Difference of the error type change the optimal response rule in the cooperation

     Mimicry is widely observed strategy for avoiding attack by other animals and efficiency predation. There is a strategy of mimicry simulating chemical trait among animals that mainly recognize environment by sensing chemical signals, and this strategy is called chemical mimicry. Some parasites whose hosts are ants are typical example of chemical mimicry organisms. Ants distinguish their nestmates from others by chemical signal on cuticula, so chemical mimicry parasite can intrude into host colony with mimicking odor of host. Chemical mimicry in parasite of ant is roughly classified in two types: simulating host’s chemical trait (mimic) and having faint body odor (cryptic). Ants are forced to accept cryptic parasite because refusing ants having faint chemical trait would also cause them to reject newly emerged workers that lack chemical signals. Although cryptic parasites seem to be favorable, it is observed many parasites using mimic strategy and very few parasites adopting cryptic strategy.      There are many theoretical studies about mimicry, but there are no studies to consider the evolution of two strategies, mimic and cryptic. I investigate what are the conditions in which cryptic and mimic strategy of parasites evolve. I assume two dimensional chemical traits. Ants accept other ants if the ratio of chemical traits of others is close to the ratio of its own traits, and if the absolute amount of chemical traits is smaller than own traits. There are other colonies but the same species around parasite colony, and the difference of chemical traits among parasites is proportional to the absolute amount of chemical traits. I calculate fitness of parasite by benefit of acceptance by host and cost of miss-acceptance to other colonies. I found if the recognition ability of host is low, crypsis is favorable. And if the recognition ability of host is high and the competition with other colonies is strong, mimicry can be evolved. From these results, I consider the parasite strategy in real world.