© Benaki Phytopathological Institute
Toxicity of insecticides on
Trichogramma cacoeciae
63
2012; Blibech
et al.,
2015).
Toxicity of different classes of insecti-
cides to
Trichogramma
spp. vary. Synthet-
ic pyrethyroid insecticides appear to be the
most harmful class (Youssef
et al.,
2004; Ab-
dulhay and Rathi, 2014; Sohrabi and Amini,
2015; Thubru
et al.,
2016); Furthermore, the
effect of deltamethrin on pupae of
Tricho-
gramma oleae
(Voegele and Poitale)
, T. ca-
coeciae
,
and
T. bourarachae
Pintureau and
Babault persisted for 30 days following ex-
posure (Blibech
et al.,
2015).
Τhe neonicotinoid insecticide acet-
amiprid was harmful as regards adult emer-
gence and rates of parasitism of
Trichogram-
ma evanescens
Westwood (Jiu-Sheng
et al.,
2010). Thiacloprid was harmful to
T. cacaoe-
ciae
adults but harmless to larvae and pupae
(Schuld and Schmuck, 2000).
Organophosphate insecticides have
been shown to be harmful to eggs of
T. ev-
anescens
and
Trichogramma platneri
Nagar-
katti (Jiu-Sheng
et al.,
2010; Brunner
et al.,
2001) and moderately harmful to
T. cacoeci-
ae
(Youssef
et al.,
2004).
Insect growth regulators and insect
growth inhibitors (fenoxycarb, difluben-
zuron and lufenuron) have been reported
not to be harmful to adults, pupae or eggs
of
T. cacoeciae
(Hassan
et al.,
1998; Brunner
et al.,
2001; Abaar
et al.,
2010). Consoli
et al.
(2001) found that lufenoron and triflumuron
did not affect parasitism efficiency in
T. gal-
loi
Zucchi, although they were harmful when
applied to larvae and caused 100% death
rate in adults when applied to eggs.
Abdelgader and Hassan (2012) reported
that azadirachtin was harmful to
T. cacoeci-
ae
adults, which were exposed to residues
on glass plates and slightly to moderately
harmful regarding adult emergence when
applied to parasitized host eggs at different
time intervals.
Herein, we studied lethal, sublethal and
persistence effects of ten insecticides, which
are commonly used
in date palm production
in Saudi Arabia, on
T. cacoeciae
. Adults of the
parasitoid were exposed to dry residues of
the highest recommended rates of the test
insecticides thus at very high risk (Hassan
et
al.,
2000), likely resulting in the greatest de-
gree of harm. The outcome of lethal/subleth-
al effects together with the results on the in-
secticide persistence will contribute to the
selection of insecticides that pose lower risk
to the parasitoid and to determine the con-
ditions of safe use in IPM programs in date
palm plantations (Grutzmacher
et al.,
2004).
Material and Methods
Trichogramma cacoeciae cultures
Trichogramma
cacoeciae
was selected
among
Trichogramma
spp. for the bioassays
as it is easy to rear and handle in the labo-
ratory (Hassan 1998).
Trichogramma cacoeci-
ae
was obtained from a colony maintained at
the Excellence Research Center for palms and
dates at the King Faisal University. The colo-
ny originated from parasitized Lepidopter-
an eggs on leaves of cruciferous, tomato and
other Solanaceae plants cultivated at Al-Has-
sa fields, Eastern province of Saudi Arabia.
Adults of
T.
cacoeciae
were reared on eggs of
Ephestia cautella
(Walker) (Lepidoptera: Pyra-
lidae) (Suh
et al.,
2000), in an insect growth
chamber maintained at 23 ±2 ºC and 75 ±5%
relative humidity (RH) with a 16:8 L:D cycle.
Insecticides
Lethal and sublethal effects on
T.
ca-
coeciae
were assessed for 10 common-
ly used and commercially available insecti-
cides in Saudi Arabia against pests of date
palms. The insecticides are presented in Ta-
ble 1 and contain active substances which
belong to different chemical groups (pyre-
throids, organophosphates, carbamates, In-
sect Growth Regulators and plant extracts).
Lethal effects of insecticides
Lethal effects of insecticides were as-
sessed on
T. cacoeaciae
adults after exposure
to dry residues on glass plates using the high-
est recommended application rates (Hassan
et al
., 2000). Glass tubes (2.5 x 20 cm) were
treated by adding 5 ml of an aqueous insec-
ticide solution which covered the inner sur-
face; the tubes were then emptied and left to
