الفهرس 
Materials and mithodsOnly 14 pages are availabe for public view
 |  | from | 167 |  |  |
| | | from | 167 | | |
Abstract
The purpose of our study was to further investigate the immediate
and delayed toxicity of abamectin (Avermectin B1) and thuringiensin (13-
exotoxin of Bacillus thuringiensis), representing novel classes of
unconventional insecticides, on :both laboratory and field strains of
cotton leafworm, Spodoptera littoralis (Boisd.), as an aid to the field use
of such compounds in pest management programmes. This work
included fourth parts summarized as follows:
Part I
”Biological Activity of Abamectin and
Thuringiensin against Cotton Lcafworm,
Spodoptera littoralis (Bois d.}”
,
In this part we evaluated abamectin and thuringiensin as well as
diflubenzuron to determine their biological activity against laboratory
and field strains of S. littoralis following larval feeding on leaves treated
with sublethal concencentrations of such compounds. Fourth-instar
larvae were fed, for 72h, castor bean leaves treated with sublethal
concentrations, causing ca. 20-60% mortality 3 days after treatment, of
each compound tested. The survivors were allowed to complete their
development until pupation. The delayed effects of these chemicals on
pupation, emergence. and fecundity were determined for both strains
tested .
._--’- - -- - _.- -
1.19
The results obtained from this work can be summarized as follows :
1- The larval mortality following 72h-feeding on leaves treated with
sublethal concentrations of test compounds reached 20-57% by day 3
after treatment. It seems that abamectin and thuringiensin were
similar to diflubenzuron indicating slow acting toxicity at which the
latent toxicity was consistent with a disruption of the molting process
from fourth to fifth ins tar. Thuringienzin appeared to be more
effective than other compounds, at tested concentrations.
2- Percent pupation reported for surviving larvae, following feeding on
treatd leaves, demonstrated that all sublethal concentrations of any
tested compounds significantly decreased pupation percentages
compared to those reported for the untreated control. For example, in
the field strain, pupation percents reported at concentration of 0.1
ppm were 9.5, 16.7, and 12.9%, for abamectin, thuringiensin, and
diflubenzuron, respectively, compared to those reported for the
untreated control (- 70.8 %).
3- The mean weight of pupae recorded at test concentrations, III
susceptible strain, was generally not significantly different than that in
the control treatment. However, the mean weight of pupae recorded
in case of field strain was clearly decreased in all insecticide
treatments, especially abamectin and thuringiensin, compared to those
of the untreated control. For example, the mean weights reported, at
concentration of 0.001 ppm were 183.3, 177.9,and 209.7 mg for
treatments of abamectin, thuringiensin, and diflubenzuron ,
1 20
respectively, compared to that of control (.....231.7 mg). It seems that
reduction in pupal weight was proportional to concentration.
4- All insecticide treatments resulted in decreasing adult emergence than
that of the control. In general, thuringiensin treatments, at any of the
tested concentrations exhibited clearly decreasing in adult emergence,
either in susceptible or field strain, compared to the other
compounds. For example, in the field strain, emergence percentages
recorded at concentration of 0.001 ppm were 83.3, 53.3, and 77.5%,
for treatments of abamectin, thuringiensin, and diflubenzuron,
respectively. Reduction in adult emergence seems to be proportional
to concentration.
5- It was obvious, also, that all compounds tested, especially
thuringiensin, caused clearly reduction in the fecundity of moths
developing from larvae fed treated leaves compared to those
developing from larvae fed untreated leaves. The reduction in
fecundity of moths in the field strain was much more happened in the
susceptible strain. For example, in the field strain, the mean numbers
of eggs deposited, at 0.01 ppm, were 520, 202, and 362/0 , for
treatments of abamectin, thuringiensin, and diflubenzuron,
respectively, compared to that of the control(l840 eggs/ 0 ). It seems
also that reduction in fecundity was proportional to concentration.
PART II
Histopathological Effects of Abamectin and
Thuringiensin on The Cotton
Leafworm, Spodoptera littoralis
----- - - ---- -- -_.-----
121
histopathological changes in the midgut of cotton leafworm, S. littoralis,
larvae resulted from feeding on abamectin-, thuringiensin-, or
diflubenzuron- treated leaves; in an attempt to understand the nature and
significance of such changes.
The results obtained in this study can be summarized as follows:
1. The midgut of a normal 4lh.-instar larva consists of a single cellular
layer resting upon a basement membrane which is surrounded
externally first by circular then longitudinal muscles. The cellular
layer, the epithelium, consists of columnar-cells, each with a large
granular nucleus, which are interspersed with cluster of small
regenerative cells, also resting upon the basement membrane. The
lumen is surrounded by a peri trophic membrane.
2. Feeding of 4th-instar larvae on abamectin-treated leaves (0.01 ppm),
for 72h, ’caused an obvious cytological changes in the midgut. The
epithelial cells showed marked disintegration and disorganization. A
few scattered groups of the epithelial cells were separated from their
inner ends, and were sloughed into’ the lumen of the gut. The cell
walls appeared to be indistinct and destroyed in some instances.
The histopathological symptoms caused in the midgut of larvae fed
leaves treated with the lower concentration tested (0.001 ppm) of
abamectin were somewhat less than those caused by the higher
concentration used. However, the epithelial cells showed marked
degeneration, the cell walls were indistinct, and the cells appeared to
be elongated.
3. Strong histopathological symptoms were clearly shown in the midgut
of larvae fed leaves treated with thuringiensin, at 0.0 1 ppm. The
--~_.------
1 22
epi thelial cells of the midgut in most areas showed marked
generation. Cell boundaries disappeared, and scattered groups of the
epithelial cells were sloughed off into the lumen. Also, the basement
membrane and surrounding muscles detached from the epithelium in
some areas.
It was evident that the lower concentration tested, 0.00 1 ppm, had also
some histological changes in the midgut. Where, the epithelial cells
showed marked degeneration, and elongated throughout the whole
section. There was fading of cellular boundaries.
4. The histopathological symptoms in the midgut of larvae after
feeding on diflubenzuron-treated leaves, at 0.01 ppm, were less
pronounced than those caused by either abamectin or
thuringiensin. The epithelial cells of the midgut, in some areas,
were disorganized and disintegrated. There was elongation of
epithelial cells and fading of their boundaries. In addition. a few
scattered groups of epithelial cells were sloughed off into the
lumen or III the space between the epithelium and the
peritrophic membrane. Vacuolations were observed in the
epithelium in some areas, and also the basement membrane and
surrounding muscle layer, in some regions. showed marke
degeneration. The degeneration of midgut epithelium caused by the
lower concentration tested, 0.001 ppm, of diflubenzuron was unlike
that caused by concentration of 0.01 ppm, in that the cells did not
slough off, as well as the basement membrane and surrounding muscle
layer unaffected.
-~ -_ .. -----.- -~----_._----
123
that caused by concentration of 0.01 ppm, in that the cells did not
slough off, as well as the basement membrane and surrounding muscle
layer unaffected.
PART III
nBiochemical Effects of Abamectin and
Thuringiensin on The Cotton Leafworm,
Spodoptera Littoralis”
- In this part of our present study an attempt was made to elucidate
the possibility of biochemical effects of abamectin and thuringiensin on
the activity of digestive enzymes and also of non-specific esterases in S.
_littoralis larvae. The fifth-instar larvae were fed, for only 1 day, on
leaves treated with sublethal concentrations, ranged from 5 to 200 ppm,
through three successive generations. Larvae, then, were allowed to feed
untreated leaves for 2 successive days. The activity of both digestive
enzymes, i.e. invertase, amylase, and trehalase, and non-specific
esterases, i.e. a-esterase and I}-esterase.was determined during the 3-day
feeding period, compared to that of control where larvae were fed on
untreated leaves.
The results of our present study can be summarized as follows:
1. It was evident that feeding of larvae on abamectin-treated leaves, at 5
ppm, through F1-generation resulted in a suppression of the activity
---- ---- --- - - --- ---------
124
On the other hand, the weight of larvae fed on treated leaves
decreased continuously; this decrease, in most cases, seemed to be
directly proportional to the lower enzymatic activity. where the
larval weights for the control larvae were gradually increased
reaching the maximum on the third day.
2. At F3-generation, where larvae fed on abamectin-treated leaves, at
200 _ppm, the inhibitory effects were reported for only trehalase
activity which decreased by 60% than that of control, at I-day period
after trearment. Moreover, amylase activity was reduced by 21 and
46%, at 2-and 3-day periods, respectively, compared to that of
control.The larval weights showed a slight decrease during 3-day
feeding period compared to that of control.
3. Similar inhibitory effects of thuringiensin on larval digestive enzymes
were also obtained, at Fl-generaltion, where larvae were fed on
thuringiensin-treated leaves, at 5 ppm. Larval amylase activity was
reduced by 63, 40 and 77%, at 1-, 2-, and 3-day period, respectively,
compared to that of control. Invertase activity was also decreased by
54 and 76%, at 2- and 3-period. However, the trehalase activity was
less sensitive than amylase and invertase. The decrease occurred in the
weights of larvae fed treated leaves was generally proportional to the
lowered enzymatic activity.
4. At F3-generation, where larvae fed thuringiensin-treated leaves, at
200 ppm, the inhibitory effects of thuringiensin on the activity of
._--- - ----_._-- -----------------
12’5
digestive enzyme was clearly shown at 2- and 3-period days. The
trehalase activity was affected to a lesser extent.
5. The acnvity of both a-esterase and (3-esterase in larvae fed on
abamectin-treated leaves, at 5 ppm, through Pj-generation, was
reduced by 28 and 30%, respectively, than that of control, at l-day
period after treatment. The reduction caused in enzyme activities was
also reported at 3-day period, though larvae were allowed to feed on
untreated leaves. Similar inhibitory effects on enzyme activities were
also observed when larvae were fed leaves treated with 200 ppm,
through. the F3-generation. However, the reduction caused in ((-
esterase or B-esterase activity, at 1-day period, was much more than
that occurred in larvae fed on leaves treated with 5 ppm, indicating
only 42 and 34%, respectively, of that of control.
6. The inhbitory effects of thuringiensin on the activity of both cesterase
and B-esterase was relatively less than that caused by
abamectin. For example, the activity of a-esterase and B-estcrase in
larvae fed on treated leaves, at 5 ppm, uhrough the FI -generation, was
decreased by only 19 and 20%, respectively than that of control.
Similar inhibitory effects were observed at 3-day period. However,
the inhibitory effects of thuringiensin on such enzyme activities were
more affected, when larvae were allowed to feed leaves treated with
the higher concentration of 200 ppm~ through the F3 -generation. For
example, at l-day period, the activity of a-esterase and b-esterase was
decreased by 38 and 41%, respectively, than that of control.
- ---- _. - --. _.---
126
PART IV
If Joint Action of Abamectin or Thuringiensin with :
Organophosphorus Carbamate, and Pyrethroid Insecticides on
Spodoptera littoralis (Boisd.) Larvae”
In t.his part, we evaluated the joint action of binary mixtures of
either abamectin (Avermectin Bj ) or thuringiensin (B-exotoxin of
Bacillus thuringiensis) with certain insecticides represented the main
chemical groups of pesticides, i.e. organophosphates, carbamates, and
synthetic pyrethroids, on laboratory-reared larvae of the cotton
Ieafworm, Spodoptera littoralis (Boisd.), to determine whether the
binary mixtures exhibited synergistic activity against this insect.
The influence of different insecticide : abamectin (or thuringiensin)
ratios on t.he synergistic activity and toxicity of the mixtures was
examined. Mixing ratios (insecticide: abamectin [or thuringiensinl)
tested were 99:1, 19:1,9:1,4:1,1.5:1, and 1:1, respectively. These ratios
were used to produce a series of binary mixtures (insecticide +
abamectin [or thuringiensinl) that contained 99 + 1%, 95 + 5%, 90
+10%, 80 + 20%, 60 + 40%, 50 + 50% respectively. Dosage-mortality
data were obtained for all mixtures, where the method of Sun & Johnson
(1960) was used to test for synergism and to compute the joint toxicity
of the binary mixtures. The joint toxicity coefficients of the binary
mixtures tested were calculated on basis of LCso values, at 48 and 72h
after treatment, against fourth-instar S. littoralis larvae. The results
obtained in this study can be summarized as follows:
.- -- ._. -- .- -- -- ’-.- -----
_. -~ --- - ----_.--_._------
127
reported that, with the exception of chlorpyrifos + abamectin
mixture, at ratio of 1:1, all other mixing ratios tested exhibited
clearly antagonistic action.
Data also reported, at 72h after treatment, for the profenfos +
abamectin mixtures, indicated that most mixing ratios tested exhibited
synergistic activity, especially ratios of 99:1,1:1, and 9:1 indicating
CC with ca. 468, 227, and 181, respectively.
The mixtures of pirimi phos-ethyl+abamecti n, especially those
combined at ratio of 99: I, were 5A-fold more toxic to the larvae, at
48h after treatment, than insecticides alone; whereas most other
mixing ratios resulted in antagonistic action.
Low synergistic activity was obtained by the mixtures of acephate +
abamectin, at.ratios of 4: 1 and 1.5: 1, indicating CC=111.9 and 140.9,
respectively, however, antagonistic action was reported by the other
tested ratios.
The mixtures of methamidophos + abamectin exhibited synergistic
activity, at 72h after treatment, at ratios of 9:1, 19:1,99:1, and 1:1,
indicating CC= 310.3, 292 , 9, 179,1, and 141,3, respectively.
2. Data concerned the joint action and toxicity of carbamate insecticides,
methomyl and thiodicarb, with abamectin showed that all tested
mixtures tested of methomyl + abamectin,· at 72h after treatment,·
resulted in antagonistic activity compared to the insecticides alone.
Howvere, the toxicity data, at 72h, indicated that all mixtures of
thiodicarb + abamectin exhibited low synergistic activity indicating
CC ranged from 118.6 (at ratio of 1:1) to 150.4 (at ratio of 9: 1).
3. The results of joint action and toxicity of the mixtures of pyrethroid
insecticides plus abamectin indicated that all mixtures of
------------------------------------------------
128
3. The results of joint action and toxicity of the mixtures of
pyrethroid insecticides plus abamectin indicated that all
mixtures of deltamethrin+abamectin exhibited synergistic
activity, indicatig CC ranged from 109.8 (at ratio of insecticides
alone. However, strong antagonsitic action was reported by all
mixtures of fenpropathrin + abarnectin. The data demonstrated also
that all mixtures of fenvalerate + abamectin, with the execption of
ratio of 1:1, exhibited low synergistic activity indicating CC ranged
from 106.1 (at ratio of 9:1) to 166.2 (at ratio or 1.5:1). Similar
results were obtained when cypermethrin was combined with
abamectin at tested ratios.
4. Concern for the joint action and toxicity of the mixtures of
. organophosphorus insecticides plus· thuringiensin, our results
demonstrated that the chlorpyrifos + thuringiensin mixtures, at
ratios of 99:1 , 19:1 , 4:1 , and 1.5:1 , were 1.3-, 1.4- , 1.5-, and
1.5- fold. respetively, more toxic to S. littoralis larvae, at 48h
after treatment, than insecticides alone. Similar results were
shown by the mixtures of profenofos + thuringiensin, in which mixing
. ratios of 99: 1, 9: 1, and 19: 1 exhibited synergistic activity indicating
cotoxicity coefficients (CC) by ca. 170, 170, and 110. Synergistic
activity reported for such mixtures, especially at ratios of 99: 1 and
9: I, was increased, at 7211 after treatment. Also, all tested mixtures of
pirimiphos-ethy1 + thuringiensin showed synergistic activity,
especially those combined at ratios of 99:1, 4:1, and 1:1 indicating CC
= 475.4, 465.4, and 245.8, respectively , at 48h after treatment.
_.- .-- --- --- ._- ..~------
129
Moreover, all mixtures of methamidophos + thuringiensin exhibited
clearly synergistic activity, especially those combined at ratios of
19:1, 4:1, and 99:1 indicating CC = 769.1, 220.0, and 195.9 ,
respectively at 48h after treatment. However, all mixtures of
accephate + thuringiensin cleraly showed antagonistic activity (CC <
100), compared to insecticides alone.
5. Regarding the joint action between carbamate insecticides used, i.e.
methomyl and thiodicarb, and thuringiensin, our data showed that
methomyl + thuringiensin mixtures combined at ratios of 9: 1 and 4:1
exhibited synergistic activity ,at 48h after treatment, indicating CC=
142.6 and 196.1, respectively. However, antagonistic action was
shown when methomyl was combined with thuringiensin at ratios of
1:1.5 and 1:1. However, strong antagonism was shown when
thiodicarb was combined with thuringiensin at most mixing ratios
tested, whereas ratios of 9: 1 and 4: 1 resulted in a reasonable
synergism, compared to insecticides alone.
6. Concern to the joint action and toxicity of the mixtures of pyrethroid
insecticides plus thuringiensin, the data of cotoxicity coefficients (CC)
revealed that slight synergistic activity was reported for mixtures of
deltamethrin + thuringiensin, especially those combined at ratios of
99: 1, 9: 1, and 4:1, indicating CC = 174.2, 136.3, and 109.9,
respectively. All mixtures of cypermethrin + thuringiensin combined
at tested ratios, with the exception of ratio of 1.5:1, exhibited
synergistic activity with coefficients ranged from 125.2 (at ratio of
1:1) to 253.1 (at ratio of 19:1). Similar results were reported for the
~._- - - - --- ---- .. _.- ..--_ ....-------
130
mixtures, of fenvalreate + thuringiensin, at which any of the tested
mixing ratios were usually more toxic to the larvae than insecticides
alone. the cotoxicity coefficients reported ranged from 111.0 (at ratio
of 99:1) to 126.7 (at ratio of 4:1). However, antagonistic action was
reported for all tested mixtures of fenpropathrin + thuringiensin
indicating coefficients < 100.
7. The data also indicated , generally, that mean weight of larval body
estimated at LCso, 48h after treatment. for most tested mixtures was
decreased clearly than that for control larvae.
In general it seems that most mixtures of tested organophosphorus
insecticides with thuringiensin exhibited greater synergistic activity than
mixtures of such insecticides with abamectin. However, the synergistic
activity and toxicity of the mixtures of tested synthetic pyrethroids with
abamectin were markedly greater than the synergistic activity and
toxicity of the mixtures of tested organophosphorus insecticides with
abamectin.