Durability of Simuliid Silk Pads (Simuliidae,Diptera)

A central aspect of simuliid adaption to life in moving water is a silky secretion which they produce in their salivary glands. This secretion is spread on the substrate surface thereby enabling adhesion of the posterior abdominal hooks of the larvae to the substrate surface. Therefore, silk pads are a prerequisit for simuliid filter‐feeding as well as any kind of locomotive activity. If silk pad adhesion is weak, larvae risk drifting off, either directly or during locomotion. Properties of the adhesive (=silk) as well as the substrate surface may cause weak adhesion. A specialist such as S. noelleri which has little chance of surviving after drifting off its lake outlet habitat, should have adaptations to reduce this risk. Such an adaptation could be very durable silk pads, giving larvae the chance to be safely attached for a relatively long time. In this study larval silk pads of S. ornatum and S. noelleri were stained using Giemsa's staining procedures. Changes in silk pad structure and traces of rot after 2–33 days of exposure to stream water were recorded and compared. Silk pads of S. ornatum and S. noelleri showed differences which indicate differences in ageing processes and biochemistry of this secretion.     

Food of the New Zealand trichopterans Hydrobiosis parumbripennis McFarlane and Hydropsyche colonica McLachlan

The food of the larvae of two New Zealand Trichoptera, Hydrobiosis parumbripennis and Hydropsyche colonica, was investigated between March and November 1971 at the Wainui Valley Stream, Canterbury, New Zealand. Most samples were collected from an experimental channel constructed in the stream in 1970. The first three instars of H. parumbripennis were mainly detrital feeders, whereas the two later instars were exclusively carnivorous. In contrast, H. colonica was omnivorous. The main prey taken by H. parumbripennis were larvae of a simuliid, Austrosimulium tillyardianum, Chironomidae (subfamily Orthocladiinae), and an ephemeropteran, Deleatidium sp. The first three instars appeared to select chironomids in preference to simuliids, whereas the converse was true for the final two instars. The main prey taken by H. colonica was A. tillyardianum. The size of prey and the mean number of prey found per larva of H. parumbripennis increased with each instar. Forage ratios indicated that H. parumbripennis were eating A. tillyardianum at the same relative frequency as their abundance in the fauna, but that the chironomids and Deleatidium sp. were being preferentially selected as prey. Cased caddis larvae were avoided as food items, as was the mollusc Potamopyrgus antipodarum. Although H. parumbripennis was the most important predator of A. tillyardianum in the stream, it is considered that it has little effect on the simuliid population.     

Diel food utilization by woundfin,Plagopterus argentissimus,in Virgin River,Arizona

Synopsis Woundfin, Plagopterus argentissimus, fed predominantly on simuliid larvae during the day, and shifted to the larger Hydropsyche spp. at night. Ephemeropteran larvae were eaten nearly uniformly throughout the 24 hour period. Mean weight of food consumed varied from 20–40 mg per individual (0.7–2.5% body weight) throughout the 24 h period. Our estimated daily ration of about 8% body weight, at temperatures that varied between 15–25°C, is based upon our measure of mean gut contents over a 24h period, combined with intestinal evacuation rates suggested for other cyprinids in the literature. The relatively continuous feeding pattern suggests a foraging strategy that would minimize competition with other species for food during June, a period of minimum annual food abundance in Virgin River.     

Alpine newts (Triturus alpestris) as top predators in a high-altitude karst lake: daily food consumption and impact on the copepod Arctodiaptomus alpinus

1. Population dynamics and feeding ecology of adult and larval alpine newts (Triturus alpestris, Laurenti) were investigated in a high-altitude karts lake to estimate their feeding pressure on the copepod Arctodiaptomus alpinuf (Imhof). Estimates of population size for reproducing adults ranged from 666 to 864 individuals in the lake during July and August. Total abundance of larvae before the onset of ice cover varied considerably between 4400 and 25400 individuals in different years. 2. Arctodiaptomus alpinus was an important prey item for adult and larval alpine newts. During the second half of their aquatic period, adult newts moved to deeper water where the copepod reached its highest densities near the sediment. Adults and larvae exhibited no periodic feeding pattern. The feeding rhythm was more synchronized among the larvae than among the adults. 3. Daily food consumption, estimated using the Elliott & Persson (1978) model, reached 4–21 mg dry biomass in adults. The daily ration of larvae was about 7% of body dry weight in the temperature range 6-11°C. Compared to published estimates of daily food consumption in salmonid fishes, the feeding pressure of newts appears low.     

An assessment of biological interactions in an epilithic stream community using time-lapse cinematography

In situ time-lapse cinematography was used to record and enumerate behavioral interactions between members of an epilithic insect community in a small Michigan (U.S.A.)trout stream. 145 interactions were observed during 78 hours of filming. Most of these (98%) involved simuliid larvae. Interactions between simuliid larvae occurred at about the same frequency as interactions between simuliids and other taxa. However, interactions between simuliid larvae were less likely to lead to emigration than were interactions between blackflies and other groups. Significant short-term fluctuations of faunal density on filmed surfaces were also observed. The causes of these fluctuations appeared varied. The results of a preliminary assessment of interactions and the usefulness of this technique are discussed.     

Life history features of some macroinvertebrates in a French Polynesian stream

The invertebrate fauna of the Opunohu River catchment in Moorea, French Polynesia, studied 1988–1989, was numerically dominated by four species of neritid snails, one species of thiarid snail, two species of atyid shrimp, two species of palaemonid shrimp, and ten species of coenagrionid, chironomid, and simuliid insect larvae. Numbers of egg capsules of neritid snails were higher in riffles (maximum x density > 10,000/m² surface area) than pools, were highest in riffles in September and pools in August, and were lowest in both habitats in March and December. The snail Neritina canalis Lamarck and the shrimp Atyoida pilipes Newport, Caridina weberi DeMan, Macrobrachium lar Fabricius, and Macrobrachium australe Guerin‐Menévílle are diadromous: they enter freshwater as juveniles and migrate upstream; their larval offspring return to the ocean for growth and development. Ovigerous females of A. pilipes and M. lar were mainly found in austral fall; ovigerous females of C. weberi and M. australe were found in both austral fall and spring. Ovigerous females were the largest individuals of each shrimp species collected. Mean size of N. canalis, A. pilipes, C. weberi, and M. lar was generally larger in upstream than downstream reaches; no such difference was found for the non‐diadromous thiarid snail Melanoides tuberculata Müller. Coenagrionid, chironomid, and simuliid insect larvae have multiple cohort populations but at least one simuliid species occurs as a single cohort. Downstream habitat alteration may strongly influence the distribution of diadromous species.     

Xenochironomus ceciliae (Diptera: Chironomidae), a new chironomid species inhabiting freshwater sponges in Brazil

Chironomids living inside freshwater sponges are scarcely known, particularly in the Neotropical region where most of them are to be described. Here, male and female adults, pupa and 4th instar larva of Xenochironomus ceciliae sp. n., living in freshwater sponges of the Paraná River (Brazil) are described. The larval labrum with its several densely setose or combed structures somewhat resembling the filtering structures of simuliid larvae and the predominance of fine detritus in the larval gut contents, may indicate that the larvae of Xenochironomus ceciliae sp. n. are collector-filterers and they might be favored by the aquifer systems of the sponges.     

Spatial Distribution,Food and Activity of Gomphus pulchellus SELYS 1840 (Insecta; Odonata; Gomphidae) from a Still Water Habitat

Distribution patterns of Gomphus pulchellus larvae in different sediments with different density of prey organisms were studied in the field in a small gravel pit lake in the south of Germany. Larval burrowing behaviour at different temperatures as well as food preference, consumption rates and activity were studied in laboratory experiments. In the study lake G. pulchellus larvae lived exclusively in places where macrophytes were present and in fine sediments (mean grain size <3 mm) with detritus cover. There was a significant positive correlation between larval density and density of food organisms suggesting that abundance of food is one of the determinants of larval distribution. In late autumn larvae migrated to deeper places probably to survive the winter. Low temperatures simulated in laboratory experiments did not induce larvae to burrow deeper. Larvae were always found in a sediment depth of 0.59–0.74 cm. Experiments with mixed prey showed that G. pulchellus larvae preferred tubificid worms and chironomid larvae over gammarids and ephemerid larvae. However, chironomid larvae which stayed in their tubes had a higher survival rate than those outside of tubes. Single-prey experiments showed that G. pulchellus larvae can prey not only on benthic species but also on Daphnia from the open water. Functional-response experiments showed that one G. pulchellus larva consumes a maximum of 2 to 3 tubificid worms or chironomid larvae per day, which corresponds to a maximum biomass (freshweight) of 5 to 30 mg per day. Video recordings of activity showed that G. pulchellus larvae cover long distances of up to 52 m per night on the substrate surface and that activity on the substrate surface started after midnight and ceased before sunrise. Consumption of Zooplankton prey and high activity above the substrate is interpreted as an adaptation of G. pulchellus larvae to the life in still water habitats.     

Disappearance of koaro,Galaxias brevipinnis,from Lake Rotopounamu,New Zealand,following the introduction of smelt,Retropinna retropinna

Synopsis Koaro, Galaxias brevipinnis, were once the only fish present in Lake Rotopounamu but, after a comprehensive survey in 1990, none were found in the lake or its tributary streams. Introduced native fish, specifically smelt, Retropinna retropinna, and the common bully, Gobiomorphus cotidianus, now occur in this lake. As koaro co-exist with bullies in other lakes, but have declined in landlocked lakes containing smelt, the disappearance of koaro in Lake Rotopounamu is attributed to the introduction of smelt alone. Interspecific competition for food between 0 + year old koaro and smelt, combined with predation by 2 + year old smelt on koaro larvae, are thought to be responsible. Such a mechanism would be consistent with theoretical predictions of predator-prey regulation systems within same chain food webs. Rainbow trout, Oncorhynchus mykiss, which were introduced into a number of local lakes before smelt, and which preyed on the koaro, have been blamed for the decline of the koaro populations. However, the disappearance of koaro in Lake Rotopounamu shows that smelt can reduce koaro populations independently of trout predation.     

Biogenic methane contributes to the food web of a large,shallow lake

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Central place foraging in larvae of the charaxine butterfly,Polyura pyrrhus (L.): A case study in a herbivore

Central place foraging by larvae of the charaxine butterfly,Polyura pyrrhus, was studied. Larvae made foraging trips from the silken pads they constructed on leaflets of their foodplant,Acacia sp. A foraging trip sometimes involved complete depletion of a single patch of foodplant pinnules. Larvae which did not deplete a patch appeared to eat until they were satiated, whereas larvae which depleted a patch either visited another patch (multiple-patch foraging) or returned directly to the pad (single-patch foraging). If the food intake at the first patch was small a larva tended to make a “multiple-patch” decision, especially when the pinnule-patch was distant from the resting pad. The duration between successive foraging trips (resting time on the pad) was much longer than the round trip duration: on average about 3 h and 15 min, respectively. The resting time is suggested to be a handling time (i.e., digesting food in the gut) and was disproportional to the amount of food consumed, i.e., the handling efficiency was higher when the larva consumed a larger amount of food. This may be the reason why larvae usually ate until they were satiated. A food-intake-rate maximizing model was constructed to describe the decision rule as to whether a larva should make a single-patch or a multiple-patch foraging trip. One of the model's predictions (i.e., larvae should engage in multiple-patch foraging when the food intake at the first patch is small) qualitatively corresponds with data, however, the model does not explain the effect of travelling time on decision making in larvae. Several other factors which may influence the decision making of larvae are discussed.     

Drift behaviour and microhabitat selection in the preimaginal stages of Simulium chutteri (Diptera Simuliidae)

The aquatic stages of the cattle biting pest, Simulium chutteri Lewis utilize river flow in their dispersal and colonization behaviour. Peaks of drifting activity in S. chutteri larvae occurred in the early morning and late afternoon. It is deduced that female flies scatter eggs onto slow flowing waters upstream of rapids. Larvae hatch from drifting eggs and colonize substrates in slower flowing regions upstream of rapids, while later stage instars move into faster flowing regions within rapids where they complete their development. This microhabitat selection by S. chutteri leads to rapid attainment of large population sizes in suitable sections of river and reduces competition between different stage larvae. In their utilization of a variety of microhabitats the larvae of this species differ from co-existing simuliid species which restrict developmental stages to single habitats.Catastrophic drift was recorded for S. chutteri larvae and could be a mechanism to regulate population size.Drift of simuliid larvae off rapids was not related to benthic population densities in the rapids and was therefore not due to excessive production. It is concluded that larval drift off rapids is related to habitat disturbances associated with water flow fluctuations and the activity of aquatic predators and other animals.The distribution of S. chutteri in the Vaal River is restricted by oviposition requirements of the adult female. Knowledge of drift behaviour and water flow requirements of Simuliidae have been applied to manage the population size of S. chutteri in the Vaal River.     

Density-dependent predation ofChaoborus flavicans onDaphnia longispina in a small lake: the effect of prey size

Functional response curves of fourth instar larvae ofChaoborus flavicans preying on two size classes ofDaphnia longispina were examined throughout three summer seasons in a small forest lake. Data for each size class were fitted to Holling's disc equation. The parametersa (attack rate) andTh (handling time) were calculated for each prey size from these curves. Attack rate was greater and handling time was shorter for small (0.77 mm) than for large (1.82 mm)Daphnia. In 1:1 mixture of these prey size classes the predation rates ofChaoborus on smallDaphnia at prey densities above 20 l^–1 were greater than predicted from the single size-class experiments. The observed predation rates on largeDaphnia were lower than predicted at all prey densities. Since both single size-class and two size-class experiments were run during the same period of time the difference in observed and predicted predation rates could not be attributed to seasonal changes in prey preference ofChaoborus larvae. In experiments with a concentrated mixture of lake zooplankton (dominated byD. longispina)Chaoborus preference forDaphnia decreased as prey body size increased. There was no obvious correlation between selectivity coefficients and size-frequency distributions ofDaphnia. When medium-sizedDaphnia were omitted from calculations the preference of small over large prey did not differ significantly from the predictions of the single size-class model.     

Dietary variations of predaceous caddisfly larvae (Trichoptera: Rhyacophilidae,Polycentropodidae and Arctopsychidae) from British Columbian streams

The diets of larval Rhyacophilidae (Rhyacophila inculta), Polycentropodidae (Polycentropus variegatus) and Arctopsychidae (Parapsyche almota and P. elsis) from five streams in the University of British Columbia Research Forest, British Columbia (Canada), are recorded and related to feeding mode/constructional activities and prey representation in the habitat. Particular attention was paid to the extent of dietary overlap and the degree of intraspecific dietary variations between streams. An overall similarity of the diets of the study species was notable and all commonly consumed chironomid (Diptera) larvae, Simulium (Diptera) and Zapada (Plecoptera), although there was interspecific variation in the relative importance of these items. Polycentropus variegatus and Parapsyche spp. ate Baetis and Paraleptophlebia, the latter predators also consuming Hydrachnellae (Acarina). Other prey were generally of minor importance and consequently interspecific dietary overlaps were high. Differences in the range of prey consumed by predaceous Trichoptera were apparent. Free-foraging R. inculta which selectively consumed sedentary simuliid larvae had the narrowest niche breadth. Parapsyche spp. and Polycentropus variegatus foreguts generally contained an over-representation of chironomid larvae compared to their proportionate occurrence in the benthos, and these caddisflies exhibited high niche overlap. The relative importance of chironomids as food for Parapsyche spp. and Polycentropus variegatus is attributed to prey behaviour, i.e. drift, and poorly developed escape responses when they are caught on the predator's net.     

Effect of summer weather on internal loading and chlorophyll a in a shallow lake: a modeling approach

The effect of weather on the eutrophication of a shallow lake was estimated by a hydrodynamic lake model coupled with a simple water quality module. The model was applied to Lake Villikkalanjärvi in southern Finland. This shallow, agriculturally loaded lake may stratify during warm and calm periods in summer and as a result oxygen is often consumed from the hypolimnion, causing high internal loading of phosphorus. Vertical mixing and temperature distribution in the lake were simulated by a one-dimensional, horizontally integrated hydrodynamic model. State variables included in the water quality model were dissolved reactive phosphorus, chlorophyll a and dissolved oxygen. The model was first calibrated against observations from 1989 and 1990. Thereafter, simulations were carried out using weather data from the years 1961 to 1988. The results indicated that warm summer periods may cause high chlorophyll a concentrations due to high internal loading. In four years with exceptionally warm summers the model predicted maximum chlorophyll a concentrations almost twice as high as in years without remarkable internal loading. The model simulates accurately temperature and mixing but the reliability of water quality predictions could be improved by adding more factors regulating algal biomass and sediment phosphorus release.     

Limits for the detection of daily otolith increments in whitefish (Coregonus lavaretus L.) larvae

The formation of daily otolith increments in European lake white-fish was evaluated in the laboratory during 40 days at 4, 6, and 8 °C under limited and ad libitum food supply. Daily increments were easily identified in larvae reared at 8 °C. At 6 °C and, more, at 4 °C, an unstructured perinuclear zone was formed, and daily increments could only be recognized in the light microscope starting from 10 to 35 days after hatching. In some larvae from the 4 °C groups, no increments at all were found. Scanning electron microscopy (SEM) could not improve increment resolution. Only those increments could be viewed by SEM which were visible in the light microscope as well. We conclude that whitefish larvae which experience low (4–6 °C) temperatures during their first weeks of life, hence those which hatch in the lake, cannot be aged by the currently employed preparation techniques.     

Pollen consumed by the solitary bee Tetrapedia diversipes (Apidae: Tetrapediini) in a tropical agroecosystem

Pollen analysis of the larval food supply is an important tool for identifying the plants that provide the floral resources used by bees. The present study documents the pollen sources consumed by larvae of the solitary bee Tetrapedia diversipes in a tropical agroecosystem. A total of 60 pollen types were recorded with three families being the most important. Euphorbiaceae (60.5%), Malpighiaceae (16.8%) and Asteraceae (12.2%) pollen had the greatest representation in the samples examined. The pollen of Dalechampia dioscoreifolia predominated in the diet of the larvae of T. diversipes (RF?=?56.35%) and indicates the importance of this plant in maintaining populations of this solitary bee.     

Predation byOligotricha striata caddis larvae on amphibian eggs: Effects of a high quality food on growth rate

In the field and also in the laboratoryOligotricha striata trichopteran larvae were observed to feed onRana temporaria eggs. Laboratory experiments revealed thatO. striata larvae preferred amphibian eggs to plant matter. The jelly-like sheath of the eggs was easily penetrated. A larva consumed 1 to 2 eggs per day. The supply of high quality food in the form of amphibian eggs was found to accelerate the growth ofO. striata larvae.     

A description of larval and early juvenile development in Paralomis spinosissima (Decapoda: Anomura: Paguroidea: Lithodidae) from South Georgia waters (Southern Ocean)

The early ontogenetic stages of Paralomis spinosissima Birstein and Vinogradow, 1972, are described in detail and illustrated, with notes on morphological variability observed. Larval and early juvenile development was described to the crab I instar reared under controlled conditions of temperature and food supply. The abbreviated larval development invariably passed through two zoeal stages and the benthic megalopa stage. The larval development was completed without food supply, and food Artemia nauplii were first given after moult to the crab-I stage. Simplification and retarded development of the mouthparts are discussed as a function of lecithotrophy of these larvae and based on morphology no facultative feeding mode is suggested. Lecithotrophy in the Southern Ocean Lithodidae is discussed to be an adaptation allowing independence from seasonal food availability at high latitudes.