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Artificial diet bioassays were carried out to investigate the impact of GNA and Con A upon the development of L. oleracea larvae. GNA, at 2 % of total dietary protein, exerted a significantly detrimental effect upon larval development, growth and consumption, with little effect upon survival. Con A was shown to be the more toxic of the 2 lectins. When tested at concentrations of 2.0 %, 0.2 % and 0.02 %, Con A caused a significant decrease in survival and larval development, and caused greater reductions in larval growth and consumption compared to GNA. The potential for GNA and Con A to exert insecticidal effects via binding to the brush border membrane (BBM) and peritrophic membrane (PM) of L. oleracea larvae was investigated. Con A, which specifically binds a-D-mannopyranoside and a-D- glucopyranoside residues, was shown to bind in vitro to the majority of BBM and PM proteins. In contrast GNA, which exhibits strict specificity for a(l,3) and a(l,6)-linked D-mannose residues, bound to only 5 BBMV and 2 PM proteins. In agreement, higher levels of Con A, compared to GNA, were shown to accumulate in larval gut tissue after feeding the proteins in vivo. Despite this both lectins were shown to have a similar ability to disrupt the digestive capacity of the larval midgut. GNA and Con A stimulated similar short term elevations in BBM enzyme and soluble trypsin activities and a long-term reduction in a-glucosidase activity. Increases in levels of trypsin activity in faecal material collected from lectin-fed larvae suggested that the proteins may act by disrupting mechanisms of enzyme recycling. Aminopeptidase, an abundant and avidly binding BBM protein (120 kDa), was identified as a major Con A binding species in L. oleracea. A 98 kDa GNA-binding BBM protein was purified and amino acid sequence data was obtained from digest polypeptides allowing oligonucleotide primers to be designed. Subsequent attempts to amplify (by PCR and RT-PCR) fragments containing coding sequence corresponding to the 98 kDa protein were unsuccessful. This was attributed to oligonucleotide degeneracy together with the low abundance and relatively large size of the protein. The potential for GNA and Con A to exert systemic effects upon I. oleracea was demonstrated by the detection of both lectins in the haemolymph of larvae exposed to experimental diets. GNA was detected in haemolymph of larvae exposed to experimental diet for just 2 hours. In contrast, no Con A was detectable in haemolymph extracted from larvae fed for 24 hours, although it was present in the haemolymph after 5 days of exposure to the diet. That GNA and Con A may act directly upon organs other than the insect gut was indicated by the detection of lectins in vivo in malpighian tubule and fat body tissue extracts. A significant reduction in haemocyte abundance in haemolymph samples extracted from lectin-fed larvae suggested that both GNA and Con A may also act by disrupting the immune system of L. oleracea.

Movement is one way herbivores respond to their host plant, yet the movement of relatively immobile insects has received little attention. We studied how the movement and density of apterous soybean aphids responds to a resistant soybean variety and different temperatures. In Chapter One, we examined aphid movement both within and between soybean plants that varied in their resistance to aphids. Aphids on resistant plants had a wider dispersal, apparently due to greater aphid movement. Consequently, aphids on resistant plants could move to neighboring susceptible plants, thereby increasing their density. In Chapter Two, we measured aphid density and dispersal on resistant and susceptible plants when insects and plants were exposed to two different temperatures. Here, movement behavior was affected by both plant resistance and temperature. Moreover, temperature and plant resistance interacted to influence aphid density. Our results indicate the important role that movement can play in an herbivore's response to plant resistance.

Inositol pyrophosphates (PP-InsPs) are a family of molecules recently discovered to be implicated in a number of plant pathways such as auxin regulation, phosphate (Pi) sensing, and jasmonate-(JA)-regulated plant defense. Transgenic plants that overexpress inositol tetrakisphosphate 1-kinase (ITPK1) and the kinase domain of the dual domain diphosphoinositol pentakisphosphate kinase 2 (VIP2KD) have been previously studied to display uniquely elevated PP-InsPs. Here it is reported that the JA defense pathway is constitutively upregulated in VIP2KD OX plants, resulting in a lower rate of herbivory on the transgenic plants. ITPK1 OX, although also having elevated PP-InsPs, was fed upon by insect larvae comparably to Wild-Type Arabidopsis (WT). The data implicate VIP2, InsP8, and possibly the PP-InsP biosynthesis as a whole. / Master of Science in Life Sciences / Plants and insects have been evolving defenses against each other since they first emerged together post-Cambrian explosion. They each have evolved targeted metabolic pathways to produce chemicals with which to repel, harm, or even trick one another. In Arabidopsis thaliana, one of the most widely studied defense mechanisms is the jasmonic acid defense pathway, which responds to the herbivory of insects like caterpillars by setting off an array of genetic switches. The plant enters a stressed state wherein it represses the genes focused on growth and development and encourages the expression of genes focused on protecting vital resources and thwarting the attacker. This work examines a connection between the phosphate-sensing pathways and the jasmonic acid defense pathways in plants, and the following data show that plants with elevated inositol pyrophosphates (a phosphate storage molecule) are resistant to the herbivory of common pest caterpillars.

published_or_final_version / abstract / toc / Botany / Doctoral / Doctor of Philosophy

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Made available in DSpace on 2014-06-11T19:25:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-02-22Bitstream added on 2014-06-13T20:52:59Z : No. of bitstreams: 1 costa_en_me_jabo.pdf: 541101 bytes, checksum: 6673256645e9bf2d2bad7da0920bd80a (MD5) / Este trabalho teve por objetivo avaliar a não preferência para alimentação e tolerância, em genótipos de soja, ao ataque de Diabrotica speciosa (Germar, 1824) (Coleoptera: Chrysomelidae), assim como avaliar metodologias de pesquisa, em teste de preferência para oviposição, e avaliar graus de resistência do tipo antibiose. Os experimentos foram conduzidos em laboratório, sob condições controladas de temperatura (25 ± 2 ºC), umidade relativa (70 ± 10%) e fotofase (12 horas), exceto o experimento de não preferência para alimentação de larvas, o qual foi conduzido em condições de casa de vegetação. Foram utilizados 10 genótipos de soja para os testes de não preferência para alimentação de adultos (discos foliares e plantas jovens), quais sejam: IAC 100, BRSGO 8360, IGRA RA 626 RR, DM 339, BRS Valiosa RR, Dowling, IGRA RA 516 RR, PI 227687, PI 274454 e BR 16, dos quais seis foram selecionados para os testes subsequentes. Os experimentos de não preferência para alimentação de adultos, com e sem chance de escolha, foram realizados adotando-se dois modelos experimentais, utilizando-se discos foliares e folhas de plantas jovens de soja (não destacando-as da planta), avaliando a atratividade de adultos pelos genótipos de soja em diferentes períodos de tempo, e a área foliar consumida. Paralelamente à realização destes experimentos, foi quantificado o número de tricomas nas folhas dos genótipos de soja, com a finalidade de... / This work aimed to evaluate the non-preference for feeding and tolerance, on soybean genotypes, to the attack of Diabrotica speciosa (Germar, 1824) (Coleoptera: Chrysomelidae), as well as to assess research methodologies, in oviposition preference test, and evaluate the antibiosis type resistance degrees. The experiments were conducted in laboratory, under controlled conditions of temperature (25 ± 2 ºC), relative humidity (70 ± 10%), and photophase (12 hours), except the experiment of non-preference for larvae feeding, which was performed in greenhouse conditions. Ten soybean genotypes were used for non-preference for adults feeding tests (leaf discs and young plants), which were IAC 100, BRSGO 8360, IGRA RA 626 RR, DM 339, BRS Valiosa RR, Dowling, IGRA RA 516 RR, PI 227687, PI 274454 and BR 16, being six selected for the posterior tests. The non-preference for adults feeding experiments, carried out in free and no-choice tests, were fulfilled adopting two experiment models, using leaf discs and leaves of soybean young plants (not detaching them), assessing the adults attractiveness for soybean genotypes at different periods of time, and the leaf intake, being the value express in square centimeter for the test with leaf discs, and injury grade and leaf intake percentage for the test with young plants. Concomitantly to the performing of these experiments, the trichomes number on soybean genotypes leaves was assessed, for the purpose of observing the influence... (Complete abstract click electronic access below)