A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

Effects of dietary sucrose concentration on aphid honeydew carbohydrate levels and rates of excretion

Honeydew droplets freshly excreted by two aphid species, Myzus persicae (Sulz.) and Acyrthosiphon pisum (Harr.), feeding on nutritionally adequate, artificial diets containing 10–40% w/v sucrose, were collected in oil. The volume, frequency of excretion, and carbohydrate content of the droplets were determined by measuring the diameter of the droplets in the oil, by recording the number of droplets excreted per aphid per hour, and by using a quantitative colorimetric method for estimating carbohydrates. Rates for the intake or excretion of fluid, the intake and absorption of sucrose, and the excretion of carbohydrate were consequently calculated for the two species on each dietary sucrose concentration. The percentage of dietary sucrose absorbed by the aphids ranged from 36% on diet with 40% sucrose to 97% on diet with 10% sucrose. Such honeydew/diet relationships may allow one to use honeydew carbohydrate concentrations to estimate the sucrose concentrations of the phloem sap ingested by aphids feeding on host plants.

---

Résumé Des gouttelettes de miellat fraîchement excrétées par deux espèces de pucerons, Myzus persicae (Sulz.) et Acyrthosiphon pisum (Harr.), pucerons nourris sur des régimes nutritifs synthétiques contenant 10–40% de saccharose, ont été récupérées dans de l'huile. Le volume des gouttelettes a été déterminé en mesurant leur diamètre individuel dans l'huile, la fréquence d'excrétion établie par le nombre de gouttelettes excrétées par puceron par heure, et la teneur en glucides par une méthode d'analyse colorimétrique quantitative. Les taux d'ingestion et d'excrétion de liquide, d'ingestion et d'absorption de saccharose ainsi que les taux d'excrétion de glucides ont été par la suite calculés pour les deux espèces d'aphides nourris sur les différentes concentrations de saccharose. Le pourcentage de saccharose alimentaire absorbé par les aphides a été de 36% sur le régime contenant 40% de ce glucide, mais s'est élevé à 97% sur le régime ne contenant que 10% de saccharose. D'après ces relations miellat/régime nutritif, et en connaissant la teneur du miellat en glucides, on peut faire une approximation de la concentration du saccharose dans la sève élaborée du phloème ingérée par les aphides.

     

Thermal stratification and benthic foraging patterns of white sucker

Abundances of white sucker, 100–500 mm FL, were not significantly different among the epilimnia, metalimnia and portions of the hypolimnia shallower than 20 m in each of two lakes. However, small suckers < 200 mm were captured most frequently in the epilimnion and no white suckers were captured in the deepest region, 20–38 m, of the two lakes. White suckers consumed prey from all three temperature zones in each lake. Prominent food items were Hyalella azteca and the chironomid larvae Heterotrissocladius, Djalmabatista and Procladius. Despite differences in relative densities of benthic invertebrates among thermal zones of the two lakes, suckers in neither lake foraged exclusively on prey of epilimnetic origin. Suckers captured in the metalimnia foraged on invertebrates that were common to all three thermal zones. And, only 0–4% of the suckers captured in the hypolimnia of the two lakes contained prey that were unique to the epilimnia. Suckers caught in the hypolimnia mainly consumed deep water invertebrates; 83% of the suckers foraged in the metalimnion and hypolimnion of Islets Lake and 45% foraged in the hypolimnion in Burnt Island Lake. Consequently there was little evidence of a massive inshore feeding migration followed by a post-feeding return to the hypolimnion. Northern pike and lake trout rarely fed on white suckers in these lakes and thus piscivory was an unlikely factor in the observed distribution of suckers.     

Cost of predation avoidance in young-of-year lake trout (Salvelinus namaycush): growth differential in sub-optimal habitats

Selection of habitat to avoid predation may affect the diet of young-of-year (YOY) lake trout (Salvelinus namaycush). YOY lake trout may use inshore habitat to avoid predation; this habitat may be sub-optimal for growth. To test this, YOY lake trout were penned in nearshore and offshore pelagic areas of two arctic lakes. Toolik Lake had a lake trout population, the other lake, S6, did not. YOY lake trout in Toolik Lake lost weight, but those offshore lost less weight. The YOY lake trout in Lake S6 gained weight and those offshore gained more weight. The primary diet item of the YOY lake trout in both lakes during this experiment was the zooplankter Diaptomis probilofensis; it was also one of the most abundant species. However, its density inshore in Lake S6 was similar to inshore and offshore densities in Toolik Lake. The increased availability of alternative zooplankton prey in Lake S6 may account for the growth differential of YOY lake trout in Lake S6 relative to Toolik Lake. Bioenergetic modeling of YOY lake trout suggests that growth similar to that in the offshore of Lake S6 would be necessary for successful recruitment. If the reduced zooplankton availability in Toolik Lake leads to the reduced growth of YOY in the inshore and offshore pelagic areas, then these fish will be more susceptable to winter predation/starvation. For YOY lake trout to survive in Toolik Lake they most likely shift to feeding on benthic prey before the end of their first summer. Dept. of Chemical Engineering     

Effect of dietary nitrogen on gypsy moth larval nutritional indices, development and lipid content

Nutritional indices, development rates, percent dry weights and total lipids were determined in gypsy moth larvae (Lymantria dispar L.) reared on a high wheat germ (HWG) diet or diets prepared from lyophilized, ball-milled oak or pine foliage as the only source of dietary nitrogen (N). With regard to both total and proteinaceous N content, HWG diet>oak diet>pine diet. All nutritional indices measured were significantly lower in second instars fed pine diet vs. oak diet. Protein supplementation of pine diet with either casein or ovalbumin to bring total N up to the level present in oak diet resulted in small increased in approximate digestibility (AD) and effciency of conversion of ingested food (ECI), but relative growth rate (RGR) remained unaffected. The low RGR of larvae fed pine diet (unsupplemented or protein supplemented), as compared to those fed HWG or oak diet, was accompanied by significantly lower larval percent dry weight and percent total lipid. In contrast, RGR, larval percent dry weight and total lipid values were comparable in second instars fed HWG or oak diet. Insects reared from the first through the final instar on oak diet exhibited lower pupal weights compared to those reared on HWG. Casein addition to oak diet generally resulted in even more extended larval development times and further reduced pupal weights, but wheat germ addition to oak diet did not alter development rates and caused an increase in pupal weights.     

Retinol and α-tocopherol concentrations in whole fish commonly fed in zoos and aquariums

Retinol (n = 17 spp.) and α-tocopherol (n = 9 spp.) concentrations in whole fish utilized for captive animal feeding programs were determined by high-performance liquid chromatography (HPLC) following routine storage and preparation after commercial purchase by two zoological institutions. Vitamin A activity was calculated from retinol values and ranged from 55 IU/100 g (immature herring) to >2,000 IU/100 g (salmon) on an as-fed basis. α-Tocopherol values, a measure of vitamin E activity, ranged from 0.9 IU/100 g (butterfish) to 12.3 IU/100 g (tilapia) on a wet basis. Vitamin levels in whole fish were intermediate to values previously quantified for muscle or liver tissues alone. Vitamin concentrations in fish livers were quantified separately in seven of these species; liver contributed 35–63% of total retinol measured and 8–34% of total α-tocopherol. Based on these analyses, whole fish commonly fed in zoos, aquariums, and marine zoological parks would appear to meet vitamin A requirements established for most species without additional supplementation, whereas levels of vitamin E quantified indicate a need for supplementation of diets for piscivores.     

DIET OF WEDDELL SEALS LEPTONYCHOTES WEDDELLII AT VESTKAPP, EASTERN WEDDELL SEA (ANTARCTICA), IN RELATION TO LOCAL FOOD SUPPLY

Thirteen Weddell seals ( Leptonychotes weddellii ) were collected at Vestkapp, eastern Weddell Sea coast, in austral spring 1986. All stomachs contained partially digested food. The mean wet weight of stomach contents was 7.5 kg, 3.3% of the. mean body weight of the collected seals. Twelve fish species and three cephalopod species were identified from 372 left otoliths and 25 lower beaks, representing 58.4% of 679 total prey items obtained. Composition by number of total prey was: Chionodraco myersi (15.8%), Trematomus eulepidotus (10.0%), Pagetopsis maculatus (9.7%), Racovitzia glacialis (9.6%) and Cryodraco antarcticus (4.1%). Otoliths of the seven other fish species and beaks of the three cephalopod species together represented 9.1% of total prey numbers. The pooled wet weights calculated from 13 prey species (regressions for two octopod species were not available) amounted to 43.5 kg food mass and represented 44.7% of the combined food mass in all stomachs. Composition by mass was: C. myersi (44.5%), T. eulepidotus (19.8%), squid Psychroteuthis glacialis (8.5%), P. maculates (7.9%), C. antarcticus (7.1%) and R. glacialis (6.2%). The remaining 7 fish species together represented 5.8% by mass. Temporal variation in food availability was apparent. Midwater fish Pleuragramma antarcticum was the staple food of Weddell seals from the same area during the 1985 summer, whereas it was absent in the samples taken in spring 1986. Estimates of fish biomass from net hauls demonstrate a highly variable availability of pelagic food resources for top predators in the Vestkapp area.     

Differential diet breadths and species coexistence in leafroller-hunting eumenid wasps

There are, at least, three possible ways in which similar species coexist; resource partitioning, interference competition, and exploitation competition. Here, I investigated which way contributed to the coexistence of leafroller-hunting eumenid wasp species. Resource partitioning and, in addition, differential diet breadths proved to promote species coexistence in this case. First, I analyze the prey records and diet overlap of four eumenid species in a local area. The larger two eumenids hunted similar-sized prey items and had similar potential taxonomic prey uses. But the diet breadth of the subsocial eumenid was much wider than that of the solitary one. As a result, the diet overlap between the two large eumenids decreased. This was because the solitary eumenid attend repeatedly to the same hunting site inhabited by one abundant prey species, while the subsocial one made random hunting. On the other hand, the two medium-sized eumenids partitioned resources according to prey size. Secondly, I related these results to prey choice by several other species of eumenid obtained from literature sources. Ten Japanese common eumenids were divided into four groups according to their prey size. In each of the four groups, 2 to 3 wasp species differentiated the habitat (1 group) or coexisted by means of differential diet breadths (parallel with differential sociality, 2 groups).     

Mass rearingCeratitis capitata: reuse of the finisher larval diet

The standard finisher larval diet used at Seibersdorf for rearing the Mediterranean fruit fly,Ceratitis capitata (Wiedemann), was reused following autoclave heat-treatment to kill larvae or pupae remaining from its first use. Only when the spent diet was mixed with water (about 40% of final diet, w/w) to reconstitute fresh-diet texture, and combined with fresh starter, a similar, but still inferior in respect to larval duration and pupal recovery and size, to the fresh finisher diet production of flies was achieved. Enrichment of the autoclaved spent finisher with small quantities of nutrients gave inconclusive results. Although spent-diet pupae were significantly smaller than fresh-diet control pupae, their adults survived significantly longer than control adults.

---

Zur massenaufzucht vonCeratitis capitata: die wiesderverwendung der endkomponente der larvendiät

Zusammenfassung Die in Seibersdorf zur Aufzucht der Mittelmeerfruchtfliege,Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), verwendete Standardendkomponente der Larvendiät konnte nach Abtötung der von der Erstverwendung verbliebenen Larven oder Puppen mittels Autoklavensterilisation wiederverwendet werden. Eine zur frischen Kontrolldiät vergleichbare, jedoch bezüglich der Länge des Larvenstadiums, der Entwicklung der Puppen nach dem Schlüpfen sowie der Größe der Puppen noch immer schlechtere Fliegenproduktion wurde erreicht, wenn die wiederverwendete, autoklavierte Diät mit Wasser (ca. 40% der Enddiät, w/w) zwecks Rekonstitution zur frischen Diättexture gemischt und mit frischem Starter kombiniert wurde. Eine Anreicherung der wiederverwendeten Diätendkomponente mit geringen Mengen von Nährstoffen ergab keine schlüssigen Resultate. Obwohl Puppen der wiederverwendeten Diät signifikant kleiner als Puppen der Frischdiät-Kontrolle waren, überlebten deren Erwachsene signifikant länger als die Erwachsenen der Kontrolle.

     

Intraspecific resource partitioning in a headwaters stream fish,the pearl dace Semotilus margarita (Cyprinidae)

Synopsis Pearl dace, Semotilus margarita, are common in slow-moving channels and pools of the headwaters of the Brokenhead River. From May to September age groups 0, 1 and 2+ were partially segregated in space based on water depth with age 0 occupying shallow pools and shallow channels. Age 1 were abundant in shallow pools and deep channels while age 2+ occurred in deep channels and deep pools. In November all age groups coexisted in deep pools. Pearl dace are omnivorous consuming invertebrates, plant material, and detritus. From May to September age groups 0 and 1 consumed mainly terrestrial invertebrates (Diptera, Hymenoptera, Thysanoptera) but age 1 consumed more detritus than age 0. Age 2+ consumed mainly aquatic Diptera larvae. Although all ages consumed aquatic insects almost exclusively in November differences in diet between age groups still existed. Younger fish fed higher in the water column than older fish. Intraspecific resource partitioning of food and space occurs between age groups and this combined with the omnivorous diet is highly adaptive to the headwaters of streams.