BIOMETRY AND LIFE CYCLE OF Chironomus ... - SciELO

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
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.
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
Figure 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.
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 (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 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.
768 OCT 2008, VOL. 33 Nº 10