
Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 16788060 EISSN: 16788060
Vol. 91, Num. 2, 1996, pp. 241242

Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(1), Mar/Apr
1996
RESEARCH NOTE: Comparison of the Blood Meal Size among
Triatoma infestans, T. guasayana and T.
sordida (Hemiptera: Reduviidae) of Argentina under Laboratory
Conditions
Silvia Pietrokovsky, Victoria Bottazzi, Nicolas Schweigmann, Ana
Haedo, Cristina WisniveskyColli^+
Unidad Ecologia de Reservorios y Vectores de Parasitos,
Departamento de Ciencias Biologicas, Facultad de Ciencias Exactas
y Naturales, Pabellon II, 4. Piso, Ciudad Universitaria, 1428
Nunez, Buenos Aires, Argentina
Code Number: OC96047
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[TABLE AT END OF TEXT]
Key words: blood meal size  Triatoma guasayana 
Triatoma sordida  Triatoma infestans
Recent studies performed in the Chaco forest of Santiago del
Estero, Argentina, suggested the existence of a wild
Trypanosoma cruzi cycle, which would involve opossums as
main reservoirs of this protozooa and Triatoma guasayana
Wygodzinsky & Abalos and T. sordida Stal as its triatomine
vectors (N Schweigmann 1994 Doctoral Thesis University of Buenos
Aires). In addition, they were the only wild triatomines found
in the peridomiciles of that rural area (P Gajate et al. 1993
Medicina 53: 76). Therefore, aiming to achieve a better
knowledge of their efficiency as vectors of T. cruzi, we
decided to carry out several biological studies on these species.
Some authors have found a positive correlation between the
amount of ingested blood by different triatomines and their
subsequent infection rate by T. cruzi (DM Minter et al.
1978 Trans R Soc Trop Med Hyg 72: 8491, DA Mello,
C Chiarini 1980 Rev Brasil Biol 40: 327334). Moreover,
the developmental stage of triatomines would also modulate the
infection outcome (NR Phillips, DS Bertram 1967 J Med Entomol
4: 168174). Since the meal size may affect the vectorial
capacity of triatomines, we compared this variable among third
and fifth instars of T. guasayana, T. sordida and T.
infestans.
All nymphs used in this experiment were provided by the
insectary of the Servicio Nacional de Chagas, Cordoba, Argentina.
Third and fifth instars of the three species were arranged in six
groups consisting of 50 insects each throughout the experiment.
Jars containing triatomines were kept at 28 C and 70% RH and
exposed to a photoperiod of 11:13 (L:D).
After a 20daystarvation period, the mean initial weights of
the speciesinstars mentioned above were obtained by weighing ten
batches of five individuals each. Then, insects were allowed to
feed ad libitum during an hour on a restrained chicken and
weighed again individually. The meal weight, defined as the
difference between the final weight of each triatomine and the
mean initial weight, was used as an indicator of the meal size.
Literature data indicate that a profuse diuresis takes place
after feeding (SH Maddrell 1964 J Exp Biol 41: 163176).
To obtain a constant value reached after diuresis, the fully
engorged insects of each group were weighed individually at hours
0, 4, 12 and 16 after feeding. The four mean meal weights thus
obtained were compared by ANOVA and Scheffe tests. Results showed
that mean weights from hours 12 and 16 were not significantly
different in all experimental groups. Therefore, the meal weights
obtained at hour 12 were chosen to compare instars and species
by a two way ANOVA and Scheffe tests.
The mean initial weight and the meal weight of the studied
triatomines and their standard errors are shown in the Table.
T. infestans evidenced the largest meal weight and T.
sordida the lowest (p<0.05). As expected, fifth nymphs took
larger meals than third nymphs (p<0.05), and for both stages
T. infestans ranked first (p<0.05). T. sordida
third and fifth instars showed a mean initial weight about 3/4
of T. guasayana s initial weight (Table) in spite of the
fact that the meal weight of their third nymphs showed no
significant differences. However, T. guasayana fifth
nymphs ingested a larger bloodmeal than that of T. sordida
(p<0.05). This lack of linear relationship between the mean
initial weight and the size of the bloodmeal when we compared the
same instars of various triatomine species had also been observed
by AP Szumlewicz (1975 Laboratory colonies of triatominae p. 63
82. In PAHOWHO American Tripanosomiasis Research Brazil).
The blood meal differences observed among the studied
triatomines suggest that after the ingestion of T.cruzi
contaminated blood T. infestans would have more chance to
acquire the infection than T. guasayana or T.
sordida, and between the wild species, T. guasayana
would reach the highest infection rate. The interaction between
the triatomine vector and the parasite constitutes a complex
system involving several factors such as the insect age and the
number of parasites ingested by the bug, as well as the intensity
of host parasitemia, the T. cruzi strain and the
reciprocal adaptation between the vector and the parasite (R
Zeledon 1987 Chagas' Disease Vectors Vol II: 5975, ES
Garcia, P Azambuja 1991 Parasitol Today 7: 240244).
Triatomines show different susceptibility to different parasite
populations, and this may explain why some authors found a
relationship between the blood meal size and the infection rate
for different triatomine species while others did not (MA Miles
et al. 1975 Trans R Soc Med Hyg 69: 377382).
However, it is clear that a species intaking larger blood meals
would have a higher probability of becoming infected when it
feeds on a host undergoing the chronic phase of the infection.
RA Neal and RA Miles (1977 Rev Inst Med Trop S o Paulo 19:
177181) stated that the distribution of trypomastigotes in the
blood stream is more uniform in high than in low intensity
infections because in the latter parasites are released
asinchronically and the time lapse in which they are circulating
varies.
Further work involving local T. cruzi populations is
needed to determine whether T. guasayana and T.
sordida are good vectors in the wild and/or the domestic
cycles of the Chaco Region of Argentina. Current studies
undergoing in our laboratory may reveal some aspects about this
point.
This research work was performed with the financial support of
the Secretaria de Ciencia y Tecnica of the Universidad de Buenos
Aires, Argentina.
+Corresponding author. Fax: 541373.6102
Received 16 May 1995
Accepted 3 January 1996
TABLE
Mean initial and meal weights (+/SE) of third and fifth nymphs
of Triatoma infestans, T. guasayana and T.
sordida, obtained after the diuresis period
Mean initial weight^a+/SE Mean meal weight^b+/
SE (mg)
(mg)

Species Instar

Third Fifth Third Fifth

T. infestans 7.8+/0.19 73.8+/3.70 22.13+/1.12
147.43+/6.93
T. guasayana 5.2+/0.23 47.4+/2.64 12.98+/0.34
115.06+/5.02
T. sordida 3.8+/0.09 38.5+/2.07 11.96+/0.40
68.91+/3.05

15.69+/0.56 110.57+/4.01
a: obtained from starved nymphs, 20 days after their last
moult.
b: mean meal weigth = final weight  initial weight. It
was obtained from 50 triatomines per group. Final weights at
hour 12 after feeding were chosen to calculate the meal weight
of each group.
Copyright 1996 Fundacao Oswaldo Cruz
