Page 41 - Volume 2, Issue 1, January 2009

Michaelakis et al. 42
© Benaki Phytopathological Institute
inclusion in Annex I of the Directive 98/8/EC,
European Union banned the use of this ac-
tive substance in the member states. After
that there is a pressing need of finding oth-
er efficient insecticides to replace temephos
in mosquito control programs and in the at-
tract-and-kill strategy as well.
Nowadays, the main tendency for the
control of vectors without the presence
of disease is to use more environmenta-
ly friendly chemicals such as insect growth
regulators (IGRs) (14).
For that reason, the IGR pyriproxyfen
was tested for its residual effect over a 6-day
period and compared with temephos in or-
der to assess it as a possible control agent
for the attract-and-kill strategy, in combina-
tion with the above mentioned oviposition
attractant agents.
Although pyriproxyfen is a rather new in-
sect growth regulator, its mode of action has
already been well studied on mosquitoes as
well (5, 9). As a member of the IGR family it
has a remarkable larvicidal activity and good
efficacy against many mosquito species in
a variety of mosquito breeding sites (5, 18).
Additionally, it has been reported that py-
riproxyfen appears to be highly selective for
mosquitoes and causes the minimum unde-
sirable effects on the environment and pub-
lic health (13).
Furthermore, as it is known that some
IGRs or other larvicides have a negative ef-
fect on oviposition activity (1, 11, 19) the at-
tractiveness of the water as an oviposition
site when pyriproxyfen or temephos is add-
ed was also examined.
Biological control agents such as Bacillus
thuringiensis subsp. israelensis (B.t.i.) were not
used in this study as according to the litera-
ture, the registered in Greece products have
virtually no residual effect against mosquito
larvae beyond application (4).
Materials and Methods
Mosquito rearing
The Cx. pipiens biotype molestus colony
used was maintained at the Benaki Phyto-
pathological Institute, for more than two de-
cades. Adults were kept in wooden framed
cages (33×33×33 cm) with 32×32 mesh at
25±2°C, 80±2% relative humidity and a pho-
toperiod of 14:10 (L:D) h. Cotton wicks satu-
rated with 10% sucrose solution were pro-
vided to the mosquitoes as food source.
Females laid eggs in round, plastic contain-
ers (10 cm diameter × 5 cm depth) filled with
150 ml of tap water. Egg rafts were removed
daily and placed in cylindrical enamel pans
in order to hatch (35 cm diameter × 10 cm
depth). Larvae were reared under the same
temperature and light conditions and were
fed daily with baby fish food (TetraMin®,
Baby Fish Food) at a concentration of 0.25
g/l of water until pupation. Pupae were then
collected and introduced into the adult rear-
ing cages (6).
Insecticide formulations
Formulated products that are common-
ly marketed in Greece of 0.5% pyriproxyfen
(Sumitomo Corporation Hellas S.A., SUMI-
LARV) and 50% temephos (Basf Agro Hellas
S.A., ABATE 50 EC) were tested at the dos-
es of 2 mg/l and 0.15 ml/l, respectively. The
dosages were equivalent to the lowest rec-
ommended label rates for each active sub-
stance.
Larvicidal bioassays
The bioassay method followed was
based on the standard test for determining
the susceptibility or resistance of mosquito
larvae to insecticides (22). However, in the
present study, besides the typical bioassay
where larvae of 3rd and early 4th instars are
used, we carried out bioassays with one-day
egg rafts as well. Aqueous insecticide stock
solutions were prepared in conical flasks as
follows: Four to six consecutive dilutions
were prepared as working solutions in a
3-litre glass jar, depending on the active in-
gredient, to obtain the desirable concentra-
tion. Before their use, glass jars were stored
uncovered under similar conditions as with
mosquito rearing. Glass jars filled with tap
water were used as controls. Bioassays were
performed for 6 days, after the preparation