Because of recent advances in genotic insect control theory, it has become important to investigate the fitness effects of, and isolation procedures for, homozygous autosomal translocations. I isolated 57 autosomal translocations in Drosophila melanoqaster. Of these 21 were homozygous viable. From data obtained during the isolation of these trunslocations and from fitness tests and competition cage experiments, rhe following points can be made; (1) Between one in ten and one in one hundred homozygous viable laboratory produced translocations are likely to be of value in field tests of genetic insect control procedures. (2) Translocations which produce high levels of unbalanced gametes when heterozygous do not tend to be lass fit in the homozygous state than others. Therefore screening procedures dependent only on reduced progeny production from translocation heterozygote parents should be satisfactory for the isolation of useable stocks. (3) Translocations whose breakpoints are vary near the center of chromosomes tend to produce small progeny reduction in the heterozygous state, making these translocations useless as negative heterotic carriers of useful genes. (4) Those translocations which are the result of multiple break events tend to be less fit than simple double-break translocations and therefore should be discarded. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Studies were carried out to evaluate the repellent properties of the seeds of alligator pepper, <i>Aframomum melegueta </i>and Black pepper, <i>Piper guineense, </i>and ginger, <i>Zingiber officinale </i>rhizomes against <i>S. zeamais</i>. In 4-way olfactometry bioassays, <i>S. zeamais</i> adults showed strong attraction to maize and wheat seed volatiles but were significantly repelled by odours emanating from the seeds of <i>A. melegueta</i>, <i>P. guineense</i> and <i>Z. officinale</i> rhizomes. In field trials crushed <i>A. melegueta </i>seeds and <i>Z. officinale </i>rhizomes, significantly repelled <i>S. zeamais</i> from traditional maize granaries with treated maize cobs giving higher germination than untreated cobs. Laboratory reproductive potential studies showed that <i>A. melegueta </i>and <i>Z. officinale </i>powders caused significant adult mortality and reproductive potential deterrence against <i>S. zeamais</i> resulting in a reduction in F₁ progeny emergence. Olfactometer bioassays also confirmed that vacuum distilled <i>A. melegueta</i> and <i>Z. officinale </i>extracts and oleoresins were repellent towards adult <i>S. zeamais</i> when tested alone, and in combination with maize grains. Bioassay-guided liquid chromatography of the distillates showed that fractions containing polar compounds accounted for the repellent activity. Coupled gas chromatography-mass spectrometry (GC-MS), followed by GC peak enhancement and enantioselective GC using authentic compounds, identified 3 major compounds in the behaviourally active <i><span style='text-transform:uppercase'>A. melegueta </i>fraction to be (<i>S)</i>-2-heptanol, (<i>S)</i>-2-heptyl acetate and (<i>R)</i>-linalool in the ratio 1:6:3. <i>Z. officinale</i> had 1,8-cineole, neral and geranial in the ratio of 5.48:1:2.13. The identification of these behaviourally active compounds provides a scientific basis for the observed repellent properties of <i><span style='text-transform:uppercase'>A. melegueta </i>and <i>Z. officinale </i>extracts, and demonstrates the potential for their development in stored-product protection at the small-scale level in Africa.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Year: 2016. / Entomopathogenic nematodes in the genera Heterorhabditis and Steinernema have emerged excellent as non-chemical alternatives for control of insect pest population. They have a specific mutualistic symbioses with bacterial symbionts in the genera Photorhabdus and Xenorhabdus, respectively. Native EPN species that are able to tolerate environmental stress including desiccation are of great interest for application. The aim of this study was to isolate indigenous EPN species from soil samples collected from Brits, North West province in South Africa, and to investigate their ability to tolerate desiccation stress. The second aim was to isolate the bacterial symbiont and sequence, assemble and annotate its whole genomic DNA. Insect baiting technique and White trap method proved useful in the recovery of nematodes from collected soil samples and infected cadaver, respectively. Molecular identification based on the amplification of the 18S rDNA and phylogenetic relationships revealed high affinity of the unknown EPN isolate 10 to Steinernema species and due to variation in evolutionary divergence distance, the unknown isolate was identified as Steinernema spp. isolate 10 . Isolates 35 and 42 revealed high similarity to Heterorhabditis zealandica strain Bartow (accession number: GU174009.1), Heterorhabditis zealandica strain NZH3 (accession number: EF530041.1) and the South African isolate Heterorhabditis zealandica strain SF41 (EU699436.1). Both Steinernema spp. isolate 10 and Heterorhabditis species could tolerate desiccation. Steinernema spp. isolate 10 was tolerant up to 11 days of desiccation exposure in loamy sand and up to 9 days of exposure in river sand, causing 26, 6% and 13, 4% cumulative larval mortality after 96 hours, post resuscitation by rehydration, respectively. Heterorhabditis spp. could tolerate desiccation up to 13 days of exposure and induced 26.6% cumulative larval mortality on both loamy and river sand after 96 hours post resuscitation. Swarming, aggregation, coiling and clumping behavioural characteristics were observed when Steinernema spp. isolate 10 was exposed to desiccation and Heterorhabditis species displayed no similar behavioural characteristics associated with desiccation tolerance. Morphological characteristics of the unknown Steinernema spp. isolate 10 have been described, and the thick cuticle and sheath which are both associated with tolerance to desiccation stress have been noted. The bacterial symbiont was isolated from larval hosts infected with Steinernema spp. isolate 10 and molecular identification through NCBI Blastn based on the 16S rDNA revealed high affinity to Xenorhabdus bacterial species. Phylogenetic relationships and evolutionary divergence estimates 16 revealed genetic variation and the species was identified as Xenorhabdus bacterial isolate. The genome assembly of Xenorhabdus bacterial isolate using CLC Bio revealed a total length of 4, 183, 779 bp with 231 contigs (>=400bp), GC content of 44.7% and N50 of 57,901 bp. Annotation of the assembled genome through NCBI PGAAP annotation pipeline revealed 3,950 genes (3,601 protein coding sequences (CDS) and 266 pseudogenes), 12 rRNAs and 70 tRNAs. RAST annotation revealed 55 of virulence, disease and defense subsystem features which are involved in the pathogenicity of Xenorhabdus bacterial isolate. The ability of EPNs to tolerate environmental stress is highly crucial and one of the determining factors for biocontrol potential and successful application, thus the indigenous desiccation tolerant EPN isolate, Steinernema spp. isolate 10 holds great potential as a biological control agent. The genome sequencing and annotation reveals insight to behavioural and physiological attributes of bacterial symbionts and this study will contribute to the understanding of pathogenicity and evolution of the bacteria–nematode complex. / GR 2016

Thesis (Ph. D.)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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After a brief introduction, the species of Citrus on which the investigations were carried out are mentioned. This is followed by an account of the methods of collection used, and a discussion of their relative merits. The main method used was that in which the trees were fumigated with hydrocyanic acid gas, and the insects falling from the trees were taken up on sheets. The location of the areas where collections were made are then given. An annotated list of the species taken by the fumigation method follows, and the numerical data obtained at the same time regarding the species present is given in an abbreviated form and discussed. A more detailed discussion of the relative abundance of the species is then undertaken. The discussion of the ecology of the insects commences with the insects listed according to their activities, so far as known, and an account of five trees of striking faunal differences is given. A broader discussion of citrus ecology is then given, based on the data previously presented; this ends with a short reminder of the inherent 'oneness' of the insect with its environment.

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No description available.