No description available.

Petri dish and olfactometer tests demonstrated that Goniozus natalensis (Gordh) females exhibit a host-searching response upon contact and at a short distance by olfaction, to a kairomone in the frass of its natural host Eldana saccharina (Walker). The host-searching response was found to be elicited by E. saccharina frass from a range of substrates, namely: two host plants of E. saccharina, papyrus and sugarcane, and four media: sugarcane, papyrus, and cellulose based media and a synthetic medium containing no plant material. The host-searching response was not elicited by Sesamia calamistis (Hamps) sugarcane medium frass. The sexual state and age of G. natalensis females were found to influence the host-searching behaviour. Mated females showed the behaviour in the petri dish bioassays only after completing their preoviposition time of two to three days, whilst virgin females took longer, even though their preoviposition time was found to be the same. The response to male or female produced E. saccharina sugarcane frass was not statistically different, nor was there a statistically significant preference for either frass type, given the choice. Four way olfactometer tests showed that an E. saccharina sugarcane frass odour elicited a host-searching behaviour in mated two to three day old G. natalensis females. Various solvents were tested for their ability to isolate the kairomone from E. saccharina sugarcane frass. Chloroform proved to be the best solvent when tested in petri dish and olfactometer bioassays. The preliminary results of the GC/MS analysis of the chloroform extract of E. saccharina sugarcane frass are presented. The chemicals identified are compared with chemicals identified as host location kairomones for other insect parasitoid-host studies. / Thesis (M.Sc.)-University of Natal, 1990.

The influence of foraging ants on the insect fauna within the canopy of the tree species Terminalia sericea, Burkea africana and Ochna pulchra was studied in an area of typical South African savanna, over a two year period. The number of individual insects and their species composition was compared on unbanded, ant-infested plants and on banded plants where ants had been excluded. Differences in the level of herbivory recorded on banded and unbanded trees were related to the guild composition of insects within the canopy, and the results are discussed in terms of plant protection as a consequence of ant - insect interactions. Twenty-six ant species were recorded on the study trees at Nylsvley, with individuals belonging to the genus Crematogaster being numerically abundant and dominant within the canopy of each species of tree. These dominant ant species influenced the insect fauna by their strong dependence on honeydew, encouraging a build up in numbers of Homoptera on the branches and leaves of foraged trees, and supporting homopterous populations within the confines of their nest compartments . The exclusion of ants from trees led to fewer "mobile" homopterans (Aphididae, Membracidae, Psyllidae and Cicadellidae) and "sessile" homopterans (mainly Coccidae but also Pseudococcidae). Pyrethrum spraying showed that the guild composition of non-homopterous insects was similar on banded and unbanded trees. Differences in the level of herbivory on banded and unbanded trees suggested that, although slight, foraged trees were protected from some damage by the presence of ant species within the canopy. A trend did exist towards a greater number of insect individuals and species on unbanded trees, and it is postulated that during the period 1982 1984 when drought conditions prevailed over Nylsvley, ants do not reduce insect numbers through predation or disturbance but simply deter phyllophagous feeding. A separate experiment showed that Crematogaster constructor would feed on the eggs and early instar larvae of the saturnid moth, Cirina forda, but low numbers of lepidopterous larvae on the trees may have forced ants to seek honeydew. The negative impact of large homopterous populations on foraged trees was only seen in an isolated field observation where Polyrachis schistacea was found to associate with the lac insect Tachardina sp . . In conclusion it can be said that where homopterans are not the dominant phyllophages, plants do benefit from foraging populations of ants in that damage to the leaves is reduced.

Arbuscular mycorrhizal (AM) fungi are naturally occurring in roots of terrestrial plants. AM fungi are capable of benefiting the host plant through various mechanisms such as enhanced nutrient supply, alleviation of environmental stress and inhibition of plant fungal pathogens. AM fungal spore-associated bacteria have been previously isolated and shown to have plant growthpromoting (PGP) abilities by several authors. Some bacterial isolates are able to promote AM fungal colonisation of host plants and are known to be mycorrhizal helper bacteria (MHB). This study focused on the isolation of AM fungal spore-associated bacteria, characterization of the isolates according to plant growth promoting abilities and evaluation of their potential to enhance plant growth and mycorrhizal colonisation. AM fungi were extracted from soils sampled from natural indigenous forest sources, raspberry (Rubus idaeus cv. Heritage) and strawberry (Fragaria ananassa) farms in South Africa and from a raspberry (Rubus idaeus cv. Autumn Bliss) plantation in Argentina. A total of 52 sporeassociated bacteria were isolated from the external and internal surfaces of AM fungal spore morphotypes from the two countries. The bacterial isolates were evaluated for their PGP abilities such as phosphate solubilisation, indole-3-acetic acid production, ammonia production and inhibition of the fungal pathogens Fusarium oxysporum and Phythophthora nicotianae through mechanisms such as siderophore and/ or hydrolytic enzyme production. A total of 23 bacterial isolates from both South Africa and Argentina showing the most potential to be PGP, were identified molecularly as belonging to the genera Acinetobacter, Alcaligenes, Bacillus, Microbacterium, Micrococcus, Serratia and Staphylococcus. The ability of ten selected bacterial isolates showing multiple PGP capacity were evaluated for their plant growth promotion and mycorrhizal colonisation enhancement ability on raspberry (Rubus idaeus cv. Meeker). Significant differences in increased shoot and root dry weights were shown by the treatments compared to the uninoculated control. The highest increase in shoot and root dry weights were shown by South African (Bacillus mycoides) and Argentinean (Alcaligenes faecalis) isolates. AM fungal colonisation was significantly enhanced by the South African (Bacillus mycoides) and Argentinean (Micrococcus luteus) isolates compared to the AM fungal singly inoculated control.

No description available.

No description available.

Thesis (M.S.)--Georgia Southern University, 2007. / "A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." In Biology, under the direction of Alan Harvey. ETD. Electronic version approved: July 2007. Includes bibliographical references (p. 59-64) and appendices.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 12, 2009) Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This study describes the effect of the root hemi-parasitic angiosperm Rhinanthus minor on the structure of the communities in which it lives and seeks to elucidate a mechanism through which the parasite acts to effect these changes in the community. Field manipulations reveal that R. minor suppressed the growth of grasses and legumes in a newly sown meadow whilst promoting the forbs within one growing season. In contrast the removal of R. minor from mature meadow plots did not influence their composition. After an additional growing season the parasite did not further influence the composition of the new meadows but removal did begin to benefit the biomass of mature plots. In isolation the parasite caused most damage to grasses whilst leaving legumes and forbs undamaged. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to the forbs. Consequently the parasite was able to moderate intra-specific competition between grasses and forbs. I thus hypothesised that forbs were able to prevent the parasite form abstracting resources where as grasses could not. Tracer experiments using isotopically e5N) labelled potassium nitrate confirmed this hypothesis showing that more of the resources taken up by the host were stolen by the parasite from grasses than from forbs. There was much variability in the translocation of resources from the legume studied. The reasons underlying the differential uptake of resources were highlighted using histological studies which showed that all of the forbs possessed successful resistance mechanisms to the parasite whilst no successful resistance was observed in the grasses or legumes. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death at the host-parasite interface and host lignification. I therefore propose that differential host resistance may underlie this parasite's community level effects as forbs possess a resistance capacity that other potential hosts do not.