Plasmodium falciparum gametocytes: their longevity and infectivity.

The longevity and infectivity of isolated populations of Plasmodium falciparum gametocytes were studied. Following chloroquine treatment gametocyte numbers fell with a constant rate of loss over a period of 16-24 days; the populations had a half-life of 2-4 days. The sex ratio stayed constant throughout at 4 female: 1 male. The ability of the microgametocytes to exflagellate and the infectivity of the population to mosquitoes persisted for 3 weeks. Antibodies to the gametocytes were detected but not in every patient studied. It was concluded that the gametocytes of P. falciparum are both long-lived and show persistent infectivity to mosquitoes. They can stimulate antibody production but the immune response appears to play no part in their elimination, which probably takes place in the spleen as a part of the normal process of removing old, damaged and malformed red cells.     

The Hydrobia ulvae-Maritrema subdolum association: influence of temperature,salinity, light,water-pressure and secondary host exudates on cercarial emergence and longevity

The effects of environmental factors and exudates from the amphipod Corophium volutator on the emergence of Maritrema subdolum cercariae (Digenea: Microphallidae) from the snail Hydrobia ulvae were investigated in the laboratory. Increasing the temperature (15 to 25 degrees C) caused an overall 11-fold increase in emergence rate under varying salinities (24 to 36 per thousand). The effect of salinity depended on the experimental temperature. Emergence increased with increasing salinity at higher temperatures, but decreased with increasing salinity at 15 degrees C.Whereas the different levels of salinity had no effect, increasing the temperature significantly reduced the life span of cercariae. In comparison with complete darkness, light caused a two-fold increase in emergence, whereas an increment of the water pressure from 1.0 to 1.3 ATM (corresponding to 0 and 3 m of depth) left the shedding rate unaffected. Unidentified exudates from the second intermediate host, C. volutator, significantly depressed the cercarial emergence rate. The main transmission window of M. subdolum seems to occur during low water in tidal pools where light levels are high and solar radiation rapidly elevates the water temperature, as well as salinity through evaporation. The consequence of such a transmission strategy is discussed in relation to the impact of M. subdolum on the population dynamics of the second intermediate host.     

Effect of selected chemical agents on longevity and infectivity of Schistosoma mansoni cercariae.

The effects of various chemical agents on longevity of the cercariae of Schistosoma mansoni Sambon, 1907, were investigated. The median lifetime of cercariae maintained in dechlorinated tap water (DTW) was 10.5 hr. Increasing concentrations of sodium chloride added to distilled water increased the median lifetime to an optimum of 10 hr at 0.01 M; higher salt levels decreased longevity. At this optimum sodium chloride level, concentrations of glucose between 0.003 M and 0.03 M enhanced median survival to 13–14 hr. Using Tris-HCl buffers the effects of pH and ionic strength were examined. Cercarial longevity increased from 3.5 to 25 hr as pH increased from 6.4 to 9.0, and 0.01 M Tris was superior to 0.001 M Tris at a given pH. The greatest median lifetime (26 hr) was obtained in 0.01 M Tris, pH 9.0. Infectivity of cercariae in Tris at this optimal pH was compared to that in DTW. Maintenance in DTW resulted in greater worm burdens in mice than did treatment with Tris. This suggested that factors which affect cercarial longevity may not influence infectivity in the same manner. The effects of rotenone, Antimycin A, dinitrophenol, and potassium cyanide on cercarial viability suggested the existence of a functioning terminal electron transport chain similar to that of mammalian systems.     

Effects of atrazine, endosulfan and butylated hydroxyanisole on glutathione-S-transferases in Orthosia gothica

Atrazine (1,000 ppm), endosulfan (1 ppm) or butylated hydroxyanisole (BHA) (1,000 ppm) added to a semi-synthetic diet of Orthosia gothica for 2 days in the last instar did not change the soft tissue cytosolic glutathione-S-transferase (GST) activities towards 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and cumene hydroperoxide (CU). However, all three pesticides changed the GST subunit composition compared with the control as observed by reverse phase high performance liquid chromatography of the isozymes purified by glutathione-Sepharose affinity chromatography. The changes seem to have occurred mainly in the GST class 2 subunit. There is no obvious explanation for the changes, which may be a result of interactions between xenobiotic and GST in the cytosol as well as changes in the level of regulation of synthesis. However, the observation added to our knowledge of the processes involved when pesticides are degraded by GSTs in vivo.     

Effects of tunicamycin on rotavirus morphogenesis and infectivity

The functions of the two rotavirus glycoproteins were investigated by using tunicamycin and a variant of SA11 rotavirus having nonglycosylated VP7. Results showed that glycosylation of VP7 is not required for normal viral morphogenesis and infectivity and suggested that the nonstructural glycoprotein is involved in assembly of the outer capsid.     

Effects of pollination on floral attraction and longevity

The end of a flower's attraction to pollinators may be due toa range of visible cues such as permanent flower closure, acolour change, and withering or abscission of the petals. Floralattraction may be reduced by pollination. Pollination-inducedconclusion of floral attraction is often due to a colour changeor to flower closure. This may or may not be followed by a reductionin floral longevity, defined as the time to petal withering,wilting or shattering. In a few species floral longevity isincreased following pollination-induced flower closure or apollination-induced change in colour. Floral attraction, therefore,has to be disting uished from floral longevity. A literature survey shows that pollination rapidly reduces floralattraction in numerous orchids, but among other plant familiesonly about 60 genera have been found to show pollination-inducedshortening of floral attraction. Although only a few specieshave been investigated, it was invariably established that theeffect of pollination is blocked by inhibitors of ethylene synthesisor ethylene perception, hence is mediated by ethylene. The flowersthat cease to be attractive to pollinators, shortly followingpollination, tend to be from families that are known mainlyto comprise species in which flower longevity, petal colour,or flower closure, is sensitive to exogenous ethylene. Thisindicates that the effect of pollination on floral attractionis generally mediated by endogenous ethylene. Numerous species reportedly show a decrease in the period offloral attraction after exposure to ethylene, whereas only fora small number of species a decrease in the period of floralattraction induced by pollination has been observed. This discrepancymay be due to the greater attention that has been paid to theeffects of ethylene. Nonetheless, the possibility remains thatendogenous ethylene has a role in changing perianth form andcolour in addition to signalling the occurrence of pollination. Key words: Ethylene sensitivity, flower closure, flower longevity, pollination, petal colour, petal wilting, petal withering, petal abscission     

Effects of exercise on longevity of rats

It has been postulated that life span is inversely related to energy expenditure. If this is correct, regularly performed exercise could accelerate the aging process. In two early studies, exercise shortened the life span of rats; the results of these studies have been cited as evidence for the concept that an increase in energy expenditure accelerates aging. However, subsequent studies have not confirmed this finding. Instead, the weight of evidence now indicates that rats that exercise regularly have a longer average life span than sedentary, ad libitum-fed controls. Freely eating sedentary rats become obese, indicating that their food intake is in excess of their energy requirements. Available evidence seems compatible with the interpretation that exercise results in improved survival in rats by countering deleterious effects of a sedentary life combined with overeating.     

Chronobiological aspects of the host-parasite relationships between Biomphalaria glabrata and Schistosoma mansoni: cercarial production and infectivity, and growth kinetics of the host

In the Biomphalaria glabrata-Schistosoma mansoni association, variations in cercarial production, in cercarial infectivity, and in the growth of infected snails are rhythmic. These chronobiological aspects are correlated with the dynamics of the intramolluscan larval stages of the parasite during the course of the infection. Rhythmic variations in the growth kinetics of infected snails are interpreted in terms of host-parasite metabolic exchanges.     

Effects of atrazine on osmoregulation in the Chinese mitten crab,Eriocheir sinensis

This study integrates results from acute contamination with atrazine of isolated perfused gills, and from in vivo chronic contamination of euryhaline Chinese mitten crabs, Eriocheir sinensis, acclimated to freshwater. Atrazine 1 mg/l in contact with the basolateral membrane (IN) increases the transepithelial potential difference (TEP) from -20.8 +/- 4.9 to -29.7 +/- 3.8 mV in isolated perfused posterior gills (P < 0.01). This effect is only partially explained by a modification of Na(+) and Cl(-) active influxes. No TEP modification is detected when atrazine is added (OUT) indicating that molecular mechanisms located on the basolateral membrane are likely to be the only ones affected. Another explanation would be that cuticular barrier prevents atrazine penetration into the gill. Haemolymph osmolarity, Na(+) and Cl(-) concentrations of crabs living in freshwater contaminated with atrazine 1 mg/l during 14 days are not significantly modified. We conclude that although atrazine can disturb osmoregulatory mechanisms of isolated gills, this pollutant would be of minor importance in affecting osmoregulatory capacities of the Chinese mitten crab in natural conditions.     

Effects of warming on root diameter,distribution, and longevity in an alpine meadow

Roots form one of the most important carbon (C) pools in alpine ecosystems. Uncertainty about the effects of warming on root dynamics limits our ability to predict how C will transfer between biological and atmospheric pools in alpine regions under global warming. We used a minirhizotron technique to gain a better understanding of the response of alpine plant roots to warming. We looked for effects on root diameter, root depth in the soil, and root lifespan under a controlled asymmetrical warming (1.2/1.7 °C during daytime/nighttime) experiment during the growing season of 2009 in an alpine meadow on the northern Tibetan plateau. Roots became smaller in diameter, moved toward the upper soil layers, and showed significantly shorter lifespans in heated (H) than in unheated (UH) plots. Furthermore, in H treatment plots root lifespan was more strongly influenced by the time of root emergence rather than by root diameter. These results provide evidence that alpine plants may respond to climate change by altering their roots so that they are thinner, distributed shallower and turning over faster, suggesting that soil C flow and nutrient cycling would be accelerated resulting from the fast turnover of fine roots under elevated temperatures.     

Influence of methods of preparation on the infectivity, agglutination, activity, and ultrastructure of bloodstream trypanosomes

Contrary to the reports of others, the surface coat of Trypanosoma brucei brucei was not removed by extensive washing in the various media investigated; in fact, other than a deformed profile when washed in saline, ultrastructure was little affected by column separation and washing in any of these media. Washing in saline increased the agglutinability but reduced the activity and infectivity of the organisms. Washing in bicine-buffered saline-glucose did not impair activity or infectivity but increased agglutinability, albeit to a lesser extent than after washing in phosphate-buffered saline-glucose. The inclusion of 0.1% serum or plasma in the washing medium (phosphate-buffered saline-glucose or bicine-buffered saline-glucose) increased the activity of the T. b. brucei and did not increase agglutinability or impair infectivity. T. congolense and T. vivax were more susceptible to ionic strength changes than were T. b. brucei or T. lewisi, in that not only was their activity impaired, but they began to aggregate on standing in lower ionic strength buffers.     

Effects of host desiccation on development, survival, and infectivity of entomopathogenic nematode Steinernema carpocapsae

This study investigates the effect of host desiccation on entomopathogenic nematode (EPN) development, emergence, infectivity, and cross-protection against secondary environmental stress. Galleria mellonella hosts infected with the EPN Steinernema carpocapsae A10 were allowed to dehydrate in an environmental chamber for up to 56 days at 23 degrees C achieving a weight loss of approximately 86% by day 44 post-infection. Host carcasses were rehydrated on water-saturated filter paper in White traps to collect emergent infective juveniles (IJ) at specific time intervals. Populations were counted with an apparent peak coinciding with desiccated hosts rehydrated at 24-day post-infection. Desiccation-stressed IJ populations from each time interval were tested for infectivity, and cross-resistance to secondary temperature and pH stresses and were found to have significant increases in both infectivity and protection from extremes of temperature and pH compared with controls. Total aqueous soluble protein profiles from control and desiccation-stressed IJs were analyzed using 10% SDS Laemmli gels. Several novel proteins were over-expressed in EPN from hosts subjected to desiccation suggesting the induction and expression of stress response genes.     

Further research on the production, longevity and infectivity of the zoospores of Leptolegnia chapmanii Seymour (Oomycota: Peronosporomycetes)

The effect of temperature on the production, survival and infectivity of zoospores of an Argentinean isolate of Leptolegnia chapmanii was determined under laboratory conditions. Production of zoospores of L. chapmaniiin vitro and in vivo upon first and fourth instars larvae of the mosquito Aedes aegypti was studied at three different temperatures. Zoospores from infected larvae were infective to mosquito larvae for 51, 12, and 5 consecutive days when maintained at 25, 35, and 10 °C, respectively. Maximum zoospore production in infected fourth-instar larvae was 9.6 ± 1.4 × 10⁴ zoosp/larva at 48 h at 25 °C. The average number of zoospores produced by individual fourth-instar Ae. aegypti larvae infected with L. chapmanii was 3.57 ± 0.46 × 10⁵ zoospores during 6 consecutive days at 25 °C. Zoospore production in vitro was also affected by temperature with a maximum of zoospores (n = 47,666/ml) produced at 25 °C. When zoospores produced in vitro were used as inoculum against Ae. aegypti larvae at 25 °C, larval mortality was recorded for 5 consecutive weeks. The encystment process for zoospores took 17-20 min; the germination of cysts (excystment) occurred 5 min after exposure in water to mosquito larvae. The minimal time of contact between zoospores and mosquito larvae to develop infection was two minutes. Infection took place by zoospore attachment onto and then penetration through the larval cuticle or by ingestion of cysts as was confirmed by histological studies. Temperature directly affected infectivity and production of zoospores in vivo and in vitro although L. chapmanii zoospores tolerate a wide range of temperatures.     

Effects of microgravity and hypergravity on aging and longevity of insects

The effects of microgravity and hypergravity on aging are still poorly documented, particularly in mammals. However, there is a growing interest for the use of the fruit fly, Drosophila melanogaster, and this species may be now considered as a model organism in gravitational biology studies dealing with aging.     

Effects of diet on longevity and fecundity of the spined stilt bug, Jalysus wickhami

We evaluated the suitability of selected food items for the adult spined stilt bug, Jalysus wickhami Van Duzee (Hemiptera: Berytidae), by providing one of seven diet treatments: (1) prepupae of the parasitoid, Cotesia congregata (Say) (Hymenoptera: Braconidae), on a leaf of tobacco (Nicotiana tabacum L., NC 2326) (Solanaceae); (2) C. congregata prepupae alone (i.e., no tobacco leaf); (3) eggs of the parasitoid's host, Manduca sexta (L.) (Lepidoptera: Sphingidae), on a tobacco leaf; (4) M. sexta eggs alone; (5) tobacco aphids, Myzus nicotianae Blackman (Homoptera: Aphididae), on a tobacco leaf; (6) a tobacco leaf alone; and (7) no prey and no tobacco. A tobacco leaf was necessary for the long-term survival of stilt bugs, but prey source did not affect longevity. Regardless of the prey type, stilt bugs with access to a tobacco leaf lived 21–23 days, while stilt bugs without access to tobacco lived less than 12 days. Animal prey provided a protein source required for egg deposition in J. wickhami, and prey species differed in their relative nutritive values. Female stilt bugs that fed on M. sexta eggs or on C. congregata prepupae were significantly more fecund (102 and 106 nymphs per female, respectively) than females that fed on tobacco aphids (24 nymphs per female). Results suggest that stilt bugs may feed on tobacco aphids and C. congregata prepupae when other prey are unavailable.     

Effects of six sugars on the longevity,fecundity and nutrient reserves of Microplitis mediator

Parasitoid adults can directly feed on floral nectar and honeydew containing monosaccharides and disaccharides. Oligosaccharides such as maltose, melezitose and raffinose are also found in honeydew but are rare in floral nectar. The effects of six different sugar resources on the longevity, fecundity and nutrient reserves of Microplitis mediator, a larval endoparasitoid in the cotton bollworm Helicoverpa armigera (Hübner) were determined in our laboratory. The results showed that both food and sex affected longevity of this wasp. Females and males of M. mediator fed with 1 M sucrose solution survived longer than controls fed with water (5.7- and 3.7-fold longer, respectively). When provided with sucrose, glucose or fructose solutions, the parasitoid generated 3.6- to 3.7-fold more offspring than controls, and 60–75% of these progenies were produced during the first 5 days. When separately given fructose, sucrose or glucose, this wasp accumulated fructose and total sugar at the highest level, which means a high sugar levels might lead to prolonging longevity and more offspring in M. mediator. In addition, compared with organisms fed galactose or raffinose, M. mediator fed sucrose or fructose accumulated high glycogen levels. Furthermore, in M. mediator, the lipid content declined with the advancing age. Females showed the slowest lipid metabolic rates when fed with sucrose, glucose, fructose, mannose and galactose solutions versus when fed with raffinose and control. In addition, only sucrose had a significant effect on lipid levels in males nearing the end of life.     

Effects of ammonium-N on development and infectivity of the take-all fungus

Effects of applications of a mixture of ammonium sulphate and mono-ammonium phosphate and of ammonium nitrate on the incidence of take-all disease of wheat (caused by Gaeumannomyces graminis var. tritici) and on subsequent inoculum levels were studied in field and glasshouse experiments. In a field experiment in Western Australia, on a sandy soil at pH 5·4, nitrogen applications had no detectable effect on disease severity at anthesis, but ammonium sulphate treatment increased the number of propagules of the pathogen in the soil. In a pot experiment, in which seed was sown in the field experiment soils, disease was greater in soil from plots treated with ammonium sulphate and least in soil from the nil-nitrogen plots, reflecting the respective inoculum levels in the field plot. However, treatment of the soils of lower inoculum with ammonium sulphate and ammonium nitrate during this pot experiment decreased disease. A second pot experiment confirmed the effectiveness of ammonium sulphate and ammonium nitrate in reducing take-all at lower inoculum levels, and their ineffectiveness at higher inoculum levels.     

Effects of atrazine on Ochrobactrum anthropi membrane fatty acids.

Ochrobactrum anthropi is a gram-negative bacillus recognized as a human opportunist pathogen isolated in clinical specimens and not of clinical significance. We report a new aspect of this bacterium, that it has been isolated from activated sludge. In fact, it is able to grow on atrazine (2-chloro-4-ethylamino-6-isopropyl-amine-s-triazine) by utilizing it as the only source of carbon. Our results show that atrazine (0.03 g/liter) causes a dramatical increase in the degree of saturation of membrane fatty acids. Analysis and identification of bacterial fatty acids were performed by gas chromatography and gas chromatography-mass spectrometry techniques.