Finding the right one : Host-plant choice and its transgenerational influence on behaviour and life-history traits in Spodoptera littoralis

Herbivorous insects have an intricate relationship with their host plants, which they use as food, oviposition substrate, as well as a rendezvous site for mating. For generalist herbivorous insects that have a wide host range, finding a suitable host plant in a complex environment is of great importance for their offspring’s development and survival. Most herbivorous insects use olfactory cues for host-plant location, where changes in odour profiles of plants due to extrinsic factors from both biotic and abiotic stressors must be taken into consideration when locating a suitable host. Several generalist insects are known to use odour cues experienced during their larval development to facilitate hostplant location in the adult stage, even if they undergo complete metamorphosis between the two developmental stages. This may funnel individuals onto a particular plant species, increasing the chances of their offspring ending up in a matching environment to that of the parent. The use of previous experience is thought to facilitate transgenerational acclimatization, where parents acclimatize their offspring to the environment that they experienced.This thesis investigates how herbivory influences host-plant choice in the generalist moth Spodoptera littoralis (paper I) and the transgenerational impact of plant choice on preference and life-history traits (papers II and III).I found that herbivory by conspecifics influenced host-plant location and preference hierarchies of S. littoralis in a sex-specific manner where the odours released from damaged plants were driving the behavioural shifts. Furthermore, I found that (previous) parental experience does not influence host-plant location in neonate larval or adult females, but that host-plant choice relies on innate preference hierarchies and withingenerational phenotypic plasticity. Moreover, I demonstrated how transgenerational acclimatization could influence developmental traits while reproductive output shows no signs of transgenerational acclimatization but rather the opposite. Thus, the use of previous experience may be a way to facilitate host-plant location in adult individuals, which comes at the expense of the reproductive output of their offspring.The findings in this thesis emphasize the complexity of host-plant choice in generalist insects and the influence the plant community have on behaviour and life-history traits within- and across-generations.