Seasonal variation in abiotic factors and ferulic acid toxicity in snail‐attractant pellets against the intermediate host snail Lymnaea acuminata

Laboratory evaluation was made to access the seasonal variations in abiotic environmental factors temperature, pH, dissolved oxygen, carbon dioxide, electrical conductivity and ferulic acid toxicity in snail‐attractant pellets (SAP) against the intermediate host snail Lymnaea acuminata in each month of the years 2010 and 2011. On the basis of a 24‐h toxicity assay, it was noted that lethal concentration values of 4.03, 3.73% and 4.45% in SAP containing starch and 4.16, 4.23% and 4.29% in SAP containing proline during the months of May, June and September, respectively, were most effective in killing the snails, while SAP containing starch/proline + ferulic acid was least effective in the month of January/February (24‐h lethal concentration value was 7.67%/7.63% in SAP). There was a significant positive correlation between lethal concentration value of ferulic acid containing SAP and levels of dissolved O₂/pH of water in corresponding months. On the contrary, a negative correlation was observed between lethal concentration value and dissolved CO₂/temperature of test water in the same months. To ascertain that such a relationship between toxicity and abiotic factors is not co‐incidental, the nervous tissue of treated (40% and 80% of 24‐h lethal concentration value) and control group of snails was assayed for the activity of acetylcholinesterase (AChE) in each of the 12 months of the same year. There was a maximum inhibition of 58.43% of AChE, in snails exposed to 80% of the 24‐h lethal concentration value of ferulic acid + starch in the month of May. This work shows conclusively that the best time to control snail population with SAP containing ferulic acid is during the months of May, June and September.     

番木瓜种子形成与结构的显微研究

首次报道了番木瓜种子的形成与结构,其胚珠倒生,长珠柄,双层珠被,不形成珠孔,合点端存在承珠盘。种子的种皮由外至内包括三部分,即透明的网膜状假种皮、皱褶致密的外种皮和粘稠的内种皮,其中内外种皮的最内侧各有一层褐色和透明状的厚壁细胞,粘稠的内种皮将这两层厚壁细胞粘连为一整体,最后形成坚硬的壳状物。种皮内包含有正常发育的子叶形胚与细胞型胚乳。     

Geographical distribution and habitat preferences of the invader freshwater snail species Lymnaea columella (Mollusca: Gastropoda) in South Africa

The present geographical distribution of Lymnaea columella, as recorded in the National Freshwater Snail Collection, is described and discussed. It appears that L. columella is the most successful colonist of all the freshwater snail species in South Africa, and, together with Bulinus tropicus and Lymnaea natalensis, it forms the most widely distributed freshwater snail species in the region. Data regarding the 2,341 discovery sites of L. columella recorded by collectors during surveys are analysed. L. columella cluster mainly in rivers or streams with perennial, slow flowing, or stagnant freshwater with many plants and a mud substrate. L. columella is regarded as a more effective intermediate host for the transmission of fascioliasis than the indigenous snail species. The economical implications of this are discussed briefly in the light of its success as an invader species.     

草甘膦、草铵膦喷施对槟榔根系形态及生理的影响

除草剂防除杂草的同时会给非靶标作物带来药害,频繁使用除草剂的海南槟榔园叶片黄化症状更加明显,我们推测除草剂可能导致槟榔根系退化,从而引起叶片黄化。本试验以幼龄期槟榔与成龄期槟榔为研究对象,测定草甘膦和草铵膦使用后槟榔根系生长发育形态与相关生理指标。结果表明：（1）在幼龄期槟榔根系中,主要以直径为0～1.5mm的根为主要根系结构,数量上占到总根的88%以上,表面积占到了总根的68%以上。草甘膦和草铵膦喷施显著降低了槟榔幼苗根系鲜重、干物质积累量,白色吸收根的比例、吸收根活力。（2）在成龄期槟榔气生根中,喷施草甘膦和草铵膦均引起气生根药剂残留,且农残随施用浓度增加而变高;喷施草甘膦和草铵膦,阻碍了槟榔气生根发育。草甘膦处理第14天后气生根死亡数达到最大,而草铵膦处理第28天后达到最大。（3）草铵膦损害了气生根组织结构,使新根内皮层排列稀疏,表皮组织厚度增加,木栓化程度加深,导致根表皮细胞大量死亡,抑制了气生根伸长与增粗。上述研究结果表明草甘膦和草铵膦通过木栓化加速根系死亡调控槟榔根系生长与发育。     

淹水对番木瓜光合和叶绿素荧光特性的影响

通过袋栽试验,研究了淹水对番木瓜光合和叶绿素荧光特性的影响。结果表明,淹水降低番木瓜叶片的净光合速率、蒸腾速率、气孔导度、胞间CO2浓度和PSII有效光化学量子产量（YIELD）、光合电子传递速率 (ETR)和光化学荧光淬灭系数 (qP),提高其非光化学荧光淬灭(qN)值,同时影响其叶绿素荧光诱导曲线。淹水28 h和52 h后,番木瓜叶片的光合作用明显降低,对照和淹水处理之间的气体交换参数和叶绿素荧光参数差异极显著（P<0.01）。     

茎弯曲处理对番木瓜开花结果的影响

对“苏罗”和“台农2号”番木瓜2个品种植株进行茎弯曲处理,研究其对番木瓜开花结果的影响。结果表明,茎弯曲处理对“苏罗”和“台农2号”番木瓜都具有降低最低结果高度、增加长圆形果实和长圆形两性花数量的显著效应;当茎弯曲长度在20.00-35.00cm时,随着茎弯曲长度的增加,其对降低番木瓜最低结果高度、增加长圆形果实和长圆形两性花数量的效应愈强;茎弯曲处理对营养繁殖的“苏罗”和种子繁殖的“台农2号”番木瓜开花结果的影响趋势一致。     

缓释肥料对番木瓜光合特性的影响

通过盆栽试验,研究缓释肥料对番木瓜叶片光合和叶绿素荧光特性的影响。结果表明,施用缓释肥料促进番木瓜叶片叶绿素的合成,提高番木瓜叶片的净光合速率、气孔导度、蒸腾速率、光化学量子产量、光合电子传递速率、光化学淬灭系数、非光化学淬灭系数,降低胞间二氧化碳浓度和非光化学淬灭系数,其中以缓释肥料SRF-4处理的效果优于SRF-3处理和复合肥CPF处理。     

The uptake and distribution of radioselenium in the larvae of Fasciola hepatica and its snail host Lymnaea columella

Radiolabeled metacercariae of Fasciola hepatica were obtained in vivo by incubating infected Lymnaea columella snails with 20 muCi radioselenomethione (75Se-M) per snail in 5 ml of water for 5 h, or in vitro by incubating a batch of unlabeled F. hepatica metacercariae with 75Se-M for 24 h. Radioassay showed that only 5% of the 75Se-M was incorporated into maritas (juvenile flukes) from the in vivo labeled metacercariae. The inner cyst wall of in vivo labeled metacercariae contained 46% of the total activity, of which 21% was dissolved in the excysting medium. The outer, tan-colored cyst wall contained 49% of the radioactivity. Through diffusion/attachment, maritas from in vitro labeled metacercariae could occasionally be labeled with 0.4% of the total radioactivity. However, the activity was lost after inoculation into the body of mice. The outer and inner cyst walls of in vitro labeled metacercariae contained 92% and 7.6%, respectively, of the total activity. Microautoradiography demonstrated that 75Se-M was evenly distributed in the body of marita and the cyst wall of inner and outer layers from an in vivo labeled metacercaria. A 9 X 4 micron rectangularly-shaped aggregate of Ag degree grains was present on the outer periphery of the inner cyst wall. Microautoradiography of in vitro labeled metacercariae demonstrated a significant concentration of Ag degree grains on the cyst walls. The ventral plug contained fewer Ag degree grains per unit area compared to the other portion of the inner cyst wall. Uptake and distribution of 75Se-M in the snail host were also studied. It appeared that rediae and cercariae tended to concentrate the label in the foot, the mantle and the digestive gland. Little or no radioactivity was present in the areas where F. hepatica larvae were not found.     

Effects of Chloroformic Extracts from Washed and Unwashed Papaya Seeds (Carica papaya) on the Sperm Concentration of Dogs

Papaya seeds (Carica papaya Linn) have been found to have a significant effect on sperm characteristics in some mammals, including humans, but no studies have investigated the effects on dogs. In the present study, a significant decrease in sperm concentration was observed in a group of dogs treated with extracts from washed papaya seeds, but no decrease was observed in the group of dogs treated with non‐washed seeds. An important effect of extract components from washed seeds such as fatty acids is probably involved in the reduction of sperm production because of Sertoli cell damage, as has been suggested for langur monkeys. Dilution of the active components in the non‐washed papaya seeds or interference with some of the components may reduce the expected effect on spermatogenesis. This first report on the effects of a chloroformic extract of papaya seeds in dogs suggests that an increased dose is necessary to achieve azoospermia.     

Distribution and habitats of the snail Lymnaea truncatula, intermediate host of the liver fluke Fasciola hepatica, in South Africa

This paper focuses on the geographical distribution and habitats of Lymnaea truncatula, the intermediate, snail host of the liver fluke, Fasciola hepatica, as reflected by the 723 samples in the database of the National Freshwater Snail Collection, Potchefstroom, South Africa. The 221 different loci (1/16-degree squares) on record reflect an extensive but discontinuous distribution, except in Lesotho and in parts of the Mpumalanga, Gauteng and North West provinces of South Africa. Although recorded from 12 different types of waterbody, it was mostly (42.0%) recovered from swamps. Most samples (45.8%) were collected in habitats with slow-flowing water. A muddy substratum was recorded for 62.5% of the samples. Most samples (86.3%) were collected in habitats with a mean annual air temperature of 10-20 degrees C, and more than 69% came from localities with a mean annual rainfall of 600-900 mm. An integrated decision tree constructed from the data indicated that temperature and types of waterbody play a decisive role in determining the presence of L. truncatula in a given area. A temperature index calculated for all mollusc species ranked L. truncatula second in a total of 53 species according to its association with low temperatures. It remains to be established whether its distribution is indeed discontinuous, and whether its preference for a particular habitat, amphibious habits and ability to aestivate could have resulted in some populations having been overlooked during surveys.     

The occurrence of the snail Lymnaea columella on grazing areas in New South Wales and studies on its susceptibility to Fasciola hepatica

Field surveys were carried out in the Lismore and Casino area for the presence of fresh water snails potentially responsible for the transmission of trematodes in ruminants. Although the North American snail, Lymnaea columella has previously only been reported from metropolitan areas, large populations of the snail were found east of Lismore. Natural infection with F. hepatica was detected in some of the snails and laboratory studies showed that this snail species was highly susceptible to infection with miracidia of F. hepatica and produced viable metacercariae. Three species of planorbid snails, Helicorbis australiensis, Pygmanisus pelorius and Gyraulus gilberti were also found. The first 2 planorbid species were infected with paramphistomid cercariae.     

Influence of copper sulphate on the water and electrolyte balance of the freshwater snail Bulinus (Bulinus) tropicus

The water and electrolyte balance of Bulinus (Bulinus) tropicus, a freshwater pulmonate, was determined when subjected to different sublethal concentrations of copper sulphate. It was found that the lethal dose (LD₅₀), which is the dose lethal to 50% of the snails, is 1,0 ppm in water of pH 8,5. Increasing dosages disturb the ionic and water balance. Haemolymph concentrations of Na ⁺ , Ca²⁺ and Cl^- decrease markedly. The rates of ion influx and efflux for Ca²⁺ , Na ⁺ , Cl^- and ³H₂0, measured With their corresponding radioisotopes, were drastically changed. The results indicate that the physiological effects of copper are not limited to particular organs or tissues but probably occur throughout the snail body. The possible effect of copper sulphate on the in- tegumental exchange mechanisms for Ca²⁺, HCO3^-, Na⁺ , K⁺ and Cl^- are discussed.     

Oxygen consumption and responses of the freshwater snail Bulinus (Physopsis) globosus to gradients of different oxygen tensions

A gradient or choice apparatus, based on the ‘fluvarium’ principle and suitable for testing the responses of the freshwater snail Bulinus (Physopsis) globosus to different partial oxygen tensions was used. In a gradual oxygen gradient established with this apparatus, B. (P.) globosus shows a significant preference for oxygenated water. In experiments with a choice between low and high partial oxygen tensions, B. (P.) globosus shows a greater preference for oxygenated water. Oxygen consumption rates vary considerably among individuals and decreases when lowering the Pq in the water.     

Distribution, habitats and role as intermediate host of the freshwater snail, Bulinus forskalii, in South Africa

This paper focuses on the geographical distribution and habitats of Bulinus forskalii, the snail intermediate host of the conical fluke of equids, Gastrodiscus aegyptiacus as reflected by the 1209 samples in the database of the National Freshwater Snail Collection of South Africa. The 362 different loci on record represent an extensive distribution in KwaZulu-Natal Province, the Limpopo Province, the coastal areas of the Eastern Cape Province and the south-eastern part of the North West Province. Although it was recorded from all types of water-body represented in the database, the highest percentages of samples were recovered from dams (30.4%) and brooks (28.2%). The majority of samples came from perennial habitats (59.1%), 60.7% from habitats with standing water, 54.0% from habitats with clear water and 71.8% from habitats of which the water was described as fresh. The majority of samples (39.5%) were collected in habitats of which the substratum was recorded as muddy. The highest percentage of samples, by far (81.5%), was collected in habitats that fell within the mean yearly temperature interval ranging from 15-20 degrees C. An integrated decision tree constructed from the data in the database indicated that temperature and type of water-body played a decisive role in determining the presence of B. forskalii in a given area. The results of experimental exposure to miracidia of a local strain of both Schistosoma haematobium and Schistosoma mattheei in the laboratory indicated that a local strain of B. forskalii was incompatible with both these strains of parasite. Research to clarify the role of B. forskalii in the transmission of both Calicophoron microbothrium and G. aegyptiacus in South Africa, is recommended.     

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Experimental evidence that copper is taken up by the freshwater snail Bulinus tropicus through a process of adsorption

In this investigation the mechanism of copper uptake by freshwater snails was examined. The experiments investigated the following: the uptake of copper by the snail, the release of copper from the snail, the decrease of copper in the exposure medium, and the relationship between copper uptake and snail metabolism. The results of the investigation provide evidence that copper is taken up by a process of adsorption rather than by active absorption.     

Soil type and the distribution of Lymnaea truncatula

Habitat distribution of the snail Lymnea truncatula, the intermediate host of the liver fluke Fasciola hepatica, was related to a soil map in a part of Dyfed in South Wales. There was a close association with wet soils in general but, within these areas, habitats were concentrated in very wet localities of restricted size, such as ditches and seepages. Vegetation characteristic of these habitats is described. Soil maps could be a useful tool for the veterinary officer, agricultural adviser and research worker in identifying fluke-prone land.