Experimental Assessment of Interactions between Larval Coleomegilla maculata and Coccinella septempunctata (Coleoptera: Coccinellidae) in Field Cages

This experimental field study examined the interactions between larvae of Coccinella septempunctata L., an introduced Palearctic species, and Coleomegilla maculata (Degeer), a Nearctic species. The interactions were examined in 5.8-m³ field cages enclosing potatoes infested with Myzus persicae (Sulzer) (Homoptera: Aphididae). Intra- and interspecific interactions were compared by using 4 measurements: developmental time and survival from 1st instar to adult, adult weight for each coccinellid species, and M. persicae density. No significant differences were found between intra-and interspecific treatments in C. maculata survival: 19.6 and 18.3%, in 1992 and 5.7 and 3.3%, in 1993, respectively; or developmental time: 24.6 and 25.4 d in 1992 and 20.4 and 20.6 d in 1993, respectively. In 1992, no significant differences were observed between the intra- and interspecific treatments in C. septempunctata survival (38.3 and 39.2%) or developmental time (20.0 and 20.5 d). In 1993, no C. septempunctata survived to adults at the relatively lower prey densities. Interspecific interactions between C. septempunctata and C. maculata larvae did not significantly affect M. persicae density, compared with densities in intraspecific cages.