Movements of self-marked caddisfly larvae, Chyrnda centralis (Trichoptera: Limnephilidae), in a Sierran spring stream, California, U.S.A.

SUMMARY. 1. The tendency of larvae of Chyranda centralis to mark themselves by adding coloured plastic segments to their cases was used to study instream movements of the species. Plastic strips of different colours were placed at measured distances down a small spring stream and larvae cut pieces and incorporated them in their cases.
2. Over 50% of the marked population moved upstream into cooler water prior to pupation in an exceptionally dry year. The greatest distance moved upstream by a single larva was 56.9m, In a wet year, when daytime stream temperatures were cooler, 11–28% of the marked population moved upstream. Downstream movement occurred in both years late in the fifth instar.
3. Larvae selected yellow in preference to other colours in laboratory tests and they preferred heavy, textured plastic to light, smooth plastic as they neared pupation.
4. Upstream movements, found also in Desmana bethula (Trichoptera: Limnephilidae) in the same spring stream, may be an adaptation for avoiding pupation in areas of high temperature, low oxygen concentration, or intermittent flow.     

Respiratory behaviour of larvae of four species of the Family Polycentropodidae (Trichoptera)

Larvae of Plectrocnemia conspersa and Polycentropus flavomaculatus from flowing water and Cyrnus flavidus and Holocentropus picicornis from still water were selected for study. In the above sequence, these larvae are associated with increasing ranges of temperature in their natural habitats. Experimental determination of lethal temperatures and investigations on ventilation frequency indicated that the larvae were increasingly tolerant of temperature in the same sequence of species. C. flavidus and H. picicornis showed infrequent ventilation which was little affected over wide ranges of temperature and dissolved oxygen but was stimulated erratically by water flow. P. conspersa and P. flavomaculatus showed more active ventilation which was more sensitive to changes in temperature and dissolved oxygen and was decreased by water flow. Consideration of ventilation in relation to oxygen uptake in P. conspersa and P. flavomaculatus suggests that ventilation activity may account for some 60–70% of active oxygen uptake. Differences in ventilation behaviour may thus be important in limiting larval distribution in stream systems.     

Depth selection by larval Ischnura verticalis (Odonata: Coenagrionidae): effects of temperature and food

SUMMARY. 1. Water temperatures in a shallow, weedy bay of a reservoir in southern Ontario were related to depth; mid-day temperatures in summer were approximately 30°C at the water surface and 20°C below 25 cm.
2. In the laboratory, larval Ischnura verticalis released in a thermal gradient (warmest water near the surface) did not remain near the surface any more than larvae in isothermal conditions. However, larvae in both isothermal and gradient conditions tended to spend more time close to the surface than expected by chance.
3. Larvae provided with food at all depths spent more time near the surface than did larvae with no food. Larvae provided with one feeding site in the coldest water remained near the food as much as did larvae provided with a single feeding site in the warmest water.
4. Results suggest that selection of microhabitats is based primarily on food availability and secondarily on proximity to the surface.     

Radio tracking and activity monitoring of the dobsonfly larva,Protohermes grandis (Megaloptera: Corydalidae)

Summary A miniature crystal-controlled radio transmitter, 7x17x2 mm³ and 185 mg in water, was attached to the back of prothorax of individual dobsonfly larvae, Protohermes grandis. Positions of these larvae in the stream bed were determined using a loop antenna, and they were tracked for 19 days. Actograms were also taken by recording the frequency variation of transmitting signals which were changed according to the larval posture. Larvae changed their positions in the stream bed in some nights, but never in the daytime. However, in most nights (92.7%), they continued to stay at the same position. Actograms revealed that larvae were quite motionless in most time (90.8% of daytime and 89.7% of night). Thus, larvae use the ambush mode of foraging in the central part of riffles where prey are continuously redistributed and sufficient oxygen is supplied with a water current.     

A new species of Acentrella Bengtsson (Ephemeroptera: Baetidae) from Great Smoky Mountains National Park,USA

Acentrella barbarae sp. n. is described from eggs, larvae, and imagines collected from Great Smoky Mountains National Park, North Carolina and Tennessee, USA. Larvae were collected from cobble-pebble substrate in stream rapids. Life stages were associated by rearing. Eggs have longitudinal chorionic ridges with small, longitudinal furrows. Larvae are distinguished by having segment 3 of the labial palp apically rounded, abdominal terga with posteromedian projections, and tibiae and tarsi with relatively short setae on the outer margins. Imagines are distinguished by the colouration and posterior elevation of abdominal terga. Other Acentrella larvae occur in the same streams as the new species, including A. parvula, which we report from Tennessee for the first time. We provide an updated key to the larvae of North American Acentrella species.     

Life history variation in a dobsonfly, Protohermes grandis (Megaloptera: Corydalidae): effects of prey availability and temperature

SUMMARY. 1. The life cycle of a predatory insect, Protohermes grandis (Megaloptera: Corydalidae), was compared in four streams in central Japan. The effects of annual temperature regime and prey availability on life history characteristics were also assessed.
2. The larval period was 2 years and small adults emerged in the Morito River, where summer water temperature was high and large prey scarce.
3. In the Nagura River, rich in large prey, the larval period was also 2 years in spite of slightly lower temperature, and the adult size was largest among the streams.
4. In Anado Fork with a low summer temperature, the larval development took 3 years, and large adults emerged. Large prey were abundant in this stream.
5. Seasonal abundance of large prey also affected the time large larvae left the stream to pupate. Larvae emigrated earlier in streams where the density of large prey sharply decreased after spring, than in streams where large prey were available throughout the year.     

The repair of larval cells and other larval activities in Geotrupes spiniger Marsham and other species (Coleoptera, Scarabaeidae)

Abstract. 1. G. spiniger larvae repaired openings in their cells by excavating dung from the brood-mass and placing it in the edge of the hole. Thrusting with the head sealed small holes but pushed dung away from larger defects. Sliding and somersaulting movements allowed repair of different parts of a defect. Repair was provoked by contact with the defect, not by changes in humidity.
2. Dung excavated at the anterior end of the cell was transferred by somersaulting, and thrust into the posterior end to seal off foreign bodies. Burrowing by the larvae depended on similar behaviour which moved the whole cell within the brood-mass.
3. Larvae were sensitive to surface contact, making a coordinated attack on a source of stimulation. They also moved towards dung and wet soil.
4. Fluid regurgitated by disturbed larvae killed blowfly larvae when injected, and repelled earthworms.
5. To construct a pupal cell, excavated material was transferred by somersaulting and used to build a transverse partition without the usual vigorous thrusting movements. The ability to re-initiate pupal cell formation was retained for about 4 days.
6. Larvae enclosed in artificial brood-balls enlarged defects while attempting to repair them, but larvae just prior to pupation taken from recently made pupal cells could repair such defects.
7. Aphodius fossor larvae rarely attempted to repair openings in their cells and usually escaped by burrowing (as above), but opening a recent pupal cell always provoked repair.
8. Repair by G. spiniger larvae is closely related to other larval activities but lacks several features that are important for repair by species developing in freestanding brood-balls.     

Asymmetric resource competition in a filter-feeding stream insect (Hydropsyche siltalai; Trichoptera)

SUMMARY. 1. Field experiments in a lake outlet stream were carried out on filter-feeding larvae of the caddisfly Hydropsyche siltalai Döhler, to assess whether microhabitat quality, establishment and growth rate is affected by position (upstream—downstream) within a dense aggregation of larvae.
2. Artificial substrates holding high-density aggregations of hydropsychid larvae were used. Marked III-instar H. siltalai larvae were implanted either in the upstream end or in the downstream end of an aggregation and recovered after 17 days.
3. Larvae recovered from the downstream end of an aggregation were smaller than those that had been implanted in the upstream end.
4. Fewer larvae had settled in the downstream end of aggregations compared to the exposed upstream part.
5. Naturally colonizing H. sitalai larvae were, in contrast to implanted larvae, more numerous behind aggregations. Small (first and second instar) Hydropsyche angustipennis (Curtis) and/or H. pellucidula (Curtis) larvae were more numerous in front of aggregations.
6. Current velocities, measured with a microcurrent velocity meter, and density of drifting prey, were significantly lower behind aggregations of hydropsychid larvae. Food availability decreased by about 50% behind aggregations.     

Trichomycetes from China and the description of three new Smittium species

Trichomycetes were recovered from the guts of aquatic insect larvae collected from a stream in the Qinling Mountains in western China. These collections included Smittium hecatei, known only from Spain, as well as Smittium simulii and Stachylina penetralis, which appear to be more widely distributed. Caudomyces japonicus, previously recorded only from Japan, also is reported from crane fly larvae (Antocha sp.) from China. We describe three new species, Smittium chinliense from a tipulid host, as well as Smittium naiadis and Smittium nodifixum, both from chironomid larvae. A probable new species of Gauthieromyces was collected in mayfly nymphs and is illustrated but not described here.     

Survival of Diplectrona modesta banks (Trichoptera : Hydropsychidae) during short periods of desiccation

Larvae of the caddisfly, Diplectrona modesta (Hydropsychidae), were found to be permanent inhabitants of a small, intermittent, headwater stream in southern Ontario. They survived desiccation for at least four weeks in summer. A laboratory experiment gave a mean survivorship of 50% after 30 days without water in stream gravel and stones after the larvae had been permitted to construct their shelters. Survivors were those that constructed their tubes deep in the substrate.     

Function of Ventral and Lateral Processes in Larvae of Chironomus (Diptera, Chironomidae)

Oxygen consumption by larvae of five Chironomus species from the Plumosus group belonging to different larval forms was studied. Larvae of C. agilis ( f. l. reductus) were unable to utilize oxygen at its concentrations lower than 1 mg/l. Larvae of C. plumosus ( f. l. plumosus) used oxygen from water at concentrations higher than 0.7 mg/l; pupas of this species and larvae of C. borokensis ( f. l. plumosus) utilized oxygen at concentrations lower than 0.4 mg/l. C. entis and C. muratensis (both-- f. l. semireductus) utilized oxygen from water at its concentrations up to 0.05 mg/l. The lack of correlation between the rate and ability of larvae to use oxygen at low concentrations and the degree of development of processes allows suggesting that these structures are not additional respiratory organs, as is commonly accepted. At the same time, ability of species to inhabit under conditions of oxygen deficiency correlates directly with the size of the processes. Therefore, ventral and lateral processes are suggested to perform a function of excretion of anaerobic metabolism metabolites.     

Ecology of leptocerid caddisfly larvae in an intermittent South Australian stream receiving Eucalyptus litter

SUMMARY. 1. Brown Hill Creck, a small intermittent stream in dry sclernphyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs of Eucalyptus obliqua litter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days.
2. Only two fully aquatic insect species, Lepntorussa darlingtoni and Lectrides varians (Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundant L. darlingtoni ingests organic and microbial material from leaf surfaces, whereas L. varians is a leaf shredder.
3. Larval processing budgets based on laboratory and fleid experiments indicated that L. variant has a greater impact on litter decomposition rates than L. darlingtoni . However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences. L. variaus larvae process a small proportion of the total litter input.     

Simulium metallicum cytospecies E larval habitat characterization in the Altamira focus of onchocerciasis, northern Venezuela

Abstract. Simulium metallicum sibling species E was identified cytotaxonomically from an onchocerciasis focus at Altamira in northern Venezuela. S. metallicum E larvae were sampled monthly from two small mountain streams over a 15-month period (July 1990 to September 1991) and eleven habitat variables were measured at two altitudes. One stream consistently harboured much higher densities of S. metallicum E larvae than the other, with three annual peaks of abundance: during the dry season and at the beginning and end of the rainy season. These peak densities were correlated with high rainfall 4 months previously. Larvae were most abundant on submerged rocks and fallen leaves, in small shallow areas characterized by slow water current, high conductivity and sparse terrestrial vegetation cover. Stream variables which best explained the temporal changes in abundance were water discharge and conductivity. The population dynamics of S. metallicum E appeared to be influenced primarily by interactions between stream discharge and substrate stability. Relevance of these results to vector control with larvicides is discussed.     

The location of parasites within their hosts: the behavioural component in the larval migration of Nippostrongylus bras1l1ensis in the tissues of the rat

The role of larval behaviour in successful completion of tissue migration is briefly discussed and it is related to the passive carriage of larvae along the ‘pipes and tubes’ of the host. Larvae of N. brasiliensis were injected into selected portions of the circulatory system and following periods of 5–60 min they were recovered from the blood, liver and lungs. Larvae were also immobilised in 0·4% piperazine, a dosage which permitted recovery in about 60 min. The dispersion of treated larvae was compared with that untreated controls. It was found that larvae were carried very rapidly in the blood stream and that they became lodged in the first capillary bed that they entered. They could not pass through capillary beds without movements (and/or secretions). A decreased number of adults developed after larvae were introduced via a series of routes which required the larvae to pass through an increasing number of ‘hurdles’ to migration.     

Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation

1. Total counts of blackfly larvae densities over 30- and 57-h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.
2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV-shielded channels were 161% and 168% higher than in the UV-exposed channels. Larval densities in UV-exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV-shielded channels were slight, and not statistically significant, during the same periods.
3. Larvae within UV-exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.
4. A cyclical pattern of UV-induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.     

Prey behaviour and size-selective predation by fish

SUMMARY 1. We investigate the role of differential activity of chiro-nomids as an explanation for the size selection of small larvae by fish.
2. In the laboratory, pumpkinseed sunfish (Lepomis gibbosus L.) selectively consumed large larvae of Chironomus tentans Fab. when no tube-building materials were available. Small larvae were selectively consumed when a mud substrate was provided but there was no difference in predation rates on large and small larvae in sand.
3. Small larvae spent more time out of their tubes than large larvae in the presence of fish, which may explain the selection for small larvae in mud. Large larvae apparently compensated for decreased foraging activity in the presence of fish by increasing activity when fish were absent. Visibility of large larvae inside tubes may account for their increased mortality in sand.
4. Our results suggest that differential activity is important in explaining the size-selective mortality observed in the field.     

ADAPTIVE COLORATION AND GENE FLOW AS A CONSTRAINT TO LOCAL ADAPTATION IN THE STREAMSIDE SALAMANDER,AMBYSTOMA BARBOURI

Predation is an important selective force that influences animal color patterns. Some larval populations of the streamside salamander, Ambystoma barbouri, inhabit streams with fish predators. Other larval salamanders are found in shallow, ephemeral streams that are predator-free. Quantitative melanophore cell counts and estimates of percent body area pigmented indicated that larval coloration is strongly correlated with stream type. Larvae that coexist with fish tend to be lighter than larvae from streams that are Ashless and ephemeral. Two approaches demonstrated that lightly pigmented salamander larvae better match the common background in relatively permanent streams and are less conspicuous to fish than dark larvae. First, using a model based on the spectral sensitivity of the fish and reflectance properties of salamanders and natural stream backgrounds, we showed that light larvae are three times more cryptic than dark larvae on rocks. Second, lighter larvae had higher survival than darker salamanders on rocks in a predator- choice experiment. It is not clear why larvae in ephemeral streams are darker. Larvae in ephemeral streams should be active to feed and develop rapidly and reach sufficient size to metamorphose before seasonal drying. Several hypotheses may explain why larvae tend to be darker in ephemeral streams, such as increased thermoregulatory ability, better screening of ultraviolet radiation (in these shallower streams), or better background matching to terrestrial predators. Among populations where salamander larvae coexist with fish, there are differences in relative crypsis. Larvae from populations with fish and relatively high gene flow from ephemeral populations (where larvae are dark) tend to be darker (with more melanophores) and more conspicuous to predators than those from more genetically isolated populations, where larvae are lighter and more cryptic. These differences illustrate the role of gene flow as a constraint to adaptive evolution.     

Interactive effects of diet and thermal regime on growth of the midge Pseudochironomus richardsoni Malloch

1. Larvae of Pseudochironomus richardsoni were reared to pupation in individual enclosures, in one of three thermal habitats in a northern California stream. The average temperature range in cold seeps was 15–21 °C, while the main channel ranged from 20 to 27 °C, and side pools ranged from 18 to 33 °C. Diet consisted of either diatoms or algal detritus.
2. Specific growth rate ranged from 0.057 to 0.267 day^–1. Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growth rate on mean microsite temperature were also significantly altered by diet. Differences in specific growth rate due to diet are magnified at higher temperatures.
3. Pupae reared on diatoms were larger than those reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relationship between pupal mass and temperature for larvae reared on diatoms.
4. The combined effects of food quality and thermal environment on growth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of food quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.     

Cannibalism and the stage-dependent transmission of a viral pathogen of the Indian meal moth, Plodia interpunctella

1. The transmission of an insect pathogen by cannibalism was studied by a series of choice and no-choice experiments.
2. Infection of Plodia interpunctella larvae with a granulosis virus occurred through cannibalism of infected larvae.
3. Depending on the larval instars of the cannibal and the victim relative to each other, preferential cannibalism of both infected and healthy larvae was observed.
4. Larvae cannibalise healthy, less vulnerable larvae preferentially, but it is argued that there is no evidence that they are avoiding infection.
5. The victim cannibalised can be explained as a balance between the reduced risk of injury and the ease of cannibalism of moribund infected individuals on the one hand and the greater food resource value of healthy individuals on the other.
6. The implications for the insect population dynamics of the transmission of the pathogen via cannibalism and the effective removal of infective particles through cannibalism by immune stages are discussed.     

Heterogeneity of resource utilization in a population of the Australian reptile tick, Aponomma hydrosauri (Denny)

Abstract. 1. The distribution of adult males, nymphs and larvae of the reptile tick Aponoma hydrosauri on their host, Trachydosaurus rugosus , in a study area near Tickera, South Australia, did not follow the Poisson distribution predicted if hosts were infested at random.
2. The non-random distribution of males can be accounted for by geographical heterogeneity in distribution. Adult females also showed geographical heterogeneity in their distribution pattern, but infested their hosts at random over all.
3. Larvae and nymphs show distribution patterns which change both with the time and the locality. However, when these biases are removed the distribution of larvae and nymphs on their hosts is still non-random.
4. Larger lizards tend to have larger numbers of ticks, but this cannot alone account for the clumped distribution.
5. A model is proposed relating the tick distribution pattern to the particular problems of a resource which is hard to find, but plentiful once found.