Abstract: The colonization and feeding behavior of the cotton aphid, Aphis gossypii Glover, on melon and cotton plants were studied in order to reveal the behavioral mechanism in formation of different host-preference biotypes. The results of the biological observation showed the number of colonizing aphids decreased significantly when they were transferred to their non-preference plant (melon or cotton). Moreover, both population reproduction coefficient and the nymphal survival rate were also significantly declined when aphids living on cotton were transferred to melon. These data suggested there were two host-preference bio types in the aphid A. gossypii, the melon biotype and the cotton biotype. Based on the comparisons of feeding behavior between these two host biotypes using electrical penetration graph (EPG), the feeding characteristics of the two host biotypes of cotton aphids on their non-preference host were found as following: (1) The feeding behavior of the melon biotype aphids was interrupted easily on the cotton, but the ability that aphid stylet locating cotton phloem was not affected by frequent interruption in the pathway penetration; (2) The feeding behavior of the cotton biotye aphids was affected so greatly on the melon that the aphids could not locate the melon phloem and feed at the sieve element within 2 hours. The biological observation and EPG feeding behavior record of these two host biotypes both suggested that the cotton biotype aphid had stricter requirement for its host plant and used the host plant more efficiently than melon biotype aphid . These findings may give clues to explain why the aphids living on the cotton and melon respectively could not successfully transfer hostplants mutually.

Key words: Aphis gossypii, melon, cotton, host preference, electrical penetration graph