Biological methods for the control of freshwater snails

As a result of the advent of new drugs and diagnostic techniques, the emphasis in the control of schistosomiasis has changed from snail control to chemotherapy for infected individuals. However, chemotherapy does not prevent reinfection and there remains a need to reduce snail densities in human water supplies. In the past, treatment with molluscicides has proved ineffective, expensive and has had environmental drawbacks. Here, Henry Madsen describes research into alternative methods of snail control. As yet, little is known of the predators and parasites of schistosome intermediate hosts, but such agents could be suitable as biocontrol agents. To date, the most promising results have been obtained from experimental introductions of competitive snail species, but this strategy still has its drawbacks under many environmental conditions and the development of a universal method of biological control for the intermediate hosts of schistosomes is still a long way off.     

Biological control and invading freshwater snails. A case study

Introductions of four species of freshwater snails occurred between 1972 and 1996 onto Guadeloupe Island. Two of them, Melanoides tuberculata and Marisa cornuarietis, were subsequently used as biological control agents against Biomphalaria glabrata, the snail intermediate host of intestinal schistosomiasis. In 1996, a general survey was carried out in 134 sites which had already been investigated in 1972. The total number of mollusc species had increased from 19 to 21. Site numbers housing B. glabrata and two other species had strongly declined. This decline may be mainly attributed to a competitive displacement by M. tuberculata and M. cornuarietis as illustrated by several biological control programmes. There were no changes in the remainder of the malacological fauna.     

江苏沿海地区农田蜗牛的发生特点与防治对策

本地区为害农作物蜗牛主要有同型巴蜗牛和灰巴蜗牛,通过田间系统调查和室内外饲养观察,基本模清了江苏沿海地区,农田蜗牛的卵期和幼贝期,是其生命活动中的薄弱环节和开展防治的有利时期,农作物的苗期和花荚期（花铃期）是对农田蜗牛最敏感的生育期,亦即需要重点保护的关键时段;秋熟作物受蜗牛危害重于夏熟作物,根据当地的气候特点,每年春夏之交4－6月和秋季8－10月的温湿度条件,最适宜于两种蜗牛的生存,活动和取食,调查结果表明,该时期亦正是本地区蜗牛发生为害的两个峰期,经过试验示范,总结出一整套农田蜗牛的综合治理措施,筛选出一批除蜗保叶效果达80％左右,捅分别用作为作物前期毒饵诱杀的颗粒剂和后期喷雾除蜗的可湿性粉剂,并且针对江苏沿海地区,农田蜗牛的发生特点和灾变规律,提出了对农作物采用“播前耕翻（爆卵）压基数,综合措施保全苗（壮苗）,中后期化防夺丰收”。的总体防治策略。     

Biological control of snails exerted byEuglandina rosea (Ferussac) in Bermuda

Résumé Cet article relate un essai de lutte biologique effectué aux Bermudes contre deux Gastéropodes nuisibles:Rumina decollata (Linné) (Achatinidae) etOtata lactea Muller (Helicidae) au moyen du mollusque carnivoreEuglandina rosea (Ferussac). 845Euglandina, ont été libérés dans l'?le en 1958 et 1960. Dès 1962, il était évident que l'opération se soldait par un succès complet contreOtata mais par un échec contreRumina. 500Euglandina ont été récoltés en quelques jours aux Bermudes et expédiés à l'?le Maurice, à Hong-kong, Nord-Bornéo et les Bahamas pour de semblables essais.      

Crayfish,catfish and snails: the perils of uncontrolled biological control

A recent proposal that the Australian redclaw crayfish Cherax quadricarinatus and hybrid catfish could potentially control the snail hosts of schistosomiasis has been criticised on the grounds that crayfish pose a severe threat to aquatic ecosystems into which it might be introduced. This note examines the issue further, pointing out that both lack the host-specificity requirement to be a successful biological control agent. The catfish Clarias gariepinus is an omnivore and snails form only a small proportion of its diet; there is no evidence to suggest that it controls snail populations anywhere in Africa. The same applies to other species that have been proposed as biological control agents. Simple laboratory experiments are not an adequate guide to the efficiency of an animal as a biological control agent and detailed ecological investigations would usually demonstrate that few African fish species have this capability.     

Designer snails

The Algorithmic Beauty of Sea Shells (2nd edn) by Hans Meinhardt Springer-Verlag, 1998. DM89.00/$54.95/￡34.00 hbk (xi+236 pages) ISBN 3 540 63919 5.     

O-Glycosylation of snails

The glycosylation abilities of snails deserve attention, because snail species serve as intermediate hosts in the developmental cycles of some human and cattle parasites. In analogy to many other host-pathogen relations, the glycosylation of snail proteins may likewise contribute to these host-parasite interactions. Here we present an overview on the O-glycan structures of 8 different snails (land and water snails, with or without shell): Arion lusitanicus, Achatina fulica, Biomphalaria glabrata, Cepaea hortensis, Clea helena, Helix pomatia, Limax maximus and Planorbarius corneus. The O-glycans were released from the purified snail proteins by β-elimination. Further analysis was carried out by liquid chromatography coupled to electrospray ionization mass spectrometry and - for the main structures - by gas chromatography/mass spectrometry. Snail O-glycans are built from the four monosaccharide constituents: N-acetylgalactosamine, galactose, mannose and fucose. An additional modification is a methylation of the hexoses. The common trisaccharide core structure was determined in Arion lusitanicus to be N-acetylgalactosamine linked to the protein elongated by two 4-O-methylated galactose residues. Further elongations by methylated and unmethylated galactose and mannose residues and/or fucose are present. The typical snail O-glycan structures are different to those so far described. Similar to snail N-glycan structures they display methylated hexose residues.     

Integrated control of pests in orchards

Résumé La ?lutte intégrée? (?integrated control? des Américains) se propose de recourir à une combinaison avantageuse des différentes méthodes chimiques, biologiques et culturales de lutte contre les ennemis des cultures. Son objet est d'accro?tre le potentiel de défense intrinsèque du milieu cultivé contre les attaques des ennemis des plantes, particulièrement en modifiant les formes usuelles de la lutte chimique pour assurer une meilleure sauvegarde des organismes utiles. Ses problèmes, singulièrement dans le cadre de la monoculture intensive, concernent: ?l'intégration? des méthodes de lutte biologique dans un programme de lutte chimique modifiée, la détermination du niveau du seuil de tolérance économique des dégats commis par les déprédateurs, la meilleure connaissance du r?le des organismes utiles comme régulateurs de la densité de population des organismes nuisibles. Pour atteindre cet objectif et résoudre ces problèmes, il est indispensable de procéder à des recherches de base approfondies.      

Integrated control of lung fluid balance

This review summarizes the highlights of the EB2004 symposium that dealt with the integrated aspects of the lung fluid balance. It is apparent that maintenance of lung fluid balance requires the proper functioning of vascular endothelial and alveolar epithelial barriers. Under physiological conditions, the transcytotic pathway requiring repeated fission-fusion events of the caveolar membrane with other caveolae solely transports albumin. Caveolin-1, which forms caveolae, and albumin-binding proteins play a central role in signaling the transcytosis of albumin. Signals responsible for increasing endothelial permeability in lung microvessels in response to inflammatory mediators were also described. These studies in gene knockout mouse models revealed the importance of Ca(2+) signaling via store-operated transient receptor channel 4 and the activation of endothelial myosin light chain kinase isoform in mediating the increase in microvessel permeability. Increases in the cytosolic Ca(2+) in situ in microvessel endothelia can occur by mitochondria-dependent as well as mitochondria-independent pathways (such as the endoplasmic reticulum). Both these pathways, by triggering endothelial cell activation, may result in lung microvascular injury. The resolution of alveolar edema, requiring clearance of fluid from the air space, is another area of intense investigation in animal models. Although beta-adrenergic agonists can activate alveolar fluid clearance, signaling pathways regulating these events in intact alveoli remain to be established. Development of mouse models in which the function of regulatory proteins (identified in cell culture studies) can be systematically analyzed will provide a better and more integrated picture of lung fluid balance. In vivo veritas!     

Integrated control of hepatic glucose metabolism.

The rates of storage and release of carbohydrate by the liver are determined by the plasma concentrations of several blood-borne signals; most important are the concentrations of glucose, and of the hormones insulin and glucagon. To understand the complex control relationships of these three signals as they affect the liver, their individual dynamic influences have been determined experimentally, and the findings have been integrated by means of a computer simulation of the pathways of hepatic glycogen metabolism. The simulation studies have led to specific hypotheses about the biochemical effects of glucose and insulin on the liver. The simulation studies have also led to the conclusion that glucose exerts a rapid moment-to-moment influence on the rate of uptake of glucose by the liver. Insulin, however, by exerting a slower influence on the sensitivity of the liver to glucose, is very effective in "optimizing" the amount of glycogen which the liver stores during food intake. Thus, integrated experimental and simulation studies can lead to a view of a physiological regulating system which does not emerge from either approach used alone.-     

Integrated control of ticks and tick-borne diseases

Integrated control of ticks and tick-borne diseases (ICTTD) is currently promoted by an international project, supported by the European Union, with the aim to increase livestock productivity through the development of improved strategies for tick control, vaccine delivery and integrated diagnostics for tickborne diseases. This paper gives a brief overview of the ICTTD project activities against the background of recent initiatives to assess the impact of ticks and tick-borne diseases in the Mediterranean region.     

The growth of juvenile snails in water conditioned by snails of a different species

Summary Two species of freshwater snails, Physa acuta and Lymnaea sp. aff. columella, were collected from Asabata marsh, Shizuoka Japan. Individuals of both species inhabit the same plants. Individuals of P. acuta are more abundant than those of L. sp. aff. columella. Experiments were conducted to examine the effect of water conditioned by snails on the growth of 10-day-old juvenile P. acuta snails. Juvenile snails in water conditioned by L. sp. aff. columella grew faster than those in water conditioned by P. acuta or only lettuce. The effects of water conditioned by P. acuta differed among the litters. The results suggest that juvenile P. acuta snails experience accelated growth in the presence of L. sp. aff. columella. The freshwater snails interacted through resource competition as well as through substances disolved in the water.     

Population genetics of freshwater snails

Freshwater snails have attracted the attention of biologists for a long time, because they are intermediate hosts of schistosomes, agents of bilharziases. However, population-genetic studies of freshwater snails have been undertaken only during the past decade, covering topics such as the relative roles of genetic drift and gene flow in subdivided populations and the roles of extinction and recolonization events in determining population structure. Other studies in freshwater snails have investigated the maintenance of sex and the evolution of selling, widening a debate restricted mainly to plant populations. The possible role of parasites in freshwater-snail population genetics has also been investigated.     

Lichen endozoochory by snails

Endozoochory plays a prominent role for the dispersal of seed plants. However, for most other plant taxa it is not known whether this mode of dispersal occurs at all. Among those other taxa, lichens as symbiotic associations of algae and fungi are peculiar as their successful dispersal requires movement of propagules that leaves the symbiosis functional. However, the potential for endozoochorous dispersal of lichen fragments has been completely overlooked. We fed sterile thalli of two foliose lichen species (Lobaria pulmonaria and Physcia adscendens) differing in habitat and air-quality requirements to nine snail species common in temperate Europe. We demonstrated morphologically that L. pulmonaria regenerated from 29.0% of all 379 fecal pellets, whereas P. adscendens regenerated from 40.9% of all 433 fecal pellets, showing that lichen fragments survived gut passage of all snail species. Moreover, molecular analysis of regenerated lichens confirmed the species identity for a subset of samples. Regeneration rates were higher for the generalist lichen species P. adscendens than for the specialist lichen species L. pulmonaria. Furthermore, lichen regeneration rates varied among snail species with higher rates after gut passage of heavier snail species. We suggest that gastropods generally grazing on lichen communities are important, but so far completely overlooked, as vectors for lichen dispersal. This opens new ecological perspectives and questions the traditional view of an entirely antagonistic relationship between gastropods and lichens.