Effect of the venom of the gregarious parasitoid Apanteles glomeratus on its hemocytic encapsulation by the host, Pieris

When eggs from the lateral oviduct of the gregarious parasitoid Apanteles glomeratus were injected with calyx fluid and venom apparatus material into host larvae, Pieris rapae crucivora, most of the eggs were not encapsulated. Apanteles eggs deposited by the parasitoid from which the venom apparatus was removed were usually encapsulated by the host. These results indicate that the parasitoid venom apparatus material is an important factor in suppressing the encapsulation of 1- or 2-day-old eggs in the host. In order to clearly demonstrate that the venom suppresses egg encapsulation but not the encapsulation of other foreign objects, DEAE-Sephadex A-50 ion-exchange particles stained with 0.001% (w/v) Congo Red solution were injected into hosts together with venom apparatus material. The Sephadex particles were encapsulated by host hemocytes. The results suggest that the venom does not inhibit the encapsulation ability of the host.     

Effects of temperature and host age upon the encapsulation of Metaphycus stanleyi and Metaphycus helvolus eggs by brown soft scale Coccus hesperidum

Encapsulation of eggs inserted by Metaphycus stanleyi (Hymenoptera: Encyrtidae) into the brown soft scale Coccus hesperidum (Homoptera: Coccidae) became more frequent as the host matured. This occurred with both laboratory reared and field-collected parasites. After parasitism for 24 hr at 27°C, encapsulation frequency did not differ in hosts reared at 20° or at 27°C, but significantly increased in hosts reared at 33°C. When parasitism and rearing were carried out at the same temperature, the percentage of eggs encapsulated increased from 48.7% at 27°C to 94.1% at 33°C. With M. helvolus, the percentage of eggs encapsulated was considerably higher than with M. stanleyi; e.g., 99.3 vs 48.7%, respectively, at 27°C. At 20° and 27°C, some M. helvolus development occurred in the larvae of brown soft scale but none at 33°C; the adult stages of the host encapsulated all the parasite eggs at these temperatures.     

Encapsulation of a parasitoid egg within its habitual host: An ultrastructural investigation

Eggs of the ichneumonid parasitoid Campoletis sonorensis oviposited within its natural host Heliothis virescens are rarely encapsulated. The chorion of eggs deposited within the natural host were ultrastructurally similar to eggs within the lateral oviduct. Less than 5% of eggs incubated in invertase or saline and injected into the host evoked a hemocytic response within 24 hr; however, all the eggs incubated in either protease or lipase prior to injection evoked a hemocytic reaction in the host within 24 hr. It would appear that encapsulation of eggs incubated in either lipase or protase resulted from modification of the chorion surface. Eggs incubated in invertase or saline were encapsulated within 72 to 96 hr while eggs incubated in the fluid from the female parasitoid oviduct were not. The ultrastructural development of the hemocytic capsule is presented and the possible role of cell contacts in capsule regulation is discussed.     

Resistance of Apanteles eggs to the haemocytic encapsulation by their habitual host, Pieris

The calyx fluid in the lateral oviduct of a gregarious parasitoid, Apanteles glomeratus contained ellipsoid particles of ca. 130 × 200 nm. These calyx fluid particles did not appear to be embedded in a fibrous outer layer on the surface of eggs in the lateral oviduct. They were not observed on the surfaces of the eggs 3 to 4 hr after being deposited into the host haemocoele. Oviposition experiments indicated that the occurrence of haemocytic defence reactions of the late 2nd instar larvae of the Pieris rapae crucivora against 1 st instar larvae of the parasitoid increased with a decreasing number of the parasitoid eggs introduced into a host, and that more than 5 to 9 parasitoid eggs were needed for suppressing the ability of the host to encapsulate its parasitoid larvae immediately after hatching. When eggs with calyx fluid obtained from egg reservoir were injected into the host, they were found to be encapsulated 1 to 2 days after the injection. They could not start their embryonic development. When calyx fluid-free 3-hr-old eggs were injected in a number of more than 5 eggs into a 5th instar larva of Pieris, 58% of 31 eggs injected had normally hatched without evoking encapsulation reactions by the host. Both electron microscopic observations of parasitoid eggs in the host haemocoele and the experimental results suggested that calyx fluid or calyx fluid particles of the parasitoid might not be involved in the encapsulation-inhibiting activity of the parasitoid eggs. Rather it was anticipated that a substance (or substances) might be secreted by the parasitoid eggs into the haemocoele of the host, which suppressed defence reactions of the host.     

Biology and behavior of Metaphycus angustifrons Compere (Hymenoptera: Encyrtidae), a newly discovered parasitoid of soft scale insects (Hemiptera: Coccidae) in California

Metaphycus angustifrons Compere has recently been found to be the most abundant parasitoid of brown soft scale, Coccus hesperidum L., in southern California. In laboratory experiments we examined several biological parameters of this species. M. angustifrons both oviposits and host feeds in brown soft scale and is a facultatively gregarious endoparasitoid of this soft scale insect. In contrast with other Metaphycus spp., M. angustifrons is a koinobiont parasitoid, allowing its host to grow up to 40% beyond its size at parasitism. Despite its high abundance on brown soft scale in the field, in the laboratory, high rates of parasitoid egg encapsulation are observed; about half of parasitized hosts failed to issue parasitoids. Furthermore, host scales that encapsulated parasitoids eggs showed significant reduction in development. Increased scale size at oviposition influences the size of emerging females but not the size of males. Female M. angustifrons are synovigenic. They emerge from their hosts without mature eggs and begin maturing eggs after they are provided a carbohydrate source. Carbohydrates prolong the life span of both female and male M. angustifrons. The size of female wasps influences egg load but not longevity. Finally, based on laboratory observations, M. angustifrons uses citricola scale almost exclusively for host feeding and not for oviposition. These results suggest that the role of this species in citricola scale’s decline in southern California in the 1950s–1960s was negligible.     

Development of the braconid wasp Cotesia flavipes in two Crambids, Diatraea saccharalis and Eoreuma loftini: Evidence of host developmental disruption

Cotesia flavipes is an important gregarious larval endoparasitoid of several crambid stem borers, including Diatraea saccharalis. The suitability of two crambid species, Eoreuma loftini and D. saccharalis, pests of sugarcane and rice in Texas, for C. flavipes development was tested. The effect of parasitization by C. flavipes on encapsulation response was assessed in vivo in both D. saccharalis and E. loftini. The results indicated that the parasitoid developed and emerged successfully in D. saccharalis larvae. Although E. loftini larvae were readily parasitized by C. flavipes parasitoids, no wasp larvae hatched from the eggs in this host because eggs were encapsulated by the host's hemocytes. The developmental fate of the E. loftini larvae with encapsulated parasitoids was variable. Most died as abnormal fifth instars or as post-wandering prepupae, while a few developed normally to the pupal stage. In vivo experiments, there was a significant reduction in the percent of beads encapsulated in parasitized larvae in both hosts. However, the percent of beads showing melanization decreased significantly in parasitized D. saccharalis larvae but did not differ significantly in parasitized or unparasitized E. loftini larvae. Our results showed that D. saccharalis is a suitable host for C. flavipes whereas E. loftini is an unsuitable host. This study indicated that lepidopteran stem borers that are taxonomically, behaviorally, and ecologically very similar can differ in their ability to encapsulate a parasitoid species.     

Encapsulation and hemocyte numbers in three lepidopteran stemborers parasitized by Cotesia flavipes-complex endoparasitoids

Determination of the potential and actual host range of a natural enemy is crucial before its importation and release for biological control. We studied some of the factors that are important in determining the physiological host range of insect parasitoids attacking lepidopteran hosts. Our experimental system consisted of novel host-parasitoid associations, with two New World pyralid stalk borers, Diatraea saccharalis and D. grandiosella; one Old World crambid borer, Ostrinia nubilalis as hosts; and three Old World microgastrine braconids, Cotesia chilonis, C. sesamiae, and C. flavipes as parasitoids. Experiments on the chronology of encapsulation of the parasitoid progeny by host hemocytes indicated that lepidopteran stemborers that are taxonomically, behaviorally and ecologically very similar differ in their ability to encapsulate a parasitoid species. D. saccharalis encapsulated C. flavipes sometimes, whereas D. grandiosella consistently encapsulated C. sesamiae and C. flavipes. C. chilonis was not encapsulated by either Diatraea host. If encapsulation occurred it did not start until four days after parasitization and continued during the following days. O. nubilalis was an unsuitable host for all three parasitoid species; parasitoid eggs were killed within 24 hours of parasitization. O. nubilalis had nearly twice as many hemocytes present in the hemolymph compared to the Diatraea species. In many of the host-parasitoid combinations, there was an initial increase of hemocyte number soon after parasitization, which was not due to mechanical damage at oviposition. There was no correlation between total numbers of hemocytes present in the host hemolymph and the observed encapsulation levels. By understanding the encapsulation response we may be able to make better predictions about the host range of a parasitoid species before its release as a biological control agent.     

Biomechanical interactions of Schistosoma mansoni eggs with vascular endothelial cells facilitate egg extravasation

The eggs of the parasitic blood fluke, Schistosoma, are the main drivers of the chronic pathologies associated with schistosomiasis, a disease of poverty afflicting approximately 220 million people worldwide. Eggs laid by Schistosoma mansoni in the bloodstream of the host are encapsulated by vascular endothelial cells (VECs), the first step in the migration of the egg from the blood stream into the lumen of the gut and eventual exit from the body. The biomechanics associated with encapsulation and extravasation of the egg are poorly understood. We demonstrate that S. mansoni eggs induce VECs to form two types of membrane extensions during encapsulation; filopodia that probe eggshell surfaces and intercellular nanotubes that presumably facilitate VEC communication. Encapsulation efficiency, the number of filopodia and intercellular nanotubes, and the length of these structures depend on the egg’s vitality and, to a lesser degree, its maturation state. During encapsulation, live eggs induce VEC contractility and membranous structures formation in a Rho/ROCK pathway-dependent manner. Using elastic hydrogels embedded with fluorescent microbeads as substrates to culture VECs, live eggs induce VECs to exert significantly greater contractile forces during encapsulation than dead eggs, which leads to 3D deformations on both the VEC monolayer and the flexible substrate underneath. These significant mechanical deformations cause the VEC monolayer tension to fluctuate with the eventual rupture of VEC junctions, thus facilitating egg transit out of the blood vessel. Overall, our data on the mechanical interplay between host VECs and the schistosome egg improve our understanding of how this parasite manipulates its immediate environment to maintain disease transmission.     

Carcinonemertes pinnotheridophila sp. nov. (Nemertea,Enopla, Carcinonemertidae) from the branchial chambers of Pinnixa chaetopterana (Crustacea,Decapoda, Pinnotheridae): description,incidence and biological relationships with the host

A new species of Carcinonemertes, C. pinnotheridophila, is described and illustrated. The worms were found in the pinnotherid crab Pinnixa chaetopterana collected from the coasts of New Jersey, North Carolina and Florida. The anatomy of the new species is compared and contrasted with that of other members of the genus Carcinonemertes and an emended generic diagnosis is provided. The nemerteans only inhabit female hosts, crabs being infested with one or two mature female worms but with no more than one ensheathed in each branchial chamber; one or more smaller male nemerteans may be associated with each female. Sheaths are attached to the medial portion of the host branchial exoskeleton, and project through an opening in the floor of the chamber to exit via another aperture in the sternum; the anterior part of the sheath opens in the excurrent canal of the branchial chamber. Female worms cement their oval egg sacs on the pleopods to which the crab's eggs are also attached. Attachment, development and hatching of both host and symbiont eggs are synchronous. The incidence of infestation, reproductive potential of the nemertean, damage to its host and tolerance of the crab's growth cycles are described.     

Nematospiroides dubius in mice selected for liability to infection: Modification of parasite biology through host selection

Brindley P. J. and Dobson C. 1982. Nematospiroides dubius in mice selected for liability to infection: modification of parasite biology through host selection. International Journal for Parasitology12: 573–578. Mice selected as liable (L) and refractory (R) over ten generations voided significantly more and less Nematospiroides dubius eggs compared with randomly mated (Rd) mice after primary infections with 100 larvae. There was little difference between the number of parasite eggs voided g^?1 faeces (epg) by individual mice on day 14 compared with day 15 after infection.However there was a significant diurnal variation in the egg values for individual mice but the mean differences observed between the R, Rd and L mice were maintained over a 24 h period. There was a strong correlation between both the total number and the number of female worms, surviving 21 days after infection, and the mean epg 14 and 15 days after infection. Female N. dubius produced more eggs in L mice and fewer eggs in R mice compared with worms in Rd mice. Similarly, worms grew longer in L mice and were shorter in R mice compared with parasites in Rd mice.     

Cultivation in vitro of Schistosomatium douthitti (trematoda: Schistosomatidae)

Cultivation in vitro of Schistosomatium douthitti (Trematoda : Schistosomatidae). International Journal for Parasitology12: 541–545. We grew S. douthitti in vitro from the cercaria to pairing ovigerous adults, using methods and media previously reported for cultivation of Schistosoma mansoni. Growth of S. douthitti in vitro was much more rapid than that of S. mansoni, but the cultures achieved a similar stage of maximal development. Cultured S. douthitti worms were smaller than those from animals and eggs were inviable. We determined that females of this species, known to produce eggs in unisexual animal infections, will also do so in culture in the absence of males.     

Exploring the efficacy of Basella alba mucilage towards the encapsulation of the hydrophobic antioxidants for their better performance

In the present study, the efficacy of Basella alba L. (commonly known as Indian spinach) mucilage (BAM) was explored for the first time towards the encapsulation of hydrophobic antioxidants. The hydrophobic antioxidants were encapsulated into the BAM matrix by modified non-solvent precipitation method and the encapsulated systems were fully characterized on the basis of TGA, DLS and SEM data. Interactions between the components of BAM matrix and the hydrophobic antioxidants are the key factors for the efficient encapsulation process. These interactions were studied with the help of spectroscopic techniques. The BAM-encapsulated antioxidants showed high pH and photo-stability. Moreover, the hydrophobic antioxidants after their encapsulation in the BAM matrix showed enhanced water solubility and hence, bioactivity in aqueous medium. Thus, BAM may be explored in future as an ideal candidate for the encapsulation and delivery of the hydrophobic bioactive compounds in cellular medium.     

Effect of the venom of the endoparasitoid,Apanteles kariyai Watanabe,on the cellular defence reaction of the host,Pseudaletia separata Walker

Although a venom apparatus is present in all female braconid wasps, the function of the venom injected into the host at the time of oviposition by the endophagous members of this group is unknown. Eggs laid by females of Apanteles kariyai, from which the venom apparatus had been removed, were encapsulated, which suggests that the fluid is necessary to enable the parasitoid eggs to escape the cellular defence reaction of the host. Studies with anti-venom serum demonstrated that the venom is attached to the surface of the egg. However, injection of DEAE-Sephadex A-50 particles (Sephadex particles) revealed that the venom alone is insufficient to inhibit the encapsulation reaction. Calyx and venom fluids together seem to be essential for evasion of the host defence reaction by the parasitoid eggs. Eighty-five % Sephadex particles, injected together with calyx and venom fluids, fail to become fully encapsulated, whereas 46% of particles injected with only the calyx fluid avoided encapsulation. Furthermore, when eggs from the lateral oviduct were injected into unparasitized larvae, together with the calyx and venom fluids, a few eggs developed successfully although they had undergone no mechanical distortion.     

Cultivation in vitro of Schistosomatium douthitti (Trematoda: Schistosomatidae)

Basch P. F. and O'Toole M. L. 1982. Cultivation in vitro of Schistosomatium douthitti (Trematoda: Schistosomatidae). International Journal for Parasitology12: 541–545. We grew S. douthitti in vitro from the cercaria to pairing ovigerous adults, using methods and media previously reported for cultivation of Schistosoma mansoni. Growth of S. douthitti in vitro was much more rapid than that of S. mansoni, but the cultures achieved a similar stage of maximal development. Cultured S. douthitti worms were smaller than those from animals and eggs were inviable. We determined that females of this species, known to produce eggs in unisexual animal infections, will also do so in culture in the absence of males.     

Changes in differential haemocyte count and in vitro behaviour of plasmatocytes from host Heliothis virescens caused by Campoletis sonorensis polydnavirus

Campoletis sonorensis is a habitual parasitoid of 3rd-instar larvae of Heliothis virescens. C. sonorensis eggs and small glass rods were encapsulated in 5th-instar host larvae implanted in the absence of wasp calyx fluid; prior injection of calyx fluid into larvae suppressed the encapsulation response. Within 8 h of calyx fluid injection there was a removal of approx. 75% of the circulating capsule-forming haemocytes (plasmatocytes). The remaining subpopulation of plasmatocytes, in addition to being incapable of encapsulating targets in vivo, spread at a significantly reduced rate in vitro. Identical changes in plasmatocyte count and behaviour were observed after injection of virus purified from calyx fluid. Additionally, the activity of calyx fluid was abolished after ultraviolet irradiation. The onset of haemocytic abnormalities occurred more rapidly after natural parasitism of 3rd-instar host larvae. The cell-free haemolymph of calyx fluid-injected 5th-instar larvae also retarded the spreading of plasmatocytes from non-injected control larvae in vitro. We conclude that the abnormalities induced in H. virescens plasmatocytes by C. sonorensis virus contribute to the suppression of encapsulation.     

Anisakis,Phocanema, Contracaecum, and Sulcascaris Spp.: Electrophoresis and thermostability of alcohol and malate dehydrogenases from larvae

Electrophoretic surveys were conducted on individual larvae of four anisakine nematode genera: Anisakis, Phocanema, Contracaecum, and Sulcascaris. The larval worms were obtained from a variety of fish and molluscan hosts from widely dispersed geographic regions. Of several enzymes detected, constant and apparently species-specific electrophoretic patterns were obtained for alcohol dehydrogenase (ADH, alcohol:NAD oxidoreductase, EC 1.1.1.1) and malate dehydrogenase (MDH, l-malate: NAD oxidoreductase, EC 1.1.1.37). ADH, in all but Sulcascaris sp., possessed two isozymes, the slower of which was sensitive to temperature and inhibitors. Failure of preelectrophoretic treatment with NAD to cause interconversion of these isozymes suggests that they are products of separate genetic loci. Both isozymes were maximally active with isopropanol, sec-butanol, and amyl alcohol. Within a given species, ADH showed negligible variation (i.e., apparent genetic polymorphism) with respect to individual larvae, site of larvae in the host, or geographical origin of the host. MDH from Anisakis, Sulcascaris, and Phocanema spp. possessed one, two, and three bands of activity, respectively; MDH is highly thermostable in Anisakis sp. but not in the other species.     

Correlative and Dynamic Imaging of the Hatching Biology of Schistosoma japonicum from Eggs Prepared by High Pressure Freezing

Background

Schistosome eggs must traverse tissues of the intestine or bladder to escape the human host and further the life cycle. Escape from host tissues is facilitated by secretion of immuno-reactive molecules by eggs and the formation of an intense strong granulomatous response by the host which acts to exclude the egg into gut or bladder lumens. Schistosome eggs hatch on contact with freshwater, but the mechanisms of activation and hatching are poorly understood. In view of the lack of knowledge of the behaviour of egg hatching in schistosomes, we undertook a detailed dynamic and correlative study of the hatching biology of Schistosoma japonicum.

Methodology/Principal Findings

Hatching eggs of S. japonicum were studied using correlative light and electron microscopy (EM). The hatching behaviour was recorded by video microscopy. EM preparative methods incorporating high pressure freezing and cryo-substitution were used to investigate ultrastructural features of the miracidium and extra-embryonic envelopes in pre-activated and activated eggs, and immediately after eggshell rupture. Lectin cytochemistry was performed on egg tissues to investigate subcellular location of specific carbohydrate groups.

Conclusions/Significance

The hatching of S. japonicum eggs is a striking phenomenon, whereby the larva is liberated explosively while still encapsulated within its sub-shell envelopes. The major alterations that occur in the egg during activation are scission of the outer envelope-eggshell boundary, autolysis of the cellular inner envelope, and likely hydration of abundant complex and simple polysaccharides in the lacunal space between the miracidial larva and surrounding envelopes. These observations on hatching provide insight into the dynamic activity of the eggs and the biology of schistosomes within the host.     

Effects of host-egg ages on host selection and suitability of four Chinese Trichogramma species,egg parasitoids of the rice striped stem borer,Chilo suppressalis

The striped stem borer, Chilo suppressalis (Walker), is one of the most economically important rice pests worldwide. However, biological control of this pest using natural-enemy insects has been rarely documented to date. With the objective of screening suitable candidate species for controlling the striped stem borer, we investigated the effect of the age of host eggs on the host selection and suitability by four indigenous Trichogramma species on their native host, C. suppressalis. The results indicated that the differently aged eggs of C. suppressalis were all accepted by T. japonicum, T. dendrolimi and T. chilonis, and there was a clear tendency to parasitize older eggs less under no-choice and choice conditions. The number of parasitized host eggs by T. ostriniae also decreased with the increasing host age in the no-choice test, but more 2-day-old host eggs were parasitized in the choice test. When 0-, 2-day-old eggs were offered, T. dendrolimi, T. japonicum and T. chilonis exhibited similar parasitism ability, whereas T. ostriniae appeared to have a stronger ability to attack the older host eggs (4-day-old). Trichogramma japonicum developed and emerged on parasitized C. suppressalis eggs of all ages tested, while showing a better adaptation to younger host eggs with significantly faster developmental time, higher survival and more female progeny on 0-day-old eggs. No adults for each of the other three Trichogramma species emerged from parasitized 4-day-old host eggs, and they had similar developmental time, survival and female progeny on parasitized 0-, 2-day-old host eggs with an exception of female progeny for T. chilonis. On 0-day-old host eggs, T. japonicum developed faster and T. ostriniae had lower progeny survival than the other three Trichogramma species evaluated, respectively. The current study provides useful information to select suitable Trichogramma species for controlling the striped stem borer, C. suppressalis.     

Discovery of Parvatrema duboisi and Parvatrema homoeotecnum (Digenea: Gymnophallidae) from Migratory Birds in Korea

Adult worms of Parvatrema spp. (Digenea: Gymnophallidae) were found in the intestines of 2 species of migratory birds, i.e., a great knot, Calidris tenuirostris, and 2 Mongolian plovers, Charadrius mongolus, in the coastal area of Gunsan-si, Jeollabuk-do in October 2009. The recovered Parvatrema worms were 79 in total number and composed of 2 species. The worms from a great knot were 289 µm in length with the oral and ventral sucker ratio of 2 : 1. They had a single vitellarium, and their intrauterine eggs were 25.0 × 17.5 µm in size. These findings were compatible with P. duboisi (Dollfus, 1923) Bartoli, 1974 (syn. P. timondavidi Bartoli, 1963). The worms recovered from the Mongolian plovers were smaller in length than P. duboisi and had 2 vitellaria. The oral and ventral sucker ratio was 2.5 : 1, and the eggs were 17.5 × 8.8 µm in size. These worms were assigned to be P. homoeotecnum James, 1964. This is the first report on the natural final hosts of Parvatrema spp. in Korea.