الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
The terrestrial slugs and snails are agricultural pests distributed throughout the world and considered serious crop pests. Moreover, they transmit diseases to plants.
The giant garden slug Limax maximus distributed in Western Palearctic, North and South America and Africa, some Pacific Islands, Australia and New Zealand. In Egypt, few studies had been carried out on L. maximus in some governorates, from which; Alexandria, Cairo, Fayoum, Giza, Ismailia, Menoufia, Sharkia and recently in Kalyobya.
Synthetic chemical molluscicides had toxic effects on non-target organisms, contaminate soil and water and may affect humans and other animals. In the contrary, the botanic molluscicids have many advantages as: low toxicity effect to non-target organisms, biodegradable, not expensive and more safely to the environment
In the present studies, laboratory bioassays were carried out for evaluating the efficacy of two botanic products, namely thymol and caffeine, as molluscicides against the Egyptian giant garden slug Limax maximus using baits with molass. The tested plant products can be arranged based to their toxic against the target slug L. maximus in following order: Thymol ˃ Caffeine, LC50 are 269.77 and 652.51 respectively.The goals of the present studies could be achieved through the following investigations:
• Descriptation of the external and internal features of L. maximus, through morphological and anatomical studies.
• Estimation of LC50 and LC90 of both thymol and caffeine molluscicides against the target slug L. maximus.
• Treatment the tested slugs with estimated LC50 and LC90 of both molluscicides.
• Studying the histological examination of both digestive gland and ovotestis (hermaphrodite gland) in untreated (control) and treated slug L. maximus.
• Studying the ultrastructure, using TEM, of digestive gland and ovotestis in control and treated slug L. maximus.
The obtained results in the present studies can be summarized in the following categories:
Histological inspection of untreated digestive gland of L. maximus has two cell-types namely: digestive and secretory cells. Digestive cell is simple columnar with round apice and narrow base, beside several vesicles of different sizes and mostly elliptical basal nucleus. Concepting secretory cell, it is pyramidal, or conical, in shape with broad base and pointed apice. Its nucleus is spherical and basal.Respecting histological changes in the digestive gland of treated L. maximus with thymol or caffeine for 48 hours included: cytoplasmic vacuolation, degeneration of some digestive and secretory cells, destroyed connective tissue, scattered of toxic agents in the secretory cells and in the acinal lumen, rupture of the apical surface of digestive and secretory cells, increased of calcium spherules in the secretory cells, wide fused vacuoles and deformation of nuclei of the most cells.
Respecting ovotestis, the histological inspection of the untreated L. maximus found that this gland consists of many lobes; each contains numerous acini. Each acinus surrounded by ancel`s layer and has several rows of spermatogenic and oogenic stages. The acini are separated by connective tissue.
Oogonia appear small cell with puny cytoplasm and spherical nuclei. Afterwards, primary oocyte, that next to the oogonia, is larger with spherical nuclei, subsequently secondary oocyte that is smaller and has scanty cytoplasm and oval nuclei.
Each acinus contained usually one large mature oocyte with spherical nucleus, beside stages of spermatogenesis.
Concerning ovotestis of treated L. maximus with both molluscicides, it showed severe damages including; lossing architecture of acini and degeneration and reduction of number of all spermatogenic and oogenic stages, wide space between acini, nuclear pyknosis and partial to complete degeneration of connective tissue and mature oocytes.
The ultrastructure observations shewed that the acini of the digestive gland of L. maximus composes of digestive and secretory cells. The digestive cell has vesicles of different sizes whereas secretory cell has secretory granules and calcium spherules.
The present studies declared cytoplasmic vacuolation, scattered toxic agents and rupture of microvilli in digestive gland-cells of treated L. maximum with both botanical materials.
The ultrastructure observation shows that the spermatogenic and oogenic stages in ovotestis of L. maximus are described as follows: Spermatogonia besides Sertoli cell followed by primary spermatocytes and secondary spermatocytes that differentiate to spermatids and finally modified to sperms. The ultrastructure of oogenic stages, indicated that the mature oocyte exhibits yolk granules, lipid droplets, mitochondria, rough endoplasmic reticulum and ribosomes. Its nucleus has euchromatin, heterochromatin and apparent nucleolus.
In addition, ovotestis of treated L. maximum by both thymol and caffeine declared irregularity of basement membrane, degenerated connective tissue cells, cytoplasmic vacuolation, degeneration of RER, nuclear rupture, vacuoles in mature oocyte, lipid droplets, beside swollen and degenerated nuclei of follicular cells.
from the above results, it could be concluded that the histological and ultrastructure aspects of digestive gland and ovotestis that had been treated with thymol and caffeine against
L. maximum caused severe damage in architecture of cells of the digestive gland and ovotestis; thereby, both botanic compounds may be of great value in the field to control the target slug, as safe and economic molluscicide, which no harm upon ecosystems instead of using chemical pesticides that could pollute the environment.