Paragnetina Media Research Articles

Ontogenic changes in prey consumption by the stoneflyParagnetina mediain relation to temporal variation in prey nutrient content

In Duffin Creek, Ontario, nymphs of the predatory stonefly Paragnetina media (Perlidae) commonly feed on detritus and three prey types: hydropsychid larvae (Hydropsyche sparna and Hydropsyche slossonae), nymphs of the mayfly Baetis tricaudatus, and chironomid larvae belonging to subfamilies Tanypodinae and Orthocladiinae. This study examined temporal changes in the nutrient (lipid and protein) content of these prey to determine if the predator tracks food resources by selecting prey on the basis of nutrient requirements at different stages in its own development. All three common prey types exhibited temporal variation in lipid levels, with peaks occurring at different times: June for the hydropsychids, August for the chironomids, and October for B. tricaudatus. Prey protein levels were less variable. The proportions of the prey types that were eaten varied throughout the year and according to predator size. For example, while small P. media ate mostly detritus, they also consumed early-instar hydropsychids during the larval recruitment period of the latter; mid-sized nymphs included more animal matter in their diet, primarily chironomid larvae; and larger nymphs primarily ate B. tricaudatus. Paragnetina media nymphs in all size categories showed an increase in body lipid level in the autumn, suggesting a general accumulation of lipid reserves in readiness for the winter, although dietary adjustment to accomplish this was detectable only in small P. media. There was no evidence to suggest that P. media selected prey on the basis of the latter's protein content. Male P. media nymphs preyed predominantly on chironomid larvae and included mites in their diet, whereas female nymphs preferred B. tricaudatus and hydropsychids. On a per milligram body mass basis, male nymphs had the higher nutrient gain, since, for both lipid and protein, intake by males was between two and three times that by females. However, male and female bodies had similar lipid contents. We conclude that whereas there is temporal variation both in the nutritional (lipid and protein) content of the common prey of P. media and in this predator's diet, there is only weak evidence for nutrient-resource tracking.

Survival and Hatching Success of Stonefly Eggs (Paragnetina media) Following Ingestion by Three Stream Fishes

ABSTRACT The effects of predation by three stream fishes (emerald shiner, creek chub, and mottled sculpin) on the survival and hatching success of eggs of the northern stonefly, Paragnetina media (Walker), were investigated with feeding and incubation experiments. Stonefly eggs displayed a 75% survival rate through the digestive system, but no statistically significant difference (p > 0.05) was observed in the recovery of intact eggs from the three fishes. Approximately 73% of the eggs that passed through the emerald shiners and mottled sculpins hatched within 60 days. Significantly fewer eggs (p = 0.002, 63%) hatched following passage through the creek chubs. Previous studies have shown that stonefly eggs can survive periods of freezing, desiccation, and harsh physical conditions. The present study shows that stonefly eggs can also survive passage through the digestive system of predatory stream fishes and this may represent a previously uninvestigated mechanism for localized dispersal.

Ontogenic changes in prey consumption by the stonefly <i>Paragnetina media</i> in relation to temporal variation in prey nutrient content

In Duffin Creek, Ontario, nymphs of the predatory stonefly Paragnetina media (Perlidae) commonly feed on detritus and three prey types: hydropsychid larvae (Hydropsyche sparna and Hydropsyche slossonae), nymphs of the mayfly Baetis tricaudatus, and chironomid larvae belonging to subfamilies Tanypodinae and Orthocladiinae. This study examined temporal changes in the nutrient (lipid and protein) content of these prey to determine if the predator tracks food resources by selecting prey on the basis of nutrient requirements at different stages in its own development. All three common prey types exhibited temporal variation in lipid levels, with peaks occurring at different times: June for the hydropsychids, August for the chironomids, and October for B. tricaudatus. Prey protein levels were less variable. The proportions of the prey types that were eaten varied throughout the year and according to predator size. For example, while small P. media ate mostly detritus, they also consumed early-instar hydropsychi...

A study of the Malpighian tubules of the plecopteran nymph Paragnetina media (Walker) (Plecoptera: Perlidae) by light, scanning electron, and transmission electron microscopy

The present study concerns the structural details of the Malpighian tubules in the nymph of the stonefly Paragnetina media. There is no external segmentation except for a distal short hyaline segment. The tubules are composed of two cell types: primary and stellate. Primary cells in the proximal and middle portions of the tubule have short infoldings of the basal membrane and the cytosol is packed with laminate spheres. Cells of the distal segment possess long and tightly packed membrane folds but are devoid of laminate spheres. The stellate cells are sparsely distributed in the middle region and make up 12% of the total cell population in the Malpighian tubule; they lack laminate spheres. Long processes of the stellate cells extend between adjacent primary cells to the luminal and outer surfaces of the tubule.

Disturbance to a stream food web by a bacterial larvicide specific to black flies: feeding responses of predatory macroinvertebrates

SUMMARY1. A field study was conducted to: (i) assess feeding habit changes of two predatory stoneflies following the loss of larval black fly (Diptera: Simuliidae) prey from two streams; and (ii) determine the relative importance of black fly larvae as prey for these and other selected predatory benthic macroinvertebrates.2. Acroneuria lycorias and Paragnetina media (Plecoptera: Perlidae) diets were monitored in response to local reductions in larval black fly populations caused by Bacillus thuringiensis var. israelensis (B.t.i.) in two Michigan streams. These predators were collected from B.t.i.‐treated and control sections of the streams, and their foreguts inspected for prey.3. Black flies were the major dietary component of both predators collected from the control sections, but the number of black flies ingested was significantly less for predators collected from B.t.i.‐treated habitats. Total number of prey ingested significantly decreased for A. lycorias, but not for P. media, and non‐black fly prey consumption significantly increased for P. media, but not for A, lycorias, following B.t.i. applications.4. In prey choice trials conducted in experimental channels, A. lycorias and P. media showed no preference between prey types (black flies and mayflies). Body mass gain of individual A. lycorias nymphs was measured, and was similar for nymphs in black fly‐rich and black fly‐poor environments. Conversely, Isoperla signata and I. dicala (Plecoptera: Perlodidae) ingested significantly more Simulium vittatum (Diptera: Simuliidae) than Baetis flavistriga (Ephemeroptera: Baetidae) or Epeorus vitrea (Heptageniidae) prey. Boyeria vinosa (Odonata: Aeshnidae) ingested significantly more B. flavistriga than S. vittatum prey.5. Reducing black fly densities in these streams, using B.t.i., indirectly and differentially affected predators. In black fly‐poor environments, feeding habits of specialist predators were most affected, and generalist predators least affected because the latter consumed alternative prey. Predator—predator and predator‐prey interactions, and prey community structure may be affected indirectly by disturbances such as B.t.i. applications by reducing food resources and forcing predation onto less preferred prey.

Feeding variability among individual aquatic predators in experimental channels

Experiments were conducted in experimental channels to study feeding variability through time and between conspecific individuals of four species of lotic predators. Large and small Rhyacophila dorsalis (Trichoptera: Rhyacophilidae) were given black fly larvae, mainly Simulium ornatum (Diptera: Simuliidae) of two size classes during laboratory feeding trials lasting up to 5 days. Acroneuria lycorias (Plecoptera: Perlidae) were also given black fly larvae (Prosimulium fuscum, S. venustum) during 11-day laboratory feeding trials. Paragnetina media (Perlidae) and Isoperla signata (Plecoptera: Perlodidae), were supplied with a mixed prey assemblage of black fly larvae and mayfly nymphs, Baetis flavistriga (Ephemeroptera: Baetidae), and Epeorus vitrea (Heptageniidae), for 9 days in field experiments. There was significant variability in the consumption of prey among individuals of R. dorsalis, this being true for both large and small predators. Significant among-predator and day-to-day feeding variability also occured with A. lycorias, P. media, and I. signata. Our experiments showed that there are significant differences in prey consumption among individual predators within a given species, and these differences need to be considered when planning, and interpreting, future studies on predator – prey interactions, particularly those conducted in experimental streams.

Relationship between Diurnal Activity Patterns, Cryptic Coloration, and Subsequent Avoidance of Predaceous Fish by Perlid Stoneflies

We demonstrate that prey (stoneflies), which are either solidly coloured or patterned, coordinate intervals of maximum daytime activity with periods when visually foraging predators (rainbow trout, Oncorhynchus mykiss) are least able to detect them. In this study, rainbow trout attacked solidly coloured stonefly nymphs (Paragnetina media) more frequently under conditions of low illumination (simulated dawn and dusk) than high illumination (simulated midday) whereas the frequency of attacks on patterned stonefly nymphs (Agnetina capitata) was reversed. Consequently, in both the presence and absence of trout, the activity (i.e. frequency of crawling) of P. media and A. capitata was highest under conditions of high and low illumination, respectively. The number of attacks by trout on all nymphs was significantly less when nymphs were on dark-brown, rather than mottled, substrates. When given a choice between dark-brown and mottled substrate, both species selected dark substrate. Suggestions that the visual acuity of predators varies as a function of light intensity and the coloration, patterning, and daytime activity of prey are corroborated for the first time.

Path and Spatial Learning in a Stonefly Nymph

The ability of an aquatic invertebrate to learn the location of a preferred resource (a group of stones that provide shelter from predators), was assessed. In the first experiment, the stonefly Paragnetina media displayed a capacity for path learning. During successive trials, stoneflies crawled between starting points and substrate assemblages (stone groupings) more quickly when both positions were fixed, than did stoneflies in aquaria in which the starting points were fixed but substrate positions were not. In the second experiment, P. media demonstrated an ability to learn to locate stone assemblages when released at variable points in aquaria (i.e., spatial learning).(...) We demonstrate that stoneflies that had learned the location of shelters experienced significantly fewer attacks from rainbow trout than naive individuals

Influence of Rainbow Trout (Oncothynchus mykiss) on Density and Feeding Behaviour of a Perlid Stonefly

Stonefly (Paragnetina media) density was reduced in a rainbow trout (Oncorhynchus mykiss) enclosure by approximately 35%, whereas in a trout exclosure no significant changes in density occurred. Of the 35% reduction, approximately two-fifths and three-fifths were attributable, respectively to direct consumption of stoneflies by trout, and emigration by stoneflies from the predator-stressed section of stream. With trout present in laboratory aquaria, predator avoidance behaviour resulted in stoneflies remaining significantly more on dark substrate on which they were less vulnerable to trout predators. Stoneflies consumed significantly fewer prey (enchytraeid whiteworms) over 24 h, in the presence of both small (2.0–4.0 cm) and large (10.0–12.0 cm) rainbow trout in aquaria, compared with stoneflies feeding in trout-free aquaria. Feeding rate and substrate selection did not differ between well-fed and starved (5 d) nymphs.

The influence of copper exposure on predator‐prey interactions in aquatic insect communities

SUMMARY. 1. Vulnerability of two species of net‐spinning caddisflies (Chimarra sp. and Hydropsyche morosa) to predation by the stonefly, Paragnetina media, was significantly greater in experimental streams dosed with copper (target concentration=6 μg 1‐1) than in control streams.2. Results of stomach analyses showed that Hydropsychidae was the major component of stonefly diets in experimental streams and that the number of Hydropsychidae per stonefly gut was significantly greater in dosed streams than controls.3. Since these results could not be predicted using single species bioassays, we suggest that such simple tests be supplemented with more environmentally realistic procedures that account for species interactions.

Distribution and innervation of sensilla on the mouthparts of the carnivorous stonefly nymph, Paragnetina media (Walker) (Plecoptera: Perlidae)

The external morphology and distribution of various types of sensilla on the mouthparts of the nymphs of Paragnetina media are described, based on light and scanning electron microscopy. Hairs of various types are arranged in distinctive patterns on each mouthpart. Scolopophorous sensilla, each consisting of a pore canal and two bipolar neurons, are present in the mandibular teeth. The elliptical type of campaniform sensilla, multiporous columnar pegs, and nonporous sensilla are concentrated on the segments of the maxillary and labial palps. The tips of the maxillary and labial palps bear a cluster of uniporous multidigitate pegs, a multiporous peg, a circular type campaniform sensillum, and several nonporous sensilla. Nonsocketed uniporous pegs crown the tip of galeae and are also scattered over the surface of the glossae and paraglossae. Possible functions of these sensilla are discussed. A cleaning method is described to visualize details with the scanning electron microscope.

A laboratory study of the vulnerability of prey to predation by three aquatic insects

The vulnerability of three different prey (Baetis spp., Ephemerella spp., and Simulium spp.) to predation by Nigronia serricornis (Megaloptera) and Paragnetina media and Agnetina capitata (both Plecoptera) was studied in recirculating Plexiglas chambers. When each prey was tested individually, Simulium was least vulnerable to predation by A. capitata and equally vulnerable with Ephemerella to P. media and N. serricornis. Baetis was the most vulnerable to predacious stoneflies while Baetis and Ephemerella were equally vulnerable to N. serricornis. When prey were tested in mixed assemblages, similar trends in prey vulnerability were seen, except that Ephemerella was more vulnerable than Simulium to P. media and N. serricornis. Our data suggest that Ephemerella is less vulnerable than Baetis to predation by stoneflies; however, they were equally vulnerable to N. serricornis, possibly because of differences in feeding behavior and morphology between stoneflies and N. serricornis. Significantly more Simulium larvae moved to the sides and ceiling plates of the experimental chambers versus the control chambers; this differential movement suggests that the presence of predators may have stimulated escape to an apparently predator-free refuge.

Feeding ecology of three predacious aquatic insects and two fish in a riffle of the Speed River, Ontario

The food habits of two fish (Etheostoma flabellare and Rhinichthys atratulus) and three predacious aquatic insects (Nigronia serricornis, Paragnetina media and Agnetina capitata) were examined for one year in a riffle of the Speed River, Ontario. Adult E. flabellare fed primarily on net-spinning caddisflies whereas juvenile E. flabellare relied heavily on chironomids. Rhinichthys atratulus had a more varied diet composed of chironomids, Antocha larvae (Tipulidae) and net-spinning caddisflies. Two of the aquatic insect predators consumed large numbers of net-spinning caddisflies; however, P. media contained large percentages of Hydropsyche and Cheumatopsyche whereas N. serricornis fed primarily on non-hydropsychid net-spinners. The diet of A. capitata was composed largely of chironomids and mayflies. Schoener's diet overlap index (α) suggested that large E. flabellare and P. media had similar diets; however, E. flabellare ingested much larger prey than P. media. Adult E. flabellare contained a significantly greater proportion of larger prey items in comparison with benthic samples whereas similar comparisons with other predators showed no selection for larger prey. These data demonstrate that E. flabellare was size selective given the range of prey sizes available whereas the other predators were not. Also, there was little dietary overlap among the fish and invertebrate predators suggesting a partitioning of resources.

Fine structure of the coniform sensillar complex on the antennal flagellum of the stonefly nymph Paragnetina media (Plecoptera: Perlidae)

Four to seven coniform sensillar complexes, each formed by 16–21 narrow spines, project perpendicularly from the distal end of middle and distal antennal flagellar segments of the stonefly nymph Paragnetina media. Each spine in the complex is innervated by two neurons with unbranched dendrites. The dendrites extend to a pear-shaped cavity in the tip of the spine. The tip of the spine is porous and contains channels filled with an amorphous material. Each pair of neurons is surrounded by three accessory cells. Based on structural similarities with the terminal multiporous sensilla of other insects, each spine in a sensillar complex represents a fundamental type of chemosensillum.

Predator–prey interactions in a stream: a combined field and laboratory study of Paragnetina media (Plecoptera) and Hydropsyche sparna (Trichoptera)

Substrate size selection, upper and lower substrate surface colonization, and net spinning were examined for the caddisfly Hydropsyche sparna in the presence and absence of the predaceous stonefly Paragnetina media. In the laboratory, I found that when stoneflies were present, caddisflies selected larger substrate and spun fewer nets. Upper and lower surface colonization of substrate did not change as a function of P. media presence. Laboratory findings were consistent with observations made of H. sparna and P. media in the Credit River, Ontario, during midsummer 1983. Based on Hess sample collections, I observed a significant negative correlation between stonefly and caddisfly densities.

LABORATORY EVALUATION OF THE INSECT GROWTH REGULATOR DIFLUBENZURON AGAINST BLACK FLY (DIPTERA: SIMULIIDAE) LARVAE AND ITS EFFECTS ON NONTARGET STREAM INVERTEBRATES

AbstractIn laboratory tests conducted under simulated stream conditions treatment with the insect growth regulator diflubenzuron at 1.0 mg/L/30 min at 15°C resulted in 100% mortality of Simulium larvae after 10 days. At 0.5 mg/L/15 min there was 97.6% mortality of S. vittatum larvae after 18 days in water at 10.5°C. Diflubenzuron was less effective when the growth rate of simuliid larvae during the test was slow due to inadequate nutrition, and it was more effective at 25 than at 20°C, but there was no difference in efficacy between 10 and 20°C. Efficacy against simuliid larvae varied inversely with their instar. Diflubenzuron at 1.0 mg/L/30 min was tested in the laboratory against selected nontarget invertebrates. Among the Ephemeroptera tested at 15°C, Baetis pygmaeus, Leptophlebia sp., and Isonychia sp. proved susceptible but not Stenonema fuscum and Ephemerella subvaria. Similarly diflubenzuron had little effect on the perlid stonefly Paragnetina media at 15°C and on the filter-feeding caddisfly Hydropsyche betteni at 20°C. Chironomid larvae (Phaenopsectra sp.) tested at 20°C were affected and the amphipods Gammarus pseudolimnaeus and Hyalella azteca were particularly susceptible at 25 but not at 15°C.

Factors Influencing the Microdistribution of Two Sympatric Species of Plecoptera: An Experimental Study

The responses of nymphs of two species of perlid stoneflies to manipulation of some important features of their microhabitats were studied in laboratory stream tanks fitted with an infrared beam interruption system. The activity of both Paragnetina media (Walker) and Phasganophora capitata (Pictet) was significantly affected by current speed and substrate size, and by an interaction between the two. Regression analysis showed that activity for P. capitata was highest at 15 and 75 cm/s and minimal between 25 and 50 cm/s, while that for P. media was highest at 15 cm/s and lowest at 25 cm/s and above. For P. media there was a significant negative relationship between substrate size and activity at a current speed of 15 cm/s. The relationship between the activity of P. capitata and substrate size was not linear. Addition of trout skin mucus to the stream tanks caused an increase in the levels of activity of P. media but a decrease in the activity of P. capitata. Addition of nymphs of the mayfly Ephemerella subvaria to the tank containing P. media produced no effect. These findings suggest mechanisms that establish different microdistributions for sympatric species.

Effect of habitable space on substrate selection by Paragnetina media (Walker) (Plecoptera: Perlidae)

A biological measure of space available within substrates was used as an index to examine substrate selection by the stonefly nymph Paragnetina media (Walker). Physical measures, such as total surface area of substrate, have not worked well in the past in explaining distribution of aquatic invertebrates. Although analysis of habitable space within substrate did not explain selection completely, the technique provided a precise measure and might be a more rigorous means by which substrate selection could be examined.

External morphology and distribution of the antennal sensilla of the stonefly, Paragnetina media (Walker) (Plecoptera : Perlidae)

The distribution and external morphology of sensilla on the antennae of nymphal and adult stonefly, Paragnetina media (Plecoptera : Perlidae) were studied with light and scanning electron microscopy. A peculiar arrangement of 3 types of sensilla was observed on the antennae of the nymphs. Thick- and thin-walled sensilla basiconica and coniform sensillar complexes occur in a group, and 6 to 7 such groups are located around the distal margin on the segments in the mid-region of the flagellum. Campaniform sensilla are concentrated in a ring around a crown of thick- and thin-walled sensilla basiconica on the distal end of the pedicel. Two types of trichoid sensilla, long wavy, and stout straight, are present on the flagellum of the nymph. Adult stoneflies have an antennal surface profusely covered only with long and short trichoid sensilla; all other nymphal type sensilla are absent. The lack of nymphal type sensilla on their antennae may be related to the adult's brief, non-feeding terrestrial life.

Relationship between gill Na+,K+-activated ATPase activity and osmotic stress in the plecopteran nymph, Paragnetina media.

A relationship between osmotic stress and gill Na+,K+-activated ATPase was observed in plecopteran nymphs acclimated to diluted creek water and a hypertonic medium. An increase of 84% in diluted creek water is presumably related to an active uptake of sodium ions from the hypotonic medium. Whereas a 21% decrease in the enzyme activity may be related to the morphological changes in the specialized cells in the gills. The Na+,K+-activated ATPase activity was also compared with the Malpighian tubules and the rectum. The highest ATPase activity of 32.6 +/- 2 mumoles Pi mg protein-1 30 min-1 was observed in the Malpighian tubules. The activity in the gills (19 +/- 1.2 mumoles Pi mg-1 30 min-1) was slightly lower than the rectum. Since the ATPase activity in the gills is quite high, the gills can be considered to play an active role in hyperosmotic regulation in plecopteran nymphs.