Development of Issoria lathonia (Lepidoptera: Nymphalidae) on zinc‐accumulating and nonaccumulating Viola species (Violaceae)

Abstract

The larvae of Issoria lathonia L. feed in natural conditions on several Viola spp., among which are the zinc-accumulating Viola calaminaria (Gingins) Lej. and the nonmetal-accumulating Viola tricolor L. To examine how I. lathonia caterpillars cope with the naturally high foliar zinc concentration of V. calaminaria, we compared the growth of caterpillars reared on leaves varying in zinc concentration. Larvae were fed in controlled conditions with V. calaminaria and V. tricolor grown on noncontaminated soil (i.e., two low-Zn diets) and with V. calaminaria grown on zinc-enriched soil (i.e., one high-Zn diet). Larvae had a higher growth rate when fed with noncontaminated V. calaminaria compared to zinc-enriched V. calaminaria, suggesting that zinc slows down larval growth. However, larvae consumed more leaves of zinc-enriched V. calaminaria (+45%; estimated from fecal mass) compared with noncontaminated V. calaminaria, suggesting that zinc accumulation would not be advantageous to plants. Caterpillars reared on high-zinc leaves regulate their internal zinc concentration through excretion of highly metal-concentrated feces. When kinetics of growth on both low-zinc diets were compared, it appeared that larval development was faster on noncontaminated V. calaminaria than on V. tricolor. This suggests that more nutrients or less feeding inhibitors in V. calaminaria account for fastest growth. Developmental rates on V. tricolor and on zinc-enriched V. calaminaria were similar, despite the high leaf zinc concentration of the latter species. Together with the abundance of V. calaminaria on calamine soils, this may explain why the largest populations of I. lathonia develop on V. calaminaria in Belgium.