BO, T

FENOGLIO, Stefano

LÓPEZ RODRÍGUEZ M., J

TIERNO DE FIGUEROA, J. M.

English

Fenoglio, Stefano

Bo, Tiziano

Institutional Research Information System University of Turin

Nymphal biology of Brachyptera risi (Morton, 1896) (Plecoptera:Taeniopterygidae) in a North Apennine stream (Italy)Stefano Fenoglio, Tiziano Bo, M. Jesus López-Rodríguez& José Manuel Tierno de FigueroaFenoglio, S., Bo, T., López-Rodríguez, M. J. & Tierno de Figueroa, J. M. 2008:Nymphal biology of Brachyptera risi (Morton, 1896) (Plecoptera: Taenioptery-gidae) in a North Apennine stream (Italy). — Entomol. Fennica 19: 228–231.Some aspects of the life history of a population ofBrachyptera risiwere investi-gated in a North Apennine stream and compared with previously studied Euro-peanpopulations. In our study area, this species showedaunivoltine fast seasonallife cycle. Nymphswere present from January to the beginning ofMay, probablyspending the rest of the yearmainly in eggdiapause. Fineparticulate organicmat-ter was the principal component of the diet, while diatoms and other algae werealso found in the guts. This finding suggests the existence of greater trophic plas-ticity of the species. Individuals of this population act as gatherer-collectors butnot as scrapers as usually pointed out for otherEuropeanpopulations.Wealso de-tected considerable amounts of animal matter in the gut contents. The density ofB. risi nymphs in the study area was very variable during the study period, rang-ing from 0 to 2,348 ind/m2.S. Fenoglio & T. Bo, Dipartimento di Scienze dell’Ambiente e della Vita, Uni-versità del Piemonte Orientale, Via Bellini 25, 15100, Alessandria, Italy; E-mails: fenoglio@unipmn.it (corresponding author), tbo@unipmn.itM. J. López-Rodríguez & J. M. Tierno de Figueroa, Departamento de BiologíaAnimal, Facultad de Ciencias, Universidad de Granada, 18071, Granada,Spain; E-mails: manujlr@ugrs.es, jmtdef@ugr.esReceived 31 August 2007, accepted 12 November 20071. IntroductionBrachyptera risi (Morton, 1896) is a specieswidely distributed in Europe. In Italy, it is a com-mon rheophilous inhabitant of the basal andsubmontane streams of the Alps and Apennines(Ravizza & Fochetti 1999). Several aspects ofadult and nymphal biology, such as nymphalfeeding, egg development, population move-ments or adult dispersal, have been studied in dif-ferent parts of the continent, particularly byMadsen (1976) and Madsen & Butz (1976), butalso by Brinck (1949) and Khoo (1964).This relatively wide knowledge of the speciesbiology is quite unusual in stonefly literature. Forthis reason, studies performed in new areas couldbe interesting in order to compare findings and toobtain a general point of viewof the nymphal bio-logy. Up to now, usually only punctual studies onparticular stonefly species from certain areas areavailable, making it impossible to detect if theircharacteristics are generalities of the species orconcrete population adaptations to particularhabitats.© Entomologica Fennica. 15 January 20092. Study area, material andmethodsWe conducted quantitative Surber sampling inthe Caramagna stream (Cassinelle, Italy: UTM464261-4939532; 280 m a.s.l.) from 4 January2005 to 2 March 2006. Samplings were mademainly every two weeks. In the sampling station,the stream is characterized by a width of 2.0–2.5m, a moderate current velocity, a riverbed com-posed of 10% sands, 30% gravels, 50% pebblesand 10% rocks, and the existence of riffles alter-nating with pools. Samples were collected ran-domly in order to represent every possible meso-habitat, using a Surber sampler.Measures of total length, pronotal width, andthird leg femur length were taken using a Nikonstereomicroscope at 60–100× magnifications,with an accuracy of 0.1 mm.For the study of the species diet, Bello & Ca-brera’s transparency method was used (Bello &Cabrera 1999), as in other papers studying Ple-coptera nymphal feeding (Tierno de Figueroa etal. 2003, Bo & Fenoglio 2005, López-Rodríguez& Tierno de Figueroa 2006). We identified thedifferent components of the gut contents and eachanimal item was sorted out to the family levelwhen possible and counted. For the remainingparts of gut content, we quantified the percent-ages that they occupied in the guts. Statisticalanalyses were performed with Statistica 7.1(StatSoft 2005).3. Results and Discussion3.1. Life cycleIn total, we took 109 Surber samples and we col-lected and measured 401 B. risi nymphs. Thethree measured parameters (total length, prono-tum width, and third leg femur length) werehighly correlated (Gamma correlation = 0.81 forpronotum width vs. femur length; Gamma corre-lation = 0.82 for pronotum width vs. total length;correlation = 0.77 for total length vs. femurlength; p<0.05 for all cases). Thus, we employedtotal length as size indicator for representing thenymphal growth.As shown in Fig. 1, nymphs were present inbenthos for a period of fourmonths, fromJanuaryto the beginning of May. Nevertheless hatchingperiod can begin slightly before, probably de-pending on the particular environmental condi-tions (Fig. 2). In fact, studies in other areas showthat the period of nymphal growth can expandeven from the end of October to the beginning ofMay (Brinck 1949, Hynes 1961).We suppose that hatching occurs at the end ofautumn or beginning of winter: B. risi spends therest of the year in egg stage, probably experienc-ing an egg diapause, or as nymphs of first instarsliving in the interstitial zone. These data supportthat of other studies, suggesting the existence of along incubation period for this species, includingan egg diapause, and a posterior fast nymphalgrowth (Khoo 1964). In relation to this, Hynes(1970) noticed that this species was not sensitiveto cold weather, and in fact young nymphs do notENTOMOL. FENNICAVol. 19 • Brachyptera risi nymphal biology in NW Italy 229Fig. 1. Appearance and growth of B. risi in theCaramagna stream.Fig. 2. Density of B. risi nymphs (mean ± SE).appear until thewater is cold at the end of autumn(Hynes 1961).Based on the data, the life cycle of this speciesis univoltine, and could be classified as “fast sea-sonal” following Hynes (1970). The nymphalgrowthwas relatively constant through thewinterand the beginning of spring, when emergence oc-curs. Ravizza & Fochetti (1999) pointed out along flight period for this species in Italy, fromFebruary to June, coinciding with the period re-ported by other authors in other countries (Brinck1949). Nevertheless, the local emergence de-pends on the altitude and latitude, and conse-quently on the temperature (Brinck 1949, Ra-vizza & Fochetti 1999), the flight period beingshorter in particular localities.3.2. Feeding habitsTotally of 243 gut contents were analysed (Table1) and 174 of thempresented some kind ofmatterin the gut. Fine particulate organic matter(FPOM), the main component of the diet, wasfound in the 63.4% of the individuals. Diatomsand other algaewere present in a lower number ofindividuals (1.6% and 13.6% respectively). Curi-ously, there was a high percentage of individuals(49.8%) with sand in their gut. We also detectedthat some nymphs showed animal matter insidethe gut, indicating the possibility of predator ornecrophagous behaviour or, alternatively, of acci-dental ingestion. All these data suggest that thestudied B. risi nymphs act as gatherer-collectors(sensu Cummins & Merritt 1996), ingesting oc-casionally some animal matter.Comparing with data from literature, somenotable differences are found. Many authors (forinstance Hynes 1941, 1976, Brinck 1949, Lille-hammer 1988) pointed out thatB. risi feedmainlyon periphyton, indicating that this species acts asa scraper (sensuCummins&Merritt 1996).How-ever, in contrast to the findings of these authors,nymphs of the Caramagna population consumealmost no diatoms and other algae. Thus, the highpercentage of detritus found in their guts wouldbe collected from the substrate and not from thebiofilm.Although the presence of animal remainsin the gut of this species was previously recordedbyBrinck (1949), this is not usual formembers ofthe superfamily Nemouroidea.3.3. Population dynamicsThe density of B. risi nymphs was very variablein the study area (Fig. 2). Considering only theperiod in which nymphs were present in benthos,density ranged from 16 to 2,348 ind/m2(mean466.8 ind/m2). This high spatial and temporalvariability could be due to i) the preference of thespecies for certain substrates [for instanceMadsen (1976) pointed out the preferred sub-strate is the current-exposed surfaces of smoothstones] conditioning a contagious distribution,and ii) the displacement of nymphs during theseason [as observed by Madsen (1976) in EastJudtland].Regarding the first cause, our sampling sta-tion presented a relatively diverse substrate thatcould explain at least a part of the spatial variationin nymphal density. Regarding the temporal vari-ation, the highest density values occur at the be-ginningofwinter,when all the eggs havehatched,and a relative high density is maintained throughthe winter [as pointed by Hynes (1961) for thisspecies in a Welsh stream]. The decrease ob-served later could probably be due to the strongincrease of temperature (typical of Apenninicstreams of Piemonte) and, at the end of thenymphal growth, to the adult emergence.230 Fenoglio et al. • ENTOMOL. FENNICAVol. 19Table 1. Gut contents (% occupied in the gut) of B. risinymphs in the studied area.N Mean Std. Dev. Min. Max.% Absolutea 243 28.29 29.98 0 100% FPOMb 174 45.46 28.5 0 100% Algae indet. 174 6.45 13.59 0 66% Diatoms 174 0.76 4.96 0 33% Sand 174 34.22 30.06 0 100Trichoptera 174 0.01 0.08 0 1Chironomidae 174 0.02 0.17 0 2Simuliidae 174 0.01 0.08 0 1a) % of gut occupied by food.b) % of gut occupied by fine particulate organic matter.ReferencesBello, C. L. & Cabrera, M. I. 1999: Uso de la técnica mi-crohistológica de Cavender y Hansen en la identifica-ción de insectos acuáticos. — Bol. Entomol. Venez.14: 77–79.Bo, T. & Fenoglio, S. 2005: Age-related shift in the diet ofPerla marginata in a woodland Apenninic creek ofNWItaly (Plecoptera, Perlidae).—Entomol. Gen. 28:147–154.Brinck, P. 1949: Studies on Swedish Stoneflies (Plecopte-ra). — Opusc. Entomol. 11: 1–250.Cummins, K.W.&Merritt, R.W. 1996: Ecology and distri-bution of aquatic insects. – In: Merritt, R. W. & K. W.Cummins (eds.), An introduction to the aquatic insectsof North America: 74–86. Kendall & Hunt Publ., Du-buque, Iowa. 862 pp.Hynes, H. B. N. 1941: The taxonomy and ecology of thenymphs of British Plecoptera with notes on the adultsand eggs. — Trans. R. Entomol. Soc. Lond. 91: 459–557.Hynes, H. B. N. 1961: The invertebrate fauna of a Welshmountain stream. — Arch. Hydrobiol. 57: 344–388.Hynes, H. B. N. 1970: The ecology of running water. —The Blackburn Press, Caldwell, New Jersey. 555 pp.Hynes, H. B.N. 1976:Biology of Plecoptera.—Ann. Rev.Entomol. 21: 135–153.Khoo, S. G. 1964: Studies on the biology of Stoneflies.Ph.D. thesis, University of Liverpool, Liverpool. 162pp.Lillehammer, A. 1988: Stoneflies (Plecoptera) of Fenno-scandia and Denmark. Scandinavian Science PressLtd., Leiden. 165 pp.López-Rodríguez,M. J. & Tierno de Figueroa, J. M. 2006:Life cycle and nymphal feeding of Rhabdiopteryxchristinae Theischinger, 1975 (Plecoptera, Taeniopte-rygidae). — Ann. Soc. Entomol. Fr. 42: 57–61.Madsen, B. L. 1976: Population dynamics of Brachypterarisi nymphs (Plecoptera). — Oikos 27: 281–287.Madsen, B. L. & Butz, I. 1976: Population movements ofadultBrachyptera risi (Plecoptera).—Oikos 27: 273–280.Ravizza, C. & Fochetti, R. 1999: I Plecotteri Taenioptery-gidae della regione italica (Plecoptera). —Mem. Soc.Entomol. Ital. 77: 123–159.StatSoft Inc. 2005: STATISTICA (data analysis softwaresystem), version 7.1. [www document] URL http//www.statsoft.com.Tierno de Figueroa, J. M., Sezzi, E. & Fochetti, R. 2003:Feeding in the genus Tyrrhenoleuctra (PlecopteraLeuctridae). — Boll. Soc. Entomol. Ital. 134: 207–210.ENTOMOL. FENNICAVol. 19 • Brachyptera risi nymphal biology in NW Italy 231

Nymphal biology of Brachyptera risi (Morton, 1896) (Plecoptera:
Taeniopterygidae) in a North Apennine stream (Italy)

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Nymphal biology of Brachyptera risi (Morton, 1896) (Plecoptera:

Taeniopterygidae) in a North Apennine stream (Italy)

Nymphal biology of Brachyptera risi (Morton, 1896) (Plecoptera: Taeniopterygidae) in a North Apennine stream (Italy)

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