Showing papers on "Larva published in 2002"

Ecology and behavior of first instar larval lepidoptera

Abstract: Neonate Lepidoptera are confronted with the daunting task of establishing themselves on a food plant. The factors relevant to this process need to be considered at spatial and temporal scales relevant to the larva and not the investigator. Neonates have to cope with an array of plant surface characters as well as internal characters once the integument is ruptured. These characters, as well as microclimatic conditions, vary within and between plant modules and interact with larval feeding requirements, strongly affecting movement behavior, which may be extensive even for such small organisms. In addition to these factors, there is an array of predators, pathogens, and parasitoids with which first instars must contend. Not surprisingly, mortality in neonates is high but can vary widely. Experimental and manipulative studies, as well as detailed observations of the animal, are vital if the subtle interaction of factors responsible for this high and variable mortality are to be understood. These studies are essential for an understanding of theories linking female oviposition behavior with larval survival, plant defense theory, and population dynamics, as well as modern crop resistance breeding programs.

Density-dependent development of Anopheles gambiae (Diptera: Culicidae) larvae in artificial habitats.

Abstract: The growth and development of Anopheles gambiae Giles larvae were studied in artificial habitats in western Kenya. Larvae responded to increasing densities by extending their development time and by emerging as smaller adults, although survival was not significantly affected. Addition of nutrients in the form of cow dung collected near the study site had no impact on larval growth and development. Regression analysis showed that female development time increased by 0.020 d and female dry mass decreased by 0.74 μg with each additional larva. By fitting the data to the pupation window model, the estimated minimum dry mass to achieve pupation was 0.130 mg and the estimated minimum time to pupation was 5 d. The most likely food source for An. gambiae larvae was algal growth, which was significantly reduced by the presence of larvae. Bacterial densities were not significantly affected by the presence of larvae although total bacteria counts were lower at the higher densities indicating they may provid...

Effects of nutrition-mediated larval condition on juvenile performance in a marine mussel

Abstract: The potential for long-lasting effects of larval experience on early juvenile stages is growing in recognition as an important aspect of the ecology of organisms with complex life cycles. For marine species, most studies of recruitment have focused on the numbers of settlers that arrive to a site, largely ignoring the potential variability in larval condition or quality and how such variability may influence the likelihood of recruitment success. In this study, I investigated the effect of larval nutritional history on early juvenile performance, and whether these effects are mediated by conditions in the juvenile habitat for the marine mussel Mytilus galloprovincialis. I raised larvae in the laboratory under different food concentrations. Larvae raised with the highest food concentrations were significantly larger in size at metamorphosis and had higher proportional lipid content at metamorphosis than those from lower food concentrations. Half of the newly metamorphosed juveniles were outplanted into intertidal and subtidal habitats for 2 wk. The other half were maintained in the laboratory at two different juvenile rations for up to 20 d. Juveniles raised with high larval food had higher juvenile growth rates and attained larger juvenile sizes than those from lower larval food in all cases. There was a significant positive relationship between size at metamorphosis and juvenile growth for juveniles maintained in the laboratory. Early juvenile growth rates did not change over time (between 10 and 20 d post-metamorphosis). Juveniles raised in higher juvenile rations had elevated growth rates and attained larger final sizes after 20 d than juveniles from low juvenile rations across all sizes at metamorphosis. For juveniles in the field, there was no effect of tidal height on growth for 2 wk post-metamorphosis. Field conditions were more favorable than laboratory conditions for juvenile growth, yet even these more favorable conditions did not compensate for the effects of larval nutritional history on early juvenile growth. Losses of juveniles from both the field and the laboratory were higher for those that had been raised in lower larval food conditions than for those that had been raised in higher larval food, suggesting that vulnerability to early juvenile mortality may also be affected by larval history.

Effects of temperature and food quality on anuran larval growth and metamorphosis

Abstract: Summary 1. Anurans exhibit high levels of growth-mediated phenotypic plasticity in age and size at metamorphosis. Although temperature and food quality exert a strong influence on larval growth, little is known about the interacting effects of these factors on age and size at metamorphosis. 2. Plasticity in growth rates, maximum larval mass, mass loss, larval period and size at metamorphosis was examined in Iberian Painted Frogs ( Discoglossus galganoi Capula, Nascetti, Lanza, Bullini & Crespo 1985) under different combinations of temperature and diet quality. 3. Temperature and diet had strong effects on the maximum size reached by tadpoles throughout the premetamorphic stages. Larval body mass varied inversely with temperature. The effect of diet depended on temperature; larvae fed on a ‘carnivorous’ diet (rich in protein and lipids) achieved a larger size than larvae offered an ‘herbivorous’ diet (rich in carbohydrates) at 17 ° C but not at 12 or 22 ° C. 4. Larval period was insensitive to diet composition, and varied only with temperature. Primarily the interacting effects of food quality and temperature affected size at metamorphosis. Size at metamorphosis varied inversely with temperature under the plant- and the animal-based diets. However, the carnivorous diet resulted in bigger metamorphs at 17 and 22 ° C, but did not influence final mass at 12 ° C. Maximum size over the larval period explained most of the variation in mass loss after the premetamorphic growing phase.

Analysis of Northern Distribution of Aedes albopictus (Diptera: Culicidae) in Japan by Geographical Information System

Abstract: Aedes albopictus (Skuse), a mosquito vector of the dengue fever virus, is prevalent in Japan, distributed widely in Honshu Island with its northern limits between latitude 38° to 40°degrees north. The factors affecting distribution of the species in the northern part of Japan were studied using the geographical information system (GIS). During 1998–2000, larval surveillance was carried out in 26 urban and rural areas in the Tohoku district, in the northern part of Honshu Island, by collecting larvae from artificial and natural habitats. Climatological analysis, using the GIS, showed that the following conditions accounted for the current distribution of Ae. albopictus: an annual mean temperature higher than 11°C and a mean temperature of the coldest month, January, higher than −2°C. A period with temperature above 11°C in the confirmed area of the mosquito successively continues for more than 186 d per year. The accumulated temperature calculated from a temperature of 11°C, which may be close to the developmental zero of Ae. albopictus, was over 1,350 degree-days. The relationship between the beginning of short-daylength, inducing egg diapause, and the monthly mean temperature during September and October necessary for successful larval development in the Tohoku district is also discussed. We also show the relationship between the current distribution of Ae. albopictus and the annual mean temperature in the United States. From these results it is predicted that Ae. albpictus will be established in some cities in northeast United States.

Allee effect in larval resource exploitation in Drosophila: an interaction among density of adults, larvae, and micro-organisms

Abstract: 1. Aggregation pheromones can evolve when individuals benefit from clustering. Such a situation can arise with an Allee effect, i.e. a positive relationship between individual fitness and density of conspecifics. Aggregation pheromone in Drosophila induces aggregated oviposition. The aim of the work reported here was to identify an Allee effect in the larval resource exploitation by Drosophila melanogaster , which could explain the evolution of aggregation pheromone in this species. 2. It is hypothesised that an Allee effect in D. melanogaster larvae arises from an increased efficiency of a group of larvae to temper fungal growth on their feeding substrate. To test this hypothesis, standard apple substrates were infested with specified numbers of larvae, and their survival and development were monitored. A potential beneficial effect of the presence of adult flies was also investigated by incubating a varying number of adults on the substrate before introducing the larvae. Adults inoculate substrates with yeast, on which the larvae feed. 3. Fungal growth was related negatively to larval survival and the size of the emerging flies. Although the fungal growth on the substrate was largely reduced at increased larval densities, the measurements of fitness components indicated no Allee effect between larval densities and larval fitness, but rather indicated larval competition. 4. In contrast, increased adult densities on the substrates prior to larval development yielded higher survival of the larvae, larger emerging flies, and also reduced fungal growth on the substrates. Hence, adults enhanced the quality of the larval substrate and significant benefits of aggregated oviposition in fruit flies were shown. Experiments with synthetic pheromone indicated that the aggregation pheromone itself did not contribute directly to the quality of the larval resource. 5. The interaction among adults, micro-organisms, and larval growth is discussed in relation to the consequences for total fitness.

Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion.

Abstract: Anuran larvae exhibit high levels of phenotypic plasticity in growth and developmental rates in response to variation in temperature and food availability. We tested the hypothesis that alteration of developmental pathways during the aquatic larval stage should affect the postmetamorphic performance of the Iberian painted frog (Discoglossus galganoi). We exposed tadpoles to different temperatures and food types (animal- vs. plant-based diets) to induce variation in the length of the larval period and body size at metamorphosis. In this species, larval period varied with temperature but was unaffected by diet composition. In contrast, size at metamorphosis was shaped by the interaction between food quality and temperature; tadpoles fed on an animal-based diet became bulkier metamorphs than those fed on plant-based food at high (22°C) but not at low (12°C) temperature. Body condition of newly metamorphosed frogs was unrelated to the temperature or food type experienced during the premetamorphic stage. Frogs maintained at high temperature during the larval period showed reduced jumping ability, especially when fed on the plant-based diet. However, when considering size-independent jumping ability, cold-reared individuals exhibited the lowest performance, and herbivores reared at 17°C the highest. Cold-reared (12°C) frogs accumulated larger amounts of energy reserves than individuals raised at 17°C or 22°C. This was still the case after correction for differences in body mass, thus indicating some size-independent effect of developmental temperature. Despite the higher lipid content of the carnivorous diet, the differences in energy reserves between herbivores and carnivores were relatively weak and associated with differences in body size. These results suggest that the consequences of environmental variation in the larval habitat can extend to the terrestrial phase and influence juvenile growth and survival.

Ecological regulation of development: induction of marine invertebrate metamorphosis.

Abstract: In the marine environment a wide range of invertebrates have a pelagobenthic lifecycle that includes planktonic larval and benthic adult phases. Transition between these morphologically and ecologically distinct phases typically occurs when the developmentally competent larva comes into contact with a species-specific environmental cue. This cue acts as a morphogenetic signal that induces the completion of the postlarval/juvenile/adult developmental program at metamorphosis. The development of competence often occurs hours to days after the larva is morphologically mature. In the non-feeding - lecithotrophic - larvae of the ascidian Herdmania curvata and the gastropod mollusc Haliotis asinina, gene expression patterns in pre-competent and competent stages are markedly different, reflecting the different developmental states of these larval stages. For example, the expression of Hemps, an EGF-like signalling peptide required for the induction of Herdmania metamorphosis, increases in competent larvae. Induction of settlement and metamorphosis results in further changes in developmental gene expression, which apparently is necessary for the complete transformation of the larval body plan into the adult form.

Characters of larvae: what are they?

Abstract: A b s t r a c t. The larval period in fishes has several definitions, each one deviating slightly from the other. Small discrepancies in the definitions, especially concerning the end of the larval period, can create misunderstandings when applied in practice. I examine the different definitions of a larva, the larval period, including metamorphosis, and the juvenile period. Various criteria used to identify the transition from the larval to juvenile periods are contradictory and refer mostly to the length of the larval period. Ignorance of definitions used to identify the juvenile period has caused many larvae to be regarded as juveniles. I discuss the feasibility of various definitions and the nomenclature on the basis of character evaluation. The occurrence of larval morphological characters, i.e. larval fin fold, differentiation of fins, temporary organs, absence of scale cover, non-adult like body proportions and pigmentation, is examined and some features are compared in eleven species. Irrespective of the different definitions of a larva, there are considerable differences in the schedule and duration of development in certain characters between species and, in terms of duration, also within species owing to environmental conditions. Ontogenetic processes seem to be sufficiently flexible to allow larvae to adapt to their environment, which on the other hand may also shape the phenotype. Determination of the environment in which a larva develops depends not only on the location of the spawning grounds but also on the dispersion of larvae. Dispersal strategies are examined in light of larval morphology and behaviour. After fin differentiation, the transition from larva to juvenile would seem to be best described by the dominant morphological changes in body proportions and coloration, combined with behavioural aspects and habitat changes. I suggest the differences and functional aspects of larvae be examined. The main character of larvae is that they are adapted to make use of resources not normally used by adults.

The evolution of metamorphosis in temnospondyls

Abstract: Temnospondyls, possible relatives of extant amphibians and crudely similar to recent salamanders, are known from larval, neotenic and metamorphosed stages. Here, ontogenetic data of various temnospondyl taxa are analysed in order to recognize metamorphosis. Here, metamorphosis is strictly defined as a shift from an aquatic to a terrestrial existence. Following a check-list of criteria, the most likely metamorphosis-induced changes are proved in three temnospondyl lineages: eryopids, zatrachydids and dissorophoids. In a few other, unrelated taxa, terrestrial adults are known but no larval or metamorphosing forms. The distribution of metamorphosis among the Temnospondyli does not strictly correlate with phylogeny, which highlights the widespread occurrence of neoteny. In each group, characteristic patterns of metamorphosis are described and compared. Among temnospondyls, dissorophoids had the most intensive type of metamorphosis, characterized by a condensed ontogeny and a relatively small body size. The result was a distinct transformed morphotype with far-reaching terrestrial adaptations.

Acceleration of Ambystoma tigrinum metamorphosis by corticotropin-releasing hormone

Abstract: Previous work of others and ours has shown that corticotropin-releasing hormone (CRH) is a positive stimulus for thyroid and interrenal hormone secretion in amphibian larvae and that activation of CRH neurons may mediate environmental effects on the timing of metamorphosis. These studies have investigated CRH actions in anurans (frogs and toads), whereas there is currently no information regarding the actions of CRH on metamorphosis of urodeles (salamanders and newts). We tested the hypothesis that CRH can accelerate metamorphosis of tiger salamander (Ambystoma tigrinum) larvae. We injected tiger salamander larvae with ovine CRH (oCRH; 1 microg/day; i.p.) and monitored effects on metamorphosis by measuring the rate of gill resorption. oCRH-injected larvae completed metamorphosis earlier than saline-injected larvae. There was no significant difference between uninjected and saline-injected larvae. Mean time to reach 50% reduction in initial gill length was 6.9 days for oCRH-injected animals, 11.9 days for saline-injected animals, and 14.1 days for uninjected controls. At the conclusion of the experiment (day 15), all oCRH-injected animals had completed metamorphosis, whereas by day 15, only 50% of saline-injected animals and 33% of uninjected animals had metamorphosed. Our results show that exogenous oCRH can accelerate metamorphosis in urodele larvae as it does in anurans. These findings suggest that the neuroendocrine mechanisms controlling metamorphosis are evolutionarily conserved across amphibian taxa.

Larval anurans with synchronous and asynchronous development periods: contrasting responses to water reduction and predator presence

Abstract: Summary 1 The larvae of pond breeding frogs experience high rates of mortality, predominantly through predation and pond desiccation. We investigated how the tadpoles of two common species of frog respond to these hazards using factorial experiments conducted in a laboratory. 2 The eastern brown froglet Crinia signifera Girard spawns in small, highly ephemeral ponds, while the spotted marsh frog Limnodynastes tasmaniensis Gunther breeds in more permanent water bodies. Prior to our experiments it was known that C. signifera siblings develop quickly and reach metamorphosis comparatively synchronously ( c . 25–35 days), while L. tasmaniensis grow and develop more slowly and time to metamorphosis is highly asynchronous ( c . 60–300 days). It was anticipated that these species would have different strategies for coping with declining water and predators. 3 A separate experiment was conducted for each species. The factors were Hydroperiod (either constant or gradually declining water volume) and Predator (either the presence or absence of a restrained mosquitofish Gambusia holbrookii Girard). A random block design was used with six replicates for each possible combination of the factors ( N = 24). Each replicate consisted of a 13-l tub of water containing 20 tadpoles. Newly emerged frogs were transferred to one of 24 vivaria. In the arrangement of the vivaria, we maintained the block design of the experiment. 4 Crinia signifera tadpoles responded to declining water by accelerating development and so reduced time to metamorphosis. However, the resulting metamorphs were smaller and survival rate in the terrestrial stage was significantly lower. This is a clear demonstration of the benefit and cost of phenotypic plasticity in metamorphic traits. 5 Limnodynastes tasmaniensis tadpoles experiencing declining water were also smaller at metamorphosis, but there was no evidence that they had reduced the time to metamorphosis compared with those in constant water. Moreover the survival rates of the resulting frogs did not differ. Consequently no adaptive plasticity can be inferred. 6 The data suggest that L. tasmaniensis has a bet-hedging strategy in which some siblings develop more quickly at the expense of size, while others take much longer but are bigger at metamorphosis as a result. 7 Tadpoles of both species showed clear behavioural responses to the presence of the predator. They tended to occupy the non-predator halves of the tubs in replicates where a mosquitofish was present. Neither species altered development rate in the presence of the predator and there was no detectable impact on survivorship in the terrestrial stage.

Carry-over effects of embryonic acid conditions on development and growth of Rana temporaria tadpoles

Abstract: 1. Conditions experienced during the early stages of development may have carry-over effects on performance during later life. The egg laying period and embryonic development of temperate and boreal zone amphibians often coincides with peak acidity resulting from spring snow-melt, but the effects of acid conditions during embryonic stage on subsequent performance are unknown. 2. We investigated the potential carry-over effects of acidity during the embryonic stage on performance up to metamorphosis in the common frog (Rana temporaria) tadpoles. There were four combinations of acid (4.5) and neutral (7.5) pH treatments applied to the egg and larval stages in a factorial laboratory experiment. In addition, we studied the difference in embryonic and larval tolerance of acidity between two populations originating from circumneutral (pH 6.6) and acidic conditions (pH 4.8). 3. The effects of acid conditions during the embryonic stage were sublethal, as indicated by delayed development and reduced size. Under acid conditions, tadpoles that had been raised in neutral water as embryos at first grew more slowly than tadpoles raised under acid conditions as embryos. At metamorphosis, no effects of embryonic acidity were detectable indicating that tadpoles were able to compensate fully for the initial reduction in growth. 4. Acid conditions during the larval period had a strongly negative effect on survival, size and age at metamorphosis. The amount of food consumed was lower under acid conditions, suggesting that reduced food consumption was at least partly responsible for the negative effects. 5. Although the two populations differed in the length of larval period, there was no indication of a differential response to the treatments in any of the metamorphic traits studied. 6. These results suggest that, although moderate acid conditions during embryonic development affect growth and development negatively, this influence does not persist after conditions have returned to normal. However, even moderately acid conditions during the larval period may have a strong negative influence on survival and performance of the tadpoles.

Increased individual growth rate and community biomass of stream insects associated with salmon carcasses

Abstract: We showed that salmon carcass tissue can increase the growth rate of individual caddisflies as well as increase the local biomass of the aquatic insect community in 3 major stream habitat types. Sixteen insect taxa were found on salmon carcasses. The 7 dominant taxa in terms of biomass all had greater biomass in containers baited with salmon flesh in all habitats sampled; however, only 5 showed a significant salmon effect at the Bonferroni adjusted α of 0.007. The larval growth of Ecclisomyia conspersa was significantly greater on salmon muscle tissue than on conditioned leaves. Asynarchus pacificus grew significantly better with a combination of salmon and conditioned leaves than with either conditioned leaves or salmon muscle tissue alone. Our findings contribute to the understanding of the transfer of marine nutrients between generations of salmonids via aquatic insects, which are important prey items of juvenile salmonids.

The life cycle of Micromalthus debilisLeConte (1878) (Coleoptera: Archostemata: Micromalthidae): historical review and evolutionary perspective

Abstract: Micromalthus debilisLeConte (1878 ), has one of the most bizarre life cycles of any metazoan. Reproduction is typically by thelytokous, viviparous, larviform females, but there is also a rare arrhenotokous phase. The active first-instar (triungulin) larva develops into a legless, feeding (cerambycoid) larva. This form either pupates, leading to a diploid adult female, or develops into any of three subsequent types of reproductive paedogenetic forms: (1) a thelytokous female that produces triungulins via viviparity; (2) an arrhenotokous female that produces a single egg that develops into the short-legged (curculionoid) larva, eventually devouring its mother and becoming a haploid adult male; or (3) an amphitokous female that can follow either of the two above reproductive pathways. We speculate that Micromalthus is dependent on maternally transmitted bacteria for the ability to digest rotting wood, and that these bacteria are senescent in males, causing males to be obligately cannibalistic. Obligate male cannibalism, in turn, would have dramatically increased the cost of males, and have created a strong selective advantage for cyclic thelytoky and the other features of the Micromalthus life cycle that minimize the role of the male.

Predation risk and competition effects on the life-history characteristics of larval Oregon spotted frog and larval red-legged frog

Abstract: We conducted an artificial pond experiment to test hypotheses about the effects of competition and non-lethal predator cues on metamorphic characteristics of sympatric Oregon spotted frogs (Rana pretiosa) and red-legged frogs (Rana aurora) in southwestern British Columbia. Tadpoles were exposed to the presence or absence of one another, two density levels and to the presence or absence of predacious odonate larvae (Aeshna palmata) isolated in enclosures. In the artificial pond study, R. aurora were significantly larger at metamorphosis (12%) and exhibited only slightly longer larval periods when exposed to Aeshna. In the presence of R. pretiosa, they significantly decreased time to metamorphosis, and were significantly larger at metamorphosis (12%) than those reared alone. Rana pretiosa in treatments with R. aurora were somewhat larger at metamorphosis when a non-lethal predator was present, and in treatments where R. pretiosa were alone with a predator tadpole mass at metamorphosis was smaller than those in the absence of Aeshna, but these results were not statistically significant. Both species reduced activity and moved away from the predator in the presence of an enclosed dragonfly larva in the laboratory. Most tadpole mesocosm experiments have found that the trade-off between size and timing of metamorphosis is extremely important to amphibians, but we suggest that the trade-off discussed in traditional amphibian models may not apply to species like R. pretiosa that are exposed to the same gape-limited predators upon reaching metamorphosis.

Coevolution of developmental plasticity and large egg size in Crinia georgiana tadpoles

Abstract: Developmental plasticity and large egg size are traits that can benefit offspring early in life, but their coevolution has rarely been examined. I experimentally manipulated water depth and food availability of larvae of the frog Crinia georgiana, a species with a large egg size that breeds in shallow seeps that often dry before tadpoles have metamorphosed. Tadpoles that were never fed completed metamorphosis at about the same time as tadpoles under constant conditions, although at much smaller body sizes and with higher mortality. Except for the earliest stage tested (Gosner stage 28), tadpoles that experienced a decrease in water depth accelerated development and completed metamorphosis earlier than tadpoles kept in constant conditions. Acceleration was not possible when food was withheld, except when water levels were also lowered and only during later developmental stages. Because acceleration of development was initiated at earlier larval stages than in small-egged species that breed in ephe...

Microcosm studies on intraguild predation between female erigonid spiders and lacewing larvae and influence of single versus multiple predators on cereal aphids

Abstract: Intraguild predation between female erigonid spiders [Erigone atra (Blackwall) and Oedothorax apicatus (Blackwall), Araneae, Erigonidae] and lacewing larvae (second instar larvae of Chrysoperla carnea (Stephens), Neuropt., Chrysopidae) and interaction effects of predator combinations on cereal aphids were investigated in a microcosm system under laboratory conditions. The microcosm experiments were run for 7 days and consisted of 15wheat seedlings, 15 Sitobion avenae (F) (Hom., Aphididae) as start population, plus a female spider or a lacewing larva or a combination of a spider plus a lacewing larva. The mortality rate of lacewing larvae was significantly increased by 44 and 31% due to intraguild predation by female spiders of E. atra and O. apicatus in comparison with lacewing larvae that were kept alone. The final aphid numbers in the microcosms were significantly reduced by all single predator treatments (spiders, lacewing larvae) and the predator combinations in comparison with controls without predators. The predation effect on aphid populations due to both spider species was similar and not statistically different. An additive effect of the predator combinations ‘spider plus surviving lacewing larva’ was found for both spider species resulting in reduced aphid numbers compared with the single predator treatments. When the lacewing larva was killed by an E. atra female the effects on aphids were non-additive, but aphid numbers were not statistically increased compared with the lacewing larva treatment. When the lacewing larva was killed by an O. apicatus female, the effects of spider and C. carnea larva were additive on aphid numbers. In the presence of additional prey (fruit flies and Collembola) intraguild predation was not found and E. atra females had no significant effect on the survival of lacewing larvae. In addition, E. atra females had no significant effect on aphid numbers in the presence of fruit flies and Collembola, but in combination with a lacewing larva that survived, a significantly greater reduction of the aphid population was observed compared with the lacewing larva treatment. The body mass of lacewing larvae at the end of the experiment was not statistically influenced by the presence or absence of an E. atra female.

Pond attributes influence competitive interactions between tadpoles and mosquito larvae

Abstract: Tadpoles and mosquito larvae often coexist in natural freshwater bodies. We studied competitive interactions between: (i) tadpoles of the striped marsh frog (Limnodynastes peronii) and larvae of the mosquito Culex quinquefasciatus; and (ii) tadpoles of the common eastern froglet (Crinia signifera) and larvae of the mosquito Aedes australis. These two sets of taxa occur in natural water bodies in the Sydney region. Laboratory trials revealed competition between mosquito larvae and tadpoles in both systems. For example, mosquitoes displayed reduced rates of survival, growth and development, and smaller size at metamorphosis, when they were raised with tadpoles. The intensity of competitive suppression was influenced by attributes such as pond size (and hence, larval density), the location of food (on the water surface vs the substrate), and the extent of opportunities for direct physical interactions between the two competing organisms. These effects differed between the two study systems, suggesting that the mechanisms of suppression also differed. Limnodynastes peronii tadpoles suppressed C. quinquefasciatus even when the two types of organisms were separated by a physical partition, suggesting that chemical or microbiological cues may be responsible. Pond attributes also affected the impact of C. signifera tadpoles on Aedes larvae, but (unlike the Limnodynastes–Culex system) these effects disappeared when densities were lowered or when the tadpoles and mosquito larvae were physically separated. Thus, direct physical interactions may suppress mosquitoes in the Crinia–Aedes system. Our results suggest that tadpoles suppress the viability of larval mosquitoes by multiple pathways.

Increase in descending brain-spinal cord projections with age in larval lamprey: implications for spinal cord injury.

Abstract: The purpose of this study was to determine whether new descending brain-spinal cord projections are added with age in larval lamprey and might contribute substantially to restoration of these projections following spinal cord injury. Retrograde horseradish peroxidase (HRP) labeling of descending brain neurons was performed in “young” and “old” larval lamprey that differed in age by at least one year. In old larval lamprey, significantly more descending brain neurons projected to specific rostral levels of the spinal cord than in young animals. Furthermore, in young and old lamprey, the main morphological change in Muller and Mauthner cells was an increase in soma size. The major conclusion from the present study is that in larval lamprey, some new brain-spinal cord projections are added with age that could be due to axonal elongation by preexisting brain neurons and/or descending projections from new neurons (i.e., neurogenesis or maturation of incompletely differentiated neurons). Following spinal cord transections, the numbers of descending projections were not significantly different than those in normal, unlesioned animals. Thus, some new descending projections are added with age, but at a relatively slow rate, and the rate does not appear to be affected significantly by spinal cord transections. Together, the present results and those from our recent double-labeling study suggest that following spinal cord transection in larval lamprey, axonal regeneration by descending brain neurons, rather than the relatively slow addition of new brain-spinal cord projections with age, probably accounts for the majority of restored projections and recovery of locomotor function. J. Comp. Neurol. 447:128–137, 2002. © 2002 Wiley-Liss, Inc.

First Report of Immatures, Genitalia and Maternal Care in Eugenysa columbiana (Boheman) (Coleoptera: Chrysomelidae: Cassidinae: Eugenysini)

Abstract: Illustrated descriptions of larvae, pupae and adult genitalia are provided for Eugenysa columbiana (Boheman) in Costa Rica. These represent the first such descriptions for the tribe Eugenysini. Females are reported as exhibiting guarding of larvae and pupae. Male presence with the female and larval group is also described. The distribution range is extended to Peru, and host plant data is recorded. A new character from the spermatheca is presented and its potential usefulness in deducing eugenysine relationships is discussed.

DESENVOLVIMENTO DE Diabrotica speciosa (Germar) (COLEOPTERA: CHRYSOMELIDAE) EM DIFERENTES HOSPEDEIROS DEVELOPMENT OF Diabrotica speciosa (Germar) (COLEOPTERA: CHRYSOMELIDAE) IN DIFFERENT HOST PLANTS

Abstract: SUMMARY The aim of this work was to determine the influence of the host plant, as food, on the larval and adult phases of D. speciosa. Larvae of this insect were reared on seedlings of bean, corn, soybean, as well as on potato tubers kept in wet vermiculite. The following biological parameters were evaluated: duration and viability of the larva-adult period and the weight of newly emerged insects (males and females). The fecundity of D. speciosa was also evaluated offering to the adults leaves of bean, soybean, corn and potato. The host plant offered as food on the larval phase influenced significantly the weight of the insects (males and females) as well as the duration and viability of the larva-adult period. The development time of the immature phases (larva + pupa) on potato (36.5 days) was longer than that on corn (25.1 days). The viability values (larva + pupa) were higher on potato (84.1%) and corn (75.9%) while on soybean and bean the viability was low (30.1% and 9.4%, respectively), characterizing these plants as inadequate hosts for the larval development of the insect. Adults of

Overwintering Population of Maize Stem Borer Chilo partellus (Swinhoe) at High Altitudes of Kashmir

Abstract: The present work regarding the overwintering population of maize stem borer Chilo partellus (Swinhoe) at larval stage was conducted in order to determine degree of overwintering population and the level of infestation of this pest at different localities of Azad Kashmir. Off 1796 stubbles of maize, present findings showed that over all high population of C. partellus (29.1%) larvae was recorded from locality Chota Gala while the lower (18.73%) was from Rawalakot locality. Whereas greater population (27.77%) of overwintering was found on the stubbles of maize genotype "Kashmir Gold" than "Sarhad White" (20.75%). A significant difference in overwintering population was found among all the studied localities. The percentage of infestation (on the basis of exit hole on stubbles) caused by C. partellus was significantly (P<0.001) high (27.77%) on "Kashmir Gold" than on the "Sarhad White" (15.99%) in all the studied areas. No clear relationship was found between the stem thickness and the overwintering population of maize stem borer or its infestation.

Morphology of the prometamorphic larva of the spadefoot toad, Scaphiopus intermontanus (Anura: Pelobatidae), with an emphasis on the lateral line system and mouthparts

Abstract: We provide a detailed description of the larval morphology of the Great Basin spadefoot toad (Scaphiopus intermontanus), a species with documented morphological variability in larval structures associated with feeding. We based our findings on laboratory-raised individuals fed a herbivorous diet. We characterized the morphology of the prometamorphic larva (limited to developmental stages 37 and 38) and then related our findings to the larval ecology of the species. Based on its morphology, such as slightly depressed body, dorsally positioned eyes, anteroventrally oriented oral disc, intermediate tail fin height and slightly attenuated tail tip, relative lack of ventral neuromasts (compared to Xenopus laevis), and pigmentation banding patterns, and habits, such as selection of breeding sites by adults and larval foraging behavior, S. intermontanus can be characterized best as belonging to a (lentic-) benthic guild of anuran larvae. Nevertheless, the larvae are capable of occupying a broader array of ecological niches. Because we characterized individuals raised on a herbivorous diet, our morphological descriptions apply only to the herbivorous S. intermontanus larva (and perhaps to those larvae that are dietary generalists and may feed carnivorously only infrequently). Our findings can serve as a baseline for future morphological and developmental comparisons with the carnivorous morphological variant of this species. J. Morphol. 252:114–130, 2002. © 2002 Wiley-Liss, Inc.

Alfalfa weevil (Coleoptera: Curculionidae) larval sampling: comparison of shake-bucket and sweep-net methods and effect of training.

Abstract: Two field-sampling methods, shake-bucket and sweep-net, were compared for use in monitoring alfalfa weevil, Hypera postica (Gyllenhal), larvae in alfalfa hay of the high plains and intermountain region of North America. In this region, alfalfa grows to sufficient height to use both methods before the more damaging late instars peak in abundance. Both methods also were compared with extracting larvae by using Berlese funnels in the laboratory. The shake-bucket method was more sensitive in detecting small larvae (first and second instars) than large larvae (third and fourth instars), and the sweep-net method detected a lower proportion of small larvae. The number of larvae collected with the shake-bucket method was strongly correlated with number of larvae recovered from Berlese funnels (total larval counts, R2 = 0.85). Correlation of the sweep-net samples with the Berlese extraction was also significant but less strong (R2 = 0.56). In addition, sampler instruction was evaluated to determine whethe...

Competition between tadpoles and mosquitoes: the effects of larval density and tadpole size

Abstract: Tadpoles and mosquito larvae compete for scarce resources in natural freshwater ecosystems, but factors determining the extent of competition between these two groups of organisms remain largely unstudied. Natural ponds display great variation both in the densities of larvae, and in the body sizes of tadpoles. We set up replicated artificial pond experiments to examine the effects of population density and tadpole size on interactions between tadpoles and mosquito larvae. We examined the effects of larval density in two systems of co-occurring tadpoles and mosquito larvae, one from brackish-water ephemeral ponds (Crinia signifera with Ochlerotatus australis) and one from permanent freshwater ponds (Limnodynastes peronii with Culex quinquefasciatus). In both systems, increasing densities of larvae suppressed growth and development both of conspecifics and of the competing taxon. In the C. quinquefasciatus–L. peronii system, larger tadpoles exerted more powerful suppression. Our results suggest that mosquito developmental rates and adult body sizes (and thus, the danger which mosquitoes pose to public health) may be reduced if natural water-bodies contain dense populations of large tadpoles.

Fitness consequences of the timing of metamorphosis in a freshwater crustacean

Abstract: Metamorphosis is a common life-cycle transition in organisms as diverse as amphibians, insects, fishes and crustaceans, and the timing of this transition often affects an individual's fitness. Here, we measured age and size at metamorphosis in laboratory-reared individuals of the freshwater copepod, Diaptomus leptopus, and then followed individuals over their entire life cycle to assess the fitness consequences of variation in age and size at metamorphosis. In 3 separate experiments, individuals were raised in different food conditions: low food (0.2 μg C/ml) switched to high food (0.7 μg C/ml), or high food switched to low food, at several different larval and juvenile stages. Control individuals were reared on high or low food concentrations over their entire life cycles. For each individual, we measured age and size at metamorphosis and age and size at maturity; for females, we also measured total lifetime egg production, longevity, and calculated a composite fitness measure, λ. Statistical analyses showed no significant effects of age or size at metamorphosis on these same traits measured at maturity, or on the fitness components we estimated. The first individuals to mature had the highest total egg production and individual fitness; differences in body size at maturation explained none of the variation observed in fitness components. Our results show that metamorphosis was uncoupled from maturity and from fitness components by growth and development achieved during the juvenile phase of the life cycle, and support the conclusion that fitness consequences of metamorphosis depend fundamentally on the organization of an organism's life cycle. They also suggest that body size plays a different life-history role in these organisms than is recognized in most poikilotherms, and suggest the hypothesis, based on laboratory experiments, that selection may act primarily on juvenile developmental rates in field populations.