop. Following the meals that went to the midgut, females showed ovarian development at least 3 times greater than in sucrose-fed, autogenous control flies. Neither small quantities of water arriving in the midgut following drinking from soaked cotton wool, nor piercing of a membrane without feeding, stimulated ovarian development. Flies exhibited different feeding behaviour namely, blood feeding, sugar feeding, and water drinking. The blood-feeding behaviour was typical of flies ingesting any of the experimental diets through membranes, or blood or saline from cotton wool. The other two types of behaviour were observed in flies which fed from soaked cotton wool. The type of behaviour was characterized by the depth of penetration of the mouthparts into the substrate, the deployment of the palps and the degree of contact between the palps and the surface. It is suggested that the stimuli which control the routing of meals to the crop or to the midgut are derived from these types of behaviour.     

The mouth apparatus of Lithodes maja (Crustacea: Decapoda) – form,function and biological role

Being able to utilize many different food resources is probably an important aspect of the success of decapod crustaceans which fill a wide range of various ecological niches worldwide. The phenomenon is facilitated by the complex mouth apparatus found in this group, whose representatives possess six pairs of mouthparts– mandibles, maxillae 1, and maxillae 2 and three maxillipeds, the first three pairs of thoracic appendages which are also specialized to food manipulation. These six pairs are able to perform a number of movements for transporting, aligning, crushing and cutting. Studies into the functional morphology of mouthparts have already been carried out in some decapod species. This study focuses on Lithodes maja, a species of the hitherto understudied king crabs (Lithodidae), chosen on the grounds of their remarkable evolutionary history as ‘derived hermit crabs’. Individuals were filmed while being presented with different kinds of food. To obtain structural information on the individual mouthpart elements as naturally arranged in relation to one another, the shape of the mouthparts was 3D‐reconstructed from micro‐CT scans. These data were complemented by scanning electron microscopy, to analyse the surface structures in detail. There is evidence that the various elements of the mouthparts of L. maja can be sorted into six functional groups: (i) transporting mouthpart elements, (ii) aligning/sorting mouthpart elements, (iii) clutching/holding mouthpart elements, (iv) tearing/cutting/crushing mouthpart elements, (v) current‐generating mouthpart elements and (vi) grooming mouthpart elements. According to our 3D reconstruction, there only seem to be minor differences in morphology and relative position between the mouthparts of L. maja and those of the closely related species, Pagurus bernhardus.     

Symmetries and homologies of Geomerida

The symmetry of Earths life cover (Geomerida) was described generally by L.A. Zenkevich (1948). It coincides with the symmetry of geographic cover. Its symmetry elements are equatorial plane and three meridonal planes corresponded to oceans and continents. The hypsographic curve with point of inflection (symmetry element) on 3 km depth line should be added to these elements. The plankton and benthos communities as well as fauna of taxons are distributed symmetrically according these symmetry elements. Zenkevich model was successfully extrapolated to plankton by K.V. Beklemishev (1967, 1969) and to abyssal benthos by Sokolova M.N. (1986). The plankton communities inhabiting symmetrically located macrocirculations are considered as homologous. The character of circulation determines the trophic structure of plankton and benthos. In the case of high productivity of plankton, benthic grazing animals feed on sedimented particles have bilateral symmetric mouthpart. Otherwise they have to acquire food from water column and use cyclomeric mouthpart. Thus, the symmetry of macrocirculations determines the symmetry distribution of benthic animals with two major symmetries of mouthparts. The peculiarities of organisms' symmetry are discussed in the context of Pierre Curie principle and the ideas of K.V. Beklemishev concerning evolution of morphological axes.     

Structural mouthpart interaction evolved already in the earliest lineages of insects

In butterflies, bees, flies and true bugs specific mouthparts are in close contact or even fused to enable piercing, sucking or sponging of particular food sources. The common phenomenon behind these mouthpart types is a complex composed of several consecutive mouthparts which structurally interact during food uptake. The single mouthparts are thus only functional in conjunction with other adjacent mouthparts, which is fundamentally different to biting–chewing. It is, however, unclear when structural mouthpart interaction (SMI) evolved since this principle obviously occurred multiple times independently in several extant and extinct winged insect groups. Here, we report a new type of SMI in two of the earliest wingless hexapod lineages—Diplura and Collembola. We found that the mandible and maxilla interact with each other via an articulatory stud at the dorsal side of the maxillary stipes, and they are furthermore supported by structures of the hypopharynx and head capsule. These interactions are crucial stabilizing elements during food uptake. The presence of SMI in these ancestrally wingless insects, and its absence in those crustacean groups probably ancestral to insects, indicates that SMI is a groundplan apomorphy of insects. Our results thus contradict the currently established view of insect mouthpart evolution that biting–chewing mouthparts without any form of SMI are the ancestral configuration. Furthermore, SMIs occur in the earliest insects in a high anatomical variety. SMIs in stemgroup representatives of insects may have triggered efficient exploitation and fast adaptation to new terrestrial food sources much earlier than previously supposed.     

Mouthpart and foregut ontogeny in larval, postlarval, and juvenile spiny lobster, Panulirus argus Latreille (Decapoda, Palinuridae)

The spiny lobster Panulirus argus has a life cycle consisting of a long-term (～9-12 months) planktonic larval period with 11 larval stages (the phyllosoma), a short (<1 month?) planktonic-to-benthic transitional postlarval stage (the puerulus), and benthic juvenile and adult phases. The mouthparts and foregut during these stages were examined and described by means of scanning electron microscopy (SEM) in an investigation of the species' developmental morphology, diet, and ecology. The phyllosoma mouthparts close to the esophagus are the labrum, mandibles, paragnaths, and first maxillae. The second maxillae and first and second maxillipeds are increasingly distant from the esophagus as the larva develops. The pair of asymmetrical mandibles bear many teeth and spines, and the molar processes form what appears to be an intricate toothed shear. The mandibles remain similar throughout the phyllosoma stages. During the molt into the puerulus, the mouthparts are greatly changed, and the second maxilla and the three maxillipeds join the other mouthparts near the esophagus. However, the transformation appears incomplete, and many of the mouthparts are not fully formed until the molt to juvenile completes their development. The phyllosoma foregut lacks a gastric mill and has but one chamber. In addition, the first two stages lack a gland filter. During the molt to puerulus, the foregut is greatly changed and subsequently is similar to typical decapod foreguts in having an anterior cardiac and posterior pyloric chamber. Only rudimentary internal armature is present. Following the molt to juvenile, the foregut is quite similar to that of the adult, which exhibits a substantial gastric mill. The 11 phyllosoma stages were separated into two groups (group A = stages 1-5, group B = stages 6-11) on the basis of changes in both mouthpart and foregut morphology. The puerulus has never been observed to feed. Nothing was observed in our investigations that would prevent feeding, though both mouthpart and foregut development appeared incomplete. The mouthpart and foregut structures of larval, postlarval and juvenile P. argus differ widely, possibly reflecting the extreme modifications for different habitats found among these life phases.     

Fine structure and sensory apparatus of the mouthparts of the pear psyllid,Cacopsylla chinensis (Yang et Li) (Hemiptera: Psyllidae)

The pear psyllid, Cacopsylla chinensis (Yang et Li) (Hemiptera: Psyllidae), is one of the most significant economic pests of pear in China, causing direct damage through feeding by the highly specialized piercing–sucking mouthparts. The ultrastructural morphology and sensory apparatus of the mouthparts of the adult were examined using scanning and transmission electron microscopy. The piercing–sucking mouthparts of C. chinensis are composed of a three-segmented labium with a deep groove in the anterior side, a stylet fascicle consisting of two mandibular and two maxillary stylets, and a pyramid-shaped labrum. Proximal to the labium, the stylet fascicle forms a large loop within a membranous crumena. Mandibles, with more than ten teeth on the external convex region, can be seen on the distal extremity. Smooth maxillary stylets are interlocked to form a larger food canal and a smaller salivary canal. One dendritic canal housing 2 dendrites is also found in each mandible. Two types of sensilla trichodea, four types of sensilla basiconica, single as well as groups of sensilla campaniformia, and oval flattened sensilla occur in different locations on the labium, whereas a kind of sensilla basiconica is at the junction of the labrum and anteclypeus. Sensilla trichodea and sensilla campaniformia, always present with denticles, are present on the middle labial segment. Three types of sensilla basiconica, two types of sensilla trichodea and two oval flattened sensilla are located on the distal labial segment. The mouthpart morphology and abundance of sensilla located on the labium in C. chinensis are illustrated, along with a brief discussion of their taxonomic and putative functional significance.     

Evaluation of tadpole mouthpart depigmentation as a diagnostic test for infection by Batrachochytrium dendrobatidis for four California anurans

The objective of this study was to evaluate the utility of gross morphologic examination of larval mouthpart defects as a diagnostic screening test to detect Batrachochytrium dendrobatidis infection in four California, USA, anuran species. We examined mouthparts of 2,034 tadpoles of Bufo boreas, Pseudacris regilla, and Rana catesbeiana collected in 2003 and 2004 and Bufo canorus collected in 2004. Data were recorded for three morphologic features: upper toothrows, lower toothrows, and combined jaw sheaths. Mouthpart defects were observed in all four species (n=757), but only two species were infected with B. dendrobatidis (n=84). Sensitivity and specificity of the mouthparts test were 76% and 58%, respectively. Forty-two percent of B. dendrobatidis-negative animals would have been designated positive based on mouthpart defects. Observed prevalence was 43%, and true prevalence was 3.0%. Tests of the null hypothesis using logistic regression analysis showed that anuran larval mouthpart defects were not associated with B. dendrobatidis infection whether mouthparts scores were tested by individual morphologic feature or in combination (P=0.37). We conclude that B. dendrobatidis infection and anuran larval mouthpart defects are two separate processes that may occur concurrently and that evaluation of tadpole oral morphology is neither an accurate nor a reliable diagnostic test for B. dendrobatidis infection for the four species tested.     

Gustatory mechanisms and sugar-feeding in the mosquito, Culiseta inornata

ABSTRACT. Gustatory hairs on the legs and mouthparts of the mosquito, Culiseta inornata , were stimulated with sucrose solutions to determine their role in the finding and consuming of nectar by females. Stimulation of tarsi initiated probing, which continued without subsequent stimulation of tarsal hairs. Turning in response to tarsal stimulation depended on which leg was stimulated. Once gustatory hairs on the labella were stimulated, turning and probing were discontinued. Stimulation of the hairs on the external surface of the labella apparently initiates the labellar opening response, while stimulation of hairs on the oral surface of the labella maintains the labellar response. Electrophysiologically recorded activity of cibarial and pharyngeal pumps was used to assess the influence of the five relevant sets of gustatory hairs on initiation of sucking. None of the sets alone were capable of initiating sucking. Sucking was initiated when the hairs on the oral surface of the labella were stimulated simultaneously with sensory hairs on the tip of the labrum. The gustatory hairs on the oral surface of the labella exerted considerable influence in determining the amount of sugar or water imbibed.     

The effect of predation risk on the predatory behaviour of a sit-and-wait predator,Ranatra dispar (Heteroptera: Nepidae), the water stick insect

Two primary defence behaviours, fore-leg extension to enhance crypsis and swimming to bottom and remaining motionless, of a predatory water bug,Ranatra dispar, are described along with their subsequent effect on foraging behaviour. It was hypothesised that hungry predators would respond less and for a shorter duration compared with recently fed individuals when exposed to a model threat stimulus, thereby tending to take a higher risk of predation during feeding than satiated animals. A greater proportion of animals responded overall with the leg extension response compared with the swimming response, although the mean duration of the former was significantly shorter than the latter response. A significantly higher proportion of nonfasted predators responded, and for a longer duration than fasted individuals. The type of model used significantly effected the proportion of animals that responded with leg extensions but not on its duration. In contrast, both number of animals and the duration of the swim/motionless behaviour were significantly effected by stimulus type. The subsequent effect of these 2 behavioural responses on feeding behaviour was examined and showed that although about the same number of predators removed prey from their mouthparts during both responses, significantly more prey were dropped, and therefore lost, during swimming. The results clearly indicate the significant effects that defensive behaviours have on time budgets in foraging behaviour.     

An excitatory state generated during feeding in the locust, Chortoicetes terminifera

Various sequences of 2 μl drops of 1·0 M sucrose and water were applied directly to the mouthparts of restrained adults of the locust Chortoicetes terminifera which had been deprived of all food for 24 hr, and the number of drops consumed was recorded. Locusts fed either single drops of sucrose solution and water in alternation or single drops of sucrose solution alternated with groups of four consecutive drops of water, consumed larger total volumes than locusts fed only drops of water or locusts offered water after having been fed partially or wholly to repletion with 1·0 M sucrose. Towards the end of meals consisting of repeated cycles of one drop of sucrose solution and four drops of water, locusts consumed the one or two drops of water which followed a sucrose drop more quickly than the drop which preceded it. Furthermore, a few locusts which received this treatment terminated their meal while either a drop of sucrose solution or the water drop which immediately followed the sucrose drop was in contact with their mouthparts. The findings provide strong evidence that stimulation received during ingestion of sucrose induces, in addition to an immediate excitatory effect on the feeding system, a perseverating state of neural excitation which, for a short time afterward, increases the chance that the insect will ingest water.     

Sensory adaptation and the regulation of meal size in the Australian plague locust, Chortoicetes terminifera

Adults of Chortoicetes terminifera consumed larger meals of sucrose solution, applied as drops directly to their mouthparts, than of water. Meal size increased with increasing sucrose concentration up to 0·5 M but meals of 1·0 M sucrose were of lower volume. Locusts fed so that there was a short interval between each successive drop of sugar solution consumed greater volumes than those fed continuously, which indicates that sensory adaptation plays a part in bringing about the termination of meals of sugar solutions. Meals of water were not increased in size by discontinuous application.     

Utility of geometric morphometrics for inferring feeding habit from mouthpart morphology in insects: tests with larval Carabidae (Insecta: Coleoptera)

Feeding habits are important life‐history traits in animals; however, methods for their determination are not well established in many species. The larvae of the beetle family Carabidae are an example. The present study tested the utility of geometric morphometrics of mouthpart morphology to infer the feeding habits of carabid larvae. Using Pterostichus thunbergi as a model system, larval feeding habits were inferred using geometric morphometrics of mouthparts and the results were compared with those obtained from rearing experiments. The rearing experiments indicated that P. thunbergi larvae are carnivores that require snails as an essential part of the diet. Through geometric morphometrics, associations between mouthpart morphology and larval feeding habits were confirmed for species in which these two traits are known. A discriminant analysis using these associations classified P. thunbergi larvae as snail/slug feeders, which is a result compatible with the rearing experiments. Geometric morphometrics also revealed that morphological integration and ontogenetic shape change might play roles in the diversification of mouthpart morphology. Overall, these results demonstrate the utility of the geometric morphometrics of mouthparts to infer feeding habit and to clarify the mechanisms of mouthpart morphological diversification in the study group, and the results also serve as a basis for future studies of other insect groups.     

Gustatory hairs on the mosquito, Culiseta inornata.

Gustatory hairs were investigated on the legs and mouthparts of Culiseta inornata (Williston) (Diptera: Culicidae). One type of hair, each innervated by four neurons, was found on the legs. Two of the neurons responded to NaCl stimulation, one neuron to water stimulation, and one neuron to sucrose stimulation. Three kinds of hairs designated Type I (T1), Type 2 (T2) and Type 3 (T3) were analyzed on the labella. The T1 hairs are innervated by one sugar neuron, one mechanoreceptor, two salt neurons and one water neuron. The T2 hairs are innervated by two salt neurons and one mechanoreceptor. The T3 hairs, located on the oral surface of the labella, are innervated by a variable number (2-5) of neurons. Precise identification of the T3 chemosensory neurons was not made because of the small size and inaccessibility of the T3 hairs. Chemosensory hairs on the tip of the labrum were tested electrophysiologically. the sequence of decreasing effeectiveness for the three salts tested was KCl greater than NaCl greater than LiCl. Labral chemoreceptors also responded positively to sucrose.     

Conservation and diversification of gene function during mouthpart development in Onthophagus beetles

The evolutionary success of insects is in part attributable to the tremendous diversification of their mouthparts, which permitted insects to radiate into novel food niches. The developmental genetic basis of mouthpart development has been well studied in at least two insect taxa possessing derived mouthparts, the hemipteran Oncopeltus fasciatus and Drosophila. However, much less is known about the regulation of mouthpart differentiation of the presumed ancestral mandibulate type. Here we aim to extend current insights into the patterning of mandibulate mouthparts through a functional genetic analysis of three leg gap genes, homothorax (hth), dachshund (dac), and Distal-less (Dll), in the dung beetle Onthophagus taurus, a species whose mouthpart arrangement has in part retained, as well as diverged form, the ancestral mandibulate mouthpart type. We specifically include in this study a first functional genetic analysis of the adult labrum, an enigmatic mouthpart whose appendicular origin has been the subject of a long-standing debate. Our results support a functional role of all three patterning genes in the development of the labium, maxilla, as well as the labrum. In contrast, mandible development appeared to rely only on the patterning functions of hth and dac, but not Dll. Here, our results raise the possibility that evolutionary changes in the dac-patterning may have played an important role in the evolutionary transition from a short, triangular mandible adapted for chewing to the elongated, flat, and blade-like mandible of modern filter-feeding scarabaeine beetles. In general, our results contribute to a growing body of studies that suggest that basic patterning genes can contribute to morphological evolution of adult features while maintaining traditional patterning responsibilities at earlier developmental stages or in other body regions.     

Acanthodiaptomus denticornis another omnivorous calanoid copepod: description of its mouth appendages and feeding experiments on animal prey

The mouthpart morphology of the freshwater calanoid copepod Acanthodiaptomus denticornis was examined with optical microscopy. The mouthparts have sharp teeth and stout appendages with clawlike setae, typical of omnivorous calanoid mouthpart morphology. Observation of the buccal aperture with Scanning Electron Microscopy shows a large opening permitting feeding on prey as large as Keratella cochlearis. These observations agree with our feeding experiments which show that A. denticornis feed on K. cochlearis.     

The phylogenetic information carried by a new set of morphological characters in planthoppers: the internal mouthpart structures and test in the Cixiidae model (Hemiptera: Fulgoromorpha)

Internal morphological structures of Cixiidae mouthparts are described and compared in various representatives of the Cixiidae and several other representatives of hemipterans. The morphological study shows that the mouthpart structures have not evolved uniformly and reveals the great disparity of these structures. Particularly, the connecting system of the mouthparts, localisation of salivary canal and shape of the mandibular and maxillar stylets provide together a new set of 17 new characters. A parsimonious analysis to evaluate the phylogenetic interest carried by these 17 selected characters shows that mouthpart structures have not evolved anarchically, but that they indeed carry some phylogenetic information that will be useful to be included in further morphological phylogenetic analysis.     

A comparative study on mouthpart morphology of certain larvae of Chironomini (Diptera: Chironomidae) with reference to the larval feeding habits

Mouthparts of six species of chironomid larvae were compared on both an intra- and inter-specific level. The species were: Chironomus riparius, Cryptochironomus defectus gr., Endochironomus albipennis, Glyptotendipes pallens, Microtendipes pedellus and Parachironomus arcuatus . The mouthpart morphology in C. defectus gr. and P. arcuatus is considerably different from the four other species and changes little between instars. Within C. riparius, E. albipennis, G. pallens and M. pedellus there is a considerable difference in the mouthpart morphology between the first instar and the remaining instars. The morphology of the mouthparts of the first instar of C. riparius, E. albipennis, G. pallens and M. pedellus resembles in many ways that found in C. defectus gr. and P. arcuatus .