The function of volatile semiochemicals in host plant choice of ovipositing manduca moths (sphingidae)
Providing favourable and secure conditions that benefit the offspring is an ubiquitous struggle among the world’s creatures. For herbivorous insects that don’t provide parental care to their offspring the choice of host plants is crucial for reproductive success. Various factors influence the performance of herbivores and have been shown to shape the choice of egg laying substrates. Among the chemical senses, olfaction plays a key role in host location for many insects. However, still little is known about the impact of olfaction on the choice among available, more or less suitable host plants. The tobacco hawk moth, Manduca sexta (Lepidoptera: Sphingidae), is a model species for olfaction, host and food search. During the studies presented in this thesis, I investigated to which extend plant odours mediate host choice at the behavioural, sensory, and processing level. This thesis presents insights into egg laying preferences, chemical identity of olfactory cues, their detection by olfactory sensilla and processing of choice‐mediating sensory input in the antennal lobe, the first centre evaluating olfactory information in the insect brain. The data demonstrate that vegetative plant volatiles suffice to mediate the choice of host species. Thus, olfaction is essential for M. sexta females, to locate, evaluate and accept host plants for egg deposition. The females perform their host choice using a host-specific olfactory ‘gestalt’, which is mainly dependent on blend composition but can be influenced by signal intensity as well. The preference for intact over feeding damaged host plants is host species-specific thereby reflecting particular characteristics of the respective herbivore-host relationship. A highly sophisticated olfactory system, which is extremely well tuned to extract information from volatile signals, ensures the selection of host plants that will most probably provide reproductive success to the ovipositing female.