Mosquito (Diptera: Culicidae) fauna in inland areas of south-west Western Australia

Abstract  Previously existing sources of data regarding mosquitoes in inland areas of south-west Western Australia are few and qualitative in nature. This is the first attempt to quantitatively investigate mosquito fauna in this region. The existing data are reviewed and compared with the results of the quantitative surveys presented in this paper. Temporal comparisons appear to indicate that mosquito community structure in the region may have changed since the initial surveys in the 1950s from a combination of freshwater-breeding species towards a strong dominance of Aedes camptorhynchus (Thomson), a major vector of Ross River virus in southern Australia. It is speculated that this shift may have been brought about by the increasing area and severity of dryland salinity in the region over the last century, and also may increase the potential for Ross River virus disease transmission.     

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax     

Eggs of the Australian saltmarsh mosquito,Aedes camptorhynchus,survive for long periods and hatch in instalments: implications for biosecurity in New Zealand

The Australian saltmarsh mosquito, Aedes camptorhynchus (Diptera: Culicidae), is a significant biting pest and disease vector and is the subject of an eradication programme in New Zealand (NZ), where it has been resident for more than 10 years. To better understand the ecology of this common and widespread pest, we studied egg longevity and hatching patterns in the laboratory. By regularly testing for the presence of viable embryos, we found that eggs may last more than 15 months when stored dry (13% viable at this time). Eggs display instalment hatching, with no more than 56% of a batch hatching upon first inundation. Further hatching may occur for at least six inundations and some unhatched eggs may remain viable even after this. Variation in hatching rates can be observed using different water types, with weaker hatching media stimulating lower hatching rates spread over more inundations. By applying average hatching rates to a non‐linear model of natural egg attrition, we showed that egg batches exposed to three inundations should be exhausted (zero live eggs present) in approximately 11 months at the conditions tested here. These findings have implications for the current eradication programme for Ae. camptorhynchus in NZ and for our understanding of the ecology of a widespread and common disease vector in Australia.     

Adult mosquito trap sensitivity for detecting exotic mosquito incursions and eradication: a study using EVS traps and the Australian southern saltmarsh mosquito, Aedes camptorhynchus

Adult mosquito traps are commonly used in biosecurity surveillance for the detection of exotic mosquito incursions or for the demonstration of elimination. However, traps are typically deployed without knowledge of how many are required for detecting differing numbers of the target species. The aim of this study was to determine the sensitivity (i.e., detection probability) provided by carbon dioxide-baited EVS traps for adult female Australian southern saltmarsh mosquitoes, Aedes camptorhynchus, a recent biosecurity problem for New Zealand. A mark-release-recapture study of three concurrently released cohorts (sized 56, 296, and 960), recaptured over four days with a matrix of 20 traps, was conducted in Australia. The detection probability for different numbers of traps and cohorts of different sizes was determined by random sampling of recapture data. Detection probability ranged from approximately 0.3 for a single trap detecting a cohort of 56 mosquitoes to 1.0 (certainty of detection) when seven or more traps were used. For detection of adult Ae. camptorhynchus around a known source, a matrix of traps provides a strong probability of detection. Conversely, the use of single traps deployed over very large areas to detect mosquitoes of unknown entry pathway is unlikely to be successful. These findings have implications for the design of mosquito surveillance for biosecurity.     

Distribution of saltmarsh plant communities associated with environmental factors along a latitudinal gradient on the south‐west Atlantic coast

Aim To produce an inventory of south‐west Atlantic saltmarshes (from latitude 31°48′ S to 43°20′ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographical variation of the main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of the reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, while the upper zones are occupied by more halophytic species) previously described; and to compare these south‐west Atlantic saltmarshes with others world‐wide. Location South‐western Atlantic saltmarshes Methods Field samples of dominant emergent plant species positioned by the global positioning system (GPS) were obtained from most coastal saltmarshes (14) between southern Brazil and northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field. Results Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., Spartina densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km², comprising 380 km² of Sp. alterniflora marsh, 366 km² of Sp. densiflora marsh, 746 km² of Sar. perennis marsh and 641 km² of brackish marsh (dominated by Juncus acutus L., Juncus kraussii Hochst., Scirpus maritimus L., Scirpus americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) Sp. densiflora and brackish species,(2) Sp. alterniflora and Sar. perennis and (3) Sp.densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The south‐west Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (< 0.5 to > 2.5 m) from latitude 31° to 43°. Main conclusions South‐west Atlantic saltmarshes are globally important by virtue of their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, south‐west Atlantic saltmarshes are better characterized by the presence of the halophytic genera Spartina and Sarcocornia. Our results support the interpretation that south‐west Atlantic saltmarshes constitute a class of temperate type (sensu Adam, 1990 ) with transitional characteristics between Australasian–South African saltmarshes and west Atlantic saltmarshes.     

Horizontal distribution affects the vertical distribution of native and invasive container‐inhabiting Aedes mosquitoes within an urban landscape

The vertical dimension constitutes an important niche axis along which mosquitoes may adjust their distribution. Here, we evaluated whether the vertical distribution of container‐inhabiting Aedes mosquitoes differs along a gradient of anthropogenic land‐use intensity within an urban landscape. Using a pulley system, we hung oviposition cups at three heights (ground level, 4.5, and 9 m) and in three habitats: forest, park, and a built environment. We hypothesized that mosquito abundance and diversity would be highest in the least disturbed forest habitat, decrease in the park, and be lowest at the UNC‐Greensboro campus. We also expected Aedes albopictus (Skuse) and Ae. triseriatus (Say) to mainly oviposit at ground level and Ae. hendersoni (Cockerell) at canopy height. Aedes albopictus was the most common species (68.8%) collected in all three habitat types and was the only species found in the built environment. In that habitat, Ae. albopictus exhibited a bimodal distribution with the lowest activity at the intermediate height (4.5 m). Aedes triseriatus (28.9%) did not differ in egg abundance between the forest and park habitats but did exhibit diverse vertical habitat use while avoiding the canopy in the park habitat. Aedes hendersoni (2.3%) was the most sylvatic species and oviposited only at ground level. Our results indicate that the vertical distribution of mosquitoes is affected by the type of habitat in which they occur, and that this variation could be driven via local‐scale modification of microclimatic factors.     

Anti-mosquito antibodies reduce the susceptibility of Aedes aegypti to arbovirus infection

Aedes aegypti (L.) mosquitoes showed a significant reduction in susceptibility to infection with Ross River virus and Murray Valley encephalitis virus when they were fed on a blood-virus mixture containing rabbit antibodies to mosquito midgut components. Presence of the antibodies did not demonstrably affect virus titres in infected mosquitoes, nor the transmission of virus from infected mosquitoes to vertebrates.     

Mosquito seasonality and arboviral disease incidence in Murray Valley, southeast Australia

Abstract. Adult female mosquito populations were monitored at weekly intervals during spring-autumn (November-March) for 4 years (1991-95) using dry-ice-baited light traps at forty sites in the Murray Valley of Victoria, Australia. Among twenty species of mosquitoes collected, Culex annulirostriswas the most abundant (66.6 ± 9.3%) followed by Cx australicus(15.3 ± 7.7%). From a total of 476, 682 mosquitoes collected, nearly all were females and only 1295 (0.27%) were males. Mosquito population densities were generally higher in 1992-93 and 1993-94 seasons than in 1991-92 and 1994-95 seasons. Greatest densities of Cx annulirostrisand Cx australicusoccurred in 1992-93, coinciding with outbreaks of Ross River (RR) and Barman Forest (BF) arboviruses causing human polyarthritis. In the majority of shires, Cx australicuswas the predominant species from spring to early summer (November and December), then was replaced by Cx annulirostrisfrom mid-summer to autumn (January-April). In three shires, Aedes bancroftianusand Ae.sagaxpredominated during the early part of the season. Densities of both Cx annulirostrisand Cx australicuswere related to temperature. Cx australicusadults were found to be trapped when the mean ambient temperature exceeded 6d?C, with peak population recorded at 20d?C. Cx annulirostrisadult density increased when the mean temperature rose above 12d?C, reaching a peak during February and March when temperature exceeded 25d?C. Cx annulirostrisdeclined rapidly from April onwards, with no adult activity evident from May to November. Population densities of Aedesspp. were generally less than reported from earlier studies, possibly due to lower rainfall in spring and summer as well as reduced flood irrigation practices. In each year, a significant correlation was detected between Cx annulirostrisdensity and RR virus incidence in humans. As Cx annulirostrisis the predominant local mosquito species and feeds on a wide spectrum of hosts including man, it seems likely that Cx annulirostrisis the major vector of RR in the inland Murray Valley region.     

Dissemination barriers to Ross River virus in Aedes vigilax and the effects of larval nutrition on their expression

Effects of larval nutrition on vector competence of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae) from Townsville, north Queensland, for Ross River virus (RR) were examined. Larvae were reared on three different diets to create three significantly different size classes of adult mosquito. These were fed on serial dilutions of RR and then sampled on alternate days so the progression of the virus through the mosquito could be examined. No differences of vector competence could be attributed to larval nutrition. Barriers to infection and the correlation between infection rate, viral titre and transmission of RR by Ae. vigilax were also examined. The mesenteronal barrier was the only infection barrier expressed. No correlation between viral titre and transmission was detected, but a strong correlation was found between salivary gland infection and transmission rate. From this it was possible to estimate that 98.7+/-1.3% of Ae. vigilax with infected salivary glands transmit RR.     

Proportions of eggs laid by Aedes aegypti on different substrates within an ovitrap in Trinidad, West Indies

Abstract. Ovitraps were exposed outdoors during wet and dry seasons in Trinidad to determine the proportions of eggs laid on three substrates: the widely-used hardboard 'paddle' (P), the water surface (W) and the inside surface of the ovitrap wall (S) in three types of blackened ovitrap: round, glass (RG), round, plastic (RP) and rectangular, plastic (SP). Of the 3556 eggs obtained, most (86.4%) were laid during the wet season when statistically significant differences were detected between substrates but not between ovitrap types. Most eggs (>80%) were laid on P, significantly fewer ( P < 0.005) on W, on S and on W + S, thus confirming the superiority of the paddle as a device for monitoring oviposition activity. Implications of these findings for the interpretation of Aedes studies using ovitraps are discussed.     

蚊浓核病毒介导的人工内含子在蚊体内外的初步应用

根据人β-球蛋白基因第一内含子5′-端供位序列与免疫球蛋白重链可变区基因3′-端受位序列构建人工内含子,将人工内含子插入重组蚊浓核病毒质粒载体p7NS1-GFP中GFP融合表达的病毒非结构蛋白NS1的编码框内,构建成载体p7NS1-Intron-GFP,与辅助载体pUCA共转染蚊C6/36细胞系,荧光显微镜下观察细胞内GFP的表达情况。纯化、回收共转染后形成重组病毒与野生病毒,共感染白纹伊蚊二龄幼虫并观察幼虫体内GFP的表达情况。结果在C6/36细胞与蚊幼虫体内均观察到GFP的高效表达,证实人工内含子无论在蚊细胞系内还是在活体幼虫内均可正常行使其自我剪切的功能,未影响到下游蛋白GFP的表达。本研究为人工内含子在蚊虫细胞内的应用奠定基础,为蚊虫及其病原体相关基因工程技术提供新的策略。     

Studies of Aedes aegypti (Diptera: Culicidae) ovipositional responses to newly identified semiochemicals from conspecific eggs

Abstract  The chemical factors influencing the selection of oviposition site by gravid females of various mosquito species have been the subject of numerous investigations. Recent studies have revealed this behaviour to be controlled by semiochemicals. Here we report studies on semiochemicals of egg origin and their effect on the ovipositional behaviour of Aedes aegypti. The compounds present in egg extracts of Ae. aegypti mosquitoes were isolated and identified by gas chromatography-mass spectrometry. They were then evaluated for their effect on ovipositional behaviour against gravid females of Ae. aegypti mosquitoes at different concentrations. Gravid female Ae. aegypti were found to be sensitive to all the identified compounds: 6-hexanolactone, methyl dodecanoate, dodecanoic acid, methyl tetradecanoate, tetradecanoic acid, methyl (Z)-9-hexadecenoate, methyl hexadecanoate (Z)-9-hexadecenoic acid, hexadecanoic acid, methyl (Z)-9-octadecenoate, methyl octadecanoate (Z)-9-octadecenoic acid and octadecanoic acid. Among them, dodecanoic and (Z)-9-hexadecenoic acids showed significant positive ovipositional response at different concentrations whereas all the esters showed deterrent/repellent ovipositional effect.     

Differential responses of Aedes and Culex mosquitoes to octenol or light in combination with carbon dioxide in Queensland, Australia

Abstract. Field studies were conducted with EVS (encephalitis vector surveillance) traps in south-eastern Queensland, Australia, to determine the relative response rates of mosquitoes to three levels (0.1, 4.5 and 30mg/h) of 1-octen-3-ol (octenol) in combination with a standard bait of 2200 g carbon dioxide (CO₂), compared with CO₂ alone or CO₂ with light from a 6V incandescent bulb. Compared to CO₂ alone, Aedes vigilax collections increased significantly when CO₂ was supplemented by all three octenol emission levels, but not by the addition of light. Furthermore, the 4.5 and 30 mg/h release rate of octenol gave a significant increase in numbers of Ae.vigilax relative to that from CO₂+ light. In contrast, collections of Culex annulirostris and Culex sitiens were not enhanced significantly by either the addition of light or octenol at all three levels. Fewer Cx sitiens were collected with octenol released at 4.5 mg/h in comparison to CO₂ alone. These differential sampling rates should be taken into account when using EVS traps.     

云南省4种伊蚊的乙型脑炎病毒分离物的研究

在云南省西南边境9县市捕获伊蚊属雌性成蚊16种19367只,用细胞法和乳鼠法分离病毒.从185批6491只白纹伊蚊中分离到病毒2株,从50批1605只剌扰伊蚊中分离到病毒2株,从23批772只窄翅伊蚊中分离到病毒2株,从4批103只阿萨姆伊蚊中分离到病毒1株.其它12种共10396只伊蚊的病毒分离物为阴性.分离到的7株病毒经免疫荧光、酶免疫、血凝抑制和中和试验鉴定,均为乙型脑炎病毒(JE virus).白纹伊蚊是野外竹林的优势蚊种.分析认为白纹伊蚊在当地乙型脑炎病毒保存和传播中起重要作用,刺扰伊蚊、窄翅伊蚊和阿萨姆伊蚊亦可参与该病毒的传播.     

云南省4种伊蚊的乙型脑炎病毒分离物的研究

在云南省西南边境９县市捕获伊蚊属雌性成蚊１６种１９３６７只,用细胞法和乳鼠法分离病毒。从１８５批６４９１只白纹伊蚊中分离到病毒２株,从５０批１６０５只剌扰伊蚊中分离到病毒２株,从２３批７７２只窄翅伊蚊中分离到病毒２株,从４批１０３只阿萨姆伊蚊中分离到病毒１株。其它１２种共１０３９６只伊蚊的病毒分离物为阴性。分离到的７株病毒经免疫荧光、酶免疫、血凝抑制和中和试验鉴定,均为乙型脑炎病毒（ＪＥｖｉｒｕｓ）。白纹伊蚊是野外竹林的优势蚊种。分析认为白纹伊蚊在当地乙型脑炎病毒保存和传播中起重要作用,刺扰伊蚊、窄翅伊蚊和阿萨姆伊蚊亦可参与该病毒的传播。     

Predation on lizard eggs by ants: species interactions in a variable physical environment

One explanation for long-term fluctuations in population density is that the intensity of interactions between species is variable. A population can experience variation in the intensity of a species interaction if (1) the density of species with which it directly interacts changes and/or (2) the strength of the interaction (i.e., per capita effects) changes. At Barro Colorado Island, Panama, the tropical lizard Anolis limifrons exhibits wide annual fluctuations in density. Previous studies have indicated that (1) the density of A. limifrons is negatively correlated with the amount of wet-season rainfall, (2) fluctuations in density are related more to variation in egg mortality than to variation in lizard mortality or to fecundity, and (3) most egg mortality is the result of predation by Solenopsis ants. We hypothesized that the amount of wet-season rainfall indirectly alters the density of A. limifrons by producing variation in the intensity of egg predation by Solenopsis. Additionally, we also wanted to determine if variation in the amount of egg mortality was influenced more by variation in the density of Solenopsis, or by variation in the rate of predation. We tested this hypothesis by manipulating litter moisture on experimental plots to simulate the wettest (HW) and driest (LW) wet seasons in the last 20 years, and then monitoring the density of Solenopsis, amount of egg mortality, and rate of predation. The amount of egg mortality was greater on the HW than on the LW treatment and all egg mortality resulted from predation by Solenopsis. ANCOVA indicated that the amount of egg mortality was significantly higher on plots with a greater density of Solenopsis. Treatment effects, however, explained more of the variation in the amount of egg mortality than did Solenopsis density. Our water manipulations did not change the density of Solenopsis, but Solenopsis found and attacked eggs faster on the HW than on the LW treatment. This suggests that moisture during the wet season modified the strength of the interaction between Solenopsis and A. limifrons, supporting the hypothesis that annual variation in the amount of wet-season rainfall indirectly produces parallel variation in annual density of lizard populations by modifying the rate of ant predation on eggs. Received: 12 October 1998 / Accepted: 31 December 1998     

鸟类调查的样线法和样点法比较:以崇明东滩春季盐沼鸟类调查为例

为了探讨样线法和样点法对盐沼湿地鸟类调查的有效性及适用性, 我们于2008年3–5月采用固定距离样线法和固定半径样点法对崇明东滩盐沼鸟类进行了调查。5次调查共记录到鸟类24种, 其中样线法记录到19种, 样点法记录到21种, 两种调查方法平均每次记录到的鸟类种数没有显著差异, 表明两种方法对盐沼鸟类种类的发现能力相似。两种方法得到的鸟类密度之间有显著的相关性,说明两种方法在反映鸟类群落中每种鸟类的相对数量方面具有可比性。但除了仅在一种调查方法中记录到的种类, 样点法调查得到的每种鸟类密度和鸟类总密度均高于样线法的调查结果。因此, 在对鸟类种群或群落的时空特征进行比较时, 需要考虑所采用的调查方法对调查结果的影响。     

The distribution of eggs per host in a herbivorous insect--intersection of oviposition, dispersal and population dynamics

1. The dynamics of parasitic organisms depend critically upon the frequency distribution of parasite individuals per host. However, the processes giving rise to this frequency distribution have rarely been modelled and tested for organisms with complex host selection behaviour. 2. In this study Microrhopala vittata, a chrysomelid beetle, was used to investigate how oviposition behaviour, movement and density of host plants interact in shaping the frequency distribution of egg clusters per host in the field. 3. Enclosures were stocked with two different host species and different beetle densities and various stochastic process models were fitted to egg cluster count data obtained from these enclosures. The different models were derived considering different scenarios, in particular whether or not plant density limits oviposition rate, whether or not ovipositing females actively seek out the most attractive plant within their perception radius and whether a female's oviposition rate is determined by plant intrinsic factors, the plant's egg cluster load or the surrounding beetle density. 4. The model parameters fitted to cage data were used to describe the frequency distribution of egg cluster counts obtained in a release experiment in the field. A total of 220 beetle pairs were released at five locations in a field where this beetle was not observed previously. Each release point was at a border between the two host species. 5. One model predicted for the preferred host species the egg cluster count frequencies in the field from parameters estimated in the cages. This model assumed that egg clusters present on a plant increased subsequent oviposition on this plant. All other models could not describe the distribution of egg cluster counts for either of the two host species. 6. The results suggest that females seek out attractive hosts actively and the attractiveness of a plant increases with its egg cluster load. This behaviour creates a frequency distribution of egg clusters per host that depends only on beetle density but not on plant density. This conclusion has important implications for modelling insect-plant interactions.