SUSCEPTIBILITY

The cultivars of some grapevines (Vitis vinifera L.) varieties, King Robi, Rebier, Flame Seedless, Thompson Seedless and Bez El-Anza were cultivated at ElSalheia, Province El. Sharkia Governorate, during the season 2010. These varieties were tested under laboratory conditions to study their relative susceptibility to the infestation of Tetranychus urticae Koch at 25 ± 5°C and 75+ 5 % R.H. King Robi variety was the most susceptible variety while Bez El-ElAnza., variety was the less susceptible one. On the other hand, Rebier, Flame Seedless and Thompson Seedless have moderate susceptibility. The highest number of eggs was noticed on King Robe variety young leaves (18.35 eggs).


INTRODUCTION
In Egypt, grapevine (Vitis vinifera L.) is one of the important horticultural crops for local consumption and exportation. Summer and Nile Chops (2011) showed that the total cultivated grape area was 180919 feddans with production 1425980 tons. Some trials were made to study the biological aspects of the phytophagous mites on grape vine by Yousef (1970), Zaher and Yousef (1972) Abd El-Hafez (1974), Yousef et al., (1980), Wahba et al., (1982) Atwa et al., (1987), Kondo et al., (1987) Bonato et at.,(1990) and Ashihara (1996).The present work aimed to study the susceptibility of five grapevines varieties in relation to some biological aspects of T. urticae.

1-Cultivated grapevine :
An area of about two feddan cultivated with five grape varieties namely, king Robe, Rebier, Flam Seedless, Thompson Seedless and Bez ElAnza at El. Salheia Province, El-sharkia Governorate in April 2010. The experiment area had not exposed to any treatment with any acaricides.
Samples of young and old leaves for each variety were taken in paper bags and directly transferred to laboratory in the same day of collection for investigation. Obtained data were subjected to one-way analysis of variance (ANOVA) and means were separated by Duncan' s multiple range tests (Duncan, 1955).

2-Biological study:-
To study the susceptibility of aforementioned grape vine varieties on the biological aspects of T. urticae, young and old leaves of five grape varieties were used for rearing the mite under constant temperature at 25 +5°C and relative humidity of 75+ 5 % R.H.. Leaves were placed on cotton wool in Petri-dishes of 12.5 cm in diameter. Suitable moisture was maintained by adding few drops of water . Pure culture of T.urticae was maintained at the laboratory. Newly hatched larvae were transferred singly to a leaf discs (1 cm in diameter) of each variety to complete their life span. Newly emerged females were copulated and left to deposited their eggs until death. The replicate repeated ten times for each variety. Examination took place twice a daily. The duration of stages, number of deposited eggs and other biological aspects were recorded.

RESULTS AND DISCUSSION
Duration of the different stages of T.urticae Koch on young leaves of five grapes. Incubation period:-A) Young grape leaves As shown in

B) Old grape leaves
The incubation period of T.urticae fed on different grape varieties lasted 4.75, 4.8, 4.7, 4.6 and 4.87 days for female while it was 5.53, 4.5, 4.5, 4.4 , and 4.8 days for the male individuals fed on the same aforementioned varieties , respectively, Table (2).

Immature stages A) Young grape leaves
The tabulated data in Table (1) denoted that there were slightly differences between the periods of the developmental stages of T.urticae when fed on different varieties of grape for females and males. The longest period was noticed for the females when the mite fed on Bez ElAnza variety (13.81 days) but the lowest one was noticed for the female on Flam seedless variety (12.10 days).On the other hand this period affected significantly where it lasted 11.75, 11.76, 11.08, 10.5 and 11.01 days when the mite fed on King Robi, Rebier, Flam Seedless, Thompson seedless and Bez ElAnza varieties, respectively on young leaves of grape at 25+5°C for male individuals.

Rebier Rebier
Male Data in Table (2) denoted that there were slightly differences between the periods of the developmental stages of T.urticae when fed on different varieties of grape for females and males. The longest period was noticed for the females when the mite fed on Rebier variety (14.79 days) but the lowest one was noticed for the female on Bez ElAnza variety (12.10 days). On the other hand this period affected significantly where it lasted 12.85, 13.01, 12.03, 11.73 and 12.01 days when males fed on old leaves of King Robi, Flam Seedless, Thompson seedless and Bez ElAnza varieties, respectively under the same conditions. Longevity:-Obtained data in tables (1&2) cleared that there were significantly differences between adult stage periods of female and male when they fed on young or old leaves of different grape varieties. However, the adult female individuals of T. urticae lasted for 18.13 days (the longest period) and 9.09 days (the lowest period ) when the female fed on the young leaves of King Robi and Bez El-Anza, respectively. On, the other hand male adulthood lasted 16.25 days (the longest period) and 7.87 days (the lowest period) when the mite fed on the young leaves of King Robe and Bez ElAnza varieties respectively. While, on the old leaves of grape the adult female of T. urticae staged 14.15 days (the longest period) (Bez ElAnza variety ) and 4.97 days (the lowest period) on Rebier variety at 25+5°C. Also, adult male lasted the longest period when it fed on Bez ElAnza Variety (12.49 days), while it was 3.89 days) (the lowest period) when the mite fed on Rebier variety .

Female longevity: a-) Preovipositon period
As shown in Table (3), it was noticed that, there is very highly significant differences between female individuals fed on the different grape varieties (young leaves).The adult female lasted 1.64 days (the longest period) when the mite fed on King Rope Variety while it was 0.50 days (the lowest period ) when the mite fed on Bez ElAnza Variety . On the other hand, the preoviposition period lasted 3.0 days on the old leaves (the longest period) on Rebier variety of grape , while it was 1.04 days when the adult female fed on Bez El-Anza variety (The lowest period).

b.) Oviposition period
Data in Tables (3 & 4), revealed that there is highly significant difference between female oviposition period when fed on (young and old leaves) different grape varieties The oviposition period lasted 15.8 days (the longest period) on young King Robi variety decreased to 7.5 days (the shortest period) on young Bez ElAnza variety. On the other hand, the longest oviposition period was obtained when the female fed on old leaves of Bez ElAnza (12.28 days), while the lowest one lasted 1.04 days for the females fed on Rebier variety .

c-) Postovipositon period
Obtained data in Tables (3 & 4) cleared that, there is no highly significant differences between female postoviposition period fed on (young and old leaves) different varieties of grape. Female postoviposition period lasted 1.03, 0.8, 0.8, 0.72 and 1.05 days on young leaves, while it was 0.69, 0.99, 0.79, 0.83 and 0.74 days on old grape leaves when females fed on King Robi, Rebier Flam Seedless, Thompson Seedless and Bez ElAnza varieties, respectively.

Fecundity
Female fecundity was highly affected when fed on both young and Rebier Rebier old leaves of different grape varieties at 25+5°C. The highest number of eggs laid by the female was observed on young King Robi variety (18.35 eggs), but the lowest number of deposited eggs was noticed when the female fed on old Rebier (5.01 eggs), Table (3). Similar results were obtained by Kondo et al.,(1987) when reared T.kanazawai Kishida on grapevine . There was higher survival rate of immature stages, development more quickly and showed a higher oviposition rate than on bean leaves.