Tesis doctoral de Alfonso Gerardo Hernandez Escareño
Surface cultivated with transgenic maize that has incorporated the insecticidal capacity of bacillus thuringiensis berl. (So called bt maize) in spain has concentrated in aragon and catalunya regions in the last years. In some areas percentage of bt maize is above 75% and this poses a risk of bt-resistance development in corn borer populations. Prevention of bt- resistance development has been implemented in practice by a double strategy of high dose expression of bt toxins in modified plants and the creation of non-bt refuges as reservoir of bt-susceptibility genes. Non-bt refuges may be implemented by mixing bt and non-bt seeds in the sowing machine, or by including non-bt strips in between bt rows or, finally by inserting in the landscape non-bt fields in the mosaic of bt fields. What is the most efficient strategy to implement refuges depends on several factors among which are dispersal behaviour of corn borer larvae and occurrence of antixenotic mechanisms in bt plants to prevent egg laying by corn borer females. The ultimate goal of this thesis has been bringing data on the two mentioned aspects of biology of sesamia nonagrioides lef. In order to define the optimal strategy to design non-bt refuges to prevent or delay bt-resistance development in that species. antixenosis was studied by allowing s. Nonagrioides females to choose a host plant to lay eggs in cages with bt and non-bt plants. Number of egg masses and eggs in each kind of plants was recorded. No antixenosis was observed as no significant differences in any of the two variables between bt and non-bt plants were found. study of larval dispersal aimed mainly to verify if the bt transgenic nature of the plant stimulate the larva to leave the plant and colonise neighbouring plants. Additionally, it was intended to know if the distance dispersed by larvae was influenced by the transgenic nature of the plant where larva was born. This was studied under both semi-controlled conditions (greenhouse) and in the field. Non-bt and bt maize plants were infested with a known number of eggs and after a certain number of days the number of larvae found on the neighbouring plants (all of them non-bt plants) located at variables distances was recorded. Main results obtained may be summarised as follows. A higher proportion of larvae issued from eggs laid on bt plants moved to surrounding plants in comparison with larvae issued from eggs hatched on non-bt plants. However, distance covered by larvae leaving the two kind of plants did not differ. Movement of larvae did not orient to a preferred direction in spite of the gradient of abiotic conditions that could have estimulated larva to look for more favourable environments. Similar results were recorded in the field and this would demonstrate that plant age do not alter tendency of larvae to leave bt plants ealier than non-bt plants. Use of rubidium as marker to track larval movement seems to be useful only in mature larvae that have fed on marked plants throughout most of their development. some consequences for implementation non-bt refuges to prevent bt-resistance development in s. Nonagrioides populations derive from the results obtained. (I) lack of antixenosis assure that non-bt fields are useful to prevent bt-resistance development. (Ii) stimulation of early larval dispersal by bt plants may reduce efficacy of mixing bt and non-bt plants in the same row. (Iii) mixing bt and non-bt plants do not lead to enhanced distance moved by dispersed larvae although it has to be taken into account that in this study plants surrounding the infested bt plant were non transgenic.
Datos académicos de la tesis doctoral «Dispersión y antixenosis en el taladro del maíz sesamia nonagrioides lef. (lepidoptera : noctuidae) frente a maíces transgénicos«
- Título de la tesis: Dispersión y antixenosis en el taladro del maíz sesamia nonagrioides lef. (lepidoptera : noctuidae) frente a maíces transgénicos
- Autor: Alfonso Gerardo Hernandez Escareño
- Universidad: Lleida
- Fecha de lectura de la tesis: 17/12/2009
Dirección y tribunal
- Director de la tesis
- Ramon Albajes Garcia
- Tribunal
- Presidente del tribunal: xavier Pons domenech
- judit Arno pujol (vocal)
- jordi Comas angelet (vocal)
- rosa Gabarra ambert (vocal)