Population dynamics of three coccinellids in flue-cured tobacco and functional response of Hippodamia convergens (Coleoptera:Coccinellidae) feeding on tobacco aphids (Homoptera:Aphididae)

The seasonal abundance of 3 species of coccinellids was observed on flue-cured tobacco, Nicotiana tabacum L., during 1997 and 1998 in Tift County, GA. The most abundant coccinellid during both seasons was the convergent lady beetle, Hippodamia convergens Guerin-Meneville, which was present from mid-May, when tobacco aphids, Myzus nicotianae Blackman, colonized the crop, until late July when sampling ended. The sevenspotted lady beetle, Coccinella septempunctata L., and the multicolored Asian lady beetle, Harmonia axyridis (Pallas), were also observed. C. septempunctata was most abundant early in the season and maintained low population levels during June and July. Conversely, H. axyridis was absent in tobacco until late May and remained abundant until sampling was discontinued. Populations of H. convergens, H. axyridis, and C. septempunctata were linearly related to tobacco aphid populations during 1998. In functional response experiments, 4th-instar larvae and adult H. convergens exhibited a type II functional response to aphid density. Fourth-instar larvae had a higher search rate and a longer handling time than adult H. convergens. Two other coccinellid species were observed at low population densities on flue-cured tobacco, Coleomegilla maculata (Mulsant) and Cycloneda munda (Say). Collectively, coccinellids may be important biological control agents of tobacco aphids on Georgia flue-cured tobacco.