Achatinidae are native to Africa. The family is represented by about 200 species in 13 genera. Several species have attained pest status within their native African range when the habitat is modified for human habitation and cropping. Furthermore, associated with the increased mobility of humans and globalization of travel and trade, several achatinids, the most notable of which is Achatina fulica Bowdich, have been accidentally or purposefully transported to areas outside their native range in Africa and further afield. In these new areas Achatinidae can cause significant economic and ecological impacts. This chapter provides a synopsis of Achatinidae as pests in tropical agriculture, focusing primarily on A. fulica, but also bringing together the relevant information on other pestiferous achatinid species.

The sewage snail Physa acuta is a serious threat to certain economic plants and to the purification plant of sewage works by rendering the biofilters ineffective. Various attempts are being made to control it. The efficacy of the predacious water bugs Sphaerodema rusticum was judged experimentally, in the laboratory in the potential control of P. acuta. It is revealed that, when supplied separately, the first, second and third instar and the adult S. rusticum did not attack P. acuta belonging to 3. 1-8 mm, 5.1-8 mm, 7.1-8 The snail Physa acuta Draparnaud is thought to be from North America from which it was introduced to Europe (Ali 1993). In recent years it has spread a good deal further. It is now common in certain parts of Australia (Madsen & Frandsen 1989) and Africa including Madagascar (Brown 1980, Curtis 1991, Brackenbury & Appleton 1993. In Asia, P. acuta has been recorded from Iran, Iraq, Israel, Japan, Macao (Madsen & Frandsen 1989), Malaysia (Ali 1993) and India (Raut et al. 1995). In all these areas P. acuta is a common inhabitant of ponds, streams, river, rice fields and municipality drains (Macha 1971, Brown 1980, Godan 1983, Alexandrawicz 1986, Appleton & Bailey 1990, Ali 1993, Brackenbury & Appleton 1993, Raut et al. 1995. P. acuta is a prolific breeder and can survive in polluted waters. It is also able to spent a considerable length of time in the agrihorticultural gardens. Consequently, it can be a serious threat to certain economic plants (Godan 1983) and to the purification plant of sewage works by rendering the biofilters ineffective (Macha 1971). Thus, it is now a serious problem. Though application of molluscicides could give a temporary relief the idea is not being used in view of possible adverse effects on the flora and fauna -algae, bacteria, amoebae and worms which occur in the biofilters. Therefore, the only option left is the employment of biological control agents. Following our record of occurrence of P. acuta in Kolkata (Calcutta), India (Raut et al. 1995) and in continuation to our studies on the bioecology of this species, we noted predation of water bugs Sphaerodema rusticum on P. acuta in the municipality drains in Kolkata. This prompted us to determine the ability of S. rusticum to control P. acuta. Accordingly, we carried out some experiments in the laboratory and the results are communicated.

An aqueous extract prepared from Kernels of the fruit of Thevetia peruviana (Pers.) Schumann (Family : Apocynaceae) was found under experimental conditions, to be toxic ti the slug Laevicaulis alte (Férussac) and the snail Achatina fulica Bowdich, the important agrihorticultural pests of Indo-Pacific countries. Concentrations as low as 1% (w/v) killed all the slugs exposed in less than 981.00 (± SD 22.76) min, and 2% of the extract killed 100% of the slugs L. alte and 50%, 50% and 30% of the snail A. fulica in between 92.34 (± SD 6.63) - 321.33 (± SD 4.14) and 271.20 (± SD 17.54) - 298.26 (± SD 16.69) min respectively. The most effective concentration of the extract was 20%; it killed 100% of exposed slugs and snails within a short time (40-50 and 90-1440 min respectively) when the extract was exposed on the soil in experimental trays or when it was applied to potato slices offered as food to the gastropods

The snails Lymnaea (Radix)

The giant African land snails Achatina fulica Bowdich occurring in Kolkata, West Bengal, India undergo aestivation with the advent of adverse conditions by the end of October or early part of November, each year. Experiments were conducted to study the factors inducing aestivation in these snails. It is revealed that the type of plant-foods, the length of starvation, the degrees of temperature and the percentages of relative humidity are the factors inducing aestivation in A. fulica of course, just at the onset of aestivation. It is also observed that, depending upon the severity of these factors the snails required different number of days to aestivate. Even, under similar situation individuals belonged to lower size groups started aestivation earlier than those of the snails belonged to higher size groups. The cumulative effects of certain above mentioned factors sometimes, either delayed or accelerated the process of aestivation.