Nutrient driven oviposition and food preference in terrestrial herbivorous insects - a choice experiment

Abstract: The presence of competitors and predators as well as plant quality affect which plants an insect feed from. These factors affect food choice through the entire insect life cycle, and is especially important when it comes to nurturing larvae. Females oviposition choice sets the initial stage for larval growth and survival, and it is therefore predicted that there is a strong selection pressure to make them oviposit on the best plants possible. This study looks into the behavior of nutrient driven ovipositing and food choice in the beetles Phratora vitellinae and Lochmaea caprea by offering individuals ten leaves of Salix viminalis, one treated with extra nitrogen in order to increase the nutritional value, and four treated with extra carbon, which should lower the nutritional value. During the choice experiment, only two females of Phratora vitellinae oviposited, making it impossible to draw any conclusion regarding nutrient driven oviposition choice. However, data showed a preference for nitrogen treated leaves and an avoidance of untreated control leaves in almost every case when looking into the largest loss of area for leaves of each treatment. When analyzing the number of leaves of each treatment that is eaten per individual there was a slight preference for nitrogen treated leaves, even though the probability of nitrogen being ranked as most preferred in this case was almost zero. Carbon treated leaves and acetone treated control leaves were equally avoided. For Lochmaea caprea, females fed from a significantly larger numer of leaves than males did (t-test, t=1.86, p=0.0003). An ANOVA showed no significant difference in C:N ratio among leaf treatments (ANOVA, F=9.28E-07, p=0.99). Since plant C:N ratio most likely will increase continuously due to CO2 emissions, the effects an increased carbon concentration in plant tissues has on oviposition and food choice in herbivorous insects is something to look further into. More studies on this subject are therefore needed.