الفهرس 
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Abstract
In recent years terrestrial gastropods have increased considerably with economic importance in Egypt. Thereby field and laboratory experiments had been carried out to study certain ecological and biological aspects of land snails infesting major crops in Kalubia Governorate. The obtained results could be summarized as follows.
1. Ecological studies:
1.1. Survey and distribution of land snails and slugs in kalubia Governorate:
Seven species of terrestrial gastropods were identified in 5 localities representing Toukh district at Kalubia Governorate. These localities were Moshtohor, El-Kady, Shams, El-Haddadin and El-Manshiia. The species included six snails and one slug. The snails were Monacha obstructa Ferussac, M cartusiana Muller, Eobania vermiculata Muller, Succinea putris Linnaeus, Helicella vestalis Piffer, Rumina decollata Linnaeus, and the slug was Lehmannia marginata Muller. M obstructa infested all examined plants in different spots especially fruit trees, field and vegetable crops. But E. vermiculata has majority on ornamental plants. On the other hand, R. decollata was determined in El-Kady village only with little number on vegetable crops and the slug L. marginata was found on swallow in Moshtohor village.
Summary
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1.2. Population dynamics:
1.2.a. Number of clutches and eggs laid by M. obstructa and E. vermiculata under field conditions:
Number of clutches and eggs deposited by M obstructa were counted in navel orange, Egyptian clover and lettuce, but E. vemiculata eggs were counted in swallow, ficus nurslings and rose, in Moshtohor, Toukh district, Kalubia Governorate. Data showed that M obstructa and E. vermiculata laid the eggs in holes in the soil as masses or solitary during 6 months started from December to May. Numbers of clutches and eggs were significantly changed during the breeding season, and the highest total numbers were recorded in February and March for M. obstructa and in February and March or January and March for E. vermiculata. The number of eggs/mass was also changed during the breeding season. The percentages of clutches were higher than solitary eggs laid by the
land snails.
1.2.b. Number of immature and adult stages of M. obstructo and E. vermiculata:
This study was carried out on navel orange, Egyptian clover, lettuce, swallow, ficus nurslings and rose in Moshtohor village, Toukh district, Kalubia Governorate. Results indicated that adult stages of M obstructa appeared in November with high percentage and decreased during spring months, but the percentages of immature stages were the highest during the end of winter and spring months. On the other hand, immature stages of E. vermiculata increased in number from February to May, but the adult stage were the highest in November and decreased or increased slightly during the growing season.
1.3. Estimation of damage caused by land snails and slugs:
This study was carried out on 10 plant species (clover, cabbage, lettuce, strawberry, artichoke, navel orange, ambergris, rose, swallow and ficus nurslings). Results showed that the percentages of damage were increased or decreased according to temperature and air humidity during the growing season, and the highest percentages were recorded in winter and spring monthes especially in March. As well as, the percentage of damage was higher on cabbage followed by clover and lettuce.
2. Biological studies:
This study was carried out in the laboratory to indicate the effect of some ecological factors on the biological aspects of the land snail M obstructa.
2.1. Effect of food:
2.1.a. Incubation period, maturity, longevity and whole life cycle:-
The snail was bred on 4 different types of food, clover, lettuce, cabbage and cucumber. Results proved that incubation period was flactuating with the type of food. The means of incubation period were 12, 11, 13 and 13.5 days, respectively. Period to maturity was the longest when the snail fed on cucumber with mean 95.4 days. And longevity period was longer in case of clover and lettuce with mean 201 and 200 days, respectively.
As well as, the whole life cycle was the longest (354 days), when the snail was bred on clover, but was 302 days only in case of lettuce.