Direct and delayed effects of low temperature on the freshwater snail Indoplanorbis exustus (Deshayes, 1934), intermediate host of schistosomias

The direct and delayed effect of short-term exposure to low temperature (17.5 °C) on growth, reproduction and longevity of adolescent and mature freshwater Indoplanorbis exustus Deshyaes (Mollusca: Gastropoda) was studied in the laboratory. We found that growth and reproduction were retarded, but were enhanced when later they were returned to ambient temperature.     

Laboratory studies on the direct effect of temperature on the freshwater vector snail,Indoplanorbis exustus (Deshyes)

The present study includes the effect of temperature on the survival of young and adult snails, embryonic development, embryonic growth and egg laying of Indoplanorbis exustus. In Indoplanorbis exustus the bottom lethal temperature was 7.0°C and 7.5°C for young and adults respectively. while the upper lethal temperature was 34.0°C and 32.0°C for young and adult snails respectively. Between the temperatures 12.5°C and 36.5°C the embryonic development was accelerated and the incubation period was shortened. The growth of embryos was found to be faster at 25.0°C. The optimum temperature for egg laying was observed at 25.0°C.     

Responses of the neurosecretory cells of the freshwater snail,Indoplanorbis exustus to hydrothermal stress

Changes in the neurosecretory cell cytology of I. exustus subjected to hypertonic saline (0.1 ml of 1.5%/snail) loading and thermal stress (35°C) for two hours, have been investigated. Of the two types of neurosecretory cells A and B that are present in the central nervous system (CNS) of I. exustus, striking changes were evident only in B cells. After both treatments, there was about 33% decline in NSM (Neurosecretory material) intensity. However, the nuclear diameter of B cells was significantly (P < 0.001) increased in the snails administrated with hypertonic saline unlike in those exposed to 35°C wherein significant (P < 0.005) decline was evident. The adaptive significance of the neuroendocrine system of I exustus is discussed in relation to hydrothermal stress.     

Observations on the hatching process and salt and water regulation in the embryos of the freshwater snail Indoplanorbis exustus

The freshwater snail Indoplanorbis exustus laid its eggs in triple layers in a gelatinous, ribbon shaped matrix. Hatching was by mechanical means. The capsular membrane of the embryos was more permeable to water than to other organic and inorganic ions.     

Ultrastructural observations on the redial tegument of Paramphistomum epiclitum from the planorbid snail, Indoplanorbis exustus.

The morphology of the tegument in the redia of Paramphistomum epiclitum (Digenea: Paramphistomidae) resembles that shown by most larval and adult digeneans; an outer surface syncytium is in continuity with the cytoplasm of in-sunken, nucleated cytons. Although tegumental cytons usually contain a single nucleus, some display up to six nuclei. The tegumental syncytium lining the pharynx of P. epiclitum rediae lack underlying cytons. The apical membrane of the tegument is elaborated by folds and microvilli, which presumably facilitate uptake of nutrients and/or exchange of ions involved in osmoregulation. A single type of secretory body, resulting from the fusion of smaller vesicles produced at Golgi complexes in the cytons, occurs throughout the tegument. Uniciliate sensory receptors occur in the surface syncytium particularly around the oral opening.     

Studies of the relationships between Schistosoma nasale and S. spindale and their snail host Indoplanorbis exustus

Infectivity and cercarial production of Indoplanorbis exustus related to variation of miracidial dose (1, 4, 10 or 20) with Schistosoma nasale and S. spindale from Sri Lanka were studied. The intermediate host-parasite relationships of the two schistosome species showed marked differences under the conditions of observation recorded in this study. Prepatent death rates (PDR) were on average higher for S. spindale (30%) than for S. nasale (10%). The size of the miracidial dose to which snails had been exposed had no effect on PDR. The infection rates (IR) were on average higher for S. nasale (41%) compared with S. spindale (27%). Highest IR occurred after exposure to 4 miracidia in S. nasale infections (79%) and after exposure to 10 miracidia in S. spindale infections (60%). The highest daily average cercarial production per snail was recorded for S. nasale at a level of 4 miracidia (1311), and for S. spindale at a level of 10 miracidia (1615). At low level (1 or 4 miracidia) of exposure, I. exustus showed a better compatibility with S. nasale than with S. spindale. An opposite tendency was observed at higher levels (10 or 20 miracidia) of exposure. Unsuccessful infections of Lymnaea luteola with either S. nasale or S. spindale indicate that this species is not involved in transmission.     

Effect of temperature on growth,reproduction and survival of the freshwater planorbid snail,Gyraulus convexiusculus,vector of echinostomiasis

Studies were carried out to investigate the effects of 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40° and 45°C on growth, sexual maturity, reproduction and survival of the freshwater planorbid snail, Gyraulus convexiusculus, vector of echinostomiasis, under laboratory conditions. The growth rate of juvenile and sexually mature snails was at minimum at 15°C and was maximum at 35°C. Sexual maturation time was minimum at 35°C and maximum at 20°C. Fecundity was minimum at 15°C and maximum at 35°C. The minimum average and maximum number of eggs per egg capsule was reached at 35°C and lowest at 15°C. 30°C was the optimum temperature for survival of juvenile snails, while sexually mature snails reached maximum survival time at 20°C.     

温度对美洲斑潜蝇发育、存活和繁殖的影响

在恒温１５,２０,２５,３０和３５℃下,对美洲斑潜蝇在菜豆上的发育和繁殖做了研究。结果表明,在１５￣３５℃范围内,未成熟期各虫态（卵、幼虫和蛹）的发育历期随温度的升高而缩短,发育速率呈逻辑斯蒂曲线变化;卵期孵化率在２５℃中最高;各温度下幼虫期存活率最高,低温１５℃和高温３５℃对蛹的存活有显示抑制作用,１５℃时蛹的死亡率达３９．６％。成虫寿命一般在２０ｄ以内,与温度呈直线负相关;繁殖力最高可达２８１     

温湿度对腐食酪螨存活和繁殖的影响

研究了33种不同温湿度处理对腐食酪螨卵发育、孵化,成螨存活和繁殖的影响。结果表明：在15±1℃、20±1℃、25±1℃、30±1℃、35±1℃5种恒温下,相对湿度低于60％腐食酪螨几乎不能存活,高湿环境条件才有利于该种群正常繁衍。在适宜相对湿度范围,湿度与腐食酪螨成螨存活率关系显著,温度与腐食酪螨卵的发育历期、成螨日均产卵量关系极显著。     

温度对传粉甲虫——棉露尾甲生长发育、存活及繁殖的影响

在光照周期为 12 L:12 D、土壤含水量为 15 %的 5种恒温条件下 (15℃、2 0℃、2 5℃、30℃和 35℃ ) ,以丝瓜花为饲料研究了棉露尾甲未成熟期 (卵期、幼虫期和蛹期 )的生长发育和存活情况 ;同时 ,在同样的光照和温度、棉球保湿的条件下 ,研究了温度对成虫寿命及繁殖的影响情况。结果表明 ,未成熟期各虫态发育速率随温度呈抛物线变化 ,30℃时发育速率最大 ;15℃时卵孵化率最高 ,2 0～ 30℃时 ,幼虫存活率、蛹羽化率显著高于低温 (15℃ )和高温 (30℃ ) ,平均分别可达 96 .3%和 93.2 % ,低温和高温对其有明显的抑制作用 ;成虫寿命同温度之间呈负的线性关系 ,雌虫寿命普遍长于雄虫 ,30℃时雌虫的产卵期最长 ,繁殖力最大 ,最高可达 14 6粒 /雌 ,产卵期和产卵量与温度之间呈抛物线关系     

温度对大猿叶虫发育、存活和繁殖的影响

在光周期14L:10D、75%RH的条件下研究不同温度对大猿叶虫Colaphellus bowringi Baly生长发育、存活率和繁殖的影响。结果表明,卵、幼虫和蛹的发育起点温度分别为11·86,11·17和10·15℃,有效积温分别为61·6,110·8和65·3日·度;22℃时卵的孵化率和蛹的羽化率最高,分别达96·04%和94·26%;滞育后成虫寿命雌虫普遍长于雄虫,25℃下的产卵期11～34d,每雌产卵量平均861粒,最高达1527粒。     

温度对异色瓢虫生长发育和繁殖的影响

为探索饲养异色瓢虫Harmonia axyridis（Pallas）的最适温度,了解其对高温的耐受性,组建了异色瓢虫在15,20,25,30和35℃下的实验种群生命表。结果表明：各虫态的发育速率随温度的升高而加快,在15℃下世代的发育历期最长（65.5d）,而30℃时仅为22.4d,20℃和25℃时分别为39.0d和23.0d。卵、幼虫、蛹和世代的发育起点温度分别为9.8,8.2,11.6和8.5℃,有效积温分别为41.1,225.6,81.6,432.6日.度。成虫寿命随温度升高而逐渐缩短,15℃时最长,为77.7d,在30℃下最短,为36.3d;单雌产卵量在25℃时最高,平均为2193.0粒,15℃时最低,为626.0粒。在25℃下,异色瓢虫的种群趋势指数和内禀增长力均较高,分别为916.7和0.15,表明25℃是异色瓢虫生长、繁殖的最适温度。     

Asymmetry as a predictor of growth, fecundity and survival

Measures of developmental stability such as fluctuating asymmetry have been assumed to predict individual performance because asymmetry reflects an inability to cope with stressful situations, and because asymmetry hampers locomotion. However, the magnitude of this relationship between important fitness components (growth, fecundity, survival) and asymmetry has never been assessed. Based on a literature survey, estimates of the correlation between asymmetry and the three fitness components are presented. Pearson's correlation coefficients weighted for sample size between asymmetry and growth, fecundity, and survival, respectively, were –0.15, –0.35, and –0.25, respectively, with all three coefficients being highly significant. All three relationships were extremely robust given very large fail-safe numbers. The results were independent of whether studies or species were used as units of analysis. Hence asymmetry is a robust predictor of performance in fitness domains such as growth, fecundity, and survival, although only accounting for 2.1%, 12.3%, and 6.0% of the variance. This may be of importance for studies of sexual selection, but also for ecological and conservation biological studies, where the performance of individuals or groups of individuals are assessed.     

Effect of temperature on development, survival, and fecundity of Microplitis manilae (Hymenoptera: Braconidae)

Microplitis manilae Ashmead (Hymenoptera: Braconidae), a larval parasitoid, is a potential biological control agent of both Spodoptera exigua (Hübner) and Spodoptera litura (F.) (Lepidoptera: Noctuidae). Aspects of the climatic requirements for development, including survival, longevity, and fecundity of M. manilae were studied at six constant temperature regimes (17, 20, 23, 26, 29, and 32°C) in the laboratory. The results showed that developmental duration for egg, larva, pupa, and the entire immature stages shortened in response to temperature increasing from 17 to 32°C. Survival rates of different developmental stages were higher at 20-29°C than at other temperatures. Longevity of M. manilae adults shortened with increasing temperature. The maximum fecundity of M. manilae female equaled 261.0 eggs/female at 26°C. Minimum threshold temperature and effective accumulated temperature for completing a generation of M. manilae were 11.04°C and 205.98 degrees-days, respectively. Both intrinsic rate of increase (r) and finite rate of increase (λ) of M. manilae did not differ between 26 and 29°C, but those were significantly higher at 26 and 29°C than at any other temperatures. The highest net reproduction rate (r(0)) was observed at 26°C, with the value of 97.77, but the lowest was 11.79 at 32°C. These results suggest that the parasitoid is well adapted to temperate and subtropical climates, which implies a significant potential for using M. manilae to control S. exigua because most of areas occupied by these two pests belong to temperate and subtropical regions in southeastern Asia.     

Patterns of density dependence in growth,reproduction and survival in the invasive freshwater snail Pomacea canaliculata in Japanese rice fields

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Effect of environmental temperature on development, fecundity, survival and predation of the snail-predatorSarcophaga misera (Dipt., Sarcophagidae)

Effect of temperature (10°–45°C) on development, fecundity, survival, population parameters, and rate of predation on snail by the flySarcophaga (Parasarcophaga) misera has been studied under controlled laboratory conditions. Temperatures ranging from 25°–30°C effected higher rate of development, fecundity, and predation on the snailIndoplanorbis exustus, than at 15°, 20°, 35° & 40°C. Longevity was maximum at 20°C. Implications of the role of temperature in influencing the biology and predation by this fly are discussed.     

Categorization of hemocytes of three gastropod species Trachea vittata (Muller), Pila globosa (Swainson) and Indoplanorbis exustus (Dehays)

Light microscopic observations were made on the hemocytes of three gastropod species namely Trachea vittata, Indoplanorbis exustus and Pila globosa. It revealed two basic types of hemocytes. They are agranulocytes and granulocytes. Agranulocytes are hyalinocytes which are round, unspread hemocytes and have a large nucleo-cytoplasmic ratio. Granulocytes are spreading hemocytes, forming numerous pseudopodia. For the purpose of differential counting, we present a categorization of the granulocytes into three sub-categories based on cell dimensions, nucleo-cytoplasmic ratio, distribution of granules in the cytoplasm and position of the nucleus. The smaller granulocytes are younger cells, and are termed Granulocytes I (Progranulocytes). The larger ones are fully developed cells that have been differentiated into Granulocyte II (basophilic) and Granulocyte III (eosinophilic).     

短时高温对莲草直胸跳甲成虫存活及繁殖的影响

采用短时高温处理研究了40～47℃高温对莲草直胸跳甲Agasicles hygrophila Selma & Vogt成虫存活以及40～44℃对雌成虫繁殖的影响。结果表明:(1)处理1h后,随着温度的上升,莲草直胸跳甲雌雄成虫的存活率均随着温度的上升而下降,44℃时,雌成虫的存活率开始显著高于雄成虫;处理温度为40℃时,雌雄成虫存活率也随着处理时间的延长而下降,7h时,雌成虫的存活率开始显著高于雄成虫。此外,雌成虫致死90%的温度和时间分别高于雄成虫1.31℃和1.29h,均表明雌成虫的耐热能力比雄成虫强,但差异仅在胁迫强度偏大时表现为显著;(2)40～44℃短时高温影响莲草直胸跳甲成虫的繁殖。与对照处理相比,40、42和44℃高温处理1h后,雌成虫的寿命和产卵量变化不显著,但均引起了其产卵前期的延长和10日龄成虫产卵停滞,44℃时,平均停滞时间达2.62d,子代卵的孵化率则从40℃的88.67%下降到44℃的79.84%,44℃时显著低于对照。