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

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 Universidad 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 (UNLP). Investigadora del Instituto de Limnología Raúl A. Ringuelet (CONICET-UNLP), Argentina.

Mercedes R. Marchese. Profesora de Biología (UNL). Investigadora INALI (CONICET-UNL), Argentina.

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

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.

Biometría e ciclo de vida de chironomus calligraphus goeldi, 1905 (diptera, chironomidae) em condições de laboratório

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 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.

KEYWORDS / Argentina / Chironomidae / Chironomus calligraphus / Life Cycle /

Received: 12/04/2007. Modified: 08/27/2008. Accepted: 08/29/2008.

Introduction

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 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 Chironomidae 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 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 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 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.

After that period, the larvae were separated and cultured individually in 10 plastic aquaria (12´21´6cm) with permanently 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 daily from each aquarium and the aquaria 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 (mm) using an optic microscope with a micrometric scale. A population growth curve showing the relationship between total body length (mm) 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 Limnología 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 (500-1045) 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.

The r (Dyar) values obtained were almost constant (1.60 ±0.02) showing the accuracy of this method in the determination of C. calligraphus larval growth rate. This value was lower than that reported for C. xanthus (1.70 ±0.032) by Trivinho-Strixino and Strixino (1982). The possibility of using Dyar r values is important for benthos, as for those insects developing some immature stages on macrophytes, being less probable to find the first instar in the field, measures can be estimated trough the r value instead (Strixino, 1973).

The regression model that best fitted for the relationship between total body length and time was y= 9536.6+(1177.8-9536.6)/(1+(x/6.8)^5.1) (R²= 0.987), showing that size increased continuously until reaching an asymptote near the 15^th day, remaining almost constant thereafter (Figure 3). C. calligraphus larvae incremented their size mostly in the earlier instars (I and II: 120.8%; II and III: 109.0%) while a smaller increment (74.6%) took place between instars III and IV. The total growth (instars I-IV) represented an increment of 706.2%.

Instar I lasted 5 ±1.2 days, with 1-2 days developing inside the mucilaginous hatching mass. Instar II lasted 3 ±0.7 days and instar III, 6 ±2.6 days. Instar IV lasted 10 ±1.7 days, with approximately 8 days corresponding to the transitional stage between larva and pupa (commonly called pre-pupa), probably due to the fact that the changes occurring in this metamorphosis step require a large amount of extra energy supply. The pupa stage lasted 10 ±2.4 days and each pupa remained in the tube of the last larval instar (IV) for 1 or 2 days after it swam to the surface, where the imago emerged in only a few minutes and lived without feeding for 2 or 3 days. The minimum immature development time (D) was of 15 days and the minimum time to complete a generation (G) was of 18 days. Thus, as emergence took an average time of 10 days (with the highest emergences between the 18^th and 22^nd day), the average generation time (G) was of 23 (18-28) days.

In the earlier stages overlapping was low, with a synchronization 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 >25°C, the overlap in the last immature stages favored long emergence duration.

Many factors, such as phylogeny, resource availability, competence and interference phenomenon, temperature, habitat stability, etc. may determine and affect the development of insects (Jackson and Sweeney, 1995; Danks, 2006). The short duration of the life cycle insures a conspicuous population growth and increases insect fitness. The cycle is considered as short when it lasts <12 days, as is the case of C. strenzkei (Fittkau, 1965) which had a G value of 10 (Danks, 2006). However, Strixino and Trivinho-Strixino (1985) considered as short the life cycle of C. xanthus with D of 15, the same value registered in the present study for C. calligraphus. Besides, there are chironomids of the same genus that have much longer developing times, as a 7 year life cycle in an Alaskan tundra pond Chironomus sp. (Butler, 1982).

Many authors reported the relation between life cycle duration and temperature (Biever, 1965; Trivinho-Strixino and Strixino, 1982; Strixino and Trivinho-Strixino, 1985), and observations carried out in the field could support the idea that although many generations occur in short periods of time during summer, other generations of C. calligraphus may occur throughout the year, with a longer life cycle duration. Despite many factors influencing the life cycle of C. calligraphus, its development is principally conditioned by temperature and life-cycle delays serve to adjust development so as to ensure seasonal coincidence (Danks, 2006).

Therefore, subtropical C. calligraphus could be described as multivoltine, with several overlapped cohorts (at least four) of short duration at high temperatures (spring-summer) with high rates of development and an exponential population growth, followed by one or two generations of longer duration in winter, when it probably remains in a dormant stage.

ACKNOWLEDGEMENTS

This study was supported by a grant from Universidad Nacional del Litoral (UNL) and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). The present paper is the Scientific Contribution N° 828 of the Instituto de Limnología "R.A. Ringuelet" (ILPLA) La Plata, Argentina.

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