Nineteen Ontario species were studied and five from outside Ontario examined. Newly emerged females were of five types: with (1) mature eggs and reduced mouth parts (Gymnopaïs spp., Cnephia spp.); (2) eggs half developed, much stored nutrient, and reduced mouth parts (C. emergens, P. alpestre); (3) eggs half developed, much stored nutrient, and piercing mouth parts (C. mutata); (4) eggs one-fifth to one-third developed, usually much stored nutrient, and piercing mouth parts (Simulium spp.); (5) eggs less than one-quarter developed, little stored nutrient, and piercing mouth parts (Prosimulium spp., Simulium spp.). In Cnephia spp. (type 1) mating occurred shortly after emergence with little flying. In C. mutata parthenogenesis is usual. Male mating flights occurred in species of Prosimulium and Simulium. But S. decorum mated on a support shortly after emergence and also just before oviposition. C. mutata fed infrequently on deer. Occasional females of S. decorum and S. vittatum (type 4) fed on mammals. Species of type 5, S. croxtoni, S. euryadminiculum, S. latipes, and S. rugglesi fed only on birds, S. venustum naturally on birds and mammals, and others naturally only on mammals. Ovarian development in species of types 4 and 5 took live or more days. In those of type 5 it began only after a blood meal that may take two weeks to acquire. Females of Prosimulium, Cnephia, and some Simulium species dropped eggs into the water while flying. Other Simulium species oviposited on water-covered surfaces either while flying or alighted, depending on conditions. Oviposition was greatest in the evening but occurred at other times when populations were large, and conditions favorable.
The outcome of dual infection of the grass Lolium perenne L. by arbuscular mycorrhizal (AM) fungi and the parasitic angiosperm Rhinanthus minor L. was investigated in a glasshouse study. Colonization of L. perenne roots by AM fungi was significantly reduced by the presence of R. minor, as was host growth which fell by 44-51 %. It was concluded that these two responses were linked, with AM colonization declining in response to the reduction in availability of host carbon. Parasite growth and reproductive output rose by 58 % and 47 % respectively when the hosts were mycorrhizal. These trends were unrelated to the attachment success of the parasite, but were accompanied by a significant increase in the formation of secondary haustoria. The benefits afforded the parasite when the hosts were mycorrhizal were attributed to increased carbon and nutrient flux resulting from alternations in sink strength. Host responses to parasitism and mycorrhizal colonization were not affected by the interaction between the two symbionts. However, the suggestion is made that the interaction between the AM fungi and parasite might have long-term ecological implications for the host species via its impact on parasite fecundity.
The effects of phosphorus supply on the outcome of interactions between the hemiparasitic angiosperm Rhinanthus minor L. with its host species Lolium perenne L. were investigated in a glasshouse experiment. Host plants were grown in 3-l pots in the presence and absence of R. minor at limiting (0.13 mM P) and optimal (0.65 mM P) concentrations of phosphorus for the growth of the host species. Phosphorus was supplied at 2-day intervals in the form of half-strength Long Ashton nitrate-based solution with phosphorus concentrations adjusted accordingly. Parasitism by R. minor significantly suppressed host growth, with final biomass losses ranging between 32% and 44%. Phosphorus supply had a marked impact on the outcome of the host-parasite interaction. By the end of the growing period, parasite biomass at 0.65 mM P was 90% lower than that achieved at 0.13 mM P. In contrast, host biomass at 0.65 mM P was 74% higher than achieved at 0.13 mM P, indicting that the negative impact of parasitism on the host species was reduced when phosphorus supply was increased. The effects of phosphorus on the host-parasite association appeared to be mediated by changes in both the morphological characteristics of the host roots and the relative sink strengths of the host and parasite.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.