© Benaki Phytopathological Institute
Insecticide toxicity on coccinellids
103
and adults of
C. undecimnotata
exposed to
1- or 8-day insecticide residues (Table 1). Ir-
respectively of the insecticide used, almost
all first instar larvae were found dead 24 h
after their exposure to the residues. Similar-
ly, all third instar larvae and adults exposed
to methomyl residues did not manage to
survive. Only a small proportion of the third
instar larvae and adults survived the expo-
sure to imidacloprid and thiacloprid resi-
dues. However, the small proportion of lar-
vae that survived insecticide exposure did
not manage to reach the adult stage. The
longevity of the adult survivors was signif-
icantly lower compared to control. Similar
were the effects of the tested insecticides
on
P. quatuordecimpunctata
(Table 2) and
O.
conglobata
(Table 3).
Imidacloprid has been exclusively test-
ed against coccinellid predators and a broad
range of its lethal and sublethal effects have
been evaluated (11, 22, 25). However, the in-
tensity of the toxic effects depends on the
coccinellid species, as well as on the rate and
methods of insecticides application (11, 25).
For example, James (11) found that the di-
rect application of imidacloprid at the rec-
ommended doses on
Stethorus punctum pic-
ipes
(Casey) and
Harmonia axyridis
Pallas was
highly toxic to larvae of both coccinellid spe-
cies. Nevertheless, Youn
et al
. (25) found that
direct application of imidacloprid at the rec-
ommended doses against all developmental
stages of
H. axyridis
was highly toxic to the
egg stage as well as to the first, second and
third instar larvae but not to the fourth in-
star larvae, pupae or adults. In our study, imi-
dacloprid was highly toxic to both larval and
adult stage of all three coccinellid species
tested. In some cases, a small proportion of
the third instar larvae or adults survived the
exposure to imidacloprid, but they did not
manage to reach adulthood or survive for
long after their exposure to the insecticide,
respectively. Although the studies on the ef-
fects of methomyl on coccinellid predators
are limited, toxic effects due to its direct ap-
plication have been reported on
H. axyridis
Pallas,
Coccinella repanda
Thunberg and
Har-
monia octomaculata
(Fabricius) (3, 11).
Table 1.
Residual toxicity of three insecticides to larvae (first and third instars) and adults of
Ceratomegilla undecimnotata
in a 24-h exposure bioassay. Mortality was assessed for larvae
1 day after exposure to insecticides, upon pupation and adult emergence and for adults 1,
10 and 20 days after exposure to insecticides.
Insecticides
% Mean mortality ± SE
1-day residues
8-day residues
First instar larvae
1 day
Pupation Adult emergence
1 day
Pupation Adult emergence
Imidacloprid 92.9 ± 7.1 a* 100 ± 0 a
100 ± 0 a
100 ± 0 a 100 ± 0 a
100 ± 0 a
Thiacloprid 100 ± 0.0 a 100 ± 0 a
100 ± 0 a
86.7 ± 13.0 a 93.3 ± 6.7 a 93.3 ± 6.7 a
Methomyl
100 ± 0.0 a 100 ± 0 a
100 ± 0 a
100 ± 0 a 100 ± 0 a
100 ± 0 a
Control
14.0 ± 5.8 b 18.0 ± 4.6 b 18.0 ± 4.6 b 14.0 ± 5.8 b 18.0 ± 4.6 b 18.0 ± 4.6 b
Third instar larvae
1 day
Pupation Adult emergence
1 day
Pupation Adult emergence
Imidacloprid 56.4 ± 9.1 b 90.8 ± 5.3 a 95.0 ± 5.0 a
84.3 ± 8.8 a 90 ± 5.0 a 95.2 ± 4.7 a
Thiacloprid 85.0 ± 15.0 ab 100 ± 0 a
100 ± 0 a
50.0 ± 18.8 b 100 ± 0 a
100 ± 0 a
Methomyl
100 ± 0.0 a 100 ± 0 a
100 ± 0 a
89.3 ± 10.7 a 96.4 ± 3.6 a 96.4 ± 3.4 a
Control
4.0 ± 4.0 c 4.0 ± 4.0 b 4.0 ± 4.0 b
4.0 ± 4.0 c 4.0 ± 4.0 b 4.0 ± 4.0 b
Adults
1 day
10 days
20 days
1 day
10 days
20 days
Imidacloprid 72.9 ± 10.4 b 93.7 ± 6.2 a
100 ± 0 a
68.6 ± 15.6 b 91.7 ± 5.3 a 91.8 ± 5.3 a
Thiacloprid 100 ± 0.0 a 100 ± 0 a
100 ± 0 a
88.9 ± 11.1 ab 94.4 ± 5.5 a 100 ± 0 a
Methomyl
100 ± 0.0 a 100 ± 0 a
100 ± 0 a
100 ± 0 a 100 ± 0 a
100 ± 0 a
Control
0.0 ± 0.0 c 5.0 ± 5.0 b 10 ± 6.1 b
0.0 ± 0.0 c 5.0 ± 5.0 b 10 ± 6.1 b
* Values within each column and developmental stage followed by the same letter do not differ significantly (Mann-
Whitney U test, P≥0.05).
1...,46,47,48,49,50,51,52,53,54,55 57,58,59,60,61,62,63,64,65