Local adaptations of larvae of the butterfly Pieris napi to physical and physiological traits of two Arabis plants (Cruciferae)

Herbivorous insects are expected to adapt to the defensive traits of local host plants. Using two closely related plants, we showed that herbivorous insects of the same species vary their adaptations according to the different traits of each of their local host plants. The leaves of the cruciferous plant Arabis flagellosa are tougher and more difficult to digest for larvae of the butterfly Pieris napi than are A. gemmifera leaves. When given A. flagellosa leaves, hatchlings from A. flagellosa fed on and ingested the leaves faster than those from A. gemmifera . Although the C/N ratios of both Arabis plants were very similar, A. gemmifera leaves were of lower intrinsic quality for larval development and were more difficult to convert to biomass than were A. flagellosa leaves. However, when A. gemmifera leaves were given, P. napi larvae originating from A. gemmifera had higher survival rates and shorter development times than did larvae originating from A. flagellosa . In addition, larvae from A. gemmifera were better able to convert leaves than were larvae from A. flagellosa . These results suggest that A. flagellosa leaves are more physically but less physiologically defended, whereas the reverse is true of A. gemmifera , and suggest that P. napi larvae adapt to the defensive traits of local host plants.