The energetic costs of case construction in the caddisfly Limnephilus rhombicus: direct impacts on larvae and delayed impacts on adults

Caddisflies, whose aquatic larvae build a portable case with silk, are a suitable model organism to test the impacts of resource allocation trade-off during development and examine the evolution of life-history strategies. In the caddisfly Limnephilus rhombicus, adult feeding is minimal. Therefore, the whole resources are acquired during the larval phase and must be allocated to case construction, growth and reproduction. In this study, the larval energetic reserves of L. rhombicus were manipulated by forcing larvae to rebuild their cases in the final larval stage. This allowed us to measure the physiological cost of construction. First, we recorded oxygen consumption during case reconstruction. Second, we measured the sugar, protein and lipid contents of larvae forced to rebuild their case and of larvae required only to re-enter on their case. Larvae had their sugar, protein and lipid content measured after the rebuilding event and 72 h later. The same analyses were carried out with adults immediately after emergence. We found that larvae forced to rebuild a case consumed 1.5 times more oxygen than control larvae. This energy expenditure generated a cost that was estimated to be a loss of larval protein of approximately 35%. Insects were unable to compensate for this loss of proteins during the end of the larval stage, and their metamorphosis to adults was also impacted. Therefore, we suggest that loss of larval protein is linked to silk production and may alter fitness.     

What does not kill them makes them stronger: larval environment and infectious dose alter mosquito potential to transmit filarial worms

For organisms with complex life cycles, larval environments can modify adult phenotypes. For mosquitoes and other vectors, when physiological impacts of stressors acting on larvae carry over into the adult stage they may interact with infectious dose of a vector-borne pathogen, producing a range of phenotypes for vector potential. Investigation of impacts of a common source of stress, larval crowding and intraspecific competition, on adult vector interactions with pathogens may increase our understanding of the dynamics of pathogen transmission by mosquito vectors. Using Aedes aegypti and the nematode parasite Brugia pahangi, we demonstrate dose dependency of fitness effects of B. pahangi infection on the mosquito, as well as interactions between competitive stress among larvae and infectious dose for resulting adults that affect the physiological and functional ability of mosquitoes to act as vectors. Contrary to results from studies on mosquito–arbovirus interactions, our results suggest that adults from crowded larvae may limit infection better than do adults from uncrowded controls, and that mosquitoes from high-quality larval environments are more physiologically and functionally capable vectors of B. pahangi. Our results provide another example of how the larval environment can have profound effects on vector potential of resulting adults.     

Relationship between photoperiod and secretion of the diapause hormone during larval stages of the silkworm, Bombyx mori L., reared on an artificial diet

The suboesophageal ganglion of the silkworm, Bombyx mori synthesizes sufficient diapause hormone to produce diapause eggs, regardless of the photoperiodic conditions experienced during the larval stages. When larvae destined to produce non-diapause eggs are implanted with the brain-suboesophageal ganglion complex from larvae which have been reared under short-day conditions, the resulting adults lay diapause eggs. The larvae receiving the complex from larvae reared under long-day conditions gave rise to adults which did not produce any diapause eggs. The brains from pupae which have been reared under long-day conditions show an activity inhibiting the secretion of diapause hormone by the suboesophageal ganglion. The mechanism through which the brain controls the secretion of diapause hormone from the suboesophageal ganglion can be modified by photoperiodic conditions during the larval stages.     

Ontogeny of the immune system in Xenopus: II. Antibody repertoire differences between larvae and adults

The larvae and adults of genetically identical clones of Xenopus each produce different populations of antibodies to dinitrophenylated keyhole-limpet hemocyanin (DNP-KLH) upon immunization. The larvae and adults differed with regard to the affinity of their IgM antibodies and the isoelectric-focusing pattern of their low-molecular-weight-Ig (IgG equivalent) antibodies. The larval antibody repertoire for DNP was not changed by the addition of adult helper T cells. Thus, the expression of a larval repertoire is the result of a B-cell pool peculiar to larvae and is not influenced, except in its quantity, by adult T cells.     

Territorial behaviour of larvae enhances mating success of male dragonflies

Laboratory experiments showed that the predatory aquatic larvae of the dragonfly, Pyrrhosoma nymphula, are territorial, defending feeding sites against intruders, and also that body length in the final instar is positively correlated with the provision of food during the last three or four larval instars. Larval length is positively correlated with larval head width which is likewise correlated with both the weight and head width of 1-day-old adults. Field observations demonstrated that larger male adults win more territorial disputes and obtain more matings near water. So the success of larvae in defending territories enhances short-term mating success in adult males.     

Larval settlement and metamorphosis in the slipper limpet Crepidula onyx (Sowerby) in response to conspecific cues and the cues from biofilm

In the marine environment, aggregated distribution in the genus Crepidula is a very common phenomenon. Works from Pechenik's group suggested that this is the result of gregarious settlement of larvae in response to cues associated with conspecific adults. In this study, we investigated the existence of larval metamorphic cues associated with adults of C. onyx, a slipper limpet introduced to Hong Kong from the U.S. in the 1970s, through a series of laboratory bioassays. The results showed that derived cues in adult C. onyx were waterborne and the waterborne cues were not derived from bacteria associated with the shell and soft body of the adult Crepidula. The natural biofilm also induced the larval metamorphosis of C. onyx. The cues from the biofilm were associated with the surface of the biofilm and were not waterborne. The aggregated distribution in nature of adult C. onyx may result from a selective larval settlement process. On a small scale in the water column near the conspecific adults, larvae of C. onyx initially detect the waterborne conspecific cues, which then lead to positive downward swimming or passive sinking. This activity increases the chances for larvae to make contact with the biofilm and to be exposed into the higher concentration of waterborne conspecific cues. This may eventually lead to the enhanced larval settlement pattern on or near the conspecific adults.     

Drosophila adult and larval pheromones modulate larval food choice

Insects use chemosensory cues to feed and mate. In Drosophila, the effect of pheromones has been extensively investigated in adults, but rarely in larvae. The colonization of natural food sources by Drosophila buzzatii and Drosophila simulans species may depend on species-specific chemical cues left in the food by larvae and adults. We identified such chemicals in both species and measured their influence on larval food preference and puparation behaviour. We also tested compounds that varied between these species: (i) two larval volatile compounds: hydroxy-3-butanone-2 and phenol (predominant in D. simulans and D. buzzatii, respectively), and (ii) adult cuticular hydrocarbons (CHs). Drosophila buzzatii larvae were rapidly attracted to non-CH adult conspecific cues, whereas D. simulans larvae were strongly repulsed by CHs of the two species and also by phenol. Larval cues from both species generally reduced larval attraction and pupariation on food, which was generally—but not always—low, and rarely reflected larval response. As these larval and adult pheromones specifically influence larval food search and the choice of a pupariation site, they may greatly affect the dispersion and survival of Drosophila species in nature.     

Ommochrome synthesis and kynurenic acid excretion in relation to metamorphosis and allatectomy in the stick insect, Carausius morosus Br.

End products of tryptophan metabolism in Carausius morosus are the ommochromes ommin and xanthommatin in the epidermis, and kynurenic acid in the faeces. During larval and adult life ommochromes and mainly kynurenic acid are formed. The concentration of kynurenic acid in the faeces of adult females is 2.5 times lower than in the larvae and in adult males. Allatectomy on the first day after a larval moult induces a much longer instar (10 days) than normal. After the following moult, the allatectomized animals are transformed into adultoids. The allatectomized and normal larvae produce similar amounts of kynurenic acid and ommochrome during the larval instar. Twenty days after last ecdysis, the ommochrome content in adult and adultoids is increased. In the faeces of adultoids, however, the concentration of kynurenic acid is higher than in normal female adults, but lower than in males and larvae.     

Tipula iridescent virus infection in the developmental stages of Tipula oleracea

Tipula iridescent virus (TIV) is infective to all four larval instars, pupae, and adults of both sexes of Tipula oleracea, and iridescence has been observed in infected insects at all these stages. Third- and fourth-instar larvae were more resistant to ingested TIV than first and second instars. When TIV was injected into the hemocoel, the results suggested a possible decrease in resistance from the third larval instar to the pupa. Incubation periods (times from injection of TIV to appearance of iridescence) were significantly shorter in older fourth-instar larvae than in younger fourth-instar or thirdinstar larvae, but variability in incubation period was significantly greater in younger fourth-instar larvae than in the other two stages. Many insects which were inoculated with TIV in one stage developed iridescence and died in later stages. The amounts of infective TIV in two infected adults were estimated.     

Immunocompetence of the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae): Variation between developmental stages and sexes in populations in China

Immune defense imposes fitness costs as well as benefits, so organisms should optimize, not maximize, their immune function through their life cycle. We investigated this issue in the red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), which is a pine-killing invasive beetle in China, though it is usually considered as a secondary pest in its native range of North America. We hypothesized that pathogen pressure may affect these beetles differently throughout their life history. We measured the insect's immunocompetence throughout life, determining encapsulation ability and phenoloxidase activity in larval stages, pupae and adults. Pupae had the highest encapsulation ability, but encapsulation was not different between final instar larvae and adults. Phenoloxidase (PO) activity was highest in final instar larvae and pupae, followed by the second instar larvae and adults. Total phenoloxidase activity increased significantly from the second instar larval stage to pupae, and then decreased in adults. Although the second instar larvae had the lowest phenoloxidase activity, more than 90% of total PO existed in the hemolymph in the form of the active enzyme, as compared with pupae, in which over 60% of PO occurred as a proenzyme. Both active PO and total PO were much higher in females than in males, though no significant differences were detected between the encapsulation ability of male and female adults. This result suggests the existence of a sexual dimorphism of immunocompetence in D. valens adults. Variations in immunocompetence across developmental stages suggest that D. valens adopts diverse investment strategies in immunocompetence during different stages. Potential reasons for variation in immunocompetence among developmental stages and between the sexes of D. valens are discussed.     

Loss of larval parasitism in parasitengonine mites

Larval Parasitengona are typically parasites, yet at least 29 species of water mites and one species of Trombidiidae forgo larval feeding and any association with a host. Species with non-feeding larvae are isolated cases within species groups or genera where the remaining species have parasitic larvae. Species without larval parasitism occur in at least 14 genera, eight families and four superfamilies of water mites; the loss of larval parasitism is presumably polyphyletic, having occurred at least 21 times. Lineages of water mites with non-feeding larvae frequently exist in parallel with almost identical populations or species that have parasitic larvae. Thus, there is tremendous potential for studies comparing the relative merits of the two life history strategies. Comparisons indicate that adults from lineages with non-parasitic larvae produce smaller numbers of larger eggs; the extra nutrition included in larger eggs permits the larvae to forgo feeding. Non-feeding larvae frequently have wider dorsal plates but reduced leg length, setal length and sclerotization when compared to parasitic larvae from sister lineages. The adults of lineages with non-feeding larvae are frequently smaller in comparison to adults of sister lineages with parasitic larvae. There is no apparent pattern in relation to habitat: lineages lacking larval parasitism occur in streams, temporary ponds and the littoral and planktonic regions of permanent lakes. © Rapid Science Ltd. 1998     

The importance of life-history stage and individual variation in the allorecognition system of a marine sponge

In marine invertebrates with complex life cycles, it may often be the case that trade-offs and behaviors differ between adult and larval stages. In this study, I examined the effects of life-history stage on allorecognition system function in the sponge, Haliclona sp. For sedentary marine invertebrates, allorecognition systems allow individuals to distinguish between genetically similar and distinct tissue they may encounter and are thought to reduce costly tissue fusion with individuals other than self or kin. Although it was found that sessile adults fused preferentially with self-tissue and exhibited a functioning allorecognition system, free-swimming larvae fused equally with sibling and non-sibling larvae resulting in swimming chimeras capable of successful metamorphosis, suggesting a stage-activated allorecognition system. In addition, adult sponges differed significantly in the propensity of their larvae to fuse suggesting variation in parental strategies. Analysis of larval swimming behavior indicated that larvae aggregate and are capable of increasing their encounters with other larvae and perhaps their probability of fusing in nature. The pursuit of fusion at this motile stage, along with evidence of a functioning adult allorecognition system, suggests that larvae may not express a recognition system, or that factors other than relatedness such as benefits to larval or adult chimeras, are involved in larval fusion and a stage-activated allorecognition system. In addition, this study demonstrates the presence of variation among individuals in the allorecognition system's ontogeny in the sponge Haliclona sp.     

Molecular identification and larval morphological description of Contracaecum pelagicum (Nematoda: Anisakidae) from the anchovy Engraulis anchoita (Engraulidae) and fish-eating birds from the Argentine North Patagonian Sea

Anisakids use invertebrates as paratenic and/or intermediate hosts as a basic feature of larval transmission. The third-stage larva usually develops in invertebrates which are prey items of finfish paratenic hosts. Contracaecum larvae molt twice inside the egg and hatch as free third-stage larvae ensheathed in the second-stage larval cuticle. Copepods act as paratenic or obligatory hosts, usually ingesting these free L3 larvae, and fish act as intermediate/paratenic or metaparatenic hosts preying on infected copepods. Fish-eating birds acquire L3 larvae by ingesting infected fish where they develop into the fourth-stage larvae and adults. Objectives of this work were to establish the specific correspondence between Contracaecum pelagicum L3 larvae parasitizing the anchovy Engraulis anchoita, and the adults parasitizing the Magellanic penguin Spheniscus magellanicus and the Imperial shag Phalacrocorax atriceps through the use of molecular markers; and, to evaluate the anisakid L3 larval recruitment and infection caused by ingestion of anchovy by S. magellanicus. Sixteen specimens of Contracaecum L3 larvae were analyzed from E. anchoita from Bahía Engaño, Chubut, eight adult nematodes from S. magellanicus and six adult specimens from P. atriceps both from the Valdés Peninsula, Chubut. All nematodes were sequenced for three genes: mitochondrial cytochrome oxidase 2 (mtDNA cox2), mitochondrial ribosomal RNA (rrnS), and the internal transcribed spacers (ITS-1 and ITS-2) of the nuclear ribosomal DNA region. Phylogenetic analyses were performed by using Maximum Parsimony (MP) analysis by PAUP. In addition, studies under SEM and LM were carried out on L3 larvae. All L3 individuals from E. anchoita, adults from S. magellanicus, and P. atriceps clustered in the same clade, well supported in the MP tree inferred from the mtDNA cox2, and rrnS gene sequences analyses. Further, the sequence alignments of L3 larvae and adults of C. pelagicum here obtained at the ITS-1 and ITS-2 regions of the rDNA matched the sequences of C. pelagicum previously deposited by us in GenBank. Nematode recruitment (R_o) was equal to 33.07 (7.20–91.14) L3 larvae for C. pelagicum in each penguin's meal of anchovy. The MP tree topologies obtained from mtDNA cox2 and rrnS genes demonstrated that specimens of Contracaecum L3 larvae from E. anchoita and C. pelagicum from S. magellanicus as well as from P. atriceps constitute a unique clade, well-distinct and supported from all the others formed by the Contracaecum spp. sequenced so far for these genes. Molecular markers are considered to be an effective tool to elucidate larval transmission. The Contracaecum L3 larval recruitment value showed that many worms fail to establish in the bird digestive tract, probably because they are below a critical size. Further work is needed to elucidate other factors (e.g., physiological, immunological) that control nematode populations in the penguin digestive tract.     

Drosophila Clueless Is Highly Expressed in Larval Neuroblasts,Affects Mitochondrial Localization and Suppresses Mitochondrial Oxidative Damage

Mitochondria are critical for neuronal function due to the high demand of ATP in these cell types. During Drosophila development, neuroblasts in the larval brain divide asymmetrically to populate the adult central nervous system. While many of the proteins responsible for maintaining neuroblast cell fate and asymmetric cell divisions are known, little is know about the role of metabolism and mitochondria in neuroblast division and maintenance. The gene clueless (clu) has been previously shown to be important for mitochondrial function. clu mutant adults have severely shortened lifespans and are highly uncoordinated. Part of their lack of coordination is due to defects in muscle, however, in this study we have identified high levels of Clu expression in larval neuroblasts and other regions of the dividing larval brain. We show while mitochondria in clu mutant neuroblasts are mislocalized during the cell cycle, surprisingly, overall brain morphology appears to be normal. This is explained by our observation that clu mutant larvae have normal levels of ATP and do not suffer oxidative damage, in sharp contrast to clu mutant adults. Mutations in two other genes encoding mitochondrial proteins, technical knockout and stress sensitive B, do not cause neuroblast mitochondrial mislocalization, even though technical knockout mutant larvae suffer oxidative damage. These results suggest Clu functions upstream of electron transport and oxidative phosphorylation, has a role in suppressing oxidative damage in the cell, and that lack of Clu’s specific function causes mitochondria to mislocalize. These results also support the previous observation that larval development relies on aerobic glycolysis, rather than oxidative phosphorylation. Thus Clu’s role in mitochondrial function is not critical during larval development, but is important for pupae and adults.     

Survival and behavioral characteristics of amphidromous goby larvae of Sicyopterus japonicus (Tanaka, 1909) during their downstream migration

To understand the ecology and environmental tolerances of newly hatched larvae of the amphidromous fish Sicyopterus japonicus during their downstream migration, the salinity tolerance of eggs, 0-15 day old larvae, and adults, and the temperature tolerance, specific gravity and phototaxis of hatched larvae were examined. Tolerances of adults were measured as survival after a 24 h challenge in freshwater (FW), brackish water (1/3 SW) and seawater (SW). The survival rate of adult S. japonicus was 100% in FW and 1/3 SW, while none survived in SW. Hatching success of eggs (30 eggs each) was significantly higher in FW (mean: 73%) and 1/3 SW (73%) than in SW (19%). Tolerance of newly hatched larvae to salinity and temperature was investigated in different combinations of salinities (FW, 1/3 SW and SW) and temperatures (18, 23 and 28 °C). Larval survival was significantly different in each salinity and temperature. Survival rate was significantly higher in 1/3 SW than in FW and higher in SW than in FW at 23 °C and 28 °C. At the latter part of the experiment, there was no survival in FW and at 28 °C. Survival was higher in lower temperatures, but larval development did not occur in FW. Specific gravity of newly hatched larvae was 1.036 at 28 °C and 1.034 at 23 °C. When exposed to a light source on one side of an aquarium, larval distribution was not affected. Our results indicated larval S. japonicus are more adapted to brackish water and seawater than freshwater, while the adults and eggs are more adapted to freshwater and brackish water than seawater. This is consistent with their amphidromous life history with growth and spawning occurring in freshwater and the larval stage utilizing marine habitats.     

Pyrokinin/PBAN-like peptides in the central nervous system of mosquitoes

The pyrokinin/pheromone biosynthesis activating neuropeptide (PBAN) family of peptides is characterized by a common C-terminal pentapeptide, FXPRLamide, which is required for diverse physiological functions in various insects. Polyclonal antisera against the C-terminus was utilized to determine the location of cell bodies and axons in the central nervous systems of larval and adult mosquitoes. Immunoreactive material was detected in three groups of neurons in the subesophageal ganglion of larvae and adults. The corpora cardiaca of both larvae and adults contained immunoreactivity indicating potential release into circulation. The adult and larval brains had at least one pair of immunoreactive neurons in the protocerebrum with the adult brain having additional immunoreactive neurons in the dorsal medial part of the protocerebrum. The ventral ganglia of both larvae and adults each contained one pair of neurons that sent their axons to a perisympathetic organ associated with each abdominal ganglion. These results indicate that the mosquito nervous system contains pyrokinin/PBAN-like peptides and that these peptides could be released into the hemolymph. The peptides in insects and mosquitoes are produced by two genes, capa and pk/pban. Utilizing PCR protocols, we demonstrate that products of the capa gene could be produced in the abdominal ventral ganglia and the products of the pk/pban gene could be produced in the subesophageal ganglion. Two receptors for pyrokinin peptides were differentially localized to various tissues.     

Developmental analysis of two mutations affecting chemotactic behavior in Drosophila melanogaster.

InDrosophila melanogaster, gusA^Q1, a cold-sensitive mutation, affects the behavior of larvae and adults tested with quinine sulfate. The temperature-sensitive period ofgusA^Q1 occurs during embryogenesis. Another cold-sensitive mutation,gusE^N13, alters the response of adults to quinine sulfate without affecting larval behavior. The temperature-sensitive period of this mutation is during the third larval instar.     

Relationship between adult and larval host plant selection and larval performance in the generalist moth, Trichoplusia ni

Adult oviposition preferences are expected to correlate with host plant suitability for the development of their offspring. For most lepidopteran species, this is particularly important as the hatching neonate larvae of many species are relatively immobile. Thus, the site of oviposition chosen by a female adult can greatly influence the probability of survival for her offspring. In the present study, we investigated the oviposition preference of adult Trichoplusia ni moths for six plant species to determine whether they could accurately rank the suitability of the plants for larval development. We also compared oviposition preferences to neonate larval acceptance and preference to determine whether the adult host range matched that of larval diet breath. Our results indicate that in two-choice and no-choice tests adult T. ni were able to rank the plants accurately, with the exception of anise hyssop. However, when given a choice of all six plants together, they laid more eggs on a plant that was not suitable for larval survival. Larvae accepted and fed on all plants in no-choice tests, and accurately ranked them according to larval performance. We conclude that neonate larvae are better able than adults to rank plants according to larval performance, and that larval diet breadth is wider than the range of plants accepted by adults. We also provide a discussion of the reduced accuracy of adult oviposition preference with increased plant choices.     

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite. International journal for Parasitology4: 183–191. Migration of the pre-intestinal larval stages of N. brasiliensis was studied in rats undergoing either primary or challenge infections. In rats undergoing a primary infection, more than 67 percent of larvae successfully migrated from the skin to the oesophagus by 70 h after infection, and subsequently over 90 per cent of these larvae became established in the small intestine as sexually mature adults. In immune rats undergoing a second infection, 46 per cent of larvae completed migration to the oesophagus by 70 h and of these, only 1·6 per cent became established in the intestine to produce eggs. These inhibitory effects on the pre-intestinal and intestinal larval stages were even more pronounced in immune rats undergoing a third or fourth infection and in addition, there was a prolonged sojourn and substantial retention of larvae in their lungs. There was no evidence that the immune response had an adverse effect on oesophageal fourth stags larvae as these organisms (obtained from immune donors) were able to establish and develop to maturity when transferred per os to normal animals.Syngeneic transfer of immune mesenteric lymph node cells to normal recipients, caused expulsion of parasites from the intestine but failed to effect migration of pre-intestinal larval stages. The implications of these findings are discussed in the context of current knowledge of the mechanisms of immunity to helminths.