DEVELOPMENT OF JANCZEWSKIA MORIMOTOI (CERAMIALES) ON ITS HOST LAURENCIA NIPPONICA (CERAMIALES,RHODOPHYCEAE)1

Janczewskia morimotoi Tokida was successfully cultured from spore to reproductive maturity on its host Laurencia nipponica Yamada. The spore penetrates the host without requirement for wound or abrasion sites, growing between host cortical cells and developing a superficial and an endophytic system simultaneously. During the juvenile period, when the parasite is nonpigmented, it differentiates a cortex and the proliferating endophytic filaments enlarge causing a displacement of layers of host cells into the parasitic tissue. Host cells contacted by cells of the parasite exhibit increased wall thickness, cytoplasmic density and vesicle formation. Pit connections between host and parasite cells were rarely observed whereas penetration of host cell walls was seen commonly. As the parasite increases in size, its cells become pigmented evenly throughout the cortex and host cells show less obvious reactions to the parasite. At this same time, the parasite develops branches and reproductive structures. Host plant segments less than 3 cm long failed to grow when infected with spores of the parasite whereas longer segments were not significantly affected by the parasite. In the absence of the host, the parasite cannot complete its development. Although J. morimotoi is well pigmented at maturity, the absence of pigmentation in the juvenile stage, penetration of host cells, and effect on host growth in culture strongly suggest that it is parasitic during at least its early development.     

The cephalic labial gland secretions of two socially parasitic bumblebees Bombus hyperboreus (Alpinobombus) and Bombus inexspectatus (Thoracobombus) question their inquiline strategy

Social parasitic Hymenopterans have evolved morphological, chemical, and behavioral adaptations to overcome the sophisticated recognition and defense systems of their social host to invade host nests and exploit their worker force. In bumblebees, social parasitism appeared in at least 3 subgenera independently: in the subgenus Psithyrus consisting entirely of parasitic species, in the subgenus Alpinobombus with Bombus hyperboreus, and in the subgenus Thoracobombus with B. inexspectatus. Cuckoo bumblebee males utilize species‐specific cephalic labial gland secretions for mating purposes that can impact their inquiline strategy. We performed cephalic labial gland secretions in B. hyperboreus, B. inexspectatus and their hosts. Males of both parasitic species exhibited high species specific levels of cephalic gland secretions, including different main compounds. Our results showed no chemical mimicry in the cephalic gland secretions between inquilines and their host and we did not identify the repellent compounds already known in other cuckoo bumblebees.     

Structure of floral galls of Byrsonima sericea (Malpighiaceae) induced by Bruggmanniella byrsonimae (Cecidomyiidae,Diptera) and their effects on host plants

Galls are anomalies in plant development from parasitic origin, and affect cellular differentiation or growth of plants. This parasite–plant interaction occurs in many environments and typically in vegetative organs of plants. The existence of galls in reproductive organs and their effects on the host plant are seldom described in the literature. In this paper, we present a novel study of galls in plants of the neotropical region. Galls of Bruggmmaniella byrsonimae develop in the flower buds of Byrsonima sericea DC. (Malpighiaceae) and affect development of the reproductive organs and the reproductive effort of these plants. The sepals and petals show hypertrophy of parenchyma tissues after differentiation, and the stamens exhibit degeneration of the sporogenic tissue. The gynoecium is not entirely developed; ovary and ovules are often absent. Changes in vascular tissues are also frequent, which may indicate high demand for nutrient resources by the new tissues initiated by the larva. We compared the amount of inflorescences, galls and fruits to evaluate possible effects on host reproduction. The results suggest that the Cecidomyiidae galls in flower organs affect fruit set and the reproductive success of B. sericea.     

Nutrient-dependent patterns in the sex ratio of Ovomermis sinensis (Nematoda: Mermithidae), a biological control agent of Helicoverpa armigera (Lepidoptera: Noctuidae)

Ovomermis sinensis (Nematoda: Mermithidae) is an entomophilic nematode and a potential biocontrol agent of lepidopteran pests, including Helicoverpa armigera. The sex ratio of a species can be used to regulate the size of the reproductive population. Parasitic load, parasitic period, host instar, and body size were examined to identify factors affecting the O. sinensis sex ratio. We tested the hypothesis that the O. sinensis sex ratio is correlated with host nutrient supply and the nutrients absorbed by the nematodes. The results show that the proportion of male O. sinensis increased with parasitic load but decreased with host instars and body size. Moreover, the parasitic period of males was significantly shorter than that of females. However, all the factors (host and nematodes) affecting the sex ratio were significantly modified by restricting the host diet, which increased the proportion of males. In turn, juveniles that absorbed fewer nutrients tended to develop into males. Taken together, our findings suggest that factors impacting the O. sinensis sex ratio are related to host nutrient status and provide parameters for mass rearing and a release strategy for this natural enemy.     

Biochemical and morphological evidence for host race evolution in desert mistletoe,Phoradendron californicum (Viscaceae)

Allozymes and morphological characters were used to test whether host race evolution—the genetic divergence of parasitic populations caused by adaptation to different host species—has occurred in desert mistletoe,Phoradendron californicum. Populations ofPhoradendron californicum from two hosts,Acacia greggii andProsopis glandulosa, were surveyed from the Mojave and Colorado deserts. Electrophoretic data indicated genetic differentiation of mistletoes occurring on these hosts. Three of four morphological characters (internode length, main shoot lateral shoot diameter ratio and berry color) also showed significant host-specific differentiation. These data support the hypothesis that host race formation has occurred or is occurring in this parasitic angiosperm.     

Host influence on floral variability inOrthocarpus densiflorus (Scrophulariaceae)

This study investigates the influence of host plants on the expression of floral variability in the hemiparasiteOrthocarpus densiflorus (Scrophulariaceae), to determine if interaction with host plants can facilitate the expression of normally hidden genes. Style extension inO. densiflorus is highly uniform in natural populations, with less than 1% of the individuals exhibiting an aberrant extended-style condition. Both seed treatment with giberellic acid and parasitic development with host plants significantly facilitates the expression of extended-style in progenies that show only minimal expression when grown autotrophically. Artificial selection experiments demonstrate the range of potential phenotypic variation to be under genetic control, and differentially influenced by the host environment. Although the biochemical basis of the host influence is unknown, some host plants produce stimuli that apparently disrupt buffering inO. densiflorus and expose normally unexpressed genetic variability to selection. If variation in other traits is similarly affected, the influence of host chemistry may provide parasitic plants with a greater than normal opportunity for rapid selectional change.     

The species of Ibidoecus (Phthiraptera) on Threskiornis (Aves)

The species of Ibidoecus parasitic on the Ibis genus Threskiornis are reviewed-clausus (Giebel), dianae Tandan, insularis sp.n., tandani sp.n., threskiornis Bedford-and a key for their identification presented. The host and geographical distribution of the phthirapteran parasites of this genus are discussed.     

Biochemical Aspects of Parasitism by the Angiosperm Parasites: Phenolics in Parasites and Hosts

the contents of total phenolics in three parasitic angiosperms, Cuscuta species, Orobanche aegyptiaca and Dendrophthoe falcata and their respective hosts, were colorimetrieally determined. A biochemical comparison was made of the phenolics on the basis of the ability of alcoholic extracts of the tissues to inhibit amylose phosphorylase in vitro. High concentration of phenolics seemed to be a general feature of parasitic angiosperms. An increase in the concentration of the phenolics occurred in the tissues of infected hosts, in comparison with controls. the phenolics of Orobanche and mistletoe had inhibitory activity against amylose phosphorylase, but those of Cuscuta developed the inhibitory ability only when growing on hosts which themselves possessed inhibitory phenolics. the inhibitory activity of host phenolics was sometimes altered as a result of infection by parasite. Although the hosts often exerted some influence on the concentration and the inhibitory activity of phenolics in the parasites, there was no direct relationship between host and parasite phenolics. the sum of the phenolics in the tissues of parasite and the infected bost generally exceeded the phenolics in the tissues of the control host. The content of phenolics and their inhibitory activity did not appear to be directly related to the resistance of a host or to the extent of its susceptibility to parasite infection.     

Host‐driven divergence in the parasitic plant Orobanche minor Sm. (Orobanchaceae)

Many parasitic angiosperms have a broad host range and are therefore considered to be host generalists. Orobanche minor is a nonphotosynthetic root parasite that attacks a range of hosts from taxonomically disparate families. In the present study, we show that O. minor sensu lato may comprise distinct, genetically divergent races isolated by the different ecologies of their hosts. Using a three‐pronged approach, we tested the hypothesis that intraspecific taxa O. minor var. minor and O. minor ssp. maritima parasitizing either clover (Trifolium pratense) or sea carrot (Daucus carota ssp. gummifer), respectively, are in allopatric isolation. Morphometric analysis revealed evidence of divergence but this was insufficient to define discrete, host‐specific taxa. Intersimple sequence repeat (ISSR) marker‐based data provided stronger evidence of divergence, suggesting that populations were isolated from gene flow. Phylogenetic analysis, using sequence‐characterized amplified region (SCAR) markers derived from ISSR loci, provided strong evidence for divergence by clearly differentiating sea carrot‐specific clades and mixed‐host clades. Low levels of intrapopulation SCAR marker sequence variation and floral morphology suggest that populations on different hosts are probably selfing and inbreeding. Morphologically cryptic Orobanche taxa may therefore be isolated from gene flow by host ecology. Together, these data suggest that host specificity may be an important driver of allopatric speciation in parasitic plants.     

HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA)1

Some chytrids are host‐specific parasiticfungithat may have a considerable impact on phytoplankton dynamics. The phylum Chytridiomycota contains one class, the Chytridiomycetes, and is composed of five different orders. Molecular studies now firmly place the Chytridiomycota within the fungal kingdom. Chytrids are characterized by having zoospores, a motile stage in their life cycle. Zoospores are attracted to the host cell by specific signals. No single physical–chemical factor has been found that fully explains the dynamics of chytrid epidemics in the field. Fungal periodicity was primarily related to host cell density. The absence of aggregated distributions of chytrids on their hosts suggested that their hosts did not vary in their susceptibility to infection. A parasite can only become epidemic when it grows faster than the host. Therefore, it has been suggested that epidemics in phytoplankton populations arise when growth conditions for the host are unfavorable. No support for such a generalization was found, however. Growth of the parasitic fungus Rhizophydium planktonicum Canter emend, parasitic on the diatom Asterionella formosa Hassal, was reduced under stringent nutrient limitation,because production and infectivity of zoospores were affected negatively. A moderate phosphorous or light limitation favored epidemic development, however. Chytrid infections have been shown to affect competition between their algal hosts and in this way altered phytoplankton succession. There is potential for coevolution between Asterionella and the chytrid Zygorhizidium planktonicum Canter based on clear reciprocal fitness costs, absence of overall infective parasite strains, and possibly a genetic basis for host susceptibility and parasite infectivity.     

Differential response of stomata to air humidity in the parasitic mistletoe (Phthirusa pyrifolia) and its host,mandarin orange (Citrus resitulata)

Measurements of CO₂ and H₂O exchange rate and the calculated leaf conductance of attached leaves were conducted over a range of leaf-to-air vapour pressure difference (VPD) (1.5 to 5.5 kPa) to compare the response of the parasitic mistletoe, Phthirusa pyrifolia, with that of its host, the mandarin orange, Citrus reticulata. Seedlings of the host infected with the parasite were grown in well-watered and adequately fertilized large pots outdoors at the CIAT headquarters, Palmira, Colombia, South America. Observations of leaf anatomy of the parasite and nutrient analysis of young tissues of both the parasite and host were made. The photosynthetic rate of the host decreased linearly with increased VPD, whereas the parasite showed a constant rate. This trend coincided with similar responses in leaf conductance. Due to the insensitivity of the parasite stomata, the transpiration rate increased linearly with VPD as compared with an initial increase and then a decrease in the host transpiration rate. The higher photosynthetic rate and the closure of stomata of the host resulted in high water use efficiency as compared with that of the parasite. The parasite accumulated in its leaves more N, P, K and less Ca and Mg than the host. The significance of the host-parasite differential response to air humidity is discussed in relation to mechanism underlying stomatal sensitivity and in the context of host-parasite association.Visiting Scientist, Coordinator, and Research Assistant of the Cassava Physiology Program.     

Social parasites among African allodapine bees (Hymenoptera,Anthophoridae, Ceratinini)*

Among the numerous nonparasitic allodapine bees there are 11 known species with parasitic or probably parasitic habits. These species live in nests of their close relatives, the female parasite replacing an egg-layer of the host. Seven of the parasitic species are distributed among four otherwise nonparasitic genera, while four species of parasites are placed in three exclusively parasitic genera. The parasites have mostly arisen independently from different nonparasitic forms. There is much convergence among the parasitic forms involving such characters as the flattened or concave face, reduced eyes, reduced mouthparts, reduced wing venation, and reduced pollen-carrying scopa. In the most specialized parasitic genera the mouthparts are so small as to be almost surely useless for obtaining food from flowers. Such bees must feed in the host nest, and are not found on flowers. Their wings must be adequate to take them to a new host nest but the reduced venation and eyes must reflect the reduced locomotary and sensory needs of a bee that does not visit flowers. In this paper a new, presumably parasitic Allodapula is described as is a parasitic Braunsapis, a parasitic Allodape, and a Eucondylops. A previously described Macrogalea is recognized as a parasite for the first time. A new genus and species of parasites Nasutapsis straussorum, allied to Braunsapis, is also described. All these forms are from Africa.     

Ultrastructure of infection of Cokeromyces recurvatus by Piptocephalis unispora (Mucorales)

Infection of the mucoraceous host Cokeromyces recurvatus by Piptocephalis unispora was studied ultrastructurally, using a new technique involving yeast-phase cells of the host to obtain large numbers of infection sites for thin-sectioning. Morphologically, the haustorial apparatus was similar to that of fungi parasitic on higher plants, and comprised an appressorium, a neck region with a collar and a neck ring, and a lobed region surrounded by a sheath matrix enclosed in an extra-haustorial membrane. Penetration of the host by the infection peg probably involved both enzymatic degradation and physical pressure. Reaction of the host to infection is described and the results related to the theory of host infection by haustorial fungal parasites.     

Strongyloides spearei n. sp. (Nematoda: Strongyloididae) from the common wombatVombatus ursinus (Marsupialia: Vombatidae)

Strongyloides spearei n. sp. is described from the small intestine of the common wombatVombatus ursinus from Healesville, Victoria. The new species is distinguished from all known congeners by: the triangular shape of the stoma and the length of the parasitic female; the blunt spicules in the free-living male; and the presence of eggs in the faeces of the host.S. spearei andS. thylacis Mackerras, 1959 form a separate group withinStrongyloides based on both species infecting marsupials, having directly recurrent ovaries in the parasitic female and having blunt spicules in the free-living male. The histological localisation ofS. spearei is predominantly within the crypts of the small intestine.     

PARASITIC INTERACTIONS AND VEGETATIVE ULTRASTRUCTURE OF CHOREOAEMA THURETII (CORALLINALES,RHODOPHYTA)1

The monotypic coralline red alga, Choreonema thuretii (Bornet) Schmitz (Choreonematoideae), grows endophytically within three geniculate genera of the Corallinoideae. Although the thallus of Choreonema is reduced, lacks differentiated plastids, and is endophytic except for its conceptacles, its status as a parasite has been questioned because cellular connections to the host had not been ob served. Transmission electron microscopy, however, disclosed a previously undescribed type of parasitic interaction in which Choreonema interacts with its host through specialized cells known as lenticular cells. These small, lens-shaped cells are produced from the single file of host-penetrating vegetative cells. Pit plug morphology between vegetative and lenticular cells is polarized. Plug caps facing the vegetative cell have normal coralline morphology, while those facing the lenticular cell are composed of three layers. Regions of lenticular cells near host cells protrude toward the host cell; upon encountering the host cell wall, the prolrusion produces numerous finger-like fimbriate processes that make cellular connections with the host cell. Lenticular cells may extend several protrusions toward a host cell or penetrate more than one host cell; two or more lenticular cells may also penetrate the same host cell. The lack of secondary pit connections, cell fusions, and passage of parasitic nuclei suggest that this parasitic relationship may be evolutionarily older than previously reported cases of parasitism in red algae.     

Adoption of lycaenid Niphanda fusca (Lepidoptera: Lycaenidae) caterpillars by the host ant Camponotus japonicus (Hymenoptera: Formicidae)

Caterpillars of the parasitic lycaenid butterfly are often adopted by host ants. It has been proposed that this adoption occurs because the caterpillars mimic the cuticular hydrocarbons of the host ant. This study aimed to examine whether caterpillars of the Japanese lycaenid butterfly Niphanda fusca induce adoption by mimicking their host ant Camponotus japonicus. Behavioral observations conducted in the laboratory showed that most second‐instar caterpillars were not adopted, whereas most third‐instar caterpillars were successfully adopted by host workers. A chemical comparison detected no characteristic differences in the cuticular hydrocarbon profiles between second‐ and third‐instar caterpillars. However, morphological features of the caterpillars differed between the second and third instars; third‐instar caterpillars developed exocrine glands (ant organs) such as tentacle organs and a dorsal nectary organ. These results suggest that multiple chemical signatures, not only cuticular hydrocarbons, may be important for invasion of the host ant nest.     

The hitchhiker's guide to parasite dissemination

Toxoplasma gondii (T. gondii) is a parasitic protist that can infect nearly all nucleated cell types and tissues of warm‐blooded vertebrate hosts. T. gondii utilises a unique form of gliding motility to cross cellular barriers, enter tissues, and penetrate host cells, thus enhancing spread within an infected host. However, T. gondii also disseminates by hijacking the migratory abilities of infected leukocytes. Traditionally, this process has been viewed as a route to cross biological barriers such as the blood–brain barrier. Here, we review recent findings that challenge this view by showing that infection of monocytes downregulates the program of transendothelial migration. Instead, infection by T. gondii enhances Rho‐dependent interstitial migration of monocytes and macrophages, which enhances dissemination within tissues. Collectively, the available evidence indicates that T. gondii parasites use multiple means to disseminate within the host, including enhanced motility in tissues and translocation across biological barriers.     

Transcriptomic characterization of gall tissue of Japanese elm tree (Ulmus davidiana var. japonica) induced by the aphid Tetraneura nigriabdominalis

Insect galls are abnormal plant tissues induced by parasitic insect(s) for use as their habitat. In previous work, we suggested that gall tissues induced by the aphid Tetraneura nigriabdominalis on Japanese elm trees are less responsive than leaf tissues to jasmonic acid (JA), which is involved in the production of volatile organic compounds as a typical defensive reaction of plants against attack by insect pests. A comprehensive analysis of gene expression by RNA sequencing indicated that the number of JA responsive genes was markedly lower in gall tissues than in leaf tissues. This suggests that gall tissues are mostly defective in JA signaling, although JA signaling is not entirely compromised in gall tissue. Gene ontology analysis sheds light on some stress-related unigenes with higher expression levels in gall tissues, suggesting that host plants sense aphids as a biotic stress but are defective in the JA-mediated defense response in gall tissues.     

Nanocladius (Plecopteracoluthus) asiaticus sp. n. (Diptera: Chironomidae) Phoretic on Dobsonfly and Fishfly Larvae (Megaloptera: Corydalidae)

The adult male, adult female, pupa, and larva of Nanocladius (Plecopteracoluthus) asiaticus sp. n. (Diptera: Chironomidae) are described and illustrated. Larvae live in coarse silken nets which usually are attached to the ventral side of the mesothorax of larval dobsonflies and fishflies (Megaloptera: Corydalidae) dwelling in stream riffles. The host species are Protohermes grandis and Parachauliodes continentalis in Japan, Protohermes costalis and Neochauliodes sinensis in Taiwan, and Neurhermes maculipennis in the Malay Peninsula. Larvae are not parasitic but may have a commensal relationship with their hosts; they feed on algae and detrital material caught on their silken nets, or on the body surface of their hosts. Pupation occurs in the fine silken net fixed to the lateral side of host thoracic regions, or occasionally to the undersides of hind legs.