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General Introduction 22 lived but it increases if the adult is long lived (as they have more time in locating the female amidst the pheromone plumes) (Campion et al., 1989). This control method is sustainable as pheromones are non-toxic, non pollutant, naturally occurring compounds and can be used without causing harm to human health or the environment. Since they are species specific, they do not affect other non-target or beneficial insects. This is not to say that there are no limitations to this method. Because pheromones are insect specific and occur in specific ratios of the major and minor components of the pheromone, the target range is limited (Campion et al., 1989). Its effectiveness is limited to just one particular species and different blends have to be synthesized for different target insects. The timing of application has to be precise for it to be effective. The insect density in the controlled area has to be monitored. Low density in a large area is preferred as a lower population of mating adults have less chance of locating mates in larger areas. If the control area has uncontrolled regions nearby, for example home gardens, then mated females from these areas can migrate and lay eggs in the controlled region. The larvae from these eggs will still cause damage to plants in the controlled region. Finally, the cost effectiveness of such a system is questionable as pheromones are expensive to synthesise and are unstable volatiles that disintegrate easily in the environment (Bakke and Lie, 1989; Campion et al., 1989; Wall, 1989). Mass trapping of insects is achieved by using lures such as sex pheromones and plant volatiles of host plants to direct insects to traps (Haynes et al., 1986). Once trapped, the insects are killed, either by toxins in the trap or by depriving them of oxygen. The traps may also be coated with sticky substances to which the insects get stuck and die. Mass trapping is done to reduce the population of insects so that less mating pairs are available and the number of offspring in the new generation is reduced (Bakke and Lie, 1989). The effectiveness of mass trapping is reduced in highly populated areas when the traps become full quickly. When sex pheromones are used as the lure, only male moths are caught, and the males that are not caught can fertilise more than one female hence a high proportion of the males have to be caught to render this method effective. Another approach that has been used in the control of insect pests is lure and kill. A lure, such as sex pheromone that is able to attract insects is associated with an insecticide that acts to kill the insects. The effectiveness of this system depends on
General Introduction 23 the attractiveness of the lure and the ability of the insecticide to infect and kill the insect (Haynes et al., 1986). One approach to overcome the shortfalls of mass trapping and lure and kill is lure and infect (Suckling and Karg, 1999). This has been used on insects such as tobacco budworm (Jackson et al., 1992), codling moth (Hrdy et al., 1996) and diamondback moth (Pell et al., 1993). This approach uses lures such as pheromones combined with insect pathogens such as virus, bacteria or fungi to attract insects to the lure source (O‟Callaghan and Jackson., 1993). Once infected, the insects act as vectors of the disease and spread it across the population. An advantage of using such an approach is the speed with which the disease spreads in the population and with the insect themselves acting as vectors for the pathogen, the continuous need for the lure source to be maintained and the number of lure sources is reduced (Suckling and Karg, 1999). The downfall of this system is that bacterial toxins and viruses are pathogenic only when consumed hence the lure system has to be designed such that the pathogen is consumed by the insects. Also, for the pathogen to spread in the population, the infected males have to mate to pass on the pathogen to the females, which must then be able to spread it to the surface of the eggs they lay, which will eventually have to be consumed by the larvae at eclosion. The success of the lure and infect approach using bacteria or virus as the pathogen hence largely depend on the efficiency by which these series of events take place. When fungi is used as the pathogen, the lure has to be presented in such a way that it is able to attract the adult insects and keep them within the vicinity of the lure long enough for the fungi to be picked up. The adult has to be able to spread the fungi to other insects in the population before dying or upon death; the fungi will grow on the dead insect and spread within the population. However, the fungi might be susceptible to environmental factors such as ultra violet (UV) radiation and die, a limiting step to the success of this system. Economic production of the pathogen, maintenance of the pathogen in the environment, development of an efficient delivery system and ability of the pathogen to spread across the population are factors that have to be taken into consideration when designing lure and infect control strategies (Suckling and Karg, 1999). Other methods of reducing the damage caused to plants are spraying the host plants with feeding and ovipostion deterrents. Oviposition deterrents will prevent females
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Page 3 and 4: Abstract Abstract Olfaction or the
Page 5 and 6: Acknowledgements Acknowledgements I
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The roles of Epiphyas postvittana G
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4.1 Introduction 4 Identification o
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Identification of putative odorant
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5.1 Introduction 5 Concluding Discu
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Concluding Discussion 127 VOBA sett
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Concluding Discussion 129 redundant
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Concluding Discussion 131 against t
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Concluding Discussion 133 sequencin
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Appendix B 135 Buffered TB (Sambroo
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Appendix C 137 C. Appendix C - Clus
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Appendix D 139 D. Appendix D - Solu
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Appendix E 141 I II
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Appendix E 143 V
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Appendix E 145 VII continued Figure
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References 147 Ansebo, L., Ignell,
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References 149 Butenandt, A., Beckm
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References 151 Fedurco, M., Romieu,
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References 153 Große-Wilde, E., St
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References 155 Hrdy, I., F. Kuldova
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References 157 Kaissling, K. E. (19
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References 159 Krieger, J., Große-
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References 161 Lopez-Gomez, R. and
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References 163 Miura, N., Nakagawa,
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References 165 Pell, J. K., Macaula
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References 167 Røstelien, T., Stra
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References 169 Stowers, L. and Loga
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References 171 Turner, C. T., Davy,
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References 173 Vogt, R. G., Riddifo
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References 175 Widmayer, P., Heifet
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