Land snails are considered a group of the most dangerous agricultural pests. These animal pests have became known for most of the Egyptian farmers because their serious damage to most crops. Therefore, the present work was carried out to throw some light on certain ecological and biological aspects of some species of land snails which help in planning the successful control programms.
1. Ecological Studies. 
1.1. Survey of land snails.
Results of the survey carried out on land snails species during the period from January 1994 till the end of December 1995 show that, four species of land snails belonging to family Helicidae were found on different crops at six districts of Sharkia Governorate. These species were the glassy clover snail, Monacha sp. which was recorded at the six districts infesting various hosts with 28.7, 13.8, 9.3, 8.5, 6.6, and 2.2 % of the total occurrence percentage of snails at Zagazig, Bilbies, Meniet El-Kamh, Abou-Hammad, Hehia and Al-Ibrahimia, respectively. The second species was the small sand snail, Helicella vestalis which considered one of the predominant species with a high occurrence percentages (27%) at Bilbies district only infesting many hosts especially fruit trees. The third species was the conical snail, Cochlicella acuta which was found at Abou-Hammad district only with a percentage of occurrence (8.5%) associated with various hosts. The fourth species was the brown garden snail, Eobania vermiculata harboring some ornamental plants at Zagazig district with the lowest percent occurrence (3.9%).
1.2. Population dynamics of the small sand snail, Helicella vestalis:
The small sand snail, Helicella vestalis was generally the most abundant species on tested fruit trees, therefor the population dynamics of this snail was carried out during 1994 and 1995 on guava, mango, navel orange, date palm and banana trees. Data showed that the infestation started with a low number in (January) for all tested crops, then increased gradually till reached the fيrst peak in March. A signifيcant positive correlation was found between mean of temperature and population density, while insignifيcant positive for relative humidity on guava during 1994, 1995 respectively. For mango trees it was significant negative correlation was found between temperature and population density, while it was positive and non signifيcant for relative humidity. On date palm trees the effect of temperature and relative humidيty on population was non signifيcant positive in the two years 1994 and 1995. The effect of temperature on population density on navel orange trees was negative and signifيcant, while it was positive and non signifيcant for relative humidity in 1994 and 1995 respectively. On banana trees, the effect of temperature was positive and non significant in 1994 while it was positive and signifيcant in 1995. For relative humidity it was negative and non signifيcant in 1994 and positive and signifيcant in 1995.
1.3. Daily activity of the small sand snail, Helicella vestalis.
Number of active snails were recorded every two hours along 24 hours in days with dark and moonlit nights during 1996 seasons on navel orange trees. Also, the effect of moonlight, temperature and relative humidity was studied; the correlation coefficient, partial regression and explained variance were calculated. It was found that the activity of Helicella vestalis infesting navel orange trees was signifيcantly differed from time to time during the day and from season to another during the year. Also, moonlight showed a signifيcant effect on the daily activity of Helicello vestalis. The lowest number of active snails was recorded in summer, while the highest one was recorded in spring of 1996 year. On the other hand, the time from 10 to 16 O'clock represented the time of the lowest activity, while the time between the mid night and six O'clock in the morning showed the period of the highest activity.
Statistical analysis revealed that a significant effect for the moonlight on the activity of Helicella vestalis infesting navel during 1996 seasons. Negative and highly signifيcant correlation between mean temperature and mean number of active snail while, positive and highly signifيcant correlation was recorded for relative humidity in days with dark and moonlit nights, respectively
1.4. Host preference and damage of Helicella vestalis.
Host preference and damage of Helicella vestalis were tested under green house conditions using four levels of artifيcial infestation (25, 50, 75 and 100 individuals / treatment) on four hosts i.e. navel orange, mango, banana and guava seedling. Data revealed that mean number of snails attacking each seedling increased signifيcantly as the infestation level increased from 25 to 100 individuals / treatment. The tested hosts were arranged according to their preference as follow: navel orange, mango, banana and guava seedling, respectively.
According to the damage caused by Helicella vestalis the results obtained indicated that infestation level had a signifيcant effect on the percent reduction of leaf area. Damage increased as the number of snails increased on the tested hosts. Percent reduction in navel orange leaf area increased signifيcantly at all tested infestation levels than the other three hosts followed by mango, guava and banana seedlings.
2. Biological Studies.
This work was carried out to through some lights on certain biological aspects of Helicella vestalis reared in two different types of soil (clay and sandy soil) under four soil moisture levels. Data obtained could be summarized as follows.
2.1. Pre-oviposition period.
Pre-oviposition period was affected signifيcantly by soil type and soil moisture. It was prolonged as the soil moisture increased, however, it was 72.16  and 44.08  days in both types of clay and sandy soils, respectively. Pre-oviposition period recorded 93.6, 50 days for 100% soil moisture and 50. 08, 38.17 for 75% of soil moisture of clay and sandy soil, respectively.
2.2. Oviposition period.
The small sand snails, Helicella vestalis did not lay any eggs at the lowest soil moisture (25%) in either types of soil. The longest egg laying period (70.5 days) was recorded in case of clay soil of 75% moisture level. It was relatively similar (46.0 and 42.6 days) for 50 and 100% moisture levels of clay soil. At 100% moisture levels of sandy soil, snails laid one egg clutch only, so oviposition period was not calculated.
2.3. Number of clutches.
The highest number of clutches was recorded for snails reared in clay soil of 75% moisture level. It decreased signifيcantly as the clay soil moisture increased to 100% or as the soil moisture level decreased to 50%. The snails of Helicella vestalis did not lay any eggs neither at 25% moisture of both types of soil nor at 50% moisture of sandy soil.
2.4. Number of eggs/ clutch.
The mean number of eggs / clutch produced per pair of the small sand snail, Helicella vestalis was signifيcantly affected by the type of soil and clay soil moisture levels. The 75% soil moisture level was the most suitable as the animals laid the highest number of eggs/clutch followed by 50% and 100% levels in case of clay soil. Both levels of moisture (75% and 100%) of sandy soil had no pronounced effect on the number of eggs/clutch.
2.5. Number of eggs / animal.
The highest mean number of eggs / animal (35.86 eggs) recorded under 75% of clay soil moisture level while the lowest one (14.73 eggs / animal) was found for the sandy soil of the same moisture level. Animals reared in clay soil laid more eggs (27.39 eggs/animal)than those of sandy soil (16.9 eggs / animal) with a signifيcant difference between them.
2.6. Depth of egg laying.
Clutches of eggs were laid deeper in clay soil (1.89 cm) than in sandy soil (l.05cm). The depth of egg laying in clay soil increased as the soil moisture decreased. Inverse was recorded for the sandy soil.
2.7. Hatchability percentages.
The hatchability percentages increase signifيcantly to 93.66% in clay soil while that of sandy soil recorded 90.31%. Hatchability percentage decreased signifيcantly as the moisture of clay and sandy soil increased to 100% or decreased to 50%.
2.8. Incubation period.
Incubation period of Helicella vestalis eggs extended from 18 to 20.67days according to the soil type and the soil moisture level. In case of clay soil, the incubation period was 19.0 days under 75% soil moisture it was prolonged 19.15 days as the moisture decreased to 50% and shortened to 18 days as the moisture increased (100%) level. Inverse effect was noticed in case of sandy soil whereas the incubation period prolonged to 20.67 days as the moisture increased to 100% but it was 18 days only under 75% of sandy soil moisture.
2.8.1. Effect   of  temperature   on   incubation   period and hatchability  percentage.
The tested degrees of temperature 15, 25, 30, 35 and 40°C. had a signifيcant effect on incubation period. The longest incubation period was recorded at the lowest temperature (15°C.) while the shortest incubation period was occurred under the higher one (35°C.). At 40°C. non of eggs was hatched. The highest hatchability percentage (98%).was recorded at 20°C.
2.9. Post-oviposition period.
Post oviposition period varied signifيcantly according to the moisture levels under the same type of soil. The longest post oviposition period was recorded for the highest level of soil moisture (100%) under both type of soil averaging of 191.5 and 176.83 days for clay and sandy soil, respectively. It was decreased as the soil moisture decreased what ever the type of soil. It was 132.0 days only at 50% moisture of clay soil and (177.5, 160.66) days at 75% of clay and sandy soil, respectively.
2.10. Life cycle.
The life cycle period of Helicella vestalis influenced signifيcantly by the type of soil and the levels of soil moisture. The shortest period of life cycle occurred under 75% moisture level, it increased as the moisture level increased and decreased in case of clay soil. The same trend was also found for sandy soil. Snails reared in clay soil had a longer life cycle period (274.7 days) than that reared in sandy soil (247.41 days) with a signifيcant difference between them.
2.11. Life span.
The life span period affected signifيcantly by the two studied factors. In clay soil snails lived longer (468.58 days) than that in sandy one (382.45 days). The life span increased gradually from 414.10 days under 25% clay soil moisture to 465.33, 482 and 512 days for 50, 75 and 100% of clay soil moisture, respectively. In case of sandy soil snails lived for a period of 461.5 days at 100% soil moisture and for 431.75, 423.92 and 385.75 days under 75, 50, 25% sandy soil moisture, respectively.
3. Control Studies on Land Snails. 
3.1. Laboratory experiments.
The effectiveness of eight pesticides againsي adult stage of tliree species of land snails (Helicella vestalis, Monacha contiana and Eobania vermiculata) was   studied under laboratory conditions using three testing methods. The results obtained could be presented as follows.
3.1.1. Direct spray technique.
On the base of LC50 values methomyl was the most effective toxicant against adults of the three tested species while pendimethaline was the least one against adults of Helicella vestalis and oxyfluorfen was the least toxic compound against M. contiana and E. vermiculata.
3.1.2. Dipping technique.
Methomyl proved to be the most effective toxicant against all the three tested species while oxyfluorfen was the least effective one.
Toxicity of any tested compound was varied according to the method of application. The tested pesticides methomyl, glyphosate, malathion, methadophos and chloropyrifos methyl used as direct spray gave good results against the adults of land snail Helicella vestalis. While paraquate and oxyfluorfen were less toxic than methomyl but pendimethalيne was the least effective one. On M. contiana, methomyl was still the most effective compound followed by glyphosate, methamidophos and chloropyrifos. Parquate and pendimthaline were less toxic than methomyl, but oxyfluorfen was the least effective one.
In case of E. vermiculata, methomyl surpassed all the tested pesticides, followed by glyphosate, chloropyrifos methamidophos, pendimethaline, paraquate and malathion but oxyfluorfen came at the end of the toxicity order.
3.1.3. Poisonous bait technique.
Six compounds were tested against the three species of land snails as poisonous baits these compounds could be descendingly arranged as follows: carbaryl > coppersulfate > aldicarb > carbosulfan > carbofuran > oxamyl against the adults of Helicella vestalis. The order of toxicity against adults of M. containa was carbaryl > aldicarb > coppersulfate > oxamyl > carbofuran > carbosulfan. The toxicity order was slightly changed to be carbary > coppersulfate > aldicarb > carbofuran > oxamyl > carbosulfan against E, vermiculata. Methomyl as direct spray and dipping technique and carbaryl as poisonous baits are the most promising compounds for controlling adults of these species.
3.1.4. Effيcacy of thiodicarb against Helicella vestalis under three levels of clay soil moisture.,
The effect of thiodicarb on adult mortality percentage and body weight reduction of treated snails was increased as the post treatment increased time at all tested soil moisture levels.
The gradual increase of mortality percentages may be due to the toxicity of thiodicarb and it's mode of action which increase the loss of water content of the treated individuals. It could be recommended that thiodicarb may be one of the promising compounds for controlling the small sand snails, Helicella vestalis at the soil moisture of 25 and 50% of water field capacity.
3.1.5. Efficacy   of thiodicarb   against  Helicella  vestalis   under three temperature degrees and 75% clay soil moisture.
Mortality percentage increased signifيcantly at 30°C. comparing with the other two degrees of temperature (10 and 20°C.). Reduction in body weight was also influenced signifيcantly by temperature and varied according to the behaviour of the individuals under different temperature degrees.
3.1.6 Effectiveness   of  certain   pesticides   on   incubation   period   and hatchability percentages of Helicella vestalis eggs.
It was found that incubation period had been affected signifيcantly by methamidophos and malathion while chloropyrifos had no effect. In case of methamidophos the concentrations of 1000 ppm and 500 ppm prolonged signifيcantly the incubation period while the other two concentrations (250 and 10 ppm) did not differ than the control. The highest concenlration (l000 ppm) of malathion prolonged signifيcantly the incubation period while the other three concentrations of malathion had no significant effect on incubation period.
All concentrations of the three tested compounds decreased signifيcantly the percent of egg hatchability comparing with the untreated control. The effect of pesticides on hatchability decreased as the concentrations decreased.
3.2. Field experiments.
Efficacy of four herbicides namely glyphosate, paraquate, oxyfluorfen, pendimethaline and four insecticides i.e. methomyl, methamidophos, cholropyrifos methyl and malathion were evaluated as direct spray against Helicella vestalis infesting citrus trees at Bilbies district. These pesticides were used at the concentrations of 0.5, 1.0, 1.5 and 2.0 % a.i as in aqueous solution. Other pesticides, i.e aldicarb coppersulfate, carbofuran oxamyl, carbosulfan and carbaryl were tested against Helicella vestalis as poisonous baits at the same concentrations of the direct spray.
3.2.1. Direct spray method.
The tested herbicides and insecticides used as direct spray had low initial activities at short time after application, the effيcacy increased as the concentrations increased from 0.5 to 2.0 %. Regarding the residual activity, methomyl gave the highest toxicity followed by methamidophos, chloropyrifos but malathion was the lowest one. As for the herbicides, they have low initial effect and moderately increased after a longer period. Glyphosate was the most effective pesticides followed by paraquate and oxyfluorfen while pendimethaline was the lowest one in this respect.
3.2.2. Poisonous baits.
The used pesticides exhibited a considerable effect against Helicella vestalis infesting mango trees when tested as poisonous baits under fيeld conditions. The pesticides had moderately effect as initial actiyities and it increased as the concentrations increased from 0.5 to 2.0 % a. i. The residual activity of aldicarb gave the highest  toxicity followed by carbafuran copper sulfate, oxamyl, carbaryl and carbosulfan.
3.3. Effect of ploughing process as a cultural control method on reduction percentage of Helicella vestalis infesting date palm trees.
The ploughing process decreased the population of the land snail Helicella vestalis immediately after one day with a percent reduction of 87.8%, this reduction % increased to 91.6% after two weeks. The ploughing process was a simple and effective method for reducing the number of individuals of Helicella vestalis infesting date palm trees especially during spring season.