Vol.18_No.2 - Pesticide Alternatives Lab - Michigan State University

Spring 2009 Resistant Pest Management Newsletter Vol. 18, No. 2
metabolizing the three most used, in present class,
insecticides – organophosphates (OP), carbamates and
pyrethroids. The molecules of all of these contain the
ethers, which can be hydrolised by esterases.
OP- resistant insects are characterized usually
by raised hydrolyze activity, accompanied by increased
contents of nonspecific esterases. Currently, there is
data about the role of the esterase hydrolysis in
pyrethroid metabolism. Different structures of
pyrethroids, as well as trance- and cis- izomers are
hydrolyzed by means of different esterases. In the
majority of insect species, hydrolysis of cis- izomers
and cian maintained insecticides occurs slowly. There
is information that in majority of dipteras and
coleopteras metabolism of pyrethroids is realized by
means of monooxygenases, but in lepidopteras and
homopteras, by means of esterases (Jshaaya, Casida,
1981).
T. Sparks and B. Hammock (1983) conducted the study
of biochemical resistant mechanisms to chitin synthesis
inhibitors using as an example diflubenzuron by means
of synergist in houseflies. The use of esterase inhibitor
DEF (S, S, S-threebutylphosphorothreetioat) and
transferase inhibitor dietylmaleat (DEM) has shown the
absence of the strong synergism. This means that
esterases and transferases do not take part in majority
of the process in detoxication of diflubenzuron.
In this investigation, esterase mechanisms of
housefly resistance in process of the resistance forming
to insecticides of different chemical classes were
researched.
NA (2% acetine) and 50 µl supernatant. After
incubation for 15 minutes, the 1 ml mixture consisted
of 1% fast blue B and 5% SDS (2:5) was added to stop
the reaction. Optic density was measured at 600 nm.
The protein concentration was defined by the
Lowry method (Lowry et al., 1951).
RESULTS AND DISCUSSION
From the six studied preparations, referring to
three different chemical insecticide classes, resistance
in the houseflies is formed quicker to pyrethroids
(fenvalerate and deltamethrin), slower to derivate of
benzylphenylurea chlorfluazuron (fig. 1). The
intermediate position is occupied by the pyrethroid
ethophenprox and organophosphates phoxim and
phosmet.
MATERIAL AND METHODS
The objects of the studies were imago of one
sensitive strain and six selected strains of housefly. The
selection used the following insecticides: from class
OP - phosmet (phtalophos, 20% e.k.), phoxim (volaton,
50% e.k.); from class pyrethroids - deltamethrin (decis,
2.5% e.k.), fenvalerat (sumicidin, 20% e.k.),
ethophenprox (trebon, 30% e.k.); from derivates of
benzylphenylurea - chlorfluazuron (eim, 12% e.k.).
The determination of resistance index (RI) to selectants
conducted was described earlier (Sokolyanskaya,
2007).
The activity of nonspecific esterases was
defined in homogenate from whole flies on rate of
hydrolysis α-naphtyl acetate (Van Asperen, 1962).
Housefly imago were homogenized in 800 мg of China
mortar and 4 ml of 0.05M tris-HCl buffer, pH=8.3,
consisting of 1mM ditiotreytol, 1mM phenyltiourea,
0.05 mg/l triton X-100. After filtration across 2 layers
of gauze, homogenate was centrifuged for 15 minutes
by 10000 g. All operations were conducted by a
temperature between 0-4С. Supernatant was used for
definition of nonspecific esterase activity. The reaction
mixture consisted of 2 ml of 0.1M sodium-phosphate
buffer, pH=7.0; 1.0 ml of 6x10 -4 M water solution -
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