Biometría y ciclo de vida de chironomus calligraphus goeldi, 1905 (diptera, chironomidae) en condiciones de laboratorio

BIOMETRY AND LIFE CYCLE OF Chironomus calligraphus Goeldi 1905 (DIPTERA, CHIRONOMIDAE) IN LABORATORY CONDITIONS Florencia L. Zilli, Luciana Montalto, Analía C. Paggi and Mercedes R. Marchese SUMMARY Chironomid larvae are important components of aquatic biota, due to their abundance and participation in food webs, and because they are considered environmental bioindicators. Many laboratory studies have analyzed the effects of pollutants on chironomids, especially on Chironomus calligraphus Goeldi, 1905. However, little is known about the life cycle attributes of Chironomidae (Diptera). The main pourpose of this study was to analyze C. calligraphus life cycle under laboratory conditions.

The growth rate was almost constant between larval instars (r= 1.60 ±0.02), the immature development time (D) was 15 days and the minimum generation time (G) was 18 days. According to these results and field observations C. calligraphus has a temperature-dependent life cycle, with several overlapped short duration cohorts in spring-summer followed by one or two generations of longer duration in winter.

BIOMETRÍA Y CICLO DE VIDA DE Chironomus calligraphus Goeldi, 1905 (DIPTERA, CHIRONOMIDAE) EN CONDICIONES DE LABORATORIO Florencia L. Zilli, Luciana Montalto, Analía C. Paggi y Mercedes R. Marchese RESUMEN Las larvas de quironómidos son componentes importantes de la biota acuática por su participación en las tramas tróficas y por ser bioindicadores de condiciones ambientales. Muchos estudios de laboratorio han analizado los efectos de diferentes contaminantes sobre quironómidos, especialmente sobre Chironomus calligraphus Goeldi, 1905. Sin embargo, poco se conoce sobre los atributos de su ciclo de vida. El objetivo de este estudio fue analizar el ciclo de vida de C. calligraphus en

condiciones de laboratorio. La razón de crecimiento entre estadios larvales fue aproximadamente constante (r= 1,60 ±0,02), el tiempo de desarrollo (D) fue 15 días y el tiempo mínimo de generación (G) fue 18 días. De acuerdo a estos resultados y a observaciones realizadas en campo, C. calligraphus es una especie con ciclo de vida temperatura-dependiente con generaciones superpuestas de corta duración en primavera-verano y con una o dos generaciones de mayor duración en invierno.

Introduction

systems of Neotropical regions like the Paraná River floodplains has been widely pointed out, there is little information on their population dynamics and bionomic attributes (Strixino, 1973; Trivinho-Strixino and Strixino, 1989; Masaferro et al., 1991; Corbi and Trivinho-Strixino, 2006). Nevertheless, it is difficult to analyze these characteristics on the field and laboratory autoecological studies are performed instead (Corbi and Trivinho-Strixino, 2006). Thus, an analysis of Chirono-

Diptera Chironomidae is the most abundant group of insects in freshwater aquatic systems (Pinder, 1983) with larval stages associated principally with benthic communities and macrophytes (Trivinho-Strixino and Strixino, 1991, 1999; Trivinho-Strixino et al., 1998; Poi de Neiff and Neiff, 2006). The immature stages of midges have an important role acting as a link between primary producers (phytoplankton and benthic algae)

and consumers, mainly fishes, but also birds and amphibians. The larvae participate in the first steps of the organic matter cycle which is used by detritivorous organisms (Paggi, 1998). Due to their high abundances throughout the year, they contribute to a large extent to the productivity of aquatic systems. On the other hand, they are widely used as bioindicator species of environmental conditions (Paggi, 1999). Although the importance of Chironomidae in aquatic

midae life cycle attributes is necessary in order to increase knowledge about aquatic biota dynamics as well as environmental health. Two species of the Chironomus genus: Chironomus (Chironomus) xanthus Rempel, 1939 (=C. domizzi Paggi, 1979; C. sancticaroli Trivinho-Strixino and Strixino, 1982) and Chironomus (Chironomus) calligraphus Goeldi, 1905 (Paggi, 1979, 1998; Marchese and Paggi, 2004) were recorded in Argentina. C. calligraphus is a pan-American chironomid with

KEYWORDS / Argentina / Chironomidae / Chironomus calligraphus / Life Cycle / Received: 12/04/2007. Modified: 08/27/2008. Accepted: 08/29/2008.

Florencia L. Zilli. Licenciada en Biodiversidad, Universidad Nacional del Litoral (UNL), Argentina. Becaria de Doctorado, Instituto Nacional de Limnología (INALI), Consejo Nacional de Investigaciones Científicas y Técnicas y Uni-

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versidad Nacional del Litoral, (CONICET-UNL), Argentina. Dirección: Laboratorio Bentos, Instituto Nacional de Limnología, Ciudad Universitaria, Santa Fe (3000), Santa Fe, Argentina. e-mail: florzeta1979@ yahoo.com.ar

Luciana Montalto. Doctora en Ciencias Biológicas, Universidad de Buenos Aires (UBA), Becaria Postdoctoral, INALI (CONICET-UNL), Argentina. Analía C. Paggi. Doctora en Ciencias Naturales, Universidad Nacional de La Plata

0378-1844/08/10/767-04 $ 3.00/0

(UNLP). Investigadora del Instituto de Limnología Raúl A. Ringuelet (CONICET-UNLP), Argentina. Mercedes R. Marchese. Profesora de Biología (UNL). Investigadora INALI (CONICETUNL), Argentina.

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BIOMETRÍA E CICLO DE VIDA DE Chironomus calligraphus Goeldi, 1905 (DIPTERA, CHIRONOMIDAE) EM CONDIÇÕES DE LABORATÓRIO Florencia L. Zilli, Luciana Montalto, Analía C. Paggi e Mercedes R. Marchese RESUMO As larvas de quironomídeos são componentes importantes da biota aquática por sua participação nas tramas tróficas e por serem bioindicadores de condições ambientais. Muitos estudos de laboratório têm analisado os efeitos de diferentes contaminantes sobre quironomídeos, especialmente sobre Chironomus calligraphus Goeldi, 1905. No entanto, pouco se conhece sobre os atributos de seu ciclo de vida. O objetivo deste estudo foi analisar o ciclo de vida de C. calligraphus em condições de

a predominantly Neotropical distribution. This species was reported to have a high potential as a nuisance to humans in the USA, mainly because it has the ability to thrive in a wide range of conditions and habitats, including small and temporary Figure waters (Spies, 2000; Spies et al., 2002). There are reports about its morphology (Goeldi, 1905; Roback, 1962; Fittkau, 1965; Paggi, 1979; Spies et al., 2002), karyology and DNA sequencing (Spies et al., 2002) as well as many ecotoxicology test studies (Iannacone and Alvariño, 1998; Iannacone and Dale, 1999; Iannacone et al., 1999), but there is no available information about the life cycle of this species. The present study provides information about the life cycle of C. calligraphus under laboratory conditions. Methods and Material Sampling Egg masses of Chironomus calligraphus Goeldi, 1905 were collected in field waters of Santo Tomé city (Santa Fe, Argentina, 31°40’2.54”S and 60°45’13.09”W) in January 2007 and transported to the laboratory, conditioned in recipients with environmental water at 21.8 ±3.2ºC. Laboratory rearing The egg masses were placed in Petri dishes and left up to

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laboratório. A razão de crescimento entre estágios larvais foi aproximadamente constante (r= 1,60 ±0,02), o tempo de desenvolvimento (D) foi de 15 dias e o tempo mínimo de geração (G) foi de 18 dias. De acordo a estes resultados e a observações realizadas em campo, C. calligraphus é uma espécie com ciclo de vida temperatura-dependente com gerações superpostas de curta duração em primavera-verão e com uma ou duas gerações de maior duração no inverno.

1. Chironomus calligraphus at larval instar IV. a: head capsule, ventral view, b: larva, lateral view.

the moment when the first instar left the mucilaginous mass that served for its nutrition. The number of eggs per mass, and the width (µm) and length (µm) of each egg were measured under an optic microscope. A f ter t hat per iod, t he larvae were separated and cultured individually in 10 plastic aquaria (12×21×6cm) with per manently oxygenated water (1 lit) at room temperature. The larvae were fed with a finely ground suspension of flaked fish food (TetraMin ®, Germany) every two days. Larvae were collected da ily from each aqua r ium a nd the aqua r ia were kept covered to retain the adults at emergence. The air temperature of 22.5-31ºC held throughout the duration of the study. Life cycle and larval instars The collected larvae (Figure 1) were fixed and conserved in 70% alcohol. The larvae head capsule width (maximum ventral width of the cephalic capsule measured transversely to the major body axis) and the total body length (from the

anterior margin of the cephalic capsule to the final portion of the last abdominal segment) were measured (µm) using an optic microscope with a micrometric scale. A population growth curve showing the relationship between total body length (µm) and time (days) was obtained. The larvae were separated into instars according to the relationship between head capsule width and total body length. In order to determine the growth rate between instars, the Dyar proportion (r; Dyar, 1890) was calculated considering its widespread application in arthropods (Strixino, 1973). The time up to eclosion, the mean duration of each instar, the immature development time D (average time from egg deposition to adult emergence, when females were available; Danks, 2006), the minimum generation time G (mean interval from oviposition to the first progeny of the next generation; Danks, 2006) and the mean generation time (G) of the population by determining the lasting time of emergence, were recorded. The studied material was deposited at the Instituto de Lim-

nología Dr. Raúl A. Ringuelet, La Plata, Argentina. Results and Discussion The eggs measured 317.7 ±20.0µm in length and 119.1 ±10.3µm in width. The range of variation in the number of eggs per mass (369-374) was lower than that registered for tropical C. xanthus (5001045) by Trivinho-Strixino and Strixino (1982). In this sense, subtropical C. calligraphus could have improved its fitness by increasing the size of each egg rather than the number. The hatching period was of approximately 3 days. The larval instars were clearly separated when measuring the head capsule width to total body length relation (Figure 2). The data collected about mean head capsule width, total body length, growth rate and duration of the different larval instars of C. calligraphus is summarized in Table I. In the second instar the larvae showed a bottom exploratory behavior and constructed the tubes. They also started to develop the tubules of the eight segments.

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chronization of larval instars (Figure 4). In the last days of the cycle an overlap was registered, when instar IV larvae (mostly as pre-pupa), pupae and adults coexisted. For C. xanthus, Trivinho-Strixino and Strixino (1982) pointed out that at high temperature (25°C constant temperature) the fast development of larvae tends to become synchronized, favoring a short emergence (3 days). In the present case, although the air temperature was in general Figure 2. Relationship between head capsule width (µm) and total body >25°C, the overlap in the last length (µm) of Chironomus calligraphus larval instars I to IV. immature stages favored long emergence duration. Many factors, such as phyTABLE I logeny, resource availability, MEAN (±SD) HEAD CAPSULE WIDTH, GROWTH RATE, TOTAL BODY LENGTH AND competence and interference DURATION OF LARVAL INSTARS OF Chironomus calligraphus phenomenon, temperature, Instars Head capsule Growth rate Total body Duration habitat stability, etc. may dewidth (µm) (r) length (µm) (days) termine and affect the development of insects (Jackson and I 115.2 ±6.9 1.58 1109.3 ±193.4 5 ±1.2 Sweeney, 1995; Danks, 2006). II 182.2 ±10.8 1.62 2449.1 ±701.4 3 ±0.7 The short duration of the life III 295.3 ±19.1 1.60 5121.1 ±750.7 6 ±2.6 cycle insures a conspicuous IV 472.8 ±30.9 1.60 8943.6 ±1672.7 10 ±1.7 population growth and increases insect fitness. The cycle pupa remained in the tube of The r (Dyar) values obis considered as short when T he reg ression model the last larval instar (IV) for tained were almost constant it lasts