This thesis describes studies on population variation in laboratory-reared cultures of the Larger Grain Borer, Prostephanutsru ncatus( Horn) (Coleoptera: Bostrichidae). Prior to its introduction into Africa around 1980, P. truncatus was not regarded as being of major economic importance. However, it has since become a major pest of stored maize and dry cassava in Africa causing over £500 million of damage per year. In order to gain a better understanding of the biology of P. truncatus, genetic, morphological and feeding behaviour variability were studied in six laboratory maintained populations collected from single locations: four from Africa (Tanzania, Kenya, Togo and Nigeria) and two from Central America (Costa Rica and Mexico), plus one recently collected field population from Tanzania. Three techniques were used: 1. Cellulose acetate enzyme electrophoresis, 2. Morphometrics and, 3. Behavioural observations, in order to explore potential usefulness of these methods in the study of geographical variation between P. truncatusp opulations. Allozyme electrophoresis (using cellulose acetate gel) as performed in this study showed that genetic variation existed in P. truncates. Of the ten enzyme loci screened, four (phosphoglucoisseo meraceg,lu tamate-oxaloacetatrtaen saminasep,e ptidarea nd malic) revealed clear variation among some of the six laboratory populations. The proportion of polymorphic loci (P) for the six populations was found to be 0.75 and the mean heterozygosity ( H) 0.247 (Togo had the highest- H=0.336 and Costa Rica the lowest- H= 0.141). Comparison of allele frequencies showed significant differences between some of the six laboratory populations (P < 0.001). Pairwise comparisons between allele frequencies for the four polymorphic loci revealed large differences in allele frequencies between the African and Costa Rican populations and great similarities in allele frequencies between African and Mexican populations. This suggests that the African populations are more closely related to the Mexican population and may first have been introduced to Africa from Mexico. No significant allele frequency differences were found between the field and laboratory reared populations from Tanzania. The morphometric study was carried out using seven male characters and nine female charactersT. he results showed that most characters( exceptf our: hindspur and hindtibia for males, and forespur and midantennal segment for females) revealed significant morphological variation between some of the six laboratory populations. All the tests: Univariate Analysis of Variance, Multivariate Analysis of Variance, Discriminant Function Analysis and Principal Components Analysis showed significant population differences. The Costa Rican population showed distinctive morphological differences from the other five populations. The recently collected field population shared similar morphological characters with laboratory reared population from Kenya. The behavioural study focused on variation in the relationship between progeny production and the degree of damage caused to maize grain and dry cassava. After eight weeks, standardised cultures differed significantly with respect to the total number of adults and larvae recorded at the end of the experiment (the populations from Mexico and Kenya had the highest number while the population from Costa Rica had the lowest). When the degree of stored product damage was considered, significant differences were again found, and the ranking was similar. The damage done was significantly correlated with the number of progeny produced (P < 0.001). Comparison of results obtained from laboratory maintained African populations with a field sample obtained from Tanzania indicates the potential usefulness of cellulose acetate electrophoresis of allozymes and morphometrics in the study of geographical variation in African P. truncatesT. his will lead to a better understanding of the biology of this economically important insect and provide more solid data on which to base control measures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:538321 |
| Date | January 2000 |
| Creators | Marshed Kharusy, Muhammed N. |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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