Absence of density-dependent prophylaxis and density- dependent phase polyphenism in a cannibalistic caterpillar, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

• Ano de defesa: 2016
• Autor(a) principal: Mattos, Marcos Vinícius Vieira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Lagartas; Lepidoptera Noctuidae; Interação genótipo-ambiente; Helicoverpa armigera; Inseto; População biológica; Entomologia Agrícola
• Link de acesso: https://locus.ufv.br//handle/123456789/26714

Phenotypic plasticity contributes to an organism's ability to respond to changes in its environment. Population density is an environmental factor for which variation may lead to changes in investment in defences against diseases. Density-dependent prophylaxis hypothesis (DDP) predicts that organisms invest more in defences against diseases when at high population densities, as the risk of disease transmission tends to increase. Density-dependent phase polyphenism (DDPP) predicts that the morphology, physiology and behaviour of organisms may vary according to their population density. These changes may be related to differences in investment in immune defences or protective behaviours. Most studies have considered physical contact as a key stimulus for the phenotypic plasticity process, however other stimuli such as substrate vibration, volatiles and pheromones may allow this process in organisms according to their density. Under these circumstances, the hypothesis of this study is that the immune system and body colour change according to population density, even without physical contact between conspecific. Thus, was tested whether DDP and DDPP can occur even without physical contact between Helicoverpa armigera caterpillars, through artificial manipulation of their population density. For this, post-eclosion larvae were placed for 10 days, solitarily or in groups, in arenas designed to avoid physical contact, but allow the perception of conspecific through other density clues. After this period, was tested whether the presence of conspecific influenced: (i) the colour of the head capsule and the body, and (ii) the immune defences (encapsulation response, haemocyte densities and lysozyme activity). The results indicate that neither body colour nor immune defences were affected by the presence of conspecific. The fact of H. armigera caterpillars decrease aggregation in later larval instars, due to their cannibal behaviour, may represent a lower disease risk, so that there is no change in the investment in immune defences. In addition, physical contact may be more important to trigger phenotypic plasticity than other density clues. In this way, avoid of conspecifics can represent the lack of the component that does not allow the process of phenotypic plasticity.