Abdominal Hemocoel Research Articles

Contraction of the Ventral Abdomen Potentiates Extracardiac Retrograde Hemolymph Propulsion in the Mosquito Hemocoel

BackgroundHemolymph circulation in mosquitoes is primarily controlled by the contractile action of a dorsal vessel that runs underneath the dorsal midline and is subdivided into a thoracic aorta and an abdominal heart. Wave-like peristaltic contractions of the heart alternate in propelling hemolymph in anterograde and retrograde directions, where it empties into the hemocoel at the terminal ends of the insect. During our analyses of hemolymph propulsion in Anopheles gambiae, we observed periodic ventral abdominal contractions and hypothesized that they promote extracardiac hemolymph circulation in the abdominal hemocoel.Methodology/Principal FindingsWe devised methods to simultaneously analyze both heart and abdominal contractions, as well as to measure hemolymph flow in the abdominal hemocoel. Qualitative and quantitative analyses revealed that ventral abdominal contractions occur as series of bursts that propagate in the retrograde direction. Periods of ventral abdominal contraction begin only during periods of anterograde heart contraction and end immediately following a heartbeat directional reversal, suggesting that ventral abdominal contractions function to propel extracardiac hemolymph in the retrograde direction. To test this functional role, fluorescent microspheres were intrathoracically injected and their trajectory tracked throughout the hemocoel. Quantitative measurements of microsphere movement in extracardiac regions of the abdominal cavity showed that during periods of abdominal contractions hemolymph flows in dorsal and retrograde directions at a higher velocity and with greater acceleration than during periods of abdominal rest. Histochemical staining of the abdominal musculature then revealed that ventral abdominal contractions result from the contraction of intrasegmental lateral muscle fibers, intersegmental ventral muscle bands, and the ventral transverse muscles that form the ventral diaphragm.Conclusions/SignificanceThese data show that abdominal contractions potentiate extracardiac retrograde hemolymph propulsion in the abdominal hemocoel during periods of anterograde heart flow.

Structural mechanics of the mosquito heart and its function in bidirectional hemolymph transport

The insect circulatory system transports nutrients, signaling molecules, wastes and immune factors to all areas of the body. The primary organ driving circulation is the dorsal vessel, which consists of an abdominal heart and a thoracic aorta. Here, we present qualitative and quantitative data characterizing the heart of the mosquito, Anopheles gambiae. Visual observation showed that the heart of resting mosquitoes contracts at a rate of 1.37 Hz (82 beats per minute) and switches contraction direction, with 72% of contractions occurring in the anterograde direction (toward the head) and 28% of contractions occurring in the retrograde direction (toward the tip of the abdomen). The heart is tethered to the midline of the abdominal tergum by six complete and three incomplete pairs of alary muscles, and propels hemolymph at an average velocity of 8 mm s(-1) by sequentially contracting muscle fibers oriented in a helical twist with respect to the lumen of the vessel. Hemolymph enters the heart through six pairs of incurrent abdominal ostia and one pair of ostia located at the thoraco-abdominal junction that receive hemolymph from the abdominal hemocoel and thoracic venous channels, respectively. The vessel expels hemolymph through distal excurrent openings located at the anterior end of the aorta and the posterior end of the heart. In conclusion, this study presents a comprehensive revision and expansion of our knowledge of the mosquito heart and for the first time quantifies hemolymph flow in an insect while observing dorsal vessel contractions.

A Novel Protein Acts as a Negative Regulator of Prophenoloxidase Activation and Melanization in the Freshwater Crayfish Pacifastacus leniusculus

Melanization is an important immune component of the innate immune system of invertebrates and is vital for defense as well as for wound healing. In most invertebrates melanin synthesis is achieved by the prophenoloxidase-activating system, a proteolytic cascade similar to vertebrate complement. Even though melanin formation is necessary for host defense in crustaceans and insects, the process needs to be tightly regulated because of the hazard to the animal of unwanted production of quinone intermediates and melanization in places where it is not suitable. In the present study we have identified a new melanization inhibition protein (MIP) from the hemolymph of the crayfish, Pacifastacus leniusculus. Crayfish MIP has a similar function as the insect MIP molecule we recently discovered in the beetle Tenebrio molitor but interestingly has a completely different sequence. Crayfish MIP as well as Tenebrio MIP do not affect phenoloxidase activity in itself but instead interfere with the melanization reaction from quinone compounds to melanin. Importantly, crayfish MIP in contrast to Tenebrio MIP contains a fibrinogen-like domain, most similar to the substrate recognition domain of vertebrate l-ficolins. Surprisingly, an Asp-rich region similar to that found in ficolins that is likely to be involved in Ca2+ binding is present in crayfish MIP. However, crayfish MIP did not show any hemagglutinating activity as is common for the vertebrate ficolins. A mutant form of MIP with a deletion lacking four Asp amino acids from the Asp-rich region lost most of its activity, implicating that this part of the protein is involved in regulating the prophenoloxidase activating cascade. Overall, a new negative regulator of melanization was identified in freshwater crayfish that shows interesting parallels with proteins (i.e. ficolins) involved in vertebrate immune response.

Drosophilaflies combine periodic heartbeat reversal with a circulation in the anterior body mediated by a newly discovered anterior pair of ostial valves and `venous' channels

Heartbeat activity in tethered adult drosophilids was recorded using a linear optosensor chip and an IR-light beam. Recording from two to five sensor elements within 250 mum along the anterior heart, it was possible to analyze periodic reversals. In intact Drosophila melanogaster and D. hydei, longer anterograde pulse periods with lower pulse rates generally alternated with shorter retrograde pulse periods having higher pulse rates. These differences are dependent on heart anatomy: a newly discovered first pair of ostia is connected to bilateral thoraco-abdominal hemolymph channels. These channels are part of a venous space separated from the abdominal hemocoel by a septum, consisting of a metanotal ridge and the pericardial diaphragm lined by a special form of fat body. The channels are sealed, and their lumen is possibly controlled by the metathoracic tergo-pleural muscle. During retrograde pulses, the heart chamber works like a suction pump, aspiring hemolymph through the first ostia from the venous channels and discharging it through a newly described caudal opening. During forward beating, the anterior chamber receives hemolymph via all inflow ostia from the entire heart and drives it like a pressure pump through the narrow aorta. Also, during forward pulses, a lateral circulation occurs in the thorax as a result of the venous supply. Inhibition of abdominal mobility leads to an irregular heart rate, with pulse-wise alternating heartbeat reversals. The possible involvement of slow abdominal movements in heartbeat periodicity is discussed. The heartbeat periods are superimposed with intermittent bouts of abdominal pumping movements.

Artificial reproduction in a hymenopteran insect, Athalia rosae, using eggs matured with heterospecific yolk proteins and fertilized with cryopreserved sperm

Previtellogenic ovaries of Athalia rosae (Hymenoptera, Symphyta, Tenthredinidae) were transplanted into the adult female abdominal hemocoel of Athalia infumata (Symphyta, Tenthredinidae), Arge nigrinodosa (Symphyta, Argidae), and Pimpla nipponica (Apocrita, Ichneumonidae). The donor oocytes accumulated heterospecific yolk proteins and matured in the A. infumata host. On average, six mature oocytes were obtained per transplanted ovary. In contrast, the donor oocytes accumulated a limited amount of yolk but did not mature in the Ar. nigrinodosa host and did not even accumulate yolk in the P. nipponica host. The eggs that matured in the A. infumata host were injected with cryopreserved A. rosae sperm that had been taken from adult male seminal vesicles and stored at –80°C. Fertilization, as confirmed by the use of visible marker mutations, was achieved and a fraction of the injected eggs developed into fertile female adults. Arch. Insect Biochem. Physiol. 43:137–144, 2000. © 2000 Wiley-Liss, Inc.

Artificial reproduction in a hymenopteran insect, Athalia rosae, using eggs matured with heterospecific yolk proteins and fertilized with cryopreserved sperm.

Previtellogenic ovaries of Athalia rosae (Hymenoptera, Symphyta, Tenthredinidae) were transplanted into the adult female abdominal hemocoel of Athalia infumata (Symphyta, Tenthredinidae), Arge nigrinodosa (Symphyta, Argidae), and Pimpla nipponica (Apocrita, Ichneumonidae). The donor oocytes accumulated heterospecific yolk proteins and matured in the A. infumata host. On average, six mature oocytes were obtained per transplanted ovary. In contrast, the donor oocytes accumulated a limited amount of yolk but did not mature in the Ar. nigrinodosa host and did not even accumulate yolk in the P. nipponica host. The eggs that matured in the A. infumata host were injected with cryopreserved A. rosae sperm that had been taken from adult male seminal vesicles and stored at -80 degrees C. Fertilization, as confirmed by the use of visible marker mutations, was achieved and a fraction of the injected eggs developed into fertile female adults.

Phylogenetic position of yeast-like symbiont of Hamiltonaphis styraci (homoptera, aphididae) based on 18S rDNA sequence

Almost all aphids harbor bacterial intracellular symbionts in mycetocytes. However, some Cerataphidini aphids do not harbor them but possess yeast-like extracellular symbionts in the abdominal hemocoel, suggesting that in a lineage of this group replacement of symbiont occurred from an intracellular bacterium to an extracellular fungus. To investigate the origin of the newly-acquired symbiont, the 18S rDNA sequence of the yeast-like symbiont of Hamiltonaphis styraci was determined by PCR direct sequencing. Molecular phylogenetic analyses indicated that the symbiont belongs to the subphylum Ascomycotina, the class Pyrenomycetes. It was also suggested that the yeast-like symbiont of H. styraci and that of planthoppers are phylogenetically very closely related to each other.

Lectin Binding to Extracellularly Melanized Microfilariae of Brugia malayi from the Hemocoel of Anopheles quadrimaculatus

Binding patterns of fluorescein isothiocyanate (FITC)- and gold-conjugated lectins to extracellularly melanized sheathed and exsheathed microfilariae of subperiodic Brugia malayi, isolated from and in situ in the abdominal hemocoel of Anopheles quadrimaculatus 72-hr postinfection, were examined. Five FITC-conjugated lectins [ Helix pomatia agglutinin (HPA), Arachis hypogaea (peanut agglutinin-PNA), Triticum vulgaris (wheat germ agglutinin-WGA), Lens culinaris (lentil-LCH), and Concanavalin A (Con A)] with specificities for different carbohydrate moieties were tested for binding to isolated melanized microfilariae and observed with transmitted light and fluorescence microscopy. All five FITC-lectins bound strongly to the acellular material accompanying the melanin deposits on the surface of isolated melanized microfilariae. Significant inhibition of FITC-lectin binding occurred when lectins were preincubated with their complementary carbohydrates before testing. H. pomatia agglutinin binding was totally inhibited by N-acetyl- d-glucosamine and N -acetyl- d-galactosamine. Other lectins were partially inhibited, such as PNA by galactose and lactose; WGA by N-acetylneuraminic acid; LCH by N-acetyl- d-glucosamine, mannose, glucose, and methyl α- d-mannopyranoside; and Con A by mannose and methyl α- d-mannopyranoside. Three gold-conjugated lectins (HPA, PNA, and Con A), examined by using transmission electron microscopy, bound to the outer surface of the acellular material associated with the melanin deposits on isolated melanized microfilarial sheaths and melanized microfilariae and to the remnants of lysed hemocytes found in the proximity of the melanized deposits. Con A in the presence of gold-labeled horseradish peroxidase, examined by using transmission electron microscopy, showed random binding within the melanized capsule formed around the microfilarial sheath in situ. These results indicate that the acellular material accompanying melanin deposits on melanized microfilarial sheaths and sheathed and exsheathed microfilariae contain several glycoconjugates with exposed carbohydrate moieties and are possibly glycoproteins. These glycoproteins could be the by-products of the activation of the prophenoloxidase by the microfilariae.

Morphology of the Midgut–Hindgut Juncture in the Ghost Shrimp Lepidophthalmus louisianensis (Schmitt) (Crustacea: Decapoda: Thalassinidea)

Abstract Unique morphological structures occur near the midgut–hindgut juncture in decapod crustaceans, and neither their fine structure nor function are well understood. In the ghost shrimp Lepidophthalmus louisianensis. structures associated with this juncture include an elongate posterior midgut caecum (PMGC) extending into the abdominal hemocoel, a massive swelling of acinar glands encasing the juncture, and a dorso‐lateral valve complex involving cuticularized lumenal surfaces of the anterior hindgut. Vivisection, histological studies (LM, TEM) and paraffin‐carving (SEM) have been applied to reconstruct morphology of these components and characterize constituent tissues. The lumen of the PMGC is lined by very elongate columnar cells underlain by a thin layer of circular muscle. The hemocoelic surface of the PMGC is covered by cells richly endowed with unique lamellar bodies. The acinar glands are composed of multiple rosettes of secretory cells, from which products appear to empty into the anterior extreme of the hindgut. The dorso‐lateral valve complex of the hindgut consists of anterior and posterior components, differing in strength of lumenal ridging and microdentition of the cuticular lining. Unique features of these structures may relate to behavioral, feeding and metabolic adaptations in this obligate fossorial crustacean.

Encapsulation and melanization responses of Armigeres subalbatus against inoculated Sephadex beads

The relationship between the surface charges of foreign bodies and the responses of the mosquitoes, Armigeres subalbatus, was investigated. Sephadex beads of varying surface charges suspended in PBS (pH 5.6) were inoculated directly into the abdominal hemocoel of mosquitoes and melanization of beads was scored at 24-hr postinoculation. It was demonstrated that Ar. subalbatus melanized only positively charged beads (and to some extent neutral beads). Male and female mosquitoes responded equally to inoculated beads. In female mosquitoes, both the melanization rates and the degree of melanization were significantly greater in the thoraces than in their hemocoels. Scanning and transmission election microscopic examinations of inoculated beads revealed an amorphous coat of loosely adhering cellular debris and melanin on the surface of the beads.

Morphine analgesia, tolerance and addiction in the cricket pteronemobius sp. (orthoptera, insecta)

The escape reaction time (ERT) of the cricket Pteronemobius sp. from the heated box begins at 48 degrees and increases with temperature until 56 degrees C, beyond which there is no further increase. The ERT (2.2 +/- 1.39 s) from the hot box at 54 degrees C is used as a model for studying the analgesic effects of opiates. Results of the present paper show that the ERT did not change after injecting the insect in the abdominal haemocoel with 0.9% saline solution, but ERT increased when 0.32, 0.52 or 0.69 mg/g of morphine is injected in the same place. The maximum ERT increase is reached at 90 min after drug injection, and the drug effect disappears 3 h after the injection. At 90 min after drug injections, the dose of 0.50 mg/g of morphine produces 50% of ERT increase, and it is referred to as the median analgesic dose (D50). 1.05 mg/g of morphine produces an ERT longer than 30 s that results in an irreversible damage to the insect. Sixty-four micrograms/g of naloxone given in addition to D50 of morphine fully blocked the effect of morphine during its 3-h action. However, more than 64 micrograms/g of naloxone alone also increase the ERT in the cricket, similar to what has been described for vertebrates. Four daily morphine injections of D50 decreased ERT in such a way that, at the fourth day, the ERT is similar to the ERT produced by saline solution; i.e., tolerance is shown. The suppression of daily morphine injections of D50 during the fifth day produced a hyperresponse to vibration (big jumps) not shown in the case of the injections of saline solution; i.e., addiction is shown.

Detection of Eastern Equine Encephalomyelitis Virus Deposition in Culiseta Melanura Following Ingestion of Radiolabeled Virus in Blood Meals

We examined deposition of eastern equine encephalomyelitis virus (EEEV) in the alimentary tract of its enzootic mosquito vector, Culiseta melanura, to detect potential sites of initial infection. Artificial viremias were created by injecting purified [3H]uridine-labeled EEEV intravenously into one-day-old chicks. Mosquitoes were allowed to engorge, incubated 1-2 hr, fixed, and whole abdomens and thoraces of 25 specimens embedded. Tagmata were sectioned, mounted on slides and coated with autoradiographic emulsion. Following exposures of 1-4 months, slides were developed and examined microscopically. In the majority of mosquitoes, label (virus) was detected only within the midgut; most virus was concentrated in a band of expressed serum adjacent to the abdominal midgut epithelium. Small amounts of virus were also deposited within folds in the cardial thoracic midgut of 96% of mosquitoes. Viral penetration into epithelial cells was detected throughout the abdominal midgut in all mosquitoes, and in the thoracic midgut of 20%. A small number (4/25) of mosquitoes examined showed signs of leaky abdominal midguts, with virus detected in the abdominal hemocoel. Concentration of EEEV in expressed serum adjacent to the abdominal midgut epithelium may enhance initial midgut infection. Leaky abdominal midguts exhibited by some mosquitoes may also facilitate rapid systemic infections of Cs. melanura. Deposition of virus in thoracic alimentary tissues suggests the possibility of early EEEV infection of the anterior midgut.

Mycetocyte symbiosis in insects.

1. Non-pathogenic microorganisms, known as mycetocyte symbionts, are located in specialized 'mycetocyte' cells of many insects that feed on nutritionally unbalanced or poor diets. The insects include cockroaches, Cimicidae and Lygaeidae (Heteroptera), the Homoptera, Anoplura, the Diptera Pupiparia, some formicine ants and many beetles. 2. Most mycetocyte symbionts are prokaryotes and a great diversity of forms has been described. None has been cultured in vitro and their taxonomic position is obscure. Yeasts have been reported in Cerambycidae and Anobiidae (Coleoptera) and a few planthoppers. They are culturable and those in anobiids have been assigned to the genus Torulopsis. 3. The mycetocyte cells may be associated with the gut, lie free in the abdominal haemocoel or be embedded in the fat body of the insect. The mycetocytes are large polyploid cells which rarely divide and the symbionts are restricted to their cytoplasm. 4. The mycetocyte symbionts are transmitted maternally from one insect generation to the next. In many beetles (Anobiidae, Cerambycidae, Chrysomelidae and cleonine Curculionidae), the microoganisms are smeared onto the eggs and consumed by the hatching larvae. In other insects, they are transferred from mycetocytes to oocytes in the ovary, a process known as transovarial transmission. The details of transmission in the different insect groups vary with the age of the mother (adult, larva or embryo) at which symbiont transfer to the ovary is initiated; whether isolated symbionts or intact mycetocytes are transferred; and the site of entry of symbionts to the egg (anterior, posterior or apolar). 5. Within an individual insect, the biomass of symbionts varies in a regular fashion with age, weight and sex of the insect. Suppression of symbiont growth rate and lysis of 'excess' microorganisms may contribute to the regulation of symbionts (including freshly-isolated preparations of unculturable forms) are used to investigate interactions between the partners. However, some methods to obtain aposymbiotic insects (e.g. antibiotics and lysozyme) deleteriously affect certain insects and aposymbionts may differ from the symbiont-containing stocks from which they were derived. 7. The mycetocyte symbionts have been proposed to synthesize various nutrients required by the insect. The symbionts of beetles and haematophagous insects may provide B vitamins and those in cockroaches and the Homoptera essential amino acids. The role of symbionts in the sterol nutrition of insects is equivocal. 8. Mycetocyte symbionts may have evolved from gut symbionts or guest microorganisms. The association is monophyletic in cockroaches but polyphyletic in many groups, including the sucking lice, beetles and scale insects.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracellular melanization in the mosquito Anopheles quadrimaculatus (Diptera: Culicidae) against the filarial nematodes, Brugia spp. (Nematoda: Filarioidea).

Intracellular melanization responses to developing larvae of Brugia species (B. malayi (Buckley), B. pahangi (Buckley and Edeson), and B. patei (Buckley, Nelson, and Heisch] in the thoracic muscle fibers of eight strains of Anopheles quadrimaculatus Say were first observed 48 to 72 h after an infective blood meal. Three to 4 d later, large numbers of melanized first-stage larvae were found within the thoracic muscle fibers. These intracellular responses were in addition to the extracellular responses to microfilariae and microfilarial sheaths of B. pahangi in the abdominal hemocoel of An. quadrimaculatus described in literature. Simultaneously, normal development of larvae of the three Brugia species also was observed in all eight strains of An. quadrimaculatus. Comparisons of melanized first-stage larvae and normally developing larvae of the three Brugia species in the thoracic muscle fibers of the eight strains of An. quadrimaculatus showed that there were distinct variations in numbers of melanized and developing larvae and percentage of females with melanized and developing larvae in different strains. Numbers of melanized first-stage larvae reflected the extent of refractoriness of An. quadrimaculatus strains. Fully melanized larvae showed no abnormalities in parasite organelles, indicating that refractoriness is due to an enhanced ability of the host to recognize the living parasite. Further comparison among the strains suggested that the mutants, Yellow Larvae and Vero Beach Colony were significantly more susceptible, and Red Stripe was the most refractory to all three Brugia species. Thus, the gene(s) controlling susceptibility and refractoriness to all three Brugia species probably occurs on the same autosomal chromosome as the mutations in these strains. The significance of intracellular melanization of filarial larvae is discussed with reference to the melanization responses to different parasites in other mosquitoes.

Further characterization of refractoriness in Aedes aegypti (L.) to infection by Dirofilaria immitis (Leidy)

Factors which control the expression of the refractory or susceptible condition to infection with Dirofilaria immitis in the mosquito, Aedes aegypti, were investigated using three protocols. (1) Microfilariae and prelarvae were injected into the hemocoel of susceptible A. aegypti. Some microfilariae and prelarvae developed to the L 1 larval stage but they failed to complete development to the infective stage. (2) Enema of microfilariae and prelarvae from infected susceptible and refractory donor females were given into the midgut of uninfected susceptible and refractory recipient females. The results indicate that the conditions which inhibit the initiation of development are present in the Malpighian tubules and not in the midgut of the refractory mosquitoes. (3) Transplants of infected Malpighian tubules from susceptible and refractory donor females were made into the abdominal hemocoel of uninfected susceptible and refractory recipient females. The results showed that the refractory condition depends on the genetic makeup of the donor, not the recipient, mosquito. The above results taken as a whole indicate that the factors which control refractoriness are not present in the midgut but are present in the Malpighian tubule cells of refractory A. aegypti.

糸状虫症に関する研究 VII : オオクロヤブカ腹部体腔内におけるマレー糸状虫幼虫の被嚢化に関する組織学的観察

Histological observations of Brugia malayi infected mosquitoes, Armigeres subalbatus, prepared at 0.5,3,12,24,48hrs and on 3,5,7,10 days after blood meal, were carried out by routine paraffin sectioning and hematoxylineosin staining method. Light brown substances around microfilari-form larvae were observed as early as 30min post-infection and some parts of them had begun to change in color from light brown to dark brown. Until 90min post-infection almost all of the larvae in the abdominal haemocoel were enclosed in a dark brown capsule. Thereafter, many round shaped cells were observed attached on the pigmented capsule until about 3hrs post-infection. The adhered cells became distinctly flattened by 24hrs post-infection and the nucleus of the individual cell became difficult to be recognized. After 48hrs post-infection, cell layer around the pigmented capsule was recognized as a faintly basophilic or brownish layer. Inside the cell layer many minute brown particles were observed from 5 to 10 day post-infection. It was clarified that cellular response by host mosquitoes lagged behind the pigmentation and that the cells of mosquitoes played a role in a series of encapsulation reactions against filarial larvae in the abdominal haemocoel.

Pseudoallocreadium alloneotenicum (Wootton, 1957) Yamaguti, 1971 (Digenea: Allocreadiidae) from Psychoglypha alascensis Banks (Trichoptera: Limnephilidae) in Vancouver, British Columbia

Allocreadium alloneotenicum was originally described by Wootton (1957, Biological Bulletin 113: 302-315) from the hemocoel of Limnephilus sp. larvae from Barnstable Co., Cape Cod, Massachusetts. In 1971 Yamaguti (Synopsis of the digenetic trematodes of vertebrates. Keigaku Publishing Company, Tokyo, 1,074 p.) established the genus Pseudoallocreadium to contain Pseudoallocreadium neotenicum (Peters, 1957) (syn. Allocreadium neotenicum Peters) and Pseudoallocreadium alloneotenicum (Wootton, 1957) (syn. Allocreadium alloneotenicum Wootton). No additional records of P. alloneotenicum exist in the literature. Between May 1979 and May 1981, 602 larvae of Lepidostoma roafi (Milne) (Lepidostomatidae) and 316 larvae of Psychoglypha alascensis Banks (Limnephilidae) were examined from Tin Can Creek in Musqueum Park near the Endowment Lands of the University of British Columbia, Vancouver, Canada. One larva of Psychoglypha alascensis was infected with a single specimen of P. alloneotenicum in the abdominal hemocoel. The trematode was mounted according to conventional techniques and deposited in the Harold W. Manter Laboratory of Parasitology, University of Nebraska State Museum, No. 22862. The worm differs slightly from those reported by Wootton (1957, loc. cit.), by possessing a longer cirrus sac (0.44 mm as compared to 0.12-0.34 mm), and more eggs (130 as compared to 45). The single record from Tin Can Creek s ggests that the prevalence of P. alloneotenicum may be much lower in the Vancouver population, 0.32% (n = 316) as compared to 30% (n = 120) reported by Wootton (1957, loc. cit.) in Massachusetts. This report constitutes a new host record as well as a new locality record for P. alloneotenicum. The only recorded hosts, Psychoglypha alascensis and Limnephilus sp., are both members of the family Limnephilidae. The discovery of P. alloneotenicum on the west coast of Canada suggests that the distribution of this species may be more widespread than was previously indicated. We wish to thank Dr. G. B. Wiggins of the Royal Ontario Museum for identifying the caddisflies and Professor M. H. Pritchard of the University of Nebraska State Museum for critically reviewing this manuscript. This research was supported by a grant to G. G. E. Scudder from the Natural Sciences and Engineering Research Council of Canada.

Crepidostomum opeongoensis n.sp. (Digenea: Allocreadiidae) from Hexagenia limbata (Serville in Guerin) in Algonquin Park, Ontario, Canada

A new species of papillose allocreadiid is described from the abdominal haemocoel of a male nymph of Hexagenia limbata from Lake Opeongo in Algonquin Park, Ontario, Canada. Crepidostomum opeongoensis n.sp. resembles Crepidostomum latum (Pigulewsky, 1931) Hopkins, 1933 and Crepidostomum brevivitellum Hopkins, 1934 in having vitellaria confined to the hindbody, but differs by possessing dorsolateral papillae of the oral sucker that are twice as wide as the dorsomedial papillae. Crepidostomum opeongoensis is further distinguished from C. latum by an oral sucker that is larger rather than smaller than the acetabulum, a body that is twice as large, and a cirrus sac that extends posterior to the acetabulum rather than ending at the midlevel of the acetabulum. It is further distinguished from C. brevivitellum by its longer ventral papillae, greater post-testicular space, and hindbody that widens rather than tapers. The discovery of ovigerous worms of C. opeongoensis in an insect is discussed in relation to other such species in the family.

Bionomics of a mermithid parasitizing snow-pool Aedes spp. mosquitoes

A mermithid nematode was isolated from all active stages of snow-pool Aedes spp. in northeastern New York. Invading nematodes initially entered the larval cephalic nervous tissue where limited development occurred, but subsequently migrated to the abdominal hemocoel of pupae and adults, where the rate of development increased sharply. Migration to the brain was a prerequisite for development in Ae. stimulons; nematodes not entering the brain elicited a host defense response. Most mermithids (64%) entering this host were encapsulated and killed before reaching the brain, but field infection rates were still high, with more than 60% of last-instar larvae successfully infected. Mermithids attacking Ae. intrudens and Ae. provocans seldom elicited an encapsulation response but nevertheless failed to complete parasitic development. Normal parasitic development with infrequent encapsulation was noted in Ae. excrucians and Ae. fitchii. Postparasites invariably emerged from adult stages, causing host death. Postparasites reared in the laboratory at 25 °C molted, mated, and began oviposition within 1 month of emergence. Resulting preparasites initiated infections in four laboratory-reared species of mosquitoes but seldom completed parasitic development. The biological control potential of this mermithid is discussed.

Laboratory studies on the biology ofOrgilus jenniae(Hymenoptera: Braconidae), a parasitoid of the potato tuberworm,Phthotimaea operculetta(Lepidoptera: Gelechiidae)

Studies were conducted on behavior, host relationships, immature morphology and population growth potential of Orgilus jenniae Marsh, an exotic parasitoid of the potato tuberworm (PTW), Phthorimae operculella (Zeller). Results were compared with similar studies on the exotic species, O. lepidus Muesebeck and O. parcus Turner, previously colonized but not established in southern California. Stalked eggs of O. jenniae are deposited in the abdominal hemocoel of host larvae. A solitary parasitoid larva develops internally, emerges before host pupation, and constructs a translucent-white cocoon within that of its host. The first of three larval instars is initially caudate- and and finally vesiculate-mandibulate; the last two are hymenopteriform. Immature dimensions and descriptions are presented. Parasitoids preferentially oviposit in first or second instar PTW in potato foliage, but there is an interaction between host age and density in tubers arising from actual parasitoid preference and characteristics of host mines. Developmental time from oviposition to adult parasitoid emergence depends on the host’s age at the time of oviposition, as the first parasitoid molt is synchronized to occurrence of the fourth host instar. Parasitism significantly reduces host larval growth. If O. jenniae has a preoviposition period, it is less than 3-hrs, but female progeny are not produced during the first 6-hrs after adult emergence or mating. A diurnal oviposition rhythm does occur, with progeny production peaking during the last half of the photophase. Courtship, mating, searching and oviposition behaviors are described. The mean fecundity was 375.2 and 436.8 eggs/female, the mean sex ratio, 23.6% and 28.4% females, and the mean adult female longevity, 25.5 and 16.9 days, when hosts were in potato tubers and foliage, respectively, at 25 ± 1 °C, 45 ± 5% RH and 12-hr photoperiod. Parasitoid life tables and statistics for hosts in potato tubers and