Academic literature on the topic 'Corn maize weevil'

HighlightsMixing amaranth grain and maize is a promising pesticide-free method for controlling maize weevils in stored maize.A 1:1 mixture by volume of maize and amaranth reduced the number of live weevils by 66% after 160 d of storage as compared to maize stored without amaranth.A further reduction in live weevils could be achieved by completely covering all maize kernels with a layer of amaranth.Insect-infested maize-amaranth mixtures had reduced spoilage due to mold during storage as compared to insect-infested maize stored without amaranth.Abstract. Amaranth (Amaranthus spp.) is used as a vegetable, food, forage, and sometimes an ornamental. Amaranth grain has higher protein content than other cereals, making it a good choice for human consumption. Maize is among the three most widely grown grains in the world, but it can experience large postharvest losses during storage due to infestation by the maize weevil (Sitophilus zeamais). Due to the small size of amaranth seeds, this study postulated that amaranth grain can be blended with maize during storage to fill the intergranular spaces between maize kernels, reducing the overall void volume to minimize maize weevil movements to access the kernels, and thereby controlling the maize weevil population. The objective of this study was to investigate the effects on maize weevil control of blending maize with amaranth grain during storage versus storing maize alone. Three 208 L (55 gal) steel barrels were loaded with 160 kg (353 lb) of maize, and three were loaded with a maize-amaranth mixture (1:1 by volume), all with initial weevil populations of 25 live weevils per kg of maize. Blending maize with amaranth for storage reduced the number of live weevils after 160 days by 66% compared to storing maize alone. Additional reduction of live weevils could be accomplished if the maize were completely covered by amaranth grain, further restricting maize weevil access to the maize kernels. Keywords: Broken corn and foreign material, Insects, Insect infestation, Mechanical damage, Moisture content, Postharvest losses, Relative humidity, Temperature, Test weight.

Thirty adult maize weevils, Sitophilus zeamais Motschulsky, were placed in six glass-fronted wooden grain storage bins filled with 7.2 kg of shelled corn at 14% moisture content. An auger plug containing a heavily sporulating culture of Aspergillus flavus Link was added to the center of three infested bins and three noninfested bins. Another three bins of corn were untreated controls. All of the bins were stored for 16 weeks at 24°C. Weevil-infested corn began significantly heating (2°C) within nine weeks and began losing weight within 12 weeks. The distribution of fungal growth, high moisture grain, corn dust caking, and maize weevils coincided, being initially restricted to the lower edges of the containers and gradually migrating upward. An unidentified species of Penicillium (bright blue) was observed sporulating within 11 weeks in weevil-infested bins. The bins containing S. zeamais lost an average of 2% of their initial wet weight, and increased in grain moisture and temperature by 20% and 5°C, respectively. Pencillium (bright blue) comprised > 95% of the inoculum present on kernels, however A. flavus comprised > 90% of the inoculum recovered from surface sterilized maize weevils. Increased mortality of teneral adults occurred in A. flavus-inoculated bins. Corn from weevil-free bins, whether inoculated with A. flavus or not, failed to support fungal growth, heat, or lose weight.

Abstract. Maize is an important crop for many smallholder farmers in the world. Maize weevils () cause a significant loss in quality and quantity during maize storage, especially in tropical regions. Hermetic storage of maize has been shown to be effective in controlling maize weevils in laboratory and field settings. The objective of this research was to test the effectiveness of steel barrels that could be used by smallholder farmers for hermetic storage. Six 208 L (55 gal) steel barrels were each loaded with 170 kg (375 lb) of maize at an average moisture of 13.4% w.b., with initial weevil population densities of 25 live weevils kg-1 (11 live weevils lb-1) of maize. All six barrels were stored at 27°C (81°F) under non-hermetic conditions for 120 d, corresponding to approximately three weevil lifecycles. After 120 d, weevil population densities had increased to an average of 99 live weevils kg-1 (45 live weevils lb-1) in all six barrels. Three of the six barrels were subsequently hermetically sealed. After an additional 30 days (150 days since experiment start), the weevil population densities were zero in every hermetically sealed barrel (100% mortality) and averaged 141 live weevils kg-1 (64 live weevils lb-1) in the non-hermetic barrels. All barrels where then exposed to non-hermetic conditions for an additional 40 days (approximately one weevil lifecycle). The barrels previously under hermetic conditions had zero live weevils, while the other barrels averaged 214 live weevils kg-1 (98 live weevils lb-1), demonstrating that all stages of weevils (eggs, larvae, and pupae) were killed. Means of barrel oxygen content, test weight (TW), moisture content (MC), temperature, and humidity were significantly different between the hermetically sealed and control treatments. In contrast, broken corn and foreign material (BCFM) and mechanical damage (MD) were not significantly different. Hermetically sealed steel barrels may be an effective maize storage option for smallholder farmers. Keywords: BCFM, Maize weevil, Mechanical damage, Moisture content, Mortality, Mycotoxins, Test weight.

Natural infestations of the maize weevil, Sitophilus zeamais (Motschulsky) were monitored in selected corn fields located in each of five major climatic or edaphic environments of Georgia. The population density and sex ratio of each population was recorded on a monthly basis during the fall and winters of 1982–83–84. Females suffered higher winter mortality than males, resulting in increasingly male-skewed sex ratios (from 0.8/1.0 to 1.6/1.0) as winter progressed. The degree of male-skewedness was positively correlated with the amount of subzero weather experienced by each population. Surviving weevil populations decreased in size as winter progressed, with the greatest reductions at the higher latitudes. No weevils survived through spring north of 33° 57′N where winter weather extremes of −15°C occurred. No true diapausing stage was found; however, cold tolerance tests indicated that winter-collected weevils were significantly more cold hardy than laboratory-reared weevils.

Pioneer variety ‘3320’ seed corn, treated with 0.5, 1.0, 1.5, or 2.0 ppm cyfluthrin, each rate of cyfluthrin + 8.0 ppm piperonyl butoxide, or each rate of cyfluthrin + 8.0 ppm piperonyl butoxide + 6.0 ppm chlorpyrifosmethyl, was stored for 10 months at ambient conditions in south Georgia. Every 2 months the corn was sampled and bioassayed with maize weevil, Sitophilus zeamais (Motschulsky), and red flour beetle, Tribolium castaneum (Herbst). Maize weevil survival on corn treated with 0.5, 1.0, and 1.5 ppm cyfluthrin ranged from 39.5 to 76.0%, 4.0 to 29.5%, and 1.0 to 11.5%, respectively. Weevils did not survive exposure on corn treated with 2.0 ppm cyfluthrin, each rate of cyfluthrin + piperonyl butoxide, or each rate of cyfluthrin + piperonyl butoxide + chlorpyrifos-methyl. F1 progeny and dockage (ground corn flour and insect frass) in incubated bioassays were correlated with initial survival. Red flour beetle survival on corn treated with cyfluthrin alone or cyfluthrin + piperonyl butoxide was variable throughout the test, although survival at any bioassay usually decreased as the rate of cyfluthrin increased. However, no F1 adults or dockage was detected in any incubated bioassay from the 12 chemical treatments.

The maize weevil (Sitophilus zeamais Motschulsky) is a serious pest of economic importance in stored grains. It causes major damage to stored maize grain thereby reducing its weight, quality and germination. An experiment was conducted in randomized complete block design (RCBD) with 3 replications to screen 32 maize genotypes against maize weevil in no-choice and free-choice conditions at Entomology Division, Khumaltar, Lalitpur (Room temperature: Maximum 24-32°C and Minimum 18-27°C). The findings showed that the maize genotypes had different response to maize weevil damage ranging from susceptible to tolerance. The genotypes Manakamana-3, Lumle White POP Corn and Ganesh-2 showed their tolerance to S. zeamais as evidenced by lower number of weevil emerged/attracted, lower amount of grain debris release and lower proportion of bored grains, while the genotype ZM-627 was the most susceptible to weevil damage in both tests. The other remaining genotypes were intermediate types. This information is useful to improve grain protection in storage and varietal improvement/release program.

A 3-yr study evaluated the effect of planting date, variety and degree of ear maturation on maize weevil, Sitophilus zeamais (Motchulsky), colonization of corn in the field. Within each plot, paper bags were used to prevent oviposition during one of three consecutive 2-wk periods beginning at the 3/4-milk-line stage. Adult emergence from bagged ears was compared to that from unbagged ears. Maize weevil adults emerged from 15.6% of all ears tested. Numbers of adults emerging from infested ears ranged from 1 to 135 with a mean (±SE) of 11.9 ± 18.5. A greater percentage of Mycogen 7559 ears were infested than those of Pioneer 3167 or Pioneer 3146, and the infested Mycogen 7559 ears also supported the emergence of a greater number of adults. A significant planting date effect was found each year of the study, but the nature of that effect was not consistent. A significant planting date-by-year interaction may have been due to weather affecting the date maize weevils were available for colonization, or more likely, to interference from earlier planted corn near our plots that attracted the first overwintering weevils. Oviposition resulting in successful emergence was found to occur during all 3 of the 2 wk exclusion periods with the last period having the greatest impact on the percentage of infested ears and the second period having the greatest impact on the number of emerging weevils per 500 g of kernels.

Plant defensins are multifunctional proteins, inhibiting the growth of fungal, anti-bacterial, altering membrane channels, inhibiting activity of trypsin and α-amylase. Plant defensin consists of 18 groups in which the group 1 includes defensins to inhibit either α-amylase enzyme or trypsin. Defensins bind to the active site of α-amylase in the weevil gut, thus inhibit starch digestion in weevils. In this report, we present the results of cloning and determining the ZmDEF1 gene sequence isolated from mRNA and DNA of Sonla province local maize and LVN99 hybrid maize cultivar. The coding region of ZmDEF1 gene isolated from some maize samples had the size of 243 nucleotides, encoding 80 amino acids. Gen ZmDEF1 isolated from DNA had the size 345bp consists of two exons and one in tron (102 bp). The nucleotide sequences of ZmDEF1 gene (DNA) of the samples have 6 positions nucleotide difference, on exon 1 has two points difference (position 43, 53), on intron has a difference (position 150), on exon 2 has 3 nucleotide site difference (203, 263 and 297 position). Deduced amino acid sequences of defensin of the Sonla local maize sample has 8 cysteines to make 4 disulfide bridges, while LVN99 hybrid maize has 7 cysteines, which can formed only 3 disulfide bridges. Transformation vector pBetaPhaso-ZmDEF1 has been designed successfully, in which ZmDEF1 is controlled by seed specific Phasoline promoter. The correct insertion and expression of ZmDEF1 was examinated in transgenic tobacco plants throught PCR and RT-PCR, respectively. These results provide an firm evident for using the designed transformation vector to produce transgenic maỉze lines with an improved resistant ability to weevils.

Shelled corn stored in metal bins was sampled for insects on farms in the three westernmost crop reporting districts of Kentucky during 1989 and 1990 to identify pest insects present, determine the relative abundance of insect pests, and determine their geographic distributions. Thirty-six species or species groups were found in this survey. The most abundant insects were maize weevil, Sitophilus zeamais Motschulsky; Angoumois grain moth, Sitotroga cerealella (Olivier); flat grain, rusty grain, and flour mill beetles, Cryptolestes spp.; sawtoothed grain beetle, Oryzaephilus surinamensis (L.); foreign grain beetle, Ahasverus advena (Waltl); red and confused flour beetles, Tribolium spp.; and hairy fungus beetle, Typhaea stercorea (L.). Greater densities and numbers of species were caught later during the storage season and greater numbers were captured from the center versus edges of bins. The unexpectedly high abundance and widespread distribution of maize weevil and Angoumois grain moth suggests that greater care needs to be taken to manage these pests because of direct feeding damage and the resulting increased susceptibility of grain to secondary insect pests (e.g., Cryptolestes spp., sawtoothed grain beetle, Tribolium spp., foreign grain beetle, and hairy fungus beetle, which were commonly found) and fungi.

Abiotic factors may interfere in production of plant secondary metabolites and consequently influence the bioactivity of these compounds on insect pests. Thus, this study aimed to evaluate the influence of different agricultural practices (irrigation, mineral fertilizer and organic manure) in chemical composition of the essential oil (EO) of Lippia gracilis and its effects on the maize weevil Sitophilus zeamais.The chemical compositions of EO from plants of L. gracilis cultured on different treatments were analyzed using GC-MS and GC-FID. The carvacrol was the major component of EO in different agricultural practices followed by thymol and ñ-cymene.These three monoterpenes were used in subsequent bioassays. Cultivation practices did not significantly affect the composition of the OEs of L. gracilis. However, small variations in the composition of EOs resulted in different biological responses to S. zeamais. All EOs of L. gracilis and its main monoterpenes applied topically showed low toxicity on S. zeamais after 84 hours exposure at a dose 10 mg g-1. However, these same compounds were highly toxic to S. zeamais by fumigation. The time required to cause 50% mortality of the pest was 28.4 hours on average, ranging from 17.3 to 40.8 hours between treatments. The toxic action of carvacrol, thymol and EOs of L. gracilis (no irrigation/fertilization mineral and 40 t ha-1 organic fertilizer) were the fastest, LT50=18,3. The magnitude of the variation of CL50 and CL99 were 1.9 and 2.1 times. The concentration needed to cause 50 to 99% mortality of the pest was on average 69 and 260 ìl l-1, respectively.Considering the LC50 and LC99, the more toxic OEs of L. gracilis were obtained from plants grown in the absence of mineral fertilizer and in the presence of organic manure with of 20, 40 and 60 t ha-1 (no irrigation) and 40 and 60 t ha-1 (with irrigation). Much of the activity of the EOs of L. gracilis is due to the major compound carvacrol. It took only 27.2 and 92.2 l ìl l-1 to cause 50% and 99 % mortality of adult S. zeamais. The toxic activity of this monoterpene was still one of the fastest (LT50 = 17.3 and LT99 = 70.8 hours). Already the thymol and ñ-cymene awere compounds of low toxicity to adult S. zeamais (LC50= 4,4 e 26,1 respectively). Generally, the EOs of L. gracilis and the monoterpenes applied at lower concentrations (0.01 and 0.1% v/v) showed a neutral effect (not significant) or attractive (negative and significant) in all periods analyzed. At concentration 10% (v/v) almost all treatments were repellents to S. zeamais at any time analyzed (repellence > 50%). Major indexes repellency (54-86%) were observed in treatments irrigated and with maximum organic manure, at concentrations of 1 and 10% (v/v). Thus, our results show the great potential of EO of L. gracilis and its major compound for the development of new products and programs for use in integrated pest management of stored grain.
Fatores abioticos podem interferir na producao de metabolitos secundarios de plantas e consequentemente influenciar na bioatividade destes compostos sobre insetos-praga. Assim, neste trabalho objetivou-se avaliar a influencia de diferentes praticas agricolas (irrigacao, adubacao quimica e organica) na composicao quimica do oleo essencial (OE) de Lippia gracilis e seus efeitos na mortalidade e repelencia do gorgulho do milho Sitophilus zeamais. As composicoes quimicas dos OEs das plantas de L. gracilis cultivadas sobre diferentes tratamentos foram analisadas usando CG-MS e CG-FID. As praticas de cultivo nao afetaram significativamente a composicao dos OEs de L. gracilis, o carvacrol foi o componente majoritario dos OEs nas diferentes praticas agricolas, seguido pelo timol e Ï-cimeno. Estes tres monoterpenos foram utilizados nos bioensaios posteriores. Pequenas variacoes na composicao dos OEs resultaram em diferentes respostas biologicas de S. zeamais. Todos os OEs de L. gracilis aplicados topicamente mostraram baixa toxicidade sobre S. zeamais apos 84 horas de exposicao na dose 10 mg g-1. Contudo, estes mesmos compostos foram altamente toxicos a S. zeamais por fumigacao. O tempo necessario para causar 50% de mortalidade desta praga foi em media 28,4 horas; variando de 17,3 a 40,8 horas entre os tratamentos. A acao toxica do carvacrol, timol e do OEs de L. gracilis (ausencia de irrigacao/adubacao mineral e 40 t ha-1 de adubacao organica) foram as mais rapidas, TL50=18,3. A magnitude da variacao das CL50 e CL99 foram de 1,9 e 2,1 vezes. A concentracao necessaria para causar 50 e 99% de mortalidade desta praga foi em media 69 e 260 Êl l-1, respectivamente. Considerando as CL50 e CL99, os OEs de L. gracilis mais toxicos foram obtidos de plantas cultivadas na ausencia de adubacao mineral e presenca de adubacao organica com 20, 40 e 60 t ha-1 (sem irrigacao) e 40 e 60 t ha-1 (com irrigacao). Grande parte da atividade dos OEs de L. gracilis deve-se ao composto majoritario carvacrol. Foram necessarios apenas 27,2 e 92,2 Êl l-1 para causar 50 e 99% de mortalidade a adultos de S. zeamais. A atividade toxica deste monoterpeno foi de TL50 = 17,3 e TL99 = 70,8 horas. Ja o timol e Ï-cimeno foram os compostos de menor toxicidade a adultos de S. zeamais (CL50= 4,4 e 26,1 respectivamente). De forma geral, os OEs de L. gracilis e os monoterpenos utilizados nas menores concentracoes (0,01 e 0,1% v/v) apresentaram efeito neutro (nao significativo) ou atrativo (negativo e significativo) em todos os tempos analisados. Ja na concentracao 10% (v/v) quase todos os tratamentos foram repelentes a S. zeamais em qualquer tempo analisado (repelencia > 50%). Maiores indices de repelencia (54-86%) foram observadas nos tratamentos irrigados com maxima adubacao organica e concentracao 1 e 10% (v/v). Assim, nossos resultados mostram o grande potencial do OE de L. gracilis e seu composto majoritario para o desenvolvimento de novos produtos e utilizacao em programas de manejo integrado de pragas de graos armazenados.

Made available in DSpace on 2016-06-02T20:36:48Z (GMT). No. of bitstreams: 1 5580.pdf: 12897921 bytes, checksum: 7de4b9e632d7de714eb77bf5afad7e21 (MD5) Previous issue date: 2013-03-27
Universidade Federal de Sao Carlos
The leaf-cutting ants are social species, living in permanent colonies. The genera of the greater importance, Atta (saúvas) and Acromyrmex (quenquéns), are the major plagues of Brazilian agriculture, to cause serious damages by its large and uncontrolled grazing, which leads to serious economic losses for many agrosystems. In the same way, the corn maize weevil, Sitophilus zeamais, belonging to the family Curculionidae, is the major pest species of stored corn. The corn grains are drilled and damaged by larvae and adults, causing numerous qualitative and quantitative losses of corn grains disabling its marketing. As the consequence, the effective control of these plagues is extremely important for agriculture and economy that aims to provide the nacional and international market quality products with high commercial value. In this context, the phytochemistry study of Annona sylvatica provides an alternative way to control these plagues, since that studies of these species showed a wide variety of natural products with promising activities, including, insecticide and fungicide, due to the large presence of acetogenins and lignans as secondary metabolites. This study allowed the isolation of fourteen compounds (four lignans, four acetogenins, three alkaloids and three steroids), however were identified eleven compounds due to the high structural complexity presented for the acetogenins. The identification techniques employed have been using single and two-dimensional spectra of 1H and 13C NMR and Mass Spectrometry (HPLC/NMR; HPLC/ESI-MS/MS e HPLC/APCI-MS/MS). For the biological tests, the ethanolic extract of the seeds stood out as potentially toxic to three bioassays cited above. The leaves and branches dichlorometanic fractions obtained by liquid-liquid partitioning of the extracts were toxic for leaf-cutting ants and their symbiotic fungus. Among the acetogenins isolated, only one of them showed a significant activity against corn maize weevil.
As formigas cortadeiras são espécies sociais, vivendo em colônias permanentes. Os gêneros de maior importância econômica, Atta (saúvas) e Acromyrmex (quenquéns), são as principais pragas da agricultura brasileira, por causarem sérios danos pela sua grande e descontrolada herbivoria, o que gera sérios prejuízos econômicos para muitos agroecossitemas. Nessa mesma vertente, o gorgulho do milho, Sitophilus zeamais, pertencente à família Curculionídea, é a principal espécie praga do milho armazenado. Os grãos são perfurados e danificados pelas larvas e adultos, inutilizando sua comercialização. Como consequência, o controle eficaz de tais pragas é de extrema importância para a agricultura e economia do país que visa oferecer ao mercado nacional e internacional produtos de qualidade e alto valor comercial. Nesse contexto, o estudo fitoquímico de Annona sylvatica fornece uma forma alternativa de controle a estas pragas, uma vez que estudos destas espécies mostraram uma ampla variedade de produtos naturais com atividades promissoras, entre elas, inseticida e fungicida, devido à ampla presença de acetogeninas e lignanas como metabólitos secundários. Este estudo resultou no isolamento de 14 compostos (quatro lignanas, quatro acetogeninas, três alcaloides e três esteroides), no entanto, foram identificados 11 compostos, devido à alta complexidade estrutural apresentada para as acetogeninas. As técnicas de identificação utilizadas foram através dos espectros uni e bidimensionais de RMN 1H e 13C e por Espectrometria de Massas (HPLC/NMR; HPLC/ESI-MS/MS e HPLC/APCI-MS/MS). Para os ensaios biológicos, o extrato etanólico das sementes destacou-se como potencial tóxico frente aos três bioensaios citados acima. As frações diclorometânicas das folhas e ramos obtidas através do particionamento líquido-líquido dos extratos foram tóxicas para as formigas cortadeiras e seu fungo simbionte. Dentre as acetogeninas isoladas, apenas uma apresentou uma atividade significativa frente ao gorgulho do milho.

The maize weevil (Sitophilus zeamais Motschulsky) is one of the most destructive storage insect pest of maize (Zea mays L.) in tropical Africa and worldwide, especially when susceptible varieties are grown. Therefore, grain resistance against the maize weevil should be part of a major component of an integrated maize weevil management strategy. The specific objectives of this study were to: i) determine farmers’ perceptions about weevil resistance in maize cultivars; ii) determine the genotypic variation for maize weevil resistance in eastern and southern Africa maize germplasm lines; iii) study the gene action conditioning weevil resistance in the inbred line populations from eastern and southern Africa maize germplasm and to measure their combining ability for yield and weevil resistance; iv) determine the effectiveness of two cycles of modified S1 recurrent selection in improving a tropical maize population “Longe5” for weevil resistance and agronomic superiority and v) evaluate the effectiveness of the “weevil warehouse techniques” compared to the “laboratory bioassay technique” as methods of maize screening against the maize weevil. A participatory rural appraisal (PRA) was conducted in three districts between December 2010 and January 2011, to gather information on the maize weevil pest status in Uganda and farmers’ perceptions about improved maize varieties and the major attributes desired in new maize varieties. Over 95% of farmers knew the maize weevil and its pest status, and were reportedly controlling the maize weevil using wood ashes, red pepper and Cupressus sempervirens. The estimated postharvest weight losses attributed to weevil damage was over 20% within a storage period of four months. The most highly ranked attributes desired in the new maize varieties included high grain yield, tolerance to drought and low nitrogen stresses, resistance to field pests and diseases, good storability and resistance to storage pests. In the search for new sources of weevil resistance, a total of 180 inbred lines from three different geographical areas were screened for weevil resistance using the laboratory bioassay technique. Eight inbred lines (MV21, MV23, MV75, MV102, MV142, MV154, MV157, and MV170) were consistently grouped in the resistant class, and therefore selected as potential donors for weevil resistance in the maize improvement programs. Large significant genetic variations for weevil resistance, and high levels of heritability (89 – 96%) were observed. The results revealed that there was no significant association between maize weevil resistance andgrain yield; suggesting that breeding for maize weevil resistance can be achieved without compromising grain yield. Eight weevil resistant and two susceptible inbred line parents were crossed in a 10 x 10 full diallel mating design and the resulting 45 experimental hybrids and their reciprocal crosses evaluated for grain yield and secondary traits under four environments, and also to determine the gene action regulating their expression. The F1 hybrid seed, F2 full-sib and F2 half-sib grain generated from the 45 experimental hybrids and their reciprocals under two environments in Namulonge, were evaluated for weevil resistance using F1 weevil progeny emergence, median development period (MDP), Dobie’s index of susceptibility (DIS), and parental weevil mortality as susceptibility parameters. The general combing ability (GCA), specific combining ability (SCA), and reciprocal effects were all significant for grain yield, with SCA accounting for over 80% of the hybrid sum of squares. Inbred line parent MV44 exhibited positive significant GCA for grain yield and thus can be utilized in the development of synthetics and hybrids. Hybrids MV21 x MV13, MV154 x MV44, and MV154 x MV102 and all hybrids between parent MV142 and the rest of the parental lines exhibited positive and significant SCA effects. For the weevil resistance parameters, the general combining ability (GCA), specific combining ability (SCA) and reciprocal effects were all significant for F1 weevil progeny emergence, MDP, and DIS in the three seed categories. The results revealed that weevil resistance was governed by additive gene action, non-additive, and maternal effects. Parents MV170 and MV142 were consistently exhibiting weevil resistance in the three seed categories and thus recommended for future breeding strategies. Furthermore, most of the hybrids generated from parental line M142 were noted to exhibit outstanding performance in terms of grain yield and weevil resistance. Another study was conducted to determine the effectiveness of two cycles of modified S1 recurrent selection towards the improvement of weevil resistance in a maize population Longe5. Over 540 selfed ears were selected from the source population (C0) and screened for weevil resistance in the laboratory at Namulonge. Based on weevil resistance characteristics, 162 genotypes were selected from C0 and recombined in an isolated field to generate cycle C1. The same procedure was used for generating cycle C2 from cycle C1, but instead 190 weevil resistant C1 genotypes were selected and recombined to form C2. Seed from cycles C1 and C2, together with that from the source population (C0), was used to plant an evaluation trial in three locations, to compare the performance of the three cycles in terms of grain yield and reaction to the major foliar diseases, and also to produce seed for subsequent screening against weevil ii infestation. A total of 54 seed samples were screened for weevil resistance in a laboratory at Namulonge, in an experiment laid out in a randomized complete block design. A reduction in grain weight loss of 65% was registered in the C2 seed, whereas in C1 seed it was 15%. A similar trend was observed for F1 weevil progeny emergence and grain damage. Grain yield results indicated a yield gain of 19% realized from cycle C2 while a yield gain of 7% was realized from cycle C1. Furthermore, reductions in disease severity of 27%, 10% and 13% were exhibited for Turcicum leaf blight (TLB), grey leaf spot (GLS) and rust disease, respectively in cycle C2. The results indicated that Longe5 can be improved for maize weevil resistance, grain yield, and resistance to foliar diseases through selection. Further recurrent selection cycles would be recommended. The last study was aimed at evaluating the potential of shelled grain and suspended ear options of the weevil warehouse technique in discriminating maize genotypes into different susceptibility classes, based on genotype response to weevil attack. It involved comparing the effectiveness of the two options under the weevil warehouse technique with the laboratory bioassay technique using grain damage and grain weight loss as the maize grain susceptibility parameters. Fourteen maize genotypes were screened using the weevil warehouse and the laboratory bioassay techniques at Namulonge. On grouping the 14 genotypes into different response classes, high levels of consistency were observed in the three screening techniques. Therefore, the two weevil warehouse screening options being faster and effective in discriminating maize cultivars towards weevil attack, they were found to be better than the laboratory bioassay technique. The minimum evaluation period required to discriminate genotypes by the two weevil warehouse options was two months from the onset of the experiment. The maize weevil was noted to be an important storage pest constraining maize production in Uganda. The major weevil control measures included proper postharvest handling procedures and use of indigenous technical knowledge. The results also revealed that host plant resistance could significantly reduce grain damage. It was further revealed that grain resistance against the maize weevil could be enhanced through hybridization and recurrent selection; thus the germplasm identified in the study can provide new sources of maize weevil resistance for commercial deployment and further breeding.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (M.S.)--University of Wisconsin--Madison, 1992.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 47-52).