الفهرس 
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Abstract
The two-spotted spider mite (TSSM), T. urticae is a cosmopolitan and extremely polyphagous species with great economic importance for crops in greenhouses and open fields. It has a wide range of hosts especially vegetable crops. This mite pest has a great effect on the plant growth and its chemical and anatomical structure which resulted in an intensive reduction in the total yield, so the present study was conducted to figure out the injury effect of T. urticae on cucumber, Cucumuis sativus L. (Hail, var.) , tomato Lycopersicon esculentum M. (Super-Strain b, var.) and sweet pepper plants, Capsicum annum L. (Top-Star, var.). Three levels of T. urticae infestation (2, 6, 12♀ / plant) were used to study their effects on the plant growth, yield and chemical contents on the previous plants under greenhouse conditions. Mite density counted through the period of infestation. Injury effect of T. urticae on the anatomical and histological changes only studied in the cucumber leaves. The obtained results in the present study could be summarized as following:
A:- Determination of the plant growth and yield losses of three vegetable crops, cucumber, tomato and sweet pepper as affected by the infestation with T. urticae.
A1:- Determination of the plant growth and yield losses of cucumber C. sativus (Hail var.) as affected by the infestation with T. urticae.
A1.1-Plant growth:
• The lowest leaf area, plant height and number of leaves were (53.68 cm.2, 53.77cm. and 10.4) comparing with the control (82.66 cm.2, 58.67cm. and 12.5), respectively, at the high infestation level (12♀ /plant).
• The reduction of fresh weight of leaves were (26.53, 37.39 and 50.32%), whereas moisture content were (9.03, 19.22 and 35.77%) at the three levels of mite infestation (2, 6, 12♀ /plant), respectively.
A1.2- Flowering and yield:
• The lowest number and weight of fruits were recorded at the high level of infestation 12♀ /plant (1.73/plant and 81.78 (g)/plant) with a reduction of (30.35 and 37.09 %), respectively.
• No significant differences in the flower numbers at all infestation levels.
A1.3- Population density of T. urticae:
A highly significant difference in the population density of T. urticae between the low level and both of medium and high infestation levels was observed. The total numbers of mites were 154.8, 284.2 and 337.2 individual with an average number of 38.7, 71.05 and 84.3 individuals/in2 in the low, medium and high infestation levels, respectively.
A2:- Determination of the plant growth and yield losses of tomato L. esculentum (Super-Strain b, var.) as affected by the infestation with T. urticae.
A2.1-Plant growth:
• The lowest leaf area, plant height and number of leaves were (19.94 cm2, 32.76 cm and 8.56) comparing with the control (48.74cm2, 45 cm and 13.31), respectively, at the high level of infestation 12♀ /plant.
• The reduction % of fresh weight of leaves were (35.68, 38.88 and 53.34%), whereas moisture percentage were (9.82, 13.21 and 19.71%) at the three levels of infestation (2, 6, 12♀ /plant), respectively.
A2.2- Flowering and yield.
• The lowest number and weight of fruits were (0.16/plant and 6.94 g/plant) with a reduction of 69.32 and 51.71 % compared with control treatment, respectively at the high infestation level of 12♀ /plant.
• The lowest number of flowers were (1.64/plant) comparing with the control (4.64/plant) at the same infestation level with a reduction of 56.19 % at the high infestation level of 12♀ /plant.
A2.3- Population density of T. urticae :
• The total number of the moving stages of T. urticae were 261, 417.4 and 809 individuals with an average of 52.20, 83.48 and 161.76 individuals / leaflet, at the three levels of infestations (2, 6, 12♀ /plant), respectively, by the end of 5th week from infestation.
A3:- Determination of the plant growth and yield losses of sweet pepper C. annum (Top-Star, var.) as affected by the infestation with T. urticae.
A3.1-Plant growth:
• The lowest values of plant height, number of leaves/plant and leaf fresh weight were (21.62 (cm.)/plant, 17.09 /plant and 0.38 (g.)) at the highest infestation level (12♀ /plant), respectively.
• The highest reduction percentages were 57.58 and 35.08% for leaf fresh weight and leaf area, respectively, at the highest level of infestation. The lowest reduction percentages were obtained at low level of infestation (6.64 and 7.42%) of plant height and number of leaves/plant, respectively.
A3.2- Flowering and yield.
• The lowest number and weight of fruits per plant were (1.11 and 18.05 (g.)) with a reduction % of 45.20 and 29.59 % as compared with control treatment, respectively, for the high level of infestation (12♀ /plant).
• The highest reduction percentage was recorded to the number of flowers /plant (73.54%) at the highest infestation level, while the lowest one was recorded to the weight of fruit/plant (11.60 %) at the lowest infestation level (2♀ /plant).
A3.3- Population density of T. urticae:
• The total numbers of mites were 24.8, 62.6 and 111.8 individuals with an average of 4.13, 10.43 and 18.63/ leaves, for the low, medium and high infestation level by the end of 6th week from mite infestation.
B- Determination of change in some chemical contents in the plant leaves of cucumber, tomato and sweet pepper infested with T. urticae
B1- Chemical constituents of cucumber leaves:
• The lowest nitrogen and total protein constituents were (3.33 and 20.82 mg. /g.), respectively, with a reduction percentage of 26.21 % at the high infestation level, followed by (3.48 and 21.76 mg. /g.) with reduction percentage of (22.86%), at the medium infestation level.
• No significant differences in the phosphorus and potassium constituents among all the infestation levels including control treatment.
B2- Chemical constituents of tomato leaves:
• The lowest nitrogen and total protein constituents were (33.04 and 206.50 mg. /g.), with a reduction percentage of (34.15 %) at the high infestation level, followed by 36.06 and 225.40 mg. /g. with reduction percentage of (28.13 %) for both nitrogen and total protein at the medium infestation level.
• The variance ratio of phosphorus constituents showed a highly significant difference.
• A slightly significant difference in the potassium constituents among all the infestation levels at the high infestation level was obtained.
B3- Chemical constituents of sweet pepper leaves:
• The lowest nitrogen and total protein constituents were (30.63 and 191.45 mg. /g), with a reduction percentage of (41.12%) at the high infestation level, followed by (37.41 and 233.80 mg/g) with a reduction percentage of (28.09 %) for both nitrogen and total protein at the medium infestation level.
• The variance ratio of phosphorus constituents showed a highly significant difference, the lowest phosphorus constituents was (0.08 mg. /g.) with a reduction percentage of 63.44% at high infestation level.
• A slightly significant difference in the potassium constituents among all the infestation levels at the high infestation level was recorded.
C- Determination of histological damage in cucumber leaves as affected by infestation with T. urticae.
C1- Effect of the infestation with T. urticae on the structure of
cucumber leaf tissues:
• The lowest thickness caused in upper and lower epidermis was recorded (12.50 and 2.96 µm) in high infestation level with (15♀) comparing with control treatment (23.65 and 15.05 µm), respectively.
• The highest total damage areas caused in spongy and palisade tissue were recorded (1.03 and 0.54 mm2/0.5cm2) in high infestation level with (15♀), respectively.
C2- Histological changes in cucumber leaves as affected by T. urticae:
• The most conspicuous damage was observed in thickness of lower epidermis than upper epidermis comparing with the control.
• The severe damage occurred in spongy tissues than palisade tissue to varying degrees depending on the level of injury.
• The damage appears as conspicuous shrinkage of palisade and spongy tissues, and cell wall of palisade and spongy tissues were collapsed and decomposed causing completely empty spaces between their cells due to loss of chloroplasts and consequently loss a large amount of chlorophyll.