الفهرس 
Materials and mithodsOnly 14 pages are availabe for public view
 |  | from | 185 |  |  |
| | | from | 185 | | |
Abstract
141
SUMMARY
Field studies were conducted throughout a period of more than two
years that extended from 1991 - 1993 on five summer plantation vegetable
plants (eggplant, tomato, okra, bean and cucumber) and five winter
plantation vegetable plants (cabbage, tomato, pea, bean and vegetable
marrow) to study the rates of infestation with Bemisia tabaci stages
throughout the whole period of plant growth. Host plants were cultivated
simultaneously at two districts (Moshtohor and El-Kanater) that lie in
Qalubia governorate at a distance of about 35km. between them. Plants
were cultivated in plots arranged in randomized complete block design of
4 replicates for each host plant. Cultivation of each plantation took place
for two successive years (1991 and 1992). Starting from the seedling stage
and on weekly intervals, the numbers of Bitabaci adults that settled on
the lower leaf surfaces were counted on each of 10 randomly chosen leaves
/ plot. Other randomized samples of 10 leaves each were randomly picked /
plot to be inspected in the laboratory for immature stage counts per 10
square inches. Sampling was done weekly until the harvesting time of each
crop. The population fluctuation of B.tabaci stages on different host plants
throughout the summer and winter plantations of two years (1991 /92 and
1992 / 93) was discussed. The means of daily daytime (maximum) and
night (minimum) temperatures and the daily mean R.H.% were recorded
and statistical analyses were made to study the effect of these factors and
their combined effect on the population of B. tabaci stages. Other leaf
samples were also picked from different host plants for counting the
---- --- ---------------
142
averages in numbers of hairs, setae and trichomes / cm2 in order to be
correlated with the rate of infestation. The pH values of fresh leaf-sap of .
different hosts were estimated, and the dried matter content of leaves were
subjected to chemical analysis to estimate the percentages of reduced
sugars, nonreduced sugars and total carbohydrates, and also estimating the
total protein content. Trials were made to find out the relationship between
each of the obtained values and the rate of infestation with B.tabaci stages.
The obtained results could be summarized as follows:
I. RELATIVE POPULATION DENSITIES OF BEMISIA TABACI
STAGES ON DIFFERENT HOST PLANTS:
LA. SUMMER PLANTATION:
I.A.I. Eggplant:
Plants were liable for infestation with B. tabaci stages throughout the
whole period of plant growth. Infestation rates were generally higher at
Moshtohor than EI-Kanater. Period of higher infestation extended from the
second week of May till the first week of July. Highest peaks of adults’
abundance were detected during the last week of Mayor in June (90.5 &
89.3 adults / 10 leaves at Moshtohor, and 50.5 & 53 adults at EI-Kanater
in 1991 and 1992, respectively). As for the pest eggs, the highest-peaks of
abundance estimated 169.8 & 88.3 eggs / 10 in.2 of eggplant leaves at
Moshtohor, and 29.5 & 33.8 eggs / 10m..2at EI-Kantater in 1991 & 1992,
respectively. The monthly averages of egg counts indicated highest
abundance during May and August. In case of nymphs, the respective
records of highest peaks averaged 144.5 & 188.5 and 34.1 & 45
- -- _. -_. ---- - - ._----.-.
143
nymphs / 10 in.2 at the two districts and in both years, Months of higher
nymphs abundance coincided with those recorded in case of the pest eggs.
I.A.2. Tomato:
All the inspected samples showed certain rates of infestation with
B.tabaci adults. Adults’ abundance reached the maxima in numbers
during May 1991 at Moshtohor and El-Kanater (44.8 & 103.3 adults,
respectively). In 1992, the peaks of abundance were recorded during
August at Moshtohor (42.3 adults) and September at El-Kanater (42.3
adults also). Peaks of eggs’ abundance occurred also during May 1991
and August 1992 at both districts. Eggs were generally more abundant
during April, May and August. The pest nymphs were less abundant than
eggs, and the peaks of nymphs’ abundance counted 46.5 & 5.8 nymphs
at Moshtohor, and 16.1 & 7.8 nymphs / 10 in.2 at El-Kanater in 1991
and 1992 summer seasons respectively. May and June appeared as
months of higher nymphs’ abundance.
I.A.3. Okra:
Heaviest infestation rate with B.tabaci adults to okra leaves was
recorded throughout 1991 summer season at Moshtohor. Adult
maximum counts averaged 51.5 adults on May, 16th 1991 & only 4
adults on August, 15th 1992 at Moshtohor, and 28.8 adults on May,
25th 1991 & 23 adults on May, 27th 1992 at EI-Kanater. Eggs of this
pest were more abundant on okra leaves during April, May and August,
while higher nymphs’ abundance was detected during June and August.
I.A.4. Bean:
Infestation with the whitefly adults occurred on bean leaves throughout
144
the whole period of plant growth, but rates of infestation varied form one
week to another. Highest peaks of abundance estimated 93 adults / 10
leaves on May, 16th 1991 & 58.5 adults on June, 27th. 1992 at
Moshtohor, and 73.5 adults on June, 22nd 1991 & 72.3 adults on June,
10th 1992 at EI-Kanater. Higher adults’ abundance occurred during May
and June than the remaining period of plant growth. Peaks in eggs
abundance were detected on April, 18th 1991 & April, 18th 1992 at
Moshtohor (170.0 & 12 eggs/l O in?, respectively). At EI-Kanater, the
peaks of egg counts averaged 30 eggs on May, 18th 1991 and 10.5 eggs
on July, 8th 1992. Highest nymphs’ abundance occurred during May 1991
in both localities, while in 1992, July was the month of higher abundance.
I.A.5. Cucumber:
Leaves of cucumber were noticed, in both districts, to be infested with
considerable numbers of adults throughout the whole period of plant
growth. The maxima averages in adult numbers counted 302.7 & 294
adults / 10 leaves at Moshtohor, and 318.5 & 230.3 adults at EI-Kanater
in 1991 & 1992, respectively. Adults showed higher abundance during
July of both seasons at Moshtohor and in 1991 at EI-Kanater, and during
June of the second season at EI-Kanater. The highest peaks of eggs’
abundance reached 1320 eggs / 10 in? and only 38 eggs at Moshtohor,
and 159.7 and 212.5 eggs at EI-Kanater in both summer seasons,
respectively. Nymph counts were generally higher in 1991 than 1992 at
both districts (overall means of 425 & 133 nymphs / 10 in.2 in 1991,
opposed to 187.5 & 31.3 nymphs / 10 in.2 in 1992 at Moshtohor and
EI-Kanater, respectively).
145
I.B. WINTER PLANTATION:
I.B.1. Cabbage:
Considerable infestation with B.tabaci adults to cabbage leaves
occurred during November and December after which the adults either
dropped in number or disappeared. Highest peaks of adults’ abundance
were detected always, in both districts during November of the two
successive winter seasons (49 & 37.3 adults at Moshtohor, and 47.5 &
44 adults / 10 leaves at EI-Kanater in 1991 & 1992, respective1y). The
whitefly eggs were of higher abundance than adults and nymphs. Highest
peaks in eggs abundance at Moshtohor estimated 192 eggs / 10 in? on
November, 9th 1991 and 373.3 eggs on December, 5th 1992, while at
EI-Kanater, those counted 448 eggs on November, 6th 1991 and 187.8
eggs on November, 16th 1992. November also proved as the month of
higher nymphs’ abundance in 1991 at Moshtohor and both seasons at
EI-Kanater, while December showed higher nymphs abundance on
Moshtohor, 1992 winter plantation.
I.B.2. Tomato:
Peaks of adults’ abundance were detected always during November,
being 100.8 & 100.3 adults / 10 leaves at Moshtohor and 118.8 &
104.5 adults at EI-Kanater in 1991 & 1992 winter seasons, respectively.
Infestation to tomato leaves with B. tabaci eggs started, considerably,
early in the season when plants were still in the seedling stage, but numbers
increased successively until reached the maxima averages of 1217.8
eggs/10 in.2 on December, 7th 1991 and 951 eggs on November, 21st
1992 at Moshtohor, and 354 eggs on November, 27th 1991 & 964 eggs /
--------- -------
146
10 in.2 on November, 16th 1992 at EI-Kanater. Highest mean monthly egg
counts were always recorded in November, followed by December. As for
the whitefly nymphs, the highest peaks of abundance were recorded in
December, 7th 1991 and November, 28th 1992 (247.3 & 919.3 nymphs /
10 in.2
, respectively) at Moshtohor, while those estimated 229 and 579.3
nymphs / 10 in.2 in both winter seasons at El-Kanater.
I.B.3. Pea:
Infestation with B.tabaci adults to pea leaves started early when plants
were still in the seedling stage. Highest mean adult counts estimated 29.5
& 28.3 adults at Moshtohor, and 29 & 27.5 adults / 10 leaves at
EI-Kanater in 1991 and 1992, respectively. Higher averages in adult
counts were always detected during November. Highest peaks in eggs
abundance estimated 26.3 & 92.3 eggs at Moshtohor, and 14 & 44.5 eggs
/ 10 in.2 at EI-Kanater in 1991 & 1992, respectively. The recorded means
of weekly counts of nymphs were much lower than those recorded in case
of eggs.
I.B.4. Bean:
Most of the weekly bean leaf samples were found infested with
B. tabaci adults. Considerable rates of infestation were recorded from the
first sample of leaves, but the highest peaks in adults’ abundance counted
73.8 & 232.5 adults at Moshtohor, and 170.3 & 203.3 adults /10 leaves
at EI-Kanater in both winter plantations, respectivley. Higher mean counts
of adults were always recorded in November. The highest mean weekly
counts of eggs were also detected during November of both winter
plantations, being 929.9 & 714.3 eggs at Moshtohor, and 247 & 728.3 eggs
147
at EI-Kanater in both seasons, respectivley. The correspondent highest
mean counts of B.tabaci nymphs estimated 381, 446.3, 43.8 and 135.5
nymphs / 10 in.2 of bean leaves, in the two districts and in both seaons,
respectively.
I.B.5. Vegetable marrow:
Heavy infestations with B.tabaci adults to vegetable marrow leaves
started early in the season· The highest mean adult counts estimated 3101.8
adults on December 14th 1991 & 2275.5 adults on November, 21st 1992
at Moshtohor, and 3073.3 adults on December, 2nd 1991 and 2651.2
adults on November, 16th 1992 at EJ-Kanater. December appeared as the
month of higher abundance in 1991, while higher abundance occurred
during November in 1992 winter plantation. The highest mean counts of
the whitefly eggs in the two successive years estimated 11209.3 & 2695.3
eggs at Moshtohor, and 5796.7 & 2431.8 eggs at EI-Kanater, respectively.
All of the mentioned 4 peaks in egg counts were discerned through
November which proved a month of highest abundance of B. tabaci eggs
throughout the winter season. Highest peaks in nymphs abundance were
estimated on December, 14th 1991 (7222.8 nymphs) and December, 5th
1992 (2638.8 nymphs) at Moshtohor, and on December, 4th 1991 (2674.5
nymphs) and November, 30th 1992 (1580.3 nymphs / 10 in.2 of leaves) at
El-Kanater, December proved the month of higher nymphs abundance at
Moshtohor, while that occurred throughout November at EI-Kanater.
148
II. INFESTATION RATES WITH BEM/SIA TABAC/ STAGES TO
DIFFERENT HOST PLANTS:
Statistical analysis was carried out on data concerning the rates of
infestation with different B.tabaci stages to different summer and winter crops
to estimate significancy between these hosts. Data may be summarized
as follows:
II.A. SUMMER PLANTATION:
II.A.I. Adults:
Host plants cultivated could be arranged descendingly according to the
rate of infestation with Bitabaci adults as cucumber, bean, eggplant,
tomato and okra.Cucumber was, significantly, the heaviest infested than the
remaining 4 host plants. Okra, on the contrary, was the least preferred
host. Bean and eggplant showed nearly the same preference rate for adults’
infestation while tomato took the fourth rank amongst the concerned
summer plants.
1I.A.2. Eggs.
Cucumber leaves received, significantly, the highest rate of infestation,
while okra plants were the least infested. Eggplant followed cucumber in
egg counts, and tomato ranked the third but with insignificant difference
than eggplant. Bean which was the second in attracting the whitefly adults,
ranked the fourth in receiving the pest eggs.
1I.A.3. Nymphs:
As mentioned with adults and eggs, cucumber harboured always the
significantly higher nymph counts, while the lowest nymph counts were
those associated with okra leaves. As indicated in case of eggs, eggplant
149
came after cucumber in the overall mean of nymph counts, but followed
with bean leaves, then tomato which took the fourth rank.
II.B. WINTER PLANTATION:
II.B.I. Adults:
Vegetable marrow leaves proved the most preferred amongst the 5 host
plants for adults’ infestation as leaves harboured, significanthy, the highest
adult numbers in both districts of investigation. On the contrary, pea leaves
harboured the lowest numbers of the whitefly adults, being relatively
nonpreferred than the remaining host plants. Bean plants came the next
after vegetable marrow, followed by tomato and then by cabbage
I1.B.2. Eggs:
Also vegetable marrow leaves received significantly, the highest
infestation levels with the whitefly eggs, while pea leaves were the least
infested. Tomato and bean came the next (after vegetable marrow)
showing nearly the same infestation level but with little tendency towards
tomato. Cabbage was less infested with eggs than bean, but more infested
than pea plants.
II.B.3. Nymphs:
As mentioned with adults and nymphs, vegetable marrow appeared
statistically the most preferred for nymphs infestation as leaves harboured,
the highest nymph counts. While, on the contrary, pea leaves were the
least infested. Tomato and bean followed vegetable marrow and both host
plants showed nearly the same preference level where the differences
between them in nymphal counts were always insignificant. Cabbage
leaves took always the fourth rank in nymphs infestation, showing also the
same order as mentioned with adults and eggs.
150
III. INFESTATION WITH BEMISIA TABACI STAGES TO
PLANTS CULTIVATED IN TWO DIFFERENT SEASONS:
As tomato and bean plants were the only cultivated in summer and
winter seasons in both sites of investigations, data concerning the rates of
infestation with different B.tabaci stages on these two host plants were
considered to compare the rates of infestation between summer and winter
plantations. Data proved generally that infestations with the whitefly
stages were extremely higher on the winter plantation than the summer
plantation host plants (about 12 and 7 times for the three stages altogether
on tomato and bean, respectively).
The obtained results showed that throughout the whole summer season,
plants showed considerable rates of whitefly infestation that varied
throughout the plant growth period, but to the level that showed insect’s
abundance in at least one of its stages during a certain period of time on
either of the two host plants or both of them. While throughout the winter
season, highest infestation level with all of the insect stages occurred on
both plants mainly during November. This high abundance at the
beginning of the winter season is expected because of the migration of
adults at the harvesting time of summer hosts to winter hosts, and also the
increased abundance helps the insect to face the drastic DROP in temperature
during the late winter months.
IV. COMPARATIVE STUDIES ON BEMISIA TABACI STAGES
POPULATION DENSITY AT TWO DISTRICTS:
Rates of infestation with Buabaci stages to different vegetable plants
151
were compared between Moshtohor and El-Kanater that lie in the same
Egyptian governorate at a distance of about 35 km, apart. Although the
same host plant species and varieties were cultivated in both sites, and the
same agricultural practices were paid to growing plants, data indicated
higher infestation rates at Moshtohor than EI-Kanater. The increase in adult
counts was insignificant, while those of eggs and nymphs were significant.
The differences were attributed to that each district has its own conditions
such as neighbouring cultivations, weed infestation, kind of soil and
presence of beneficial natural enemies. It could be concluded that
ditermination of the proper time for whitefly control must be dependent
upon close observation to plants, current inspections of leaves and real
evaluation of the rate of infestation.
v. RELATIONSHIP BETWEEN WEATHER FACTORS AND
BEMISIA TABACI POPULATION ON DIFFERENT
HOSTPLANTS:
Computer statistical analysis of data were done to study each of three
weather factors (daytime temperature, night temperature and relative
humidity) in relation to the counted numbers of Buabaci stages.
V.A. SUMMER PLANTATION:
Significant partial regression values were detected between temperature
and numbers of B.tabaci adults. The rate of increase varied on different
host plants. An increase by 10C than the mean daytime temperature,
increased the average number of adults counted on eggplant, tomato, okra,
bean and cucumber by 1.59, 1.03, 1.68 , 1.61 and 1.21 adults, respectively.
152
These increases reached 2.28, 1.51, 1.71, 1.22 and 1.42 adults on the host
o
plants respectively, by 1 C increase in the mean night temperature. The
same effect was detected on B.tabaci eggs and nymphs which increased
by the increase in temperature. On the other hand, the effect of
relative humidity on B.tabaci numbers was found, mostly, insignificant.
V.B. WINTER PLANTATION:
The relation also indicated, significantly, positive partial regression
values between temperature and B. tabaci stage numbers. Adult’ numbers
counted on cabbage, tomato, pea, bean and vegetable marrow increased by
1.22, 1.04, 1.3, 2.42 and 1.24 adults, respectively for lOC. increase in the
mean daytime temperature and by 2.09, 2.01, 1.75, 1.6 and 2.33 adults
respectively for 1°C. in the mean night temperature. The same trend of
effect of temperature was also detected on eggs. While on nymphs, the
effect was not clear on pea plants, this may be attributed to the very low
numbers of nymphs recorded on this host plant. Relative humidity
appeared, on the other hand, as a factor of minor effect.
It could be generally concluded that the most important factor was the
daytime temperature followed by night temperature, while the effect of
relative humidity seemed of minor importance. The combined effect of the
three factors was significant on adult numbers infesting all host plants
except vegetable marrow in the first season at EI-Kanater, while on eggs
and nymphs, the combined effect varied on different host plants and
seasons.
153
VI. RELATIONSHIP OF THE LEAF TRICHOME AND BEMISIA
TABACI POPULATION:
No clear correlation could be concluded between the presence and
densities of trichomes or hairs on the lower leaf-surfaces and the rates of
Bitabaci infestations. Cabbage which has glabrous leaves harboured
more immature stages than tomato and okra that have hairy leaves. Also,
tomato which has higher trichome densities on its lower leaf surfaces
harboured lower immature stage numbers than cucumber, bean and
eggplant which have ”less dense trichomes on leaves. That indicated that
densities of trichomes on leaves may not be amain factor affecting selection
for development of B. tabaci immature stages.
VII. RELATIONSHIP BETWEEN HOST LEAF PHYTOCHEMICAL
COMPONENTS AND BEMISIA TABACI INFESTATION:
No clear correlation could be detected between the recorded B. tabaci
stage infestations and the pH level in the leaves sap of the host plants
under investigation (pH ranged between 5.1 - 5.7). While, positive
correlation was detected between the percentages of reducing sugars and
also of total carbohydrates and the rate of infestation. This correlation
could not be detected in case of nonreduced sagars percentage. On the
contrary, the correlation appeared negative in case of total protein content;
i.~.,B.tabaci mean counts increase on leaves charcterized with lower
content of crude protein.