The area of each elementary plot was 1350 m2 . These plots were not previously treated with herbicides. 24 h before the beginning of the test, 5 microcosms were prepared and placed on each elementary plot. They were each made up of circular frames of 22 cm × 10 cm sunk to a depth of 5 cm in the soil so that they were firmly attached. Three juveniles of the species Achatina fulica were placed in each microcosm. Before the start of the test, measurements of the snails were taken. The length, shell diameter and mass of the snails were 3 ± 0.5 cm; 1.8 ± 0.4 cm; 5 ± 1 g respectively. A quantity of 50 g of food was deposited every three days in each environment, i.e. 10 g of leaves and 40 g of papaya fruits. The experimental units were then covered with a mosquito net to prevent the escape of snails and the intrusion of other organisms. Wooden stakes were used to hold the nets to the ground. A total of 20 microcosms were used throughout the experimental plot. The test was conducted in undergrowth, a preferred environment for snail development.Each elemental plot underwent a single herbicide treatment of 2,4-D, glyphosate or nicosulfuron at concentrations recommended by the manufacturer. The solutions were prepared with fountain water. Another elementary plot close to the previous ones is used as a negative control. Some pawpaw trees at the study site were treated with 2,4-D, glyphosate, or nicosulfuron at the beginning of the test, at a rate of one pawpaw per herbicide. The leaves and fruit of these pawpaws were used as food for the snails during the test. The first foods deposited in the microcosms were not pre-treated. They were treated at the same time as the experimental plot. Another untreated papaya tree was used as food for the control snails. The snails stayed in the environment for 28 days. Snail mass, length and shell diameter were measured weekly. Each snail was weighed individually. The length and diameter of the shell were measured with a caliper. The growth of exposed and control individuals was calculated from the increase in length, diameter and weight mass of the snail from the beginning to the end of the test. During the exposure to the different treatments, the more or less disturbed behaviors of the snails were described.The experimental unit was a 500 mL transparent plastic box. These boxes contained 200 g of decomposed wood litter previously crushed and dried, to which were added 50 eggs of Achatina fulica from the breeding environments. 24 h after oviposition, the microcosms were buried in holes whose bottom was lined with stones to ensure efficient water drainage and so that the level of the boxes was 2 cm above the surrounding soil. The microcosms were humidified with 50 mL of fountain water to bring the temperature of the environment to 26˚C ± 1˚C which is the optimal temperature for egg incubation.

The lid of the boxes was also perforated to allow good aeration of the environment. Note that this study was conducted at the same time as the study of the effects of 2,4-D, glyphosate, and nicosulfuron on the growth and reproduction of juvenile Achatina fulica snails. Microcosms for both tests were arranged horizontally at a distance of 1 m from each other. 10 microcosms were used for this test and placed on each elementary plot. These plots were treated with a single type of herbicide,either 2,4-D, glyphosate or nicosulfuron. Another plot close to the previous ones served as a negative control. Some behaviors due to the exposure of snails to herbicides could be observed during this study. These are: the ability of snails to feed normally or avoid food, nft hydroponic the activity of the animals and their spatial position in the test chamber: for example, active or inactive in the high position or on the supports, or active or inactive on the food. These behaviors are observed, on days of food change. The snails were inactive at the time of observation. They hid at the bottom of the microcosm in a hole of about 3 cm that they dug in the ground. After one minute, the snails started to be active. In the microcosms in the control and nicosulfuron-treated plots, no food remains were observed. In contrast to the above, a significant amount of decaying feed residue was observed in the microcosms on the glyphosate and 2,4-D treated plots. The greatest amount of feed was observed in the microcosms treated with 2,4-D.Statistical analyses at this level showed that growth parameters varied with the different types of 2,4-D, glyphosate and nicosulfuron treatments. Snail weight mass, shell length, and shell diameter showed significant differences at the 5% threshold . Compared to controls, 2,4-D, glyphosate and nicosulfuron inhibited snail growth. In order of toxicity, our results show that nicosulfuron is less toxic than glyphosate, which is almost equal in toxicity to 2,4-D.Egg laying took place 7 days after the establishment of the microcosms on the test and control plots. Moreover, the average number of eggs laid per microcosm and per plot was the same.From day 7 to day 14, the number of eggs laid increased significantly, reaching a peak around 200 eggs laid in the control snails. For snails treated with the different herbicides, a significant drop was observed. Oviposition was zero from day 14 to day 42 for snails in plots treated with 2,4-D and glyphosate. In the nicosulfuron-treated plot, egg laying dropped to zero on day 21.

Egg laying resumed on day 28 with an average of 150 eggs per microcosm and decreased slightly on day 35 before dropping sharply on day 42 with an average of 20 eggs. In the control snail plot, from day 14 onwards, egg laying began to decline progressively on days 21, 28, 35 and 42. This egg laying which was around 200 eggs on day 14 went down to around 80 eggs on day 42. Looking at the control curve, we can see that the egg laying starts on day 7, reaches the peak on day 14 and decreases from day 21 to day 42 . The mean number of eggs ± standard deviation laid per pair of snails in the contaminated environment was 41.66 ± 54.37; 48.83 ± 48.55 and 62.5 ± 57.81 for 2,4-D, glyphosate and nicosulfuron, respectively, compared to 123.16 ± 31.01 in the control environment. Statistical analyses revealed a significant difference at the 5% threshold between the different treatments and the number of eggs laid. From the averages obtained, it was found that all herbicide treatments of 2,4-D, glyphosate and nicosulfuron affected egg laying compared to the controls. In terms of toxic effect on oviposition, Tukey’s HSD test revealed that 2,4-D, glyphosate and nicosulfuron were equal .The phytosanitary treatments of 2,4-D, glyphosate and nicosulfuron carried out respectively on each plot induced a growth inhibition of the snails present on these plots. This growth inhibition resulted in a decrease in snail length, shell diameter and mass. This result could be explained by a decrease in consumption rate observed in the microcosms at the time of food change.Snails have the ability to detect high concentrations of pollutants in their food, which could lead to a decrease in consumption rate. Reference revealed that cadmium can disrupt the function of neurosecretory cells that secrete a growth hormone causing growth arrest. Furthermore, similar observations were made with studies conducted by. They claim that the extreme concentration of lead in the soil, detected by the snails, limits their consumption rate and thus partially inhibits their growth. Other authors have reached the same conclusion in their studies on metal contamination of Helix asperta. Compared to our where growth is inhibited, observed a dose-dependent decrease in growth and survival of snails induced by dimethoate.

According to, snails exposed by ingestion to thiamethoxam, tefluthrin and their mixtures experienced a reduction in length, shell diameter and weight mass under laboratory conditions. This difference could be due to the conditions under which the tests were performed. Our work was indeed carried out in situ in the natural environment of the snails contrary to theirs which were carried out in laboratory. Chemicals during their application are subject to several transfer mechanisms outside the plot. These matrices receive 97.7% of pesticides during phytosanitary treatments. Therefore, the amount of herbicides that could reduce snail growth is low. In addition, it was found in the present study that 2,4-D, glyphosate and nicosulfuron significantly reduce egg laying in Achatina fulica snails. This could be due to a reduction in energy reserves, nft system allocated for reproduction in the storage cells of snail tissues; this reduction is probably caused by the mobilization of these resources for the initiation of detoxification processes. Studies by revealed that the energetic cost of environmental stress results in a decrease in the amount of energy available for reproduction and growth and consequently in a reduction in the fitness of individuals. Our results are in agreement with those of. They showed that chronic exposure of snails to food contaminated with a mixture of metals composed of Cd, Cu, Pb and Zn, delays reproduction. In contrast, those of showed after 240 days of exposure to herbicides no effect on the number of egg laying. The reduced hatching rate observed in Achatina fulica is probably due to the active substances contained in the herbicides used. According to, the snail egg capsule serves as a membrane for gas exchange from the interior of the egg to the environment or vice versa. It acts as an effective barrier against water loss during the incubation period without blocking the air supply. Our results are in agreement with those of who showed that, extracts of Barringtonia racemosa has an increasingly increasing concentration, and significantly affect the hatching of Pomacea canaliculata eggs. Tests conducted on the effects of herbicides on morphological parameters and hatching rate of Achatina fulica eggs revealed increasing toxicity in the following order: nicosulfuron < glyphosate < 2,4-D. These different responses of snails exposed to these three types of herbicides could be attributed to the different nature and behavior of each herbicide in the environment. These results corroborate those of. Their studies revealed a significant reduction in snail weight mass and shell diameter as a function of treatment type.