Attraction of mosquitoes to volatiles associated with blood.

Responses of the mosquitoes Aedes aegypti, Culex quinquefasciatus, and Culex nigripalpus to volatiles and compounds associated with bovine and avian blood that were presented in collagen membranes were evaluated in olfactometer and landing assays. The presence of attractants produced by blood was supported by more attraction of all species to blood than water controls in the olfactometer. Females of Ae. aegypti and Cx. quinquefasciatus were more attracted to bovine blood than to avian blood, but there was no difference in Cx. nigripalpus responses. In landing assays, significantly more females of all species landed on casings with blood than on water controls. There was no difference in landing of Ae. aegypti on bovine or avian blood. However, significantly more females of Cx. quinquefasciatus and Cx. nigripalpus landed on avian blood compared to bovine blood. Blood presented in collagen casings was an effective method for evaluating in-flight attraction and landing in all three species. In the olfactometer, several individual compounds elicited attraction in all species, but none were as attractive as blood for all species. In landing assays, several organic acids and sulfides elicited landing, with Ae. aegypti responding to the greatest number of compounds. These assay methods are effective for evaluation of volatile compounds from blood, and although responses were obtained to several compounds, none were as effective as blood in the olfactometer and landing assays.     

Recent change in the annual pattern of sexually transmitted diseases in the United States

This study analyzed the 1999 to 2003 database of the Center for Disease Control and Prevention (CDC) for seasonal and longer-term time trends in the sexually transmitted diseases (STDs) of chlamydia, gonorrhea, and syphilis in the United States. Linear regression was used to ascertain time trends, and a linear mixed auto-regression model was applied to determine the statistical significance of the major peaks relative to the annualized time series mean. A statistically significant increasing trend during the 5 yr span was documented only in the incidence of chlamydia. No clear annual periodicity was detected in any of the STDs; instead, significant three-month cycles were documented in all the STDs, with prominent peaks evident in March, May, August, and November. The March and May peaks could be associated with the sexual activities of young adults during spring break, which for different colleges and universities, commences as early as mid- to late-February and concludes as late as early- to mid-April, when huge numbers of sexually active youth congregate at beach resort settings. We propose the August peak is representative of summer sexual activity, in particular, of youths during school recess when adult supervision is poor. Finally, the autumn peak seems to be an expression of an endogenous annual rhythm in human reproductive biology, exemplified by elevated levels of testosterone in young males and sexual activity at this time of the year.     

Recent Change in the Annual Pattern of Sexually Transmitted Diseases in the United States

This study analyzed the 1999 to 2003 database of the Center for Disease Control and Prevention (CDC) for seasonal and longer‐term time trends in the sexually transmitted diseases (STDs) of chlamydia, gonorrhea, and syphilis in the United States. Linear regression was used to ascertain time trends, and a linear mixed auto‐regression model was applied to determine the statistical significance of the major peaks relative to the annualized time series mean. A statistically significant increasing trend during the 5 yr span was documented only in the incidence of chlamydia. No clear annual periodicity was detected in any of the STDs; instead, significant three‐month cycles were documented in all the STDs, with prominent peaks evident in March, May, August, and November. The March and May peaks could be associated with the sexual activities of young adults during spring break, which for different colleges and universities, commences as early as mid‐ to late‐February and concludes as late as early‐ to mid‐April, when huge numbers of sexually active youth congregate at beach resort settings. We propose the August peak is representative of summer sexual activity, in particular, of youths during school recess when adult supervision is poor. Finally, the autumn peak seems to be an expression of an endogenous annual rhythm in human reproductive biology, exemplified by elevated levels of testosterone in young males and sexual activity at this time of the year.     

Effects of ''closed'' houses on the Aedes aegypti eradication programme in Trinidad

The effects of closed (i.e. locked) houses on the efficiency of control measures against Aedes aegypti (L.) were monitored weekly for 1 year (March 1981 to February 1982) using ovitraps in the towns of Felicity and Trincity, Trinidad. Regular anti-aegypti activities comprised source reduction, focal treatment with larvicidal 1% temephos sand granules and perifocal treatment with 40% wp fenthion. In Felicity, only 6% of houses were closed and after each treatment cycle ovitrap indices showed 100% control. In Trincity, 32% of houses were closed and after each treatment cycle reductions in ovitrap indices were less than 50%. Ae.aegypti eggs sampled in ovitraps totalled 493 (1-70 per positive paddle) in Felicity and 2310 (1-75 per positive paddle) in Trincity; twenty-three ovitraps were found to be positive in Felicity and 247 in Trincity. Ae.aegypti was successfully eliminated from Felicity during weeks 40-52 using focal/perifocal treatment monitored by ovitraps. Control failure in Trincity was attributed to the survival of untreated Ae.aegypti populations in closed houses. Recommendations to improve gaining access for inspection and treatment of closed houses include having control/surveillance workers commence activities at 06.00 hours on weekdays, to work at weekends or during school holidays, or as a last resort to invoke court orders against householders harbouring Ae.aegypti.     

Dynamics of milk ejection reflex during continuous rhythmic stimulation of areola-nipple complex of the mammary gland

In continuous 10-minute simultaneous action of the vacuum and compression stimuli at a 1 cycle/second frequency, the rate of the milk ejection from the breast was periodically changing in lactating women. The milk flow first peaks latency was 0.5-3.0 minutes, the number of peaks being 2-7 per minute with the inter-peak interval 2-4 minutes during a 10-minute milk ejection. The women revealed an individual pattern of the milk flow peaks. The findings suggest that a central gate mechanism intervenes to set the periodicity of the milk ejection.     

Diel periodicity of emergence of adult citrus rust mites in central Florida

Emergence of adult citrus rust mites, Phyllocoptruta oleivora (Ashmead) from the imagochrysafis occurred with a diel periodicity that peaked between mid morning and early afternoon. The pattern of emergence did not differ for mites reared from eggs held under different photoperiod regimes. The transition of nymphs to the imagochrysalis stage also showed a diel periodicity, occurring in the evening. The average duration of the imagochrysalis stage at 28 °C was 14–15 h.Wetting by rain or dew was simulated by immersing fruit in water each night, but the transition to the imagochrysalis stage or the subsequent emergence pattern of adults was not affected. Adult mites reared from eggs laid during two, consecutive 12-h periods emerged at the same time of day, but the peaks of emergence were separated by 24 h. Eclosion of larvae from eggs laid during two, consecutive 12-h periods did not show a diel periodicity. Eggs continuously immersed in water during their development did not hatch, whereas there was a small, but significant, reduction in the viability of eggs immersed in water each night. These results are discussed in relation to external cues that may entrain the diel patterns of development and adult emergence, and to the adaptive responses of citrus rust mite to cyclic fluctuations of key environmental variables in central Florida. This revised version was published online in August 2006 with corrections to the Cover Date.     

Better to Be in Bad Company than to Be Alone? Aedes Vectors Respond Differently to Breeding Site Quality in the Presence of Others

This study focuses on two competing species, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), both invasive mosquitoes of the New World. Context-specific competition between immature forms inside containers seems to be an important determinant of the coexistence or displacement of each species in different regions of the world. Here, competition experiments developed at low density (one, two or three larvae) and receiving four different resource food concentration, were designed to test whether Ae. albopictus and Ae. aegypti respond differently to competition, and whether competition can be attributed to a simple division of resources. Three phenotypic traits - larval development, adult survival under starvation and wing length - were used as indicators of performance. Larvae of neither species were limited by resource concentration when they were alone, unlike when they developed with competitors. The presence of conspecifics affected Ae. aegypti and Ae. albopictus, inducing slower development, reduced survival and wing length. The response to resource limitation was different when developing with heterospecifics: Ae. aegypti developing with one heterospecific showed faster development, producing smaller adults with shorter lives, while in the presence of two competitors, development increased and adults lived longer. Aedes albopictus demonstrated a better performance when developing with heterospecifics, with no loss in their development period and improved adult survival. Overall, our results suggest that response to competition can not simply be attributed to the division of resources, and that larvae of both species presented large phenotypic plasticity in their response to the presence or absence of heterospecifics and conspecifics.     

Unusual productivity of Aedes aegypti in septic tanks and its implications for dengue control

Increased DEN-2 virus transmission in Puerto Rico during 2005 prompted the implementation of a rapid intervention programme to suppress Aedes aegypti (L.) (Diptera: Culicidae) emergence, which in turn lead to the discovery of previously unknown breeding sites underground. Initially, the following control measures were applied in Playa/Playita (PP), a town of 1,400 households, to all areas where the number of pupae per person exceeded the expected threshold for dengue transmission; all containers likely to be aquatic habitats were turned over and containers too large to turn were treated with 1 p.p.m. methoprene. The impact of these interventions was evaluated by comparing the number of resting adult mosquitoes (by backpack aspiration and sweepnetting in bedrooms) pre-intervention, with numbers at 3 and 5 weeks post-intervention, and by evaluating pupal density at 4 weeks post-intervention in PP and in a nearby town, Coqui (CO; 1500 households), which was not treated. The pre-intervention and post-intervention densities of resting Ae. aegypti adults were significantly larger in the intervention town, although the density of pupae in surface containers was low and similar in both towns at 4 weeks post-intervention. At 3 weeks post-intervention, the density of resting adults decreased by only 18% of pre-intervention levels, but returned to pre-intervention levels 5 weeks after treatment. By contrast, the density of resting adults in CO steadily decreased to 48% and 61%, at 3 and 5 weeks after the initial surveys, respectively. Geographical Information Systems identified significant clustering of adult mosquitoes, which led to the discovery of underground aquatic habitats (septic tanks) that were producing large numbers of Ae. aegypti and Culex quinquefasciatus (Say) in the treated town. We calculated that septic tanks could produce > 18 000 Ae. aegypti and approximately 170 000 Cx quinquefasciatus adults per day. Septic tanks are likely to be common and widespread in suburban and rural Puerto Rico, where, apparently, they can contribute significantly to the maintenance of island-wide dengue virus endemicity.     

Observations on the seasonal prevalence and vertical distribution patterns of oviposition by Aedes aegypti (L.) (Diptera: Culicidae) in urban high-rise apartments in Trinidad, West Indies.

The seasonal prevalence and vertical distribution of oviposition of Aedes aegypti were studied for 53 wk in 1999--2000 using modified ovitraps located at several elevations. The ovitraps were positioned both indoors and outdoors in high-rise apartments in the urban township of John John, Port of Spain, Trinidad, West Indies. Of 988 ovitraps, 490 were collected during the months of the wet season, with 404 (84.4%) positive with 18,536 Ae. aegypti eggs. Of 498 ovitraps collected during the dry season, 335 (67.3%) were positive with 12,255 Ae. aegypti eggs. Data from different elevations showed that significantly more eggs were collected at 13-24 m elevations than any other elevation. The results suggest that the invasion of high rise ecosystems by Ae. aegypti can enhance transmission of dengue. This ecological shift in the Ae. aegypti population exploited new habitats associated with human activity, suggesting that strategies should be developed to educate householders as well as creating appropriate vector control measures to prevent future threats of dengue transmission.     

Serum insulin,glucose and lactate concentrations during 18-h fast in female reindeer

We investigated whether secretion of insulin occurred in the absence of feeding in a ruminant. Serum insulin, glucose and lactate concentrations were measured in three adult non-pregnant reindeer at hourly intervals during an 18-h fast (17:30-11:30 h) in October. Mean serum insulin concentration was 39+/-3 micro/ml (range 2-100). The insulin profile of two animals was characterized by a nocturnal rise and an early morning trough, followed by a mid-morning rise. Within the larger peaks, short-term oscillations occurred at 2-3-h intervals. Serum glucose concentrations significantly increased during the fast and exceeded feeding values by 31-45% at 18 h post feeding. Serum lactate concentrations declined significantly in all three animals. Residuals for serum glucose concentrations were significantly negatively correlated to residuals of serum lactate in two animals, but not the third. Serum glucose and lactate concentrations were not related to serum insulin. In conclusion, insulin secretion in reindeer shows a 2-3-h periodicity in the absence of feeding. The periodicity is of similar duration as the inter-meal interval for pen-fed reindeer during winter (2.5 h). Although not necessarily causal, the results are consistent with a hypothesized role for insulin in meal initiation.     

Prevalence and seasonality of Ascogregarina culicis (Apicomplexa: Lecudinidae) in natural populations of Aedes aegypti (Diptera: Culicidae) from temperate Argentina

Ascogregarina infections from South America were recently documented in Brazil and Argentina. The aim of this study was to report our recent findings on the prevalence and seasonality of Ascogregarina culicis in Aedes aegypti adults from temperate Argentina. Between December 2003 and May 2005, 391 females of Ae. aegypti were captured in two areas of Greater Buenos Aires. Overall prevalence of A. culicis was 21.2% (83/391), and a significant difference was observed between both areas (28.4% vs. 8%). Infected Ae. aegypti were found from November to May, with highest values in March (24-37%). Parasite prevalence and host abundance showed similar seasonal patterns. Our observations suggest a widespread infestation of A. culicis among Ae. aegypti populations from temperate Argentina.     

Water Level Flux in Household Containers in Vietnam - A Key Determinant of Aedes aegypti Population Dynamics

We examined changes in the abundance of immature Aedes aegypti at the household and water storage container level during the dry-season (June-July, 2008) in Tri Nguyen village, central Vietnam. We conducted quantitative immature mosquito surveys of 171 containers in the same 41 households, with replacement of samples, every two days during a 29-day period. We developed multi-level mixed effects regression models to investigate container and household variability in pupal abundance. The percentage of houses that were positive for I/II instars, III/IV instars and pupae during any one survey ranged from 19.5-43.9%, 48.8-75.6% and 17.1-53.7%, respectively. The mean numbers of Ae. aegypti pupae per house ranged between 1.9-12.6 over the study period. Estimates of absolute pupal abundance were highly variable over the 29-day period despite relatively stable weather conditions. Most variability in pupal abundance occurred at the container rather than the household level. A key determinant of Ae. aegypti production was the frequent filling of the containers with water, which caused asynchronous hatching of Ae. aegypti eggs and development of cohorts of immatures. We calculated the probability of the water volume of a large container (>500L) increasing or decreasing by ≥20% to be 0.05 and 0.07 per day, respectively, and for small containers (<500L) to be 0.11 and 0.13 per day, respectively. These human water-management behaviors are important determinants of Ae. aegypti production during the dry season. This has implications for choosing a suitable Wolbachia strain for release as it appears that prolonged egg desiccation does not occur in this village.     

Biomechanics of skateboarding: kinetics of the Ollie

Seven top amateur or professional skateboarders (BW=713 N+/-83 N) performed Ollie maneuvers onto and off an elevated wooden platform (45.7 cm high). We recorded ground reaction force (GRF) data for three Ollie Up (OU) and Ollie Down (OD) trials per participant. The vertical GRF (VGRF) during the OU has a characteristic propulsive peak (M=2.22 body weight [BW]+/-0.22) resulting from rapidly rotating the tail of the board into the ground to propel the skater and board up and forward. The anterior-posterior (A-P) GRF also shows a pronounced peak (M=0.05+/-0.01 BW) corresponding with this propulsive VGRF peak. The initial phase of landing in the OD shows an impact peak in VGRF rising during the first 30 to 80 ms to a mean of 4.74+/-0.46 BW. These impact peaks are higher than expected given the relatively short drop of 45.7 cm and crouched body position. But we observed that our participants intentionally affected a firm landing to stabilize the landing position; and the Ollie off the platform raised the center of mass, also contributing to higher forces.     

Distribution and environmental synchronization of the marine insect, Halobates robustus, in the Galapagos islands.

The following three aspects of the biology of the marine insect Halobates robustus were studied, during a two week observation period, at several sites in the Galapagos Islands: distribution, aggregation behaviour and rhythmicity of locomotory activity. H. robustus occurred in highest numbers on the water surface at shores fringed with mangroves. The aggregations of H. robustus varied according to their location and density. Copulating adults formed dense, floating aggregations, which tended to be close to rocks or mangroves. Late instar nymphs were less aggregated and, in lagoons (where there was some shelter from direct tidal forces), were furthest from the shore. In two types of habitat (mangrove-fringed, sandy shores and rocky shores) the aggregations of H. robustus showed a pronounced ability to maintain a floating station in relation to the surrounding environment, irrespective of tidal movements (in one case at 34 m from the nearest fixed objects). Evidence of the ability of the aggregations to maintain station on the water surface was also obtained by comparing the movements of H. robustus with those of floating polystyrene particles, which move passively with wind and tide. Laboratory observations and experiments indicated no clear periodicity in locomotory movements throughout a 24 h period. However, the frequency of encounters between individuals showed two daily peaks, post-dawn and pre-dusk, with fewer encounters during the day and only occasional encounters during the night. By shifting the light-dark cycle it was demonstrated that the daily bimodal rhythm of encounters is triggered by dawn and, since it is not maintained in constant light or dark, an 'hour-glass' mechanism is suggested. The contributions of single adults, of copulating pairs and of immature stages to the overall pattern of activity were also determined. Immature stages did not affect the overall rate of encounters significantly and the interactions between single and copulating pairs of adults appear to have been responsible for the bimodal pattern.     

Effects of Toxorhynchites moctezuma larval predation on Aedes aegypti populations: experimental evaluation

Abstract. Predatory larvae of the mosquito Toxorhynchites moctezuma were used experimentally to control a standing crop of larvae of the dengue vector mosquito Ae.aegypti. Each week, fifty Ae.aegypti first instar larvae were introduced to each of five water-filled drums (220 litres) of the type commonly used for domestic water storage in Caribbean dwellings. At the beginning of the fourth week, a certain number (0, 1, 2, 5 or 10) of first instar Tx.moctezuma larvae were introduced to each drum and the daily yield of Ae.aegypti adults from each drum was monitored thereafter. The experiment was repeated three times. With only one or two Tx.moctezuma larvae, predation on Ae.aegypti larvae stopped the output of Ae.aegypti adults for 1 week. Five or ten Tx. moctezuma prevented any Ae.aegypti emergence for up to 16 weeks. Cannibalism among Tx. moctezuma larvae was seldom observed and appeared not to be a hindrance in using this species against Ae.aegypti. Thus Tx.moctezuma is regarded as a good candidate for the biological control of Ae.aegypti by augmentative releases.     

Haemoproteus columbae: course of infection, relapse and immunity to reinfection in the pigeon.

Studies were performed on the course of infection, relapse, and immunity to reinfection in 11 young pigeons infected with the avian malaria parasite Haemoproteus columbae Kruse. The prepatent period in our experiments varied between 22 and 37 days. The intensity and length of the initial infection period showed wide variations. During this period an initial periodicity of gametocyte production of about 12 days with peaks at about 6-8 and 18-20 days after patency was observed. The various modes of infection (fly bite, intramuscular, intravenous, or intraperitoneal inoculation of sporozoites) did not influence the intensity of the initial infection. No pathogenicity due to heavy infection with the parasite was observed. There was no periodicity of relapse occurrence, nor any correlation between the frequency of relapse and the intensity of the initial infection, and the phenomenon was not influenced by seasonal changes. Pigeons (Columba livia) that had recovered from previous infections were susceptible to reinfection, whereas pigeons with chronic infection acquired immunity (premunition).     

Long-term effects of Bacillus thuringiensis subsp. israelensis on Aedes aegypti.

Immediate (24 hours exposure) and long-term (until the emergence of the adults) effects of different doses of a primary powder of Bacillus thuringiensis subsp. israelensis (B.t.i.) against first and second instar Aedes aegypti larvae were monitored. The long-term effect was dose-dependent and was materialized by a prolongation of the preimaginal development and continuous cumulative mortality until the emergence of the adults. Mortality values were higher during the fourth larval instar and the pupal stage. Some of the larvae reaching the fourth instar were smaller in size and remained in this state a 2-4 times longer period than in the control and finally died as larvae or very small pupae. The long-term effect was more intense as the treatment was applied earlier during the larval development. The correlation of the immediate lethal effect with the late effect allows the evaluation of the total impact of a larvicidal treatment.