Evidence for a negative fitness-density relationship between parent density and offspring quality for two Xenopsylla spp. parasitic on desert mammals

We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.     

Development rates of two Xenopsylla flea species in relation to air temperature and humidity

The rate of development of immature fleas, Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) was studied in the laboratory at 25 degrees C and 28 degrees C with 40, 55, 75 and 92% relative humidity (RH). These fleas are separately associated with the host jird Meriones crassus Sundevall in different microhabitats of the Ramon erosion cirque, Negev Highlands, Israel. This study of basic climatic factors in relation to flea bionomics provides the basis for ecological investigations to interpret reasons for paratopic local distributions of these two species of congeneric fleas on the same host. Both air temperature and RH were positively correlated with duration of egg and larval stages in both species. Change of humidity between egg and larval environments did not affect duration of larval development at any temperature. At each temperature and RH, the eggs and larvae of X. ramesis did not differ between males and females in the duration of their development, whereas female eggs and larvae of X. conformis usually developed significantly faster than those of males. For both species, male pupae developed slower than female pupae at the same air temperature and RH. Air temperature, but not RH, affected the duration of pupal development. At each humidity, duration of the pupal stage was significantly longer at 25 degrees C than at 28 degrees C: 15.3+/-1.7 vs. 11.7+/-1.2 days in X. conformis; 14.1+/-2.0 vs. 11.5+/-1.7 days in X. ramesis, with a significantly shorter pupal period of the latter species at 25 degrees C. These limited interspecific bionomic contrasts in relation to basic climatic factors appear insufficient to explain the differential habitat distributions of X. conformis and X. ramesis.     

Metabolic rate and jump performance in seven species of desert fleas

We hypothesized that sexual and interspecific differences in jumping performance of fleas found in our previous study are correlated with differences in resting metabolic rate (RMR) between sexes and among species. To test this hypothesis, we measured RMR of seven flea species (Xenopsylla conformis mycerini, Xenopsylla ramesis, Xenopsylla dipodilli, Parapulex chephrenis, Synosternus cleopatrae pyramidis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis). We compared RMR between sexes and among species and examined whether there is intra- and interspecific correlation between RMR and jumping ability. Both mass-specific and mass-independent RMR were the highest in female S. t. medialis, whereas mass-specific RMR was the lowest in male X. dipodilli and mass-independent RMR was the lowest in three Xenopsylla species and P. chephrenis. Mass-specific and mass-independent RMR were significantly higher in females than in males in all fleas except S. t. medialis. Differences in jumping ability between males and females were found to be correlated with sexual differences in mass-specific or mass-independent RMR. Interspecific comparison showed that the length of jump in both male and female fleas was strongly affected by their mass-specific and mass-independent RMR.     

Larval interspecific competition in two flea species parasitic on the same rodent host

Abstract.  1. The fleas Xenopsylla conformis and Xenopsylla ramesis exploit the same rodent host, Meriones crassus , and replace each other between two different habitats situated at the opposite sides of a steep precipitation gradient. It was hypothesised that the reason for this paratopic distribution is competition between larvae of the two species for food resources.
2. This hypothesis was tested by studying the performance of larvae of the two species in terms of their developmental success in mixed-species and single-species treatments under different air temperatures, relative humidities, substrate textures, and food abundance.
3. The number of individuals of X. conformis that survived until emergence depended significantly on the presence of competing species, being, in general, lower in mixed-species compared with single-species treatments. The decrease in developmental success of X. conformis in mixed-species treatments was found mainly during food shortage. In contrast, presence of the competitor did not affect the number of X. ramesis that survived until emergence. No effect of the presence of the competitor on duration of development or sex ratio was found in either species.
4. The results of this study, together with the results of our previous studies, provide an explanation for the paratopic distribution of X. conformis and X. ramesis that exploit the same host species.     

Respiratory gas exchange in the desert flea Xenopsylla ramesis (Siphonaptera: Pulicidae): response to temperature and blood-feeding

Xenopsylla ramesis is a flea species parasitizing gerbilline rodents in the deserts of the Middle East. This study was undertaken to determine metabolic requirements of the different developmental stages of the flea-life cycle as well as to investigate the metabolic response to temperature and starvation after blood feeding. A high resolution respirometry system was used to measure CO2 emission of fleas ranging in size from 0.166+/-0.006 mg (larvae) to 0.263+/-0.009 mg (adults). The free-living stages (larvae and adults) had significantly higher metabolic rates than the cocooned stages (pupae). CO2 emission rates of the larvae exceeded that of the adults by 2.6-fold and the pupae by 7.3 times. In the adults, both temperature and blood feeding significantly affected starvation-level metabolism. Metabolism was temperature dependent with an average Q10 of 2.57 for females and 2.55 for males over the temperature range of 10-30 degrees C. No consistent decline in thermal sensitivity at higher ambient temperatures was evident. Fleas that had a blood meal prior to starvation had significantly higher metabolic rates (0. 86 +/- 0.008 x 10(-3) ml mg(-1) h(-1)) than fleas, which were newly emerged unfed adults (0.56 +/- 0.1 x 10(-3) ml mg(-1) h(-1)). Water content also differed between fed (range approx. 67-69% body mass) and newly emerged adults (range approx. 73-75% of body mass). Feeding may stimulate some as yet undetermined physiological process that causes differential metabolic response in starving, fed and unfed fleas. Characteristics of gas exchange in desert-dwelling fleas are reflective of the off-host life style in the protected microenvironment of the host nest or burrow, rather than as a response to any type of environmental extreme.     

Density-dependent host selection in ectoparasites: An application of isodar theory to fleas parasitizing rodents

Parasites should make the same decisions that every animal makes regarding fitness reward. They can maximize reproductive success by selection of those habitats that guarantee the greatest fitness output. We consider the host population as a habitat of a parasite population. Consequently, hosts (=habitats) that differ quantitatively or qualitatively will support different numbers of parasites. The nature of habitat selection can be detected by isodars, lines along which habitat selection yields equivalent fitness reward. We applied this approach to study host selection of five fleas, each infesting two desert rodents. Xenopsylla conformis, Xenopsylla ramesis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis parasitize Gerbillus dasyurus and Meriones crassus. Synosternus cleopatrae pyramidis parasitizes Gerbillus andersoni allenbyi and Gerbillus pyramidum. Three fleas ( X. conformis, X. ramesis and S. c. pyramidis) were able to perceive quantitative (amount of the resource; e.g. organic matter in the nest for flea larvae) and/or qualitative (pattern of resource acquisition; e.g. host defensiveness) differences between hosts. Two other fleas did not perceive between-host differences. X. conformis was a density-dependent host selector that showed sharp selectivity at low density. X. ramesis and S. c. pyramidis were density-independent host selectors with a direct correspondence of density with habitat quality. N. i. theodori and S. t. medialis were non-selectors with no relationship at all between density and host quality. The results of the application of the isodar theory suggest that ectoparasites, like other animals, behave as if they are able to make choices and decisions that favour environments in which their reproductive benefit is maximized.     

黄曲条跳甲室内饲养方法的改进

介绍一种饲养黄曲条跳甲Phyllotreta striolata(Fabricius)的改进新方法,采用分隔式养虫笼饲养成虫和萝卜"凹"型孔饲养幼虫,结果表明,使用该方法进行饲养,卵的成活率可达89.3%,1~3龄幼虫的存活率为65.0%~70.0%,蛹的存活率达80.0%,可以有效实现黄曲条跳甲的室内饲养。     

Investigation of Bartonella acquisition and transmission in Xenopsylla ramesis fleas (Siphonaptera: Pulicidae)

Bartonella are emerging and re-emerging pathogens affecting humans and a wide variety of animals including rodents. Horizontal transmission of Bartonella species by different hematophagous vectors is well acknowledged but vertical transmission (from mother to offspring) is questionable and was never explored in fleas. The aim of this study was to investigate whether the rodent flea, Xenopsylla ramesis, can acquire native Bartonella from wild rodents and transmit it transovarially. For this aim, Bartonella-free laboratory-reared X. ramesis fleas were placed on six naturally Bartonella-infected rodents and six species-matched Bartonella-negative rodents (three Meriones crassus jirds, two Gerbillus nanus gerbils and one Gerbillus dasyurus gerbil) for 7 days, 12-14h per day. The fleas that were placed on the Bartonella-positive rodents acquired four different Bartonella genotypes. Eggs and larvae laid and developed, respectively, by fleas from both rodent groups were collected daily for 7 days and molecularly screened for Bartonella. All eggs and larvae from both groups were found to be negative for Bartonella DNA. Interestingly, two of five gut voids regurgitated by Bartonella-positive fleas contained Bartonella DNA. The naturally infected rodents remained persistently infected with Bartonella for at least 89 days suggesting their capability to serve as competent reservoirs for Bartonella species. The findings in this study indicate that X. ramesis fleas can acquire several Bartonella strains from wild rodents but cannot transmit Bartonella transovarially.     

苯醚威作用于印鼠客蚤的组织学研究

【目的】通过研究苯醚威对印鼠客蚤 Xenopsylla cheopis (Rothschild,1903)的早 3 龄幼虫和未吸血新羽化成虫的组织学变化,探讨其灭蚤机理,为鼠疫媒介蚤种的防治提供基础资料。【方法】以微量点滴法将苯醚威施药于印鼠客蚤早3龄幼虫和未吸血新羽化成虫,采用组织学、显微摄影及统计学方法观察组织变化。【结果】经苯醚威作用后,印鼠客蚤的早 3 龄幼虫的表皮增厚、卵巢芽生殖细胞萎缩、睾丸芽精原细胞间质减少;未吸血新羽化成虫的睾丸塞消失快、唾液腺细胞破坏严重、中肠上皮细胞萎缩。【结论】(1)苯醚威通过干扰印鼠客蚤幼虫的变态,引起幼虫表皮、生殖芽异常改变,不能发育为成虫而死亡;(2)苯醚威可加速印鼠客蚤新羽化雄性成虫的睾丸塞吸收;(3)苯醚威可破坏印鼠客蚤新羽化成虫的唾液腺细胞,并引起中肠上皮细胞萎缩。     

Annual cycles of four flea species in the central Negev desert

Bionomics of fleas (Siphonaptera) parasitizing rodent hosts, mostly the gerbil Gerbillus dasyurus (Wagner) and the jird Meriones crassus Sundevall (Gerbillidae), were investigated in the central Negev desert of Israel. Populations were sampled weekly (by Sherman trapping of hosts) from August 2000 to July 2001. Among 1055 fleas of nine species captured, four species predominated (94%). Two species of Pulicidae, Xenopsylla dipodilli Smit and X. ramesis (Rothschild), reproduced perennially, whereas adults of Nosopsyllus iranus theodori Smit (Ceratophyllidae) and Stenoponia tripectinata medialis Jordan (Hystrichopsyllidae) occurred only in cool months (October-March). During their main activity season on the most infested host species (estimated from > 300 trap-nights/month), prevalence of these four flea species reached 40-70%, 20-30%, 100% and 50-70%, respectively, with infestation intensities of 2-2.7, 7-12, 2-3.5 and 2.5-7 fleas per infested rodent, respectively. Xenopsylla dipodilli oviposition peaked during autumn with parous rate > 80% by September-October. During December-April, the majority of X. dipodilli females were immature and/or nulliparous (defined as having mature ovaries but no follicular relics). In contrast, X. ramesis had two reproductive peaks, in mid-spring and autumn, evidenced by the influx of immature females in late spring and summer (30-40%) and in winter (20-30%) after maximal parous rates: 80-100% in March-April and 95-100% in October-November. Nosopsyllus iranus theodori and Stenoponia tripectinata medialis adults occurred only during cool months. At the beginning of activity, during October-November, the sex ratio of N. i. theodori was strongly biased to females (86%) that were immature and/or nulliparous. In winter, adult females were 52-65% parous and 10-32% immature. In March, as the adult population of N. i. theodori declined, 78% of females were parous and 12% immature. Seasonal activity of S. t. medialis (November-March) was shorter than for the other three species; females were predominantly nulliparous in November (80%), after which the proportion of parous females increased gradually to 84% in February. Two females of S. t. medialis collected in March were mature but nulliparous, suggesting that this species of flea might 'oversummer' (as pupae or teneral adults) in the cocooned stage.     

Lack of transovarial transmission of Bartonella by rodent fleas

In this issue of Molecular Ecology, Morick et al. (2011) present an interesting study of acquisition and transmission of Bartonella by Xenopsylla ramesis fleas (Fig. 1) which infest naturally wild desert rodents from the Negev desert. A major issue with vector-borne diseases and vector-borne infection is to know whether the vector can also be a natural reservoir and transmit the infectious agent transovarially, allowing the infection to be perpetuated through successive generations of vectors. The desert flea, X. ramesis, is a flea species parasitizing gerbilline rodents in the deserts of the Middle East (Fielden et al. 2004).     

Feeding performance of fleas on different host species: is phylogenetic distance between hosts important?

We asked if and how feeding performance of fleas on an auxiliary host is affected by the phylogenetic distance between this host and the principal host of a flea. We investigated the feeding of 2 flea species, Parapulex chephrenis and Xenopsylla ramesis, on a principal (Acomys cahirinus and Meriones crassus, respectively) and 8 auxiliary host species. We predicted that fleas would perform better (higher proportion of fleas would feed and take larger bloodmeals) on (a) a principal rather than an auxiliary host and (b) auxiliary hosts phylogenetically closer to a principal host. Although feeding performance of fleas differed among different hosts, we found that: (1) fleas did not always perform better on a principal host than on an auxiliary host; and (2) flea performance on an auxiliary host was not negatively correlated with phylogenetic distance of this host from the principal host. In some cases, fleas fed better on hosts that were phylogenetically distant from their principal host. We concluded that variation in flea feeding performance among host species results from interplay between (a) inherent species-specific host defence abilities, (b) inherent species-specific flea abilities to withstand host defences and (c) evolutionary tightness of association between a particular host species and a particular flea species.     

荒漠昆虫光滑鳖甲（鞘翅目：拟步甲科：鳖甲族）的人工饲养方法

为了解决深入研究荒漠甲虫环境适应机制时所遇到的各发育阶段试虫材料短缺的问题,本文介绍了饲养拟步甲科鳖甲族昆虫光滑鳖甲Anatolicapolita Kaszab的有效方法。将早春季节在野外采集的成虫饲养在2L的塑料烧杯中,收集卵。用玻璃培养皿孵育卵;用改装的盛有沙土的矿泉水瓶单只饲养3龄以上幼虫,以防止幼虫自相残杀。为保持幼虫饲养瓶内的适当湿度,在瓶子底部加入72mL的水,再装入800g沙子,借助毛细现象,形成渐变式含水基质,在最上层的干沙表面加麦麸以饲养幼虫。如需观察计数,可将预蛹、蛹和初孵成虫置于玻璃培养皿中培养。采用此方法饲养的光滑鳖甲可顺利完成生活史,其卵的孵化率为68．67％±2．45％,1—2龄幼虫的存活率为82．95％±7．72％,3～9龄幼虫的存活率为73．80％±4．95％;预蛹、蛹和幼嫩成虫的存活率分别为84．68％±2．55％、88．45％±2．75％和90．56％±4．20％。该方法可以有效实现光滑鳖甲的室内饲养,并可用于其他一些沙栖拟步甲科昆虫的人工饲养。     

Effects of a juvenoid, DPE-28, on biology and behaviour of Culex quinquefasciatus, the human filariasis vector

Studies on the effect of a juvenoid, DPE-28 (2,4-dinitrophenyl-2',6'-di-tertiarybutyl phenyl ether) on biology and behaviour of Cx. quinquefasciatus showed that the developmental duration, sex ratio, mating success and blood feeding were considerably affected by the exposure of larvae and pupae to the compound. Exposure of fourth instar larvae to 0.007 (EI90) and 0.0019 (EI50) ppm of DPE-28 prolonged the duration of pupation by 58.6 and 52.4 hr and delayed the adult emergence by 35.4 and 17.7 hr in males and 36.8 and 21.1 hr in females respectively. Exposure of freshly ecdysed pupae to 10 and 5 ppm delayed the adult emergence with respect to the control by 54.3 and 32.4 hr in males and 55.2 and 33.2 hr in females respectively. The sex ratio of the adults emerged from treated larvae and pupae was also affected. The female mosquitoes that survived from the exposed fourth instar larvae and pupae exhibited a low blood engorgement ratio. This depression in blood feeding was more pronounced in adults emerged from treated pupae than that of treated fourth instar larvae. A significant proportion of adults emerged from treated larvae and pupae were able to feed only partially. Mating success of the treated populations declined considerably when crosses were made between the males and females emerged from treated fourth instar larvae and pupae. The adults emerged from treated larvae and pupae showed a significant reduction in the oviposition.     

In vitro survival of human pathogenic fungi in Hawaiian beach sand.

In vitro studies utilizing 4 pathogenic fungi, Trichosporon cutaneum, Candida albicans, Microsporum gypseum and Trichophyton mentagrophytes, all known from Hawaiian beaches, indicate that they survive in the fluctuating beach habitat where they can serve as potential sources of infection for significant periods of time. Survival was measured by testing the viability of propagules at intervals for 6 months. All species survived 6 months under 1 or more experimental conditions. Survival patterns showed both increases and decreases depending upon the given parameters designed to simulate various beach conditions. Propagules inoculated on hair and horn (keratinized inoculum) did not remain viable longer than propagules from pure culture suspensions (non-keratinized). Microbial antagonism was not a major factor in survival. All species survived at least 1 month in non-sterile sand inoculated with keratinized propagules. This condition approximated the natural sand habitat. Alternate wetting and drying of sand caused an overall decrease in survival time except for M. gypseum (non-keratinized inoculum) at 37 degrees C in sterile sand and T. mentagrophytes (keratinized inoculum) at 37 degrees C in non-sterile sand. Temperature was important: increasing temperature resulted in a general decrease in survival time; 45 degrees C was definitely inhibitory, with the exception of T. cutaneum which survived that level for 6 months (keratinized inoculum). Salinity did not influence survival.     

一种珍稀蝴蝶大帛斑蝶Idea leuconoe(Eriehson)的人工饲养方法

【目的】针对现有大帛斑蝶Idea leuconoe(Eriehson)饲养方法中无法有效回避高温造成的成虫大量死亡,卵空壳或干瘪失水的问题,本研究发明了一种新的繁殖网纹室来规模化人工饲养大帛斑蝶的方法。【方法】本研究测定了在新发明和普通繁殖网纹室的饲养下,大帛斑蝶的存活、交配成功率、产卵量和卵孵化率,并对新发明和普通繁殖网纹室之间的参数进行了对比。【结果】采用新发明繁殖网纹室饲养的大帛斑蝶幼虫化蛹率为90.75%±1.12%,蛹羽化率为91.36%±2.43%,均维持在90%以上,均极显著高于普通繁殖网纹室;从幼虫发育到成虫的存活率为82.93%±2.55%,也极显著高于普通繁殖网纹室;在15日龄内,相对于普通繁殖网纹室,新发明繁殖网纹室饲养的存活的成虫,取食频率较高,活跃性较高,虫体比较健壮,且此时成虫存活率显著较高,为81.22%±2.07%;利用新发明繁殖网纹室饲养的成虫,其雌蝶交配成功率为81.67%±4.77%,每雌产卵量为(269.32±9.85)粒,卵孵化率为85.88%±1.93%,均极显著高于普通繁殖网纹室;本研究新发明的繁殖网纹室,可以有效的营造一个温度显著低于空气温度的小环境,供大帛斑蝶躲避高温灼伤。【结论】通过在本研究新发明繁殖网纹室的饲养,大帛斑蝶存活率、交配成功率和繁殖力均维持在较高的水平上,显著高于普通繁殖网纹室,能够保证为市场提供充足的大帛斑蝶虫源,避免农民养殖户的损失。     

Larvae and pupae of two North American darkling beetles (Coleoptera,Tenebrionidae, Stenochiinae), Glyptotus cribratus LeConte and Cibdelis blaschkei Mannerheim,with notes on ecological and behavioural similarities

This study describes and illustrates the larvae and pupae of two North American darkling beetles (Coleoptera: Tenebrionidae) in the subfamily Stenochiinae, Glyptotus cribratus LeConte from the southeastern United States, and Cibdelis blaschkei Mannerheim from California. Both species inhabit forested regions where adults and larvae occur in soft rotten dry wood of dead branches on living trees or in sections recently fallen from them. Species identity was confirmed by rearing of adults and pupae and the discovery of both in pupal cells with associated exuvia. Specimen label data and notes on habitats are provided. Antipredator defense structures and behaviour are noted for larvae and pupae of both species.     

Temperature-dependent post-diapause development and prediction of spring emergence of the pine needle gall midge (Dipt., Cecidomyiidae)

Abstract:  We determined the influence of temperature on post-diapause development of overwintered Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae) under various treatments (12, 15, 18, 21, 24, 27 and 30°C) in an effort to predict its spring emergence. Survival and developmental period for the overwintered larvae and pupae were significantly influenced by temperature. Linear and nonlinear regression models quantitatively described temperature-dependent development and survival of T. japonensis . The survival models exhibited right-skewed bell shape patterns for all stages, indicating a more detrimental impact on survival at high temperatures. Theoretical optimum temperatures with highest survival were 22.3, 24.0 and 24.0°C for the overwintered larvae, pupae and total post-diapause development (the larvae to adults) respectively. Pupal mortality was higher at all temperatures than larval mortality and the suitable range of temperature for pupae was narrower than that of larvae. The nonlinear Briere model estimated that optimum temperatures with the fastest development were 29.1°C for larvae, 27.6°C for pupae and 27.0°C for larvae to adults. In a linear model, the lower threshold temperatures were 5.1, 7.1 and 5.9°C for larvae, pupae, and larvae to adults respectively. A predictive degree-day model was developed using trap catches of T. japonensis adult emergence during 1991–1995. The model accounted for 84.6% of year-to-year variation in adult emergence and predicted accurately the median emergence time in 1996.     

Vertical nontransovarial transmission of Bartonella in fleas

Pathogens use diverse pathways to infect host populations by vertical and/or horizontal routes. Horizontal transmission of bacteria belonging to the Bartonella genus via haematophagous vectors is well known. Vertical transmission of Bartonella species was also suggested to occur but its routes remain to be unveiled. In a previous study, we showed the absence of transovarial transmission of Bartonella species OE 1‐1 in Xenopsylla ramesis fleas, and that fleas feeding on Bartonella‐positive jirds produced Bartonella‐positive gut voids. This current study aimed to investigate whether vertical nontransovarial transmission of Bartonella occurs in fleas. For this aim, the X. ramesis–Bartonella sp. OE 1‐1 model was used. Four groups of fleas including Bartonella‐positive and Bartonella‐negative female fleas and larval offspring had access to either Bartonella‐negative or Bartonella‐positive gut voids and faeces. Sixteen per cent of flea offspring that had access to Bartonella‐positive faeces and gut voids became Bartonella positive. Our findings demonstrate that Bartonella‐positive flea faeces and gut voids are proper infection sources for flea larvae and indicate that vertical nontransovarial transmission of bartonellae occurs in fleas. This information broadens our understanding of Bartonella transmission routes in flea vectors and enlightens pathways of bartonellae transmission and maintenance in flea populations in nature.     

Different responses of two floodwater mosquito species, Aedes vexans and Ochlerotatus sticticus (Diptera: Culicidae), to larval habitat drying.

Insect larvae that live in temporary ponds must cope with a rapidly diminishing resource. We tested the hypothesis that floodwater mosquitoes would react to diminishing water levels by accelerating larval development time and emerging as smaller adults. Since a reduction in habitat size leads to increased larval densities, we also included two larval densities. Newly-hatched floodwater mosquito larvae, Aedes vexans (87.9% of emerged adults) and Ochlerotatus sticticus (12.0% of emerged adults), were taken from the field and randomly assigned to one of three water level schedules. Survival to adult emergence was significantly affected by the water level schedule. Ae. vexans adults emerged later in the decreasing schedule than the constant water schedule, but time to emergence was not affected by larval density. In the drying water schedule, Ae. vexans adults emerged 6 to 14 days after complete water removal. Adult size was significantly affected by both water level schedule and larval density. Adults of Oc. sticticus emerged earlier in the decreasing than the constant water schedule which was in accordance with our hypothesis, but size was not affected. Our results indicate two different responses of two floodwater mosquito species to diminishing larval habitat. Oc. sticticus accelerated larval development while Ae. vexans larvae showed remarkable survival in humid soil. Both species are often numerous in inundation areas of large rivers, and climatic conditions after a flood might influence which species dominates the adult mosquito fauna.