Parasitism of mosquitoes (Diptera: Culicidae) by larval mites (Acari: Parasitengona) in Adelaide, South Australia

Larval mites (Acari) from the cohort Parasitengona were collected from adult female mosquitoes captured in Adelaide, South Australia, from 1997 to 2000. Larvae from three families were identified: Arrenuridae, Hydryphantidae and Erythraeidae. Arrenurid larvae were associated with mosquitoes that use ground pools for larval habitat, while hydryphantids were associated with tree-hole and container-breeding species. Only a single erythraeid record was made. The overall prevalence of parasitism was very low (0.27% of 19 280 mosquitoes) and ranged from 0 to 5.6% for the 16 mosquito species collected. New mite–host records are presented.     

Organization of unusual idiosomal glands in a water mite, <Emphasis Type="Italic">Teutonia cometes</Emphasis> (Teutoniidae)

The unusual idiosomal glands of a water mite Teutonia cometes (Koch 1837) were examined by means of transmission and scanning electron microscopy as well as on semi-thin sections. One pair of these glands is situated ventrally in the body cavity of the idiosoma. They run posteriorly from the terminal opening (distal end) on epimeres IV and gradually dilate to their proximal blind end. The terminal opening of each gland is armed with the two fine hair-like mechanoreceptive sensilla (‘pre-anal external’ setae). The proximal part of the glands is formed of columnar secretory epithelium with a voluminous central lumen containing a large single ‘globule’ of electron-dense secretory material. The secretory gland cells contain large nuclei and intensively developed rough endoplasmic reticulum. Secretory granules of Golgi origin are scattered throughout the cell volume in small groups and are discharged from the cells into the lumen between the scarce apical microvilli. The distal part of the glands is formed of another cell type that is not secretory. These cells are composed of narrow strips of the cytoplasm leaving the large intracellular vacuoles. A short excretory cuticular duct formed by special excretory duct cells connects the glands with the external medium. At the base of the terminal opening a cuticular funnel strengthens the gland termination. At the apex of this funnel a valve prevents back-flow of the extruded secretion. These glands, as other dermal glands of water mites, are thought to play a protective role and react to external stimuli with the help of the hair-like sensilla.     

Anatomy and ultrastructure of the salivary (prosomal) glands in unfed water mite larvae Piona carnea (C.L. Koch, 1836) (Acariformes: Pionidae)

Anatomy and ultrastructure of prosomal salivary glands in the unfed water mite larvae Piona carnea (C.L. Koch, 1836) were examined using serial semi-thin sections and transmission electron microscopy. Three pairs of alveolar salivary glands shown are termed lateral, ventro-lateral and medial in accordance with their spatial position. These glands belong to the podocephalic system and are situated on the common salivary duct from back to forth in the above mentioned sequence. The arrangement of the medial glands is unusual because they are situated one after another on the medial (axial) body line, therefore they are termed anterior and posterior medial glands. The secretory duct of the anterior medial gland mostly turns right, and the duct of the posterior gland turns left. The salivary glands are located in the body cavity partly inside the gnathosoma and in the idiosoma in front of the brain (synganglion). Each gland is represented by a single acinus (alveolus) and is composed of several cone shaped secretory cells arranged around the large central (intra-acinar) cavity with the secretory duct base. The cells of all glands are filled with secretory vesicles of different electron density. The remaining cell volume is occupied by elements of rough endoplasmic reticulum, and the membrane enveloping vesicles may have ribosomes on its external surface. Large nuclei provided with large nucleoli occupy the basal cell zones. The pronounced development of the prosomal salivary glands indicates their important role in extra-oral digestion of water mite larvae.     

Correlated responses to selection for faster development and early reproduction in Drosophila: the evolution of larval traits

Studies on selection for faster development in Drosophila have typically focused on the trade-offs among development time, adult weight, and adult life span. Relatively less attention has been paid to the evolution of preadult life stages and behaviors in response to such selection. We have earlier reported that four laboratory populations of D. melanogaster selected for faster development and early reproduction, relative to control populations, showed considerably reduced preadult development time and survivorship, dry weight at eclosion, and larval growth rates. Here we study the larval phase of these populations in greater detail. We show here that the reduction in development time after about 50 generations of selection is due to reduced duration of the first and third larval instars and the pupal stage, whereas the duration of the second larval instar has not changed. About 90% of the preadult mortality in the selected populations is due to larval mortality. The third instar larvae, pupae, and freshly eclosed adults of the selected populations weigh significantly less than controls, and this difference appears during the third larval instar. Thereafter, percentage weight loss during the pupal stage does not differ between selected and control populations. The minimum amount of time a larva must feed to subsequently complete development is lower in the selected populations, which also exhibit a syndrome of reduced energy expenditure through reduction in larval feeding rate, larval digging and foraging activity, and pupation height. Comparison of these results with those observed earlier in populations selected for adaptation to larval crowding and faster development under a different protocol from ours reveal differences in the evolved traits that suggest that the responses to selection for faster development are greatly affected by the larval density at which selection acts and on details of the selection pressures acting on the timing of reproduction.     

On the origin of brood parasitism in altricial birds

The probability that obligate interspecific brood parasitism(OP), among altricial birds evolved directly from the normalbreeding (no parasitism, NP) mode or indirectly through intraspecificnest parasitism (INP) was examined by using maximum-likelihoodand parsimony approaches. We examined the probability of ancestralstates at 24 key nodes in order to test our hypotheses. Thestate of the most basal node in a tree of 565 genera of altricialbirds is equivocal; however, the state probability of NP atthis node is about 5.5-fold more likely than the state of obligateparasite. A similar trend was observed for basal nodes of mostfamilies examined. The INP state was supported only in the Hirundinidae.The high incidence of INP among martins and swallows explainsthis finding. Contrary to our predictions, even in other groupswhere there is a high incidence of INP and OP, such as in thetribe Icteri and the Old World finches, the probability of NPbeing ancestral was very high. We conclude that in all casesbut one (Hirundinidae) obligate, and probably facultative, broodparasitism evolved directly from normal breeding mode ratherthan indirectly through some other form of parasitism.     

Evolution of increased adult longevity in Drosophila melanogaster populations selected for adaptation to larval crowding

In holometabolous animals such as Drosophila melanogaster, larval crowding can affect a wide range of larval and adult traits. Adults emerging from high larval density cultures have smaller body size and increased mean life span compared to flies emerging from low larval density cultures. Therefore, adaptation to larval crowding could potentially affect adult longevity as a correlated response. We addressed this issue by studying a set of large, outbred populations of D. melanogaster, experimentally evolved for adaptation to larval crowding for 83 generations. We assayed longevity of adult flies from both selected (MCUs) and control populations (MBs) after growing them at different larval densities. We found that MCUs have evolved increased mean longevity compared to MBs at all larval densities. The interaction between selection regime and larval density was not significant, indicating that the density dependence of mean longevity had not evolved in the MCU populations. The increase in longevity in MCUs can be partially attributed to their lower rates of ageing. It is also noteworthy that reaction norm of dry body weight, a trait probably under direct selection in our populations, has indeed evolved in MCU populations. To the best of our knowledge, this is the first report of the evolution of adult longevity as a correlated response of adaptation to larval crowding.     

Temporal and spatial variation in length of larval life and size at settlement of the Hawaiian amphidromous goby Lentipes concolor

Larvae of the Hawaiian amphidromous goby Lentipes concolor settled after a mean length of larval life (LLL) of 86·2±8·5 days (n=236, range=63–106 days) at a mean size of 16·0±0·7 mm LT (n=154, range=14·1-17·9 mm). Mean LLL for L. concolor was about twice that typically reported for tropical marine gobiids. Variation in LLL (CV=10%) and size at settlement (CV=4%) were low, and comparable to that for marine gobiids. LLL and L_T were weakly positively correlated (Pearson's correlation coefficient r=0·50, P<0·0001). Larvae settled after shorter planktonic lives and at smaller sizes during months with warmer ocean temperatures. Inter-island variation in LLL did not support a dominant south-east to north-west larval drift, following the dominant south-east to north-west flow of prevailing currents in the Archipelago. Instead, recruits on Maui Island, centrally located in the archipelago, had shorter LLL than recruits to upstream Hawai'i and downstream Kaua'i islands. These findings have important implications for understanding the complex life history dynamics of amphidromous fishes as well as their management.     

Phylogenetic position of the mite family Myobiidae within the infraorder Eleutherengona (Acariformes) and origins of parasitism in eleutherengone mites

The position of the family Myobiidae in the infraorder Eleutherengona (Prostigmata) was analyzed with a cladistic parsimony approach for the first time. Species of the genera Anystis von Heyden (Anystidae), Pomerantzia Baker (Pomerantziidae), and Walytydeus Kuznetzov (Paratydeidae) were selected as outgroups. Among Eleutherengona, species of the following genera were selected as ingroup taxa: Hirstiella Berlese (Pterygosomatidae), Eucheyletia Baker, Cheyletiella Canestrini (Cheyletidae), Syringophilus Heller (Syringophilidae), Tarsocheylus Berlese (Tarsocheylidae), Heterocheylus Lombardini (Heterocheylidae), Pygmephorus Kramer (Pygmephoridae), Raphignathus Dugès (Raphignathidae), Neognathus Willmann (Caligonellidae), Storchia Oudemans (Stigmaeidae), and Tuckerella Womersley (Tuckerellidae). Three most parsimonious trees with similar topology were obtained. In all these trees, the family Myobiidae is situated outside of the clade joining the higher Raphignathae (Raphignathoidea and Cheyletoidea) and represents a branch within the earlier derivative Raphignathae. This result is based primarily on characters from leg setation and postembryonic development. The conclusion from this topology is that myobiid mites have developed some gnathosomal structures convergently with Cheyletoidea, including the stylet-like chelicerae and stylophore fused with the subcapitulum. The evolution of animal eleutherengone parasitism is discussed. Parasitism arisen independently in numerous phyletic lineages or superfamilies of Eleutherengona. The representatives of some phylogenetically distant eleutherengone lineages developed similar adaptations to predation and parasitism. However, in spite of some similarities in these adaptations, the evolutionary trends and pathways for switching to a parasitic mode of life are quite different in particular eleutherengone lineages.     

Acquisition of obligate mutualist symbionts during the larval stage is not beneficial for a coral host

Theory suggests that the direct transmission of beneficial endosymbionts (mutualists) from parents to offspring (vertical transmission) in animal hosts is advantageous and evolutionarily stable, yet many host species instead acquire their symbionts from the environment (horizontal acquisition). An outstanding question in marine biology is why some scleractinian corals do not provision their eggs and larvae with the endosymbiotic dinoflagellates that are necessary for a juvenile's ultimate survival. We tested whether the acquisition of photosynthetic endosymbionts (family Symbiodiniaceae) during the planktonic larval stage was advantageous, as is widely assumed, in the ecologically important and threatened Caribbean reef‐building coral Orbicella faveolata. Following larval acquisition, similar changes occurred in host energetic lipid use and gene expression regardless of whether their symbionts were photosynthesizing, suggesting the symbionts did not provide the energetic benefit characteristic of the mutualism in adults. Larvae that acquired photosymbionts isolated from conspecific adults on their natal reef exhibited a reduction in swimming, which may interfere with their ability to find suitable settlement substrate, and also a decrease in survival. Larvae exposed to two cultured algal species did not exhibit differences in survival, but decreased their swimming activity in response to one species. We conclude that acquiring photosymbionts during the larval stage confers no advantages and can in fact be disadvantageous to this coral host. The timing of symbiont acquisition appears to be a critical component of a host's life history strategy and overall reproductive fitness, and this timing itself appears to be under selective pressure.     

Chick parasitism by blowflies affects feeding rates in a Mediterranean population of blue tits

Offspring fitness depends on interactions between parental care and environmental constraints. It has been suggested that in altricial birds parents are able to compensate for the detrimental effects of ectoparasites by improving food provisioning. We tested this prediction in a population of blue tits highly parasitized by blowfly larvae. The frequency of parental feeding visits was significantly higher in parasitized broods than in broods experimentally deparasitized. Despite a strong increase in parental care, chicks of parasitized broods were lighter, smaller, and more anaemic than chicks in deparasitized broods. Parents invest more in feeding parasitized young but cannot fully compensate for the negative effects of parasites, hence young are in poor condition at fledging.     

Romanomermis culicivorax parasitism and the development, growth, and feeding rates of two mosquito species

The dry weight, development, and feeding rates of Culex pipiens and Toxorhynchites amboinensis larvae infected with the nematode, Romanomermis culicivorax, were measured and gross conversion efficiences were calculated. The weight of C. pipiens larvae infected at two different inoculum levels did not differ significantly from controls until day 6 postinfection (PI). Infected larvae of T. amboinensis were significantly lighter than controls at days 2, 4, and 6 PI. The rate of larval mosquito development was slowed after day 3 in parasitized individuals of both mosquito species. Infection significantly retarded the interval feeding rate of the filter-feeding C. pipiens throughout development. Infected T. amboinensis larvae consumed significantly fewer prey larvae of C. pipiens than controls. Calculation of gross conversion efficiency (GCE) showed that lightly infected C. pipiens larvae had an elevated GCE early in the infection but were less efficient relative to controls after 4 days PI. Lightly parasitized T. amboinensis had a lower total GCE than controls.     

The evolution of obligate interspecific brood parasitism in birds

We present a simple analytical model to investigate the conditionsfor the evolution of obligate interspecific brood parasitismin birds, based on clutch size optimization, when birds canlay more eggs than their optimal clutch size. The results showthat once intraspecific parasitism has appeared (i.e., femalesstart to spread their eggs over their own and other nests) the evolutionarily stable number of eggs laid in its own nest decreases.Two possible ESSs exist: (1) either the evolutionarily stablenumber of eggs laid in its own nest is larger than zero, anda fraction of the total number of eggs is laid parasitically(i.e., intraspecific parasitism); and (2) either the evolutionarilystable number of eggs laid in its own nest is zero and all eggs are laid parasitically. Since all females lay parasitically,this could favor the evolution of obligate interspecific broodparasitism. The key parameter allowing the shift from intraspecificto obligate interspecific parasitism is the intensity of density-dependentmortality within broods (i.e., nestling competition). Strongnestling competition, as in altricial species, can lead toan ESS where all eggs are laid parasitically. Altricial speciesare, therefore, predicted to evolve more easily toward obligate interspecific parasitism than precocial species. These predictionsfit the observed distribution of brood parasitism in birds,where only one species out of 95 obligate interspecific parasitesexhibits a precocial mode of development. Different nestlingsurvival functions provided similar findings (i.e., obligatebrood parasitism is more likely to evolve in altricial species),suggesting that these results are robust with respect to themain assumption of the model.     

Foliar nitrogen and larval parasitism as determinants of leafminer distribution patterns on Spartina alterniflora

ABSTRACT, 1. In northwest Florida, Hydrellia valida hew (Diptera: Ephydridae) frequently mines the leaves of salt marsh cord, grass, Spartina alterniflora . Larvae and pupae are more commonly found in shoreline plants within 3 m of the sea than in inland plants.
2. Shoreline plants contain over twice as much total foliar nitrogen as inland plants. In transects from inland to shoreline plants, leafminer density is positively correlated with total leaf nitrogen content.
3. We experimentally increased foliar nitrogen content on inland Spartina patches to levels above those of shoreline plants. Leafminer densities on experimental centres remained far below those on control edges.
4. Larval parasitism by Opius sp. (Hymenoptera: Braconidae) and Pteromalus sp. (Hymenoptera: Pteromalidae) reaches over 90%, with parasitism increasing from shoreline to inland plants. We suggest that gradients in leafminer densities are caused by differences in parasitoid abundance.     

The effect of food supply and larval cannibalism on adult size and biomass of the grazing caddis-fly Melampophylax mucoreus (Limnephilidae)

Abstract. 1. Larvae of the grazing caddis‐fly Melampophylax mucoreus were reared in a laboratory experiment investigating the effect of food availability on different substrates and cannibalism on the size and biomass of emergent adults. All experiments were performed in stream‐water filled, aerated aquaria under controlled temperature and light conditions. Larvae (fourth and fifth instar) were reared in aquaria (50 larvae in each) with three substrate scenarios: (i) limestone (LS), (ii) limestone and leaf litter (LS + L), and (iii) silicate stone (SS). 2. Cannibalism among the larvae in the LS scenario led to the highest adult dry masses (male = 5.13 ± 0.25 mg, female = 7.64 ± 0.63 mg) and to the highest mortality rate (88.7%). The SS scenario displayed the most unfavourable condition for larval growth indicated by the lowest adult dry masses (males = 3.12 ± 0.15 mg, females = 4.69 ± 0.25 mg) and a high mortality rate (81.7%). The limestone supplemented with leaf litter (ii) offered the most balanced nutrients to complete larval development and enough shelter to avoid excessive encounter rates of larvae within the aquaria, indicated by the lowest mortality rate (43.6%). Adults from the LS + L scenario showed biomasses (male = 3.94 ± 0.12 mg, female = 6.48 ± 0.24 mg) intermediate between the two other scenarios. 3. The results implied that cannibalism among larvae can lead to higher adult biomasses and therefore to increased fitness, if cannibalism supplements larval feeding requirements. Larvae developing under insufficient food availability can not compensate for this by cannibalism. Additionally, leaf litter not only provided a complementary food source for developing larvae, but also provided shelter, which reduced encounter rates. 4. Increased stress induced by high larval encounter rates (resulting in enhanced cannibalism) in the LS scenario and low food availability in the SS scenario could be indicated by premature emergence times compared with the LS + L scenario.     

Pathophysiological influences of the Heterorhabditis bacteriophora complex on fifth-instar larvae of the red humped caterpillar, Schizura concinna: Changes in feeding rate,larval weight,and frass production

At 28.5°C, oral dosages of the invasive juveniles of Heterorhabditis bacteriophora and intrahemocoelic injections of its associated bacterium, Xenorhabdus luminescens, resulted in a decrease in larval feeding rate, larval wet weight, and frass production in its host, the seventh-instar larvae of Schizura concinna.     

Life‐history trade‐offs under different larval diets in Drosophila suzukii (Diptera: Drosophilidae)

Most larval drosophilids eat the microorganisms that develop in rotting fruit, a relatively protein‐rich resource. By contrast, the spotted‐wing Drosophila suzukii Matsumara (Diptera: Drosophilidae) uniquely develops in ripening fruit, a protein‐poor, carbohydrate‐rich resource. This shift in larval nutritional niche has led to D. suzukii being a significant agricultural pest in the U.S.A. and Europe. Although occupying a new niche may benefit a species by reducing competition, adaptation in host use may generate trade‐offs affecting fitness. To test the hypothesis that fitness trade‐offs will change with adaptation to novel larval diets, D. suzukii larval development on either a diet of a fresh, ripe blueberry (a natural host) or standard artificial Drosophila media (protein‐rich) is compared and the effect of diet on development time from egg to adult, adult body size and male wing spot area, and female fecundity is assessed. Larval development time differs, with larvae on the blueberry emerging as adults earlier than those on the artificial medium, although other fitness measures do not vary between the two diets. In addition, the faster development time on a blueberry does not trade off with body size as expected, although early fecundity is delayed in females that develop on blueberries. Thus, adaptation to a novel larval diet environment does not come at a cost to the ability to develop in protein‐rich resources.     

Parental effects on the larval performance of a tapeworm in its copepod first host

Parents can influence the phenotype of their offspring through various mechanisms, besides the direct effect of heredity. Such parental effects are little explored in parasitic organisms, perhaps because in many parasites, per capita investment into offspring is low. I investigated whether parental identity, beyond direct genetic effects, could explain variation in the performance of the tapeworm Schistocephalus solidus in its first intermediate host, a copepod. I first determined that two breeding worms could be separated from one another after ~48 h of in vitro incubation and that the isolated worms continued producing outcrossed eggs, that is, rates self‐fertilization did not increase after separation. Thus, from a breeding pair, two sets of genetically comparable eggs can be collected that have unambiguous parental identities. In an infection experiment, I found that the development of larval worms tended to vary between the two parental worms within breeding pairs, but infection success and growth rate in copepods did not. Accounting for this parental effect decreased the estimated heritability for development by nearly half. These results suggest that larval performance is not simply a function of a worm's genotype; who mothered or fathered an offspring can also affect offspring fitness, contradicting the perhaps naïve idea that parasites simply produce large quantities of uniformly low‐quality offspring.     

Lunar rhythms in growth of larval fish

Growth and survival of larval fishes is highly variable and unpredictable. Our limited understanding of this variation constrains our ability to forecast population dynamics and effectively manage fisheries. Here we show that daily growth rates of a coral reef fish (the sixbar wrasse, Thalassoma hardwicke) are strongly lunar-periodic and predicted by the timing of nocturnal brightness: growth was maximized when the first half of the night was dark and the second half of the night was bright. Cloud cover that obscured moonlight facilitated a ‘natural experiment’, and confirmed the effect of moonlight on growth. We suggest that lunar-periodic growth may be attributable to light-mediated suppression of diel vertical migrations of predators and prey. Accounting for such effects will improve our capacity to predict the future dynamics of marine populations, especially in response to climate-driven changes in nocturnal cloud cover and intensification of artificial light, which could lead to population declines by reducing larval survival and growth.     

Development of feeding structures in larval fish with different life histories: winter flounder and Atlantic cod

The size at which feeding structures developed and shifts in head proportions occurred, differed between Atlantic cod Gadus morhua and winter flounder Pseudopleuronectes americanus. The sequence and timing of the development of feeding structures may not be dependent on size, but may occur because they are necessary to meet specific requirements offish larvae feeding in the plankton. In early larval stages development of feeding structures was similar in number and type and was necessary for first-feeding in both species. In later stages, significant differences between species occurred in the timing of the development of feeding structures. In cod differentiation of new structures and changes in head proportions occurred at about two-thirds of the way through larval life, which coincided with an increase in growth. In flounder changes in feeding morphology did not occur during the symmetrical larval stage, but occurred only after metamorphosis to the asymmetrical demersal juvenile stage. Differences between cod and flounder in the size at which feeding structures develop may reflect life history adaptations expressed in the duration of the pelagic larval stage, as well as differences in juvenile habitat and feeding ecology.     

Shiny Cowbird parasitism of a low quality host: effect of host traits on a parasite's reproductive success

ABSTRACT.   The reproductive success of parasitic cowbirds ( Molothrus spp.) varies among host species and is influenced by the degree of synchronization in timing of egg laying, the duration of parasite and host incubation periods, and the ability of hosts to incubate and rear parasite young. We studied the reproductive success of Shiny Cowbirds ( Molothrus bonariensis ) that parasitized the nests of Creamy-bellied Thrushes ( Turdus amaurochalinus ) in the Monte desert region of Argentina. Shiny Cowbirds frequently parasitized Creamy-bellied Thrush nests (60%), and most cowbirds synchronized egg laying with that of thrushes (79%). Most parasitic eggs (80%) hatched within 1 d of the hatching of the first host egg, and more than 91% of the eggs survived until the end of the incubation. However, only 60% of the cowbird eggs hatched and 52% of young survived. The proportion of Shiny Cowbirds eggs laid in Creamy-bellied Thrush nests that resulted in fledged young was 0.03, including eggs and young lost due to predation or desertion. Despite this low reproductive success, Creamy-bellied Thrushes were heavily parasitized by Shiny Cowbirds in our study area. Shiny Cowbirds may continue to parasitize these thrushes because of diffuse selection or because Shiny Cowbird chicks are more likely to fledge from Creamy-bellied Thrush nests in years or areas with greater food availability when brood reduction does not occur.