イヌガラシ上におけるモンシロチョウ属2種(モンシロチョウとスジグロシロチョウ)の卵分布と卵食行動

抄録

In summer, females of the Pieris butterfly species P. rapae and P. melete oviposit mainly on the wild cress, Rorippa indica, which grows along roadsides. The butterflies prefer to deposit eggs on the host plant during the bolting phase so that egg density is increased at this time. Few eggs were found on plants at the oldest phase of the life cycle which had produced seeds. The eggs deposited on a plant showed a clumped distribution. Leaves bearing multiple eggs were collected, and the shortest distance between the eggs was measured for each. The average of the shortest distance between the eggs on a leaf was about 8 mm in both 1990 and 1991. Newly hatched larvae ate their own egg shell and thereafter fed on neighboring eggs. Such egg cannibalism increased with the difference in developmental stage between the eggs of P. rapae. Intraspecific egg cannibalism was observed in P. melete as well as in P. rapae, and interspecific cannibalism also occurred. Since the females lay eggs singly and seldom return to deposit on the same host plant, the eggs on a single leaf may not be related to each other. It is considered that egg cannibalism is advantageous for larval survival on limited resources and for intake of nutrients.