A duration constant for worker-to-larva trophallaxis in fire ants

Summary The allocation of liquid food by workers to larvae, a central process in ant biology, could be regulated by the frequency of trophallaxis, its duration, or both. In 4th-instar fire ant larvae, the duration of trophallaxis, bolus size, and the rate at which boluses were swallowed were all constant, indicating that the volume of food ingested during each worker-larva trophallaxis was both small and constant. Neither larval size over a 20-fold volume range nor larval starvation had a significant effect on duration of trophallaxis (mean = 11s, SD = 2s), bolus swallowing rate (mean = 2/s, SD = 0.5/s), or bolus volume (mean = 0.0675 nl, SD = 0.0002 nl, based on the assumption that the stomodaeum's epithelial layer is not expandable). Larval body orientation and larval location within the brood pile also had no effect on duration. Durations of trophallaxis by workers of different sizes were similar. Durations of trophallaxis for 1st-, 2nd-, and 3rd-instar worker larvae were also constant but greater than that for 4th-instar worker larvae. Fourth-instar minim larvae (from founding colonies) and 4th-instar worker larvae (from mature colonies) were fed for the same duration by workers but for different durations by founding queens. Founding queens fed minim larvae longer than they fed worker larvae. The durations of feedings to 4th-instar sexual larvae were more variable than those to worker larvae. Altogether, these findings indicated that 4th-instar worker larvae ingested a small, nearly constant volume of food (mean = 1.50 nl, SD = 0.005 nl) during each trophallactic event. Consequently, the long-term allocation of liquid food by workers to these larvae is regulated by the frequency of trophallaxis. Several other ant species showed a similar brevity and constancy in the duration of worker-larva trophallaxis. This brevity of worker-larva trophallaxis is in contrast to the duration of worker-worker trophallaxis.Although the duration of worker-larva trophallaxis appears to be determined by the worker, the data are not totally consistent with this interpretation.     

Effects of cholecystokinin octapeptide (CCK-8) on food intake in adult and aged rats under different feeding conditions

The effects of CCK on food intake were investigated under fixed feeding conditions in comparison to a test meal taken after 16 h of food deprivation. The experiments were performed on young adult rats (8 weeks old) as well on aged rats (23 months old). Intraperitoneal CCK-8 (8 and 40 μg/kg) significantly reduced the size of a test meal following 16-h food deprivation. This effect was independent of the age of the rats. However, under fixed feeding conditions neither of the doses used in this study reduced food intake in the young adult rats, whereas the highest dose of 40 μg/kg did so in the aged rats. These results suggest that the hypophagic effect of exogenous CCK-8 depends on experimental conditions, food intake being reduced after a period of food deprivation but not under a fixed feeding regimen in adult animals. Furthermore, the data suggest that age is a factor contributing to the complex behavioral actions of CCK, because only old animals were more susceptible to an anorectic action of CCK under the fixed feeding schedule. An explanation may lie in an interaction of other known behavioral effects of CCK (e.g., anxiogenic, mnemonic action) with its effects under the different feeding schedules.     

Effect of prey density on behaviour and development of the predatory mosquito,Toxorhynchites towadensis

The effect of prey density on feeding behaviour, killing behaviour, and development of the predatory mosquito,Toxorhynchites towadensis, was investigated in the laboratory. The number of prey consumed per larva increased toward an upper asymptote as prey density increased. Prey consumption curves during fourth instar were concave at low prey densities but convex at high prey densities. This phenomenon was not observed during other instars. Killing without consuming any part of prey occurred at prey densities of 20 per container and over. The number of prey killed but not consumed increased linearly with the number of unconsumed prey in the container. Prey acquisition behaviour was not affected by prey densities during the prepupal period. Developmental time from first instar to adult emergence decreased with increasing prey densities, but remained constant at densities of 10 per container and over. Adult size increased with increasing prey densities but there was no effect at prey densities of 20 and over.     

Endophytes of fescue grasses enhance susceptibility ofPopillia japonica larvae to an entomopathogenic nematode

We evaluated tritrophic level interactions among fungal endophytes (Acremonium spp.) of fescue grasses (Festuca spp.), the root-feeding Japanese beetlePopillia japonica Newman larvae, and the entomopathogenic nematodeHeterorhabditis bacteriophora Poinar. Third-instarP. japonica larvae were introduced into pots containing endophyteinfected or endophyte-free plants of tall fescueFestuca arundinacea Schreber (cultivars Kentucky 31 and Georgia Jesup Improved) and the Chewings fescueFestuca rubra commutata Guad. (cultivars F-93 and Jamestown II). After two weeks, the surviving larvae were recovered, and their susceptibility to nematodes was evaluated in sand columns. Endophytes enhanced the rate of nematode-induced mortality in all cultivars except Georgia Jesup Improved, and increased the proportion of dead larvae with nematodes in all cultivars except Jamestown II. Endophytes in the cultivar Kentucky 31 were associated with improved nematode establishment in the larvae. No effect on nematode reproduction was found. Since endophytes produce biologically active alkaloids, we tested the effects of an ergot alkaloid, ergotamine tartrate, on the feeding behavior and weight ofP. japonica larvae in agar medium. The alkaloid caused feeding deterrence, and reduced the consumption of medium by the larvae, resulting in weight loss. These larvae were more susceptible toH. bacteriophora than the untreated larvae. Unfed ‘starved’ larvae were more susceptible to nematodes than those fed on untreated agar. Our results support the hypothesis that endophyte-induced starvation ofP. japonica would reduce larval vigor, and render them more susceptible to entomopathogenic nematodes.     

Effect of methoxyphenols on grain aphid feeding behaviour

Methoxyphenols might be important in the resistance of cereals to aphids. Electrical penetration graph (EPG) recordings were used to determine the effect of caffeic, ferulic and sinapic acids, and scopoletin on the feeding behaviour of the grain aphidSitobion avenae (F.). Aphids on wheat seedlings treated systemically with these phenols showed reduced ingestion of phloem sap and salivation into sieve elements in most cases. The earlier pathway phases of probing were prolonged. Moreover increase in number of probes as well as reduction of total time of probing was observed. In addition, no O-demethylase activity was found in homogenates of aphids fed on moderately-resistant (phenolic rich) or susceptible (phenolic poor) wheat varieties. The significance of these results for understanding the resistance of cereals to aphids is discussed.     

Biomass of planktonic crustaceans and the food of young cyprinids in the littoral zone of Lake Balaton

The littoral zone of Lake Balaton and its periphyton-zooplankton-fish communities have been investigated intensively in recent years. Total average number of crustacean plankton varied from 36 to 126 ind l^–1, their biomass from 0.49 to 1.86 mg ww l^–1 month^–1 at different areas of the littoral zone. In general, these values for the above parameters were higher in hypertrophic areas. 23 fish species occurred in the littoral zone with cyprinids dominating. The seasonal food spectra of Y-O-Y roach (Rutilus rutilus), white bream (Blicca bjoerkna) and bream (Abramis brema) were based mainly on planktonic crustaceans and benthic/periphytic invertebrates. According to the frequency of occurrence of crustaceans and other invertebrates, the food composition of young cyprinids differed significantly in the NE and SW-basins of the lake.     

Effect of habitat structure on the feeding efficiency of young stages of razor fish (Pelecus cultratus (L.)): an experimental approach

The effects of a submerged macrophyte (Potamogeton pectinatus), turbidity (produced by 50 mg l^–1 kaolin), and their combination on the feeding rate of young razor fish (Pelecus cultratus (L.)) were studied in the laboratory. Young razor fish showed preference for Copepoda in most of the simulated habitats. Razor fish fed more efficiently in the absence of any environmental structure, but the more structured habitats, 3 g wet wt l^–1 of simulated submerged macrophyte and turbidity combined with vegetation, had a negative impact on food consumption rates.     

A functional approach to ecomorphological patterns of feeding in cottid fishes

Synopsis One of the major goals of an ecomorphological analysis is to correlate patterns of interspecific differences in morphology with patterns of interspecific differences in ecology. Information derived from functional morphological studies may provide a mechanistic framework supporting the correlation, but the move from a correlational relationship to a causal relationship requires experimental evidence that the interspecific morphological differences create performance differences and therefore ecological differences. The goal of this study was to examine ecomorphological relationships in the diets of cottid fishes (Scorpaeniformes: Cottidae) from the northeastern Pacific by using functional classifications of predators (based on their mode of attack) and of prey (based on their anti-predator defenses). The proposed ecomorphological relationships were tested by examining capture success among the cottids in attacks on prey with different escape abilities. As predicted on functional morphological grounds, both multivariate and univariate analyses indicated that the gravimetric importance of elusive prey (i.e. fishes, shrimp, mysids, and octopods) was greater in cottid species with a larger relative mouth size. Supporting a causal link between morphology and ecology, performance tests indicated that larger-mouthed cottids had significantly higher capture success on Heptacarpus shrimp than did smaller-mouthed species. As predicted, there were no differences in capture success among predators regardless of their attack style or ecomorphological patterns in attack on crabs (Cancer and Petrolisthes spp.) when the crabs were presented on a sand surface (i.e. easy prey). Several difficulties still exist when trying to apply a functional group approach to ecomorphology. These include the behavioral plasticity of the predators, the confounding factor of evolutionary history in identifying correlated ecomorphological features, multiple morphological solutions to common functional problems, the limitations of traditional dietary studies during extremes of prey abundance, and an inadequate understanding of the anti- predator defenses of most prey, including modifications that occur during ontogeny or in different habitats.     

Tradeoffs between respiration and feeding in Sacramento blackfish,Orthodon microlepidotus

Synopsis Suspension-feeding fishes use gill structures for both respiration (lamellae) and food capture (rakers). During hypoxic exposure in eutrophic lakes or poorly circulated sloughs, many fishes, including Sacramento blackfish, Orthodon microlepidotus, increase their gill water flows, in part by increasing ventilatory stroke volumes. Stroke volume increases could compromise particle sieving efficiency by spreading interdigitated gill rakers from adjacent gill arches, although blackfish capture food particles by raker-guided water flows to a sticky buccal root. Using van Dam-type respirometers, blackfish respiratory variables and feeding efficiency (Artemia nauplii) were measured under normoxia (> 130 torr PO₂) and hypoxia (60 torr PO₂). Compared with non-feeding, normoxic conditions, gill ventilation volume, frequency, stroke volume, and gape all increased, while O₂ uptake efficiency decreased, during hypoxia and during feeding. O₂ consumption increased during feeding treatments, and % uptake of nauplii showed no difference between normoxic and hypoxic groups. Thus, blackfish display respiratory adaptations, including increased ventilatory stroke volumes, to survive in hypoxic environments such as Clear Lake, California. Importantly, they have also evolved a particle capture mechanism that allows efficient suspension-feeding under both normoxic and hypoxic conditions.