Coccinella septempunctata L. (Coleoptera: Coccinellidae), a Palearctic coccinellid, has established and rapidly spread throughout the United States. This quantitative examination of larval interactions between C. septempunctata and Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), a Nearctic coccinellid, was conducted under controlled prey densities. Larvae of both coccinellid species are affected by a limited diet [one pea aphid per day Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)] compared with an excess diet (>20 aphids per day). Larval survival decreased from 86 to 63% in C. maculata and from 84 to 33% in C. septempunctata; mean preimaginal developmental time increased from 20.6 to 26.7 days in C. maculata, and from 18.1 to 32.0 days in C. septempunctata. Additionally, on one aphid per day, mean adult weight was reduced from 12.39 to 9.79 mg in C. maculata, and from 39.57 to 14.44 mg in C. septempunctata. Interspecific interactions, favoring C. septempunctata over C. maculata at a␣low prey density (one aphid per day), take the form of␣reduced survival of C. maculata compared with C.␣septempunctata (14 versus 66%). Reduced survival of␣C. maculata may be the result of competition for aphids or intraguild predation by C. septempunctata on C.␣maculata. No interspecific interactions (measured as effects on larval survival, preimaginal developmental time, and adult weight) were observed between larvae of these two species at a high prey density (>20 aphids per predator per day).
This experimental field study examined the interactions between larvae of Coccinella septempunctata L., an introduced Palearctic species, and Co/eomegilla maculata (Degeer), a Nearctic species. The interactions were examined in 5.8-m 3 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 coccineJlid species, and M. persicae density. No significant differences were found between intraand interspecific treatments in C.
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