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:
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.
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.
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.
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.
2.1.b. Number and weight of eggs:
The snail M. obstructa laid the highest number of eggs, when it was fed on clover with mean number 165.4 eggs. Besides, the weight of eggs was higher 0.068 g in case of clover also.
2.1.c. Percentage of hatchability:-
Hatchability percentage was influenced by food type. The produced eggs by the snail were reared on cabbage and clover. The highest percentages of hatchability 87.5 and 85%, were recorded in the case of cabbage and clover while the low percentage 63% was recorded for cucumber.
Effect of temperature:
2.2.a. Incubation period, maturity, longevity and whole life cycle:
The snail was reared at 4 degrees of temperature 15, 20, 25 and 30oC and was fed on clover, lettuce, cabbage and cucumber. The results showed that incubation period was longer at 15oC and decreased when the temperature was increased, but no hatching occurred at 30oC. On the other hand, the maturity period was the longest (115 days) when the snail fed on cucumber at 15oC, and this period decreased when temperature was increased, while the lowest period was recorded when the snail fed on clover at 30oC. Data cleared also that the longevity period was the longest (232 and 230.2 days) when the snail bred on clover and cabbage at 20oC, and was the lowest in case of cucumber at 15oC.
As well as the snail lived the longest periods (343, 342 and 340.4 days), when was fed on clover, lettuce and cabbage at 20oC, while it lived the lowest period when bred on cucumber at 30oC (271 day).
2.2.b. Number and weight of eggs:-
Adults of M. obstructa producted the highest number of eggs at 20oC when fed on clover with mean number 161.4 eggs, the production was very low in number when bred on cucumber at 30oC. On the other hand, the weight of eggs was the heaviest when the snail fed on clover at 20oC also.
2.2.c. Percentage of hatchability:-
M. obstructa eggs were kept under 6 degrees of temperature 5, 10, 15, 20, 25 and 30oC. The highest percentage of hatchability (86.5%) was recorded for 20oC, while no hatching at 5 and 30oC.
2.2.d. Mortality percentage:-
The different stages, (new hatching, juvenile and adult) of M. obstructa were kept under 10, 20, 30 and 40oC in the laboratory. All stages died at 40oC during 16 days. On the other hand, the lowest percentages were recorded at 10oC for all tested stages, these were 0.2, 0.2 and 0.1%, respectively. New hatching stage was very sensitive to high temperature, while adult stage was more tolerant than other stages.
Effect of soil moisture:
2.3.a. Incubation period, maturity, longevity and whole life cycle:
The individuals of the snail were reared under 4 levels of soil moisture 25, 50, 75 and 100%, and were fed on clover, lettuce, cabbage and cucumber. Data revealed that incubation period was longer (18.5 days) under 25% moisture, and was decreased when the moisture was increased in the soil until reached 8.5 days at 100%. Like this, maturity period was the longest when the snail fed on cucumber, cabbage and lettuce (116.4, 116 and 115.3 days) under 25% soil moisture. While, it was the shortest when fed on cabbage and clover (63.4 and 68 days) under 100% moisture. Longevity period was shorter (161.2 days) when the animal was reared on cucumber at 25% moisture., and was longer (259 days) when the snail fed on clover at 75% moisture. On the other hand, the whole life cycle was the longest at 75% soil moisture when the snail was reared on lettuce and clover, it was 343 and 342 days, but the shortest period was recorded at 25% moisture when the snail fed on cucumber.
2.3.b. Number, weight and depth of the laid eggs:-
Number, weight and depth of the eggs in the soil were effected by soil moisture and foods. The lowest number of eggs deposited by the snail was recorded at 25% moisture when was fed on cucumber and the highest number was recorded at 100% moisture when reared on clover and cabbage. In addition, the largest weights of eggs were recorded in case of 75% soil moisture, and when the animal fed on cabbage, lettuce and clover. On the other hand, the depth of eggs in the soil was decreased when the level of soil moisture increased.
2.3.c. Percentage of hatchability:-
Hatchability percentage of M. obstructa eggs was different according to soil moisture. The highest percentage 96% was recorded at 75% moisture, while the lowest percentage of hatchability was recorded when the eggs were kept at 25% moisture, it was 12.5%.
Effect of soil type:
2.4.a. Incubation period, maturity, longevity and whole life cycle:-
The land snail M. obstructa was reared in different 6 types of the soil, clay + sand + peat (1:1:1), clay, clay + sand (1:1), clay + sand (3:1), clay + sand (1:3) and sand soil, and was fed on clover, lettuce, cabbage and cucumber. The results showed that incubation period was the longest in sandy soil, while the shorter was when the snail was bred in mixed soil clay + sand + peat.
Maturity period was the longest when the snail fed on cucumber in sand soil, and was the shortest when fed on clover and cabbage (69 days) in the mixed soil clay + sand + peat and on clover in clay + sand (3:1) soil. On the other hand, longevity and whole life cycle periods were the longest 240 and 351 days when the animal was reared on clover in clay + sand + peat soil. While longevity period was shorter when the snail fed on cabbage in clay + sand (1:3) and sand soils, it was 169.2 and 163.3 days and life cycle was 231.2 days only for cucumber in sand soil.
2.4.b. Number, weight and depth of the laid eggs:-
The high number of laid eggs was recorded when the snail was bred on clover in all types of soil, particularly in clay + sand + peat soil, it was 165.4 eggs. While the snail laid few number when fed on cucumber in all types of soil especially in sand soil, it was 25.2 eggs. The weight of eggs was larger when the snail was reared on cabbage in all tested soils. Besides, the depth of laid eggs was different according to the type of soil, the longest depth 2.1 cm was recorded in clay + sand + peat soil, but was 0.3 cm only in sandy soil.
2.4.c. Percentage of hatchability:-
The hatchability percentage of M. obstructa eggs was the highest when the eggs were kept in clay + sand + peat (1:1:1), clay + sand (3:1) and clay soils, it was 88, 82.5 and 81.5%, respectively. In addition, the lowest percentage was recorded in sandy soil alone.
3. Succeptibility of M. obstructa to certain foods:
In this trial 7 types of foods were tested under laboratory conditions, these types were two vegetable plants (lettuce, and cabbage), one field crop (clover), and four ornamentale plants (rose, ambergris, swallow and ficus). Results showed that the snail preferred cabbage more than all types of food, while ficus has low preference to the snail.
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