Generally, insects have a trade-off between size and number of eggs. It is well known that fitness of offspring for host plants quality vary with change in their egg size, i.e., larger egg size is advantage in lower nutrition and tougher host plants (Braby 1994). Therefore, the balance of egg size and number should be influenced by their offspring’s environment, quality of host plants. However, because the previous studies have obtained the results only from limited number of butterfly species, there are still some doubtful points, i.e., what kinds of host plants qualities determine the egg size of butterflies in general. So we studied the relationship between the egg size and each quality of the host plants, such as physical quality (leaf toughness), chemical quality (phenol or tannin concentration), LMA, and nutritional quality (CN ratio), using 84 species of butterflies.

Our results show that quantity of phenol concentration (chemical quality) is most important for the determination of the egg size of butterflies. Whereas, leaf toughness (physical quality) has weak relationship for the determination of egg size of butterflies.