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No description available.

Megastigmus spermotrophus is a parasitic chalcid wasp that spends most of its life in the seed of its host, Douglas-fir (Pseudotsuga menziesii). The adult female wasp lays its eggs into the megagametophyte deep within the ovule; the larva prevents an unpollinated ovule from aborting, redirecting resources to feed itself. Host-site selection pressures that influence female oviposition depend on a number of factors. Morphological characteristics of Douglas-fir cones including seed size, seed location, and scale thickness were measured for every ovuliferous scale. Seeds infested by M. spermotrophus as well as seeds fused to galls intiated by a competing conophyte, Contarinia oregonensis were noted. Using a generalized linear mixed effects model, I found that seed position, and the presence of C. oregonensis, were strong predictors of Megastigmus infestation. The percent of M. spermotrophus infested seed was higher in the apical and basal regions of the cone where seeds were smaller, scales were thinner and C. oregonensis were less frequently found. M. spermotrophus was also found to exploit seeds in regions of the cone, where seeds rarely complete development. These data suggest that competitors may not be the only factor influencing infestation; factors of cone morphology are also important. Douglas-fir seed does not show any anatomically detectable defense response to Megastigmus attack. To study mechanisms of host manipulation and defense response of the seed I took a genomics approach. Four types of ovules/seeds were studied: 1. pollinated & uninfested, 2. pollinated & infested, 3. unpollinated & uninfested, and 4. unpollinated and infested. A de novo reference transcriptome was assembled. Transcripts were annotated based on sequence similarity to genes of Pinus taeda, Arabidopsis thaliana, Nasonia vitripennis, and the UniProt database. Expression values were estimated based on the alignment of the original reads back onto the reference transcriptome. Differentially expressed transcripts were identified. Oviposition of M. spermotrophus caused changes in expression of Douglas-fir transcripts. Functional classification of differentially expressed transcripts between infested and uninfested seed revealed genes with possible roles in wounding, but none specific to herbivory. Infested treatments had more transcripts similarly expressed to pollinated than unpollinated seeds suggesting that M. spermotrophus is capable of manipulating gene expression. These transcripts had functional roles related to seed storage, cell division and growth, solute transport, hormone signalling, and programmed cell death among others. Overall, this study reveals a select set of genes that may be involved in stress response to wounding and also genes important for seed development and maturation. / Graduate

Animal infestations of water distribution systems are a cause of considerable concern for the water industry. The appearance of an animal at a consumer's tap often gives rise to complaints. This study, in Anglian Water, Oundle Division, Northamptonshire, U.K. investigated the ecology of the infesting community and its management. Mains sampling used sequential flushes at the hydrant and a model for animal removal was constructed. Tap sampling collected animals from filters at the tap and an index of emergence (density in a day's consumption) and degree of infestation (based on density and the ability to cause complaints) were devised. Reservoir sampling used a perspex trap to sample the water column and sediments. Methods to determine the environmental and operational characteristics of the system were also devised. Community clustering on the basis of animal density determined five distinct community types. Operational and environmental parameters did not coincide with any of the types, though correlations indicated that highest densities occurred at sites further (in time) from treatment with a low turnover time. Sites fed by slow sand filters were not recolonised by chironomid larvae nor to the degree of other sites by other taxa. No successional sequence was found and it was concluded that animals recolonised on the basis of a 'competitive lottery'. The relationship between density at the tap and in the main was considered and seasonal changes in the degree of infestation between sites confirmed that water from rapid gravity filtration leads to more severe animal problems, particularly during the summer. Benthic animals penetrated treatment in low numbers, but reservoirs near treatment were dominated by limnetic animals. Many died and became an indirect food source for infesting animals, but some survived and colonised pipes. Reservoirs at the extremes of the system were not influenced by these taxa and were 'extensions' of the distribution system.

The toxicity of Hexachlora cyclohexane (HCH) to the rat.

Heptachlor in the albino rat

Newer aspects of BHC (HCCH)

Estimation of time since death is an important variable when investigating legal cases involving decomposing human remains; however it has been sparsely studied in controlled environments. Decomposition rates are largely influenced by external factors with temperature being the most critical factor. The decomposition rates can also be influenced by insect infestation, chemical residues, and burial, yet little research has been conducted to document how various factors alter the rate and process of decomposition. A common occurrence at human remains recovery sites is the deposit of residues from criminal activities such as gunpowder and explosives. This experiment will look at gunpowder residue’s effects on porcine remains and the insect infestation after exposure. This study was conducted in two phases: the 1st experiment being conducted in the late spring and the 2nd in the early fall. For each experiment two carcasses were covered with gunpowder residue while one carcass served as a control (no residue). The physical decomposition processes as well as ambient temperature were documented for each carcass. The results for the study showed variable findings between the control and experimental subjects. The insect infestation of the remains was consistent with the data from previous entomological studies conducted from areas of similar climate and terrain. Factors that may have influenced the results are discussed in reference to the effects of the gunpowder residue on the decomposing remains.

Maize is the staple food of South Africa and its cultivation covers the largest area of farmland in the country. It plays an important role in the economy as South Africa is consuming 10 million tons of maize per annum. Most South Africans consume maize in some form or another. This commodity has regularly been associated with mycotoxigenic fungi and in some cases their respective mycotoxins. The problem is not only confined to the borders of South Africa but is a concern worldwide. Mycotoxins are known to affect both human and animal health. Some of the most well known mycotoxins are the fumonisins, deoxynivalenol and trichothecenes produced by Fusarium spp., aflatoxins and ochratoxin A produced by mostly Aspergillus spp., as well as patulin and citrinin that are produced by mainly Penicillium spp. Mycotoxins acting together and individually can be hepatotoxic, carcinogenic and teratogenic to humans and animals. The main objective of this study was to screen commercially produced maize cultivars in South Africa that would be either resistant to, or have a slower infection rate when inoculated with the ten selected mycotoxigenic fungi from South African maize. The objective was also to develop a method to detect and identify these mycotoxigenic fungi in the infected maize cultivars, using both basic microbiological and molecular means. These objectives were achieved by a series of experiments that are outlined in the individual chapters. The first part of this study evaluated the level of infestation of fungi in all the commercially produced maize cultivars in South Africa. A basic fungal enumeration and identification was carried out. This allowed the comparison of the in vivo ability of the selected cultivars to endure the natural invasion of mycotoxigenic fungi during cultivation in the same area namely Potchefstroom. As part of the maize evaluation, the cultivars were artificially inoculated with ten selected mycotoxigenic fungi, which consisted of five field fungi nl. Alternaria alternata, Fusarium graminearum, Fusarium verticillioides, Phoma sorghina and Stenocarpella maydis, and five storage fungi nl. Aspergillus flavus, Aspergillus ochraceus, Eurotium repens, Penicillium islandicum and Rhizopus oryzae under storage conditions. The ability of certain maize cultivars to resist the infestation by mycotoxigenic fungi under storage conditions was demonstrated. The second part of this study was to use basic molecular methods to detect and identify the ten mycotoxigenic fungi in the infected maize. This was done by making use of the sequence variations of the internal transcribed spacer (ITS) and D1/D2 regions of the fungal rRNA gene. Results showed that the ITS region gave better differentiation and in most cases allowed identification of the mycotoxigenic fungi. The application of the combined use of microbiological and molecular methodology for the detection and identification of mycotoxigenic fungi in maize by testing laboratories in South Africa were outlined in the final chapter. Implementation of a plan to evaluate maize cultivars in the pre-planting, harvesting and storage phases, can provide a holistic overview of the commodity and can be further implemented in the rural areas. / Dissertation (MSc)--University of Pretoria, 2010. / Microbiology and Plant Pathology / unrestricted

The risk of corn rootworm damage to continuously-grown corn was assessed in 32 fields from seven counties in Virginia in 1993 and 1994, Approximately 28% of the fields examined had economic root damage in corn left untreated with a soil insecticide. In addition, 190/0 of the fields overall had an economic loss in silage due to corn rootworm damage. A second study evaluated the effectiveness of using adult corn rootworm counts on commercial Olson yellow sticky traps and ear-zone regions of corn plants to predict subsequent damage to corn. Regression models for each sampling method were used to calculate economic thresholds of 20 adults per trap per wk for the Olson trap and 0.3 adults per stalk for the ear-zone visual count method. Adult counts on Olson traps obtained in mid-Aug correctly predicted economic damage to com 81 % of the time, and resulted in only one serious error of failing to predict economic damage to corn. A sampling plan for the use of Olson traps is suggested. A third study investigated a possible sexual dimorphism in the elytra coloration pattern of western corn rootworm, and compared the sex ratio of adults captured yellow sticky traps with those obtained by aspiration. Striped and solid variations in elytra pattern were found in both sexes of western corn rootworm; however, 98% of the adults that exhibited the solid elytra pattern were male. The sex ratio of adults varied over time; however, in all cases, sticky traps captured a significantly greater proportion of males compared with aspiration. / Master of Science