Variation in invasive plant lineages of an agricultural weed affects an insect herbivore

Nutritional differences in invasive plant lineages may influence herbivore survival and performance. Understanding the variation in plant quality and herbivore responses could assist in the selection and prioritization of potential species being developed for biological control. The two primary lineages of the invasive grass, Imperata cylindrica , have separate origins and mostly separate distributions occurring in Alabama/Mississippi (AL-type) and Florida (FL-type), USA. We conducted laboratory experiments with a generalist herbivore Spodoptera frugiperda (FAW) to examine the nutritional differences posed by the I. cylindrica lineages and leaf ages when grown at different fertilizer levels. The plant quality factors examined included leaf nitrogen, toughness, and silicon. Plant lineage influenced leaf nitrogen, and to a lesser degree, toughness but not silicon. Larvae fed young I. cylindrica leaves from high nutrient AL-type plants had 75 % survival compared to 0 % survival on all FL-type plants regardless of leaf age and fertilizer level. For comparison, larval survival was 100 % for larvae fed a preferred host, Stenotaphrum secundatum which had higher foliar nitrogen levels and lower leaf toughness relative to AL-type I. cylindrica plants. The larvae compensated for the lower nutrient level of AL-type I. cylindrica plants by increasing total consumption, although this adjustment was only partially successful and resulted in lower biomass and greater development time. Biological control agents developed for this weed may face lower survival and reduced performance when fed different lineages that vary nutritionally. Similar challenges for biological control agents may occur in other weeds with multiple invasive lineages. 248 words of 250 allowed.