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PubMed2000

Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae), a potential indicator of chronic toxicity of malathion (organophosphate insecticide).

A laboratory study on the sublethal effects of malathion on the net-spinning behavior of the caddisfly larvae Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to organophosphorus insecticides. Two anomalies were identified after chronic exposure to 0.01, 0.05, 0.1, 0.5 and 1.0 µg l(-1) malathion. The first was a distortion of the midline meshes where the normal diamond shape structure was disrupted and the meshes were separated by extra strands (called 'midline' anomaly). The second aberration observed was a significant decrease in net symmetry. Both anomalies were highly correlated to the toxic action of malathion, i.e. inhibition of the acetylcholinesterase enzyme (AChE). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses of capture nets did not show any modification of silk polypeptides after exposure to malathion, indicating that net distortions were not related to silk composition. Both anomalies seem to represent the symptoms of the specific toxic action of malathion; nevertheless, they can serve as an index of the physiological condition of the larvae, especially the midline anomaly. The symmetry of the nets decreased significantly after exposure to 0.5 and 1.0 µg l(-1). However, the toxicity curves (EC(50)) showed that the sensitivity threshold for the midline anomaly ranged from 0.11 to 0.28 µg l(-1), which reflect more realistic exposure to concentrations expected to occur in the field. Hence, the use of capture net anomalies of hydropsychid larvae could represent a valuable indicator of sublethal toxicity induced by malathion and other organophosphorus insecticides in running waters.

Journal Article↗
PubMed1997

Effects of episodic sedimentation on the net-spinning caddisflies Hydropsyche betteni and Ceratopsyche sparna (Trichoptera: Hydropsychidae).

Net-spinning caddisflies commonly inhabit the chronically sedimented waters of midwestern agricultural catchments despite the presumed costs of sedimentation-induced gill-and net-fouling. We conducted a laboratory experiment to determine whether larval growth and survival of Hydropsyche betteni and Ceratopsyche sparna are affected by daily exposure to moderate levels of sedimentation. Sedimentation did not alter the relative growth rate of either species although slight losses by H. betteni and gains by C. sparna produced significant differences between species. H. betteni had a decreased likelihood of survival in sedimentation treatments relative to controls, but significantly outperformed C. sparna overall. Larval C. sparna are reportedly more sensitive than H. betteni to the instream effects of agricultural land use; however, the results of this experiment suggest that this differential sensitivity is probably not caused by episodic increases in suspended sediment concentration.

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PubMed2000

Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae) following a sublethal chronic exposure to cadmium.

A laboratory study on the sublethal effects of cadmium (Cd) on the net-spinning process of the larvae of Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to Cd. Two major anomalies with different frequency levels were identified after chronic exposure to 0.37, 1.2, 11.6, 21.4 and 43.3 microg l(-1) of Cd. The first was a distortion of the midline meshes where the diamond-shape structure is disrupted and the meshes are separated by extra strands (called 'midline' anomaly). The second aberration consisted of a distortion of the rectilinear structure of net opening by strands being fused or added over the meshes (called 'crossover' anomaly). The midline distortion may be linked to a physiological stress caused by Cd, which can affect the control of the net-spinning process. It was not possible to relate the crossover aberrations to a specific toxic action of Cd, but data indicated that both anomalies are independent from each other and that two modes of action could be implicated. Protein analyses of capture nets have revealed silk polypeptide modifications at the highest Cd concentration tested, indicating a possible effect of Cd interaction with silk proteins. However, neither a gradient-concentration nor a time-dependent response could be established with both aberration frequencies. Silk protein modifications would rather play a secondary role in the appearance of both net anomalies, and mostly at a high concentration level. Finally, the toxicity curves (EC(50)) show that the sensitivity threshold for both types of aberration ranged from 1 to 5 microg l(-1) which is highly sensitive compared with other sublethal effects of Cd on other macroinvertebrate species. Hence, the use of capture-net anomalies of hydropsychid larvae would represent a valuable indicator of sublethal toxicity induced by Cd and possibly by other metals in running waters.

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PubMed2004

Biodiversity of Minnesota caddisflies (Insecta: Trichoptera): delineation and characterization of regions.

Despite the value of aquatic insects in aquatic ecosystem biomonitoring, few studies within North America have addressed relationships between aquatic insect assemblages and landscape-level environmental variables. In this study, over 300,000 adult caddisfly specimens representing 224 species were collected and analyzed from samples of 225 Minnesota aquatic habitats within 58 watersheds. Detrended Correspondence Analysis and a UPGMA dendrogram of caddisfly relative abundance data determined that five regions of caddisfly biodiversity exist within the state. Species richness and diversity were significantly highest in the Lake Superior and Northern regions, lowest in the Northwestern and Southern regions, and intermediate in the Southeastern region. Canonical Correspondence Analysis determined that caddisfly species composition was related to temperature, percentage of disturbed habitat, and stream gradient. Although a strong correlation between temperature and percentage of disturbed habitat made determination of the relative importance of those variables difficult, it is likely that anthropogenic disturbance has decreased caddisfly biodiversity in at least the Northwestern and Southern regions. Now that regions of biodiversity have been established, future changes to the fauna can be evaluated with greater precision and confidence. This study represents the most comprehensive faunal analysis of an aquatic insect order within the Western Hemisphere.

Animals↗
PubMed2003

Morphological characteristics of sensilla on the female ovipositor of Lype phaeopa (Psychomyiidae; Trichoptera).

An important aspect of the association of Lype phaeopa (Stephens) with submerged wood is the oviposition behavior of adult females, which preferably oviposit their eggs on moist emergent or submerged parts of woody debris with a structured surface. The eggs are commonly deposited in cracks and crevices using the elongated ovipositor. Ovipositor morphology and various sensilla on the tip and along the ovipositor were studied by scanning electron microscopy and their possible function discussed. Structure of these sensilla and pre-oviposition behavior of the females point to a preference for certain oviposition sites on woody debris. This may be a key factor for the distribution and development of the larvae.

Animals↗
PubMed2005

Reach-scale distribution dynamics of a grazing stream insect, Micrasema quadriloba Martynov (Brachycentridae, Trichoptera), in relation to current velocity and periphyton abundance.

Reach-scale temporal shifts in the distribution of larvae of a grazing caddisfly, Micrasema quadriloba (Brachycentridae), were investigated in a Japanese mountain stream. The larvae showed an aggregated distribution within the reach at the beginning of the immigration, then became randomly dispersed throughout the reach as the immigration progressed. The abundance of periphyton in the reach decreased dramatically with increasing dispersal of the larvae. Simple regression analyses revealed that the stream's flow regime was the most important environmental factor that determined the reach-scale distribution of the larvae and that the relationship between the flow regime and the distribution of the larvae shifted temporally. In addition, our results suggest that only this species of grazing insect, which was dominant in the study reach, controlled the reach-scale abundance of the periphyton.

Animals↗
PubMed1977

The embryonic development of the marine caddis fly. Philanisus plebeius Walker (Trichoptera: Chathamidae).

1. P. plebeius, a trichopteran with marine intertidal larvae, oviposits in the coelom of a starfish, Patiriella exigua. Oviposition occurs mainly in the spring and autumn months. 2. In spite of the intracoelomic location of the embryos, the development of P. plebeius follows an unmodified trichopteran mode, including the characteristic blastokinesis. Nutrients are not supplied to the caddis embryos by the host starfish. 3. Hatching takes place in the starfish coelum after 17-18 days. The newly hatched caddis larvae quickly escape to their rock pool habitat. 4. The form of the female ovipositor indicates that other species of Chathamidae utilize starfish species as oviposition hosts. 5. This mode of oviposition offers protection to the caddis embryos in the intertidal habitat.

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PubMedDate not supplied

[The conflict between optimisation and orderliness in building behaviour of the caddis fly, Chaetopteryx villosa Fabr.(Limnephilidae: Trichoptera), larvae].

The Optimal Foraging Theory predict that an animal should restrict its searching activity to those patches of environment, where the ratio of gain to time and energy spent is maximal. Experimenters usually verify the prediction against the null hypothesis of random activity distribution between patches. As animals always prefer profitable patches to some degree, experimental results can always be interpreted as confirmation of the theory. In opposite to this approach, we put forward the "regularity hypothesis". According to this hypothesis, the finding of a profitable item in some patch makes an animal to stay and test more items within the patch. The readiness to test decreases if the profitability of these items is low, and the animal eventually leaves the patch. It also searches in other patches less carefully. As a result, positive and negative responses to items are repeated by ordered series. In general, this regularity of responses helps animals to choose profitable patches. However, animals may also ignore some profitable patches because of the regularity, so that the behavioural optimazation fails. The regularity hypothesis have been tested in experiment with the search of building material and patch choice by caddisfly larvae. The first of two experimental patches contained egg shell fragments (profitable building material) mixed with a sand (unprofitable). The second patch contained sand only. Larva stayed within the first patch after a shell had been found, so that the probability to find more shells increased. However, larvae started walking after they had found several sand particles. Once starting to walk, they found new shell fragments and tested them, but tended to reject them and eventually leave the patch. Moreover, upon returning to the first patch, larvae also might reject fragments and leave the patch again. Rejections are accounted for by the fact that the duration of testing was too short to identify fragments correctly. As a result, negative responses were repeated to a certain degree independently of the profitability of building material, and the patch choice was not optimal. These results are agreed with the regularity hypothesis. It is argued that the hypothesis can be used as an alternative to the Optimal Foraging Theory.

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