Larvae of Lepidopteran Manduca sexta and Spodoptera littoralis are pests of economical importance in several horticultural and agricultural crops. Knowledge of insect feeding preferences and behavior is crucial in order to find economically and ecologically sustainable solutions to the problems caused by these herbivores. The aim of this thesis was to study the behavior and the induced feeding preferences in larvae of M. sexta and S. littoralis when reared on certain host plants. The hypothesis was that larvae of M. sexta would have an innate preference for plants of the Solanaceae family and therefore discriminate the previously experienced nonhost when faced with the choice between a true host and the previous food source.

A plant's defensive ability against herbivore attack can be influenced by many different factors, one of them being domestication. During human selection to improve the yield of plants, the resistance against herbivore attack can have been lowered, due to a trade-off for use of resources between these traits in the plants. In this thesis I investigated the effect of domestication on resistance against herbivorous insects in cotton plants. I used different varieties and species of wild and domesticated cotton in three different experiments. A feeding assay was conducted, the mortality, development time and pupal weight of larvae of the Egyptian cotton leaf worm Spodoptera littoralis was studied. In a second experiment the preference of the root-feeding beetle Agriotes spp.

This study has focused on testing the following two hypotheses:? Pest resistant plants have higher levels and/or several different kinds of secondary metabolites. ? Induced defensive systems in resistant plants are activated more rapidly than those of susceptible plants. As a background for the test of the hypotheses a short literature study was performed concerning plant defensive mechanisms in Arabidopsis thaliana.

This study was made to compare and distinguish any differences in olfactory recognition and host plant adaptation between two strains of cotton leaf worm, Spodoptera littoralis. The populations used were established in Egypt and Benin, Africa. The documentation consisted of information about (1) each of the strains development through the larval stage up to pupation on diets of cotton, clover and cowpea. (2) Their oviposition preferences as adults between cotton, clover, cowpea, maize and cabbage. (3) Electroantennographic recordings to quantify any possible responses to plant volatiles. Throughout the diet experiments the larvae from the Benin strain showed significantly a better development between artificial, clover, cowpea and cotton respectively, while the Egypt strain had significance between artificial, cotton and cowpea/clover as diet. Also noted was how the strains substantial development of weight differentiated if fed the cotton diet, followed by the cowpea diet showing that the Benin strain would develop a higher body mass on a cotton diet as well as on a cowpea diet. This trend was however switched once the pupal stage was reached, where the Egyptian strain contained a significantly greater body mass than the Benin strain on the artificial and the Benin strain a greater on cowpea, which suggests that in the end, the Benin strain develops significantly better on cowpea while the Egypt strain develops better on an artificial diet. During the oviposition experiment that both stains showed a clear difference in hierarchy of host plants considered suitable for oviposition, where the Egyptian strain is significantly more attracted to clover than the Benin strain. Also showed with electroantennographic recordings and significant values was the higher sensitivity the Egypt strain had towards (E)2-hexenal, (E/Z)-b-ocimene, (Z)-3-hexenyl acetate, Nonanal, (-)-linalool and ?-myrcene when compared to the responses from the Benin strain..

In two feeding experiments Bacillus induced priming of plant defense was tested for its effect against the generalist insect pest Spodoptera littoralis. The main hypothesis for the study was that Bacillus induced priming would enable the plant Arabidopsis thaliana to defend itself better against this insect herbivore since this priming seems to involve jasmonic acid, known to be important for plant defense to insects. A secondary objective of the study was to examine if any differences in a primed defense capability could be seen between different natural genetic variants (ecotypes) of A. thaliana reflecting habitat differences in pest pressure. The methods used for plant cultivation and Bacillus inoculation were aimed at reflecting conditions that can be expected in an agricultural cropping system. This meant that all plants were cultivated in soil, and the feeding experiments were conducted with the plants growing intact in the soil system.

Användningen av bekämpningsmedel för privat bruk i Sverige är relativt liten i jämförelse med många andra länder och beror dels på den omfattande kemikalielagstiftningen men även på det tuffa klimatet som minskar antalet skadegörare. Men även här sker bekämpning med ämnen vars effekter på icke-målinsekter inte är helt klarlagda.I denna studie har den systemiskt verkande insekticiden imidakloprid undersökts för att försöka klargöra hur ämnet, som främst används som bekämpning mot olika typer av löss, påverkar andra djur som kan komma i kontakt med det. De djur som valdes ut var pollinatören B. terrestris, fjärilslarven tillika växtätaren S. littoralis samt luspredatorn C.