Field observations on Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in Oregon
Published in Biological Control 6, 232-237 (1996)
Michael L. LaMana and Jeffrey C. Miller
Department of Entomology, Oregon State University,
Corvallis, OR 97331-2907
Recovery of exotic coccinellids in successful classical biological control programs has often been delayed from the time of release (Gordon and Vandenberg, 1991). For example, Coccinella septempunctata L. was released in the United States beginning in 1956 before a resident population was discovered in 1973 (Angelet et al., 1979). Similarly, Hippodamia (Adonia) variegata (Goeze) was released in Canada in the 1950's but not recovered until 1984 in Montreal, Quebec (Gordon, 1987) and 1992 in New York and Vermont (Wheeler, 1993). Both of these species dominanted the aphidophagous coccinellid guild in their recovery sites, with C. septempunctata and H. variegata comprising over 80% and 36% of coccinellids, respectively (Wheeler, 1993; Angelet et al., 1979).
The phenomenon of delayed post-release recovery accompanied by numerical dominance of the aphidophagous coccinellid guild has been repeated in western Oregon by the multicolored Asian ladybeetle, Harmonia axyridis Pallas. A color-polymorphic, semi-arboreal predator of certain Homoptera/Psocoptera and native to Western Asia (Hukusima & Kamei, 1970), H. axyridis was imported to the United States for biological control of pear psylla, pecan aphid and other arboreal Homoptera. Releases of H. axyridis date back to 1916 in California and in many states by USDA between 1978 and 1982 (Chapin & Brou,1991). Its establishment in North America was first recorded in Louisiana and Mississippi during 1980 (Chapin & Brou, 1991), and then in Georgia by 1990 (Tedders & Schaefer, 1994). Mass releases of H. axyridis occurred in three counties of the state of Washington in 1981-1982. A total of 37,852 adult beetles were released in Chelan, Klickitat, and Yakima Counties. Yakima Co. also was the release site of 14,376 larvae in 1978 (Coulson, 1992). On July 18, 1991, an adult was collected in Kings Co., Washington. No known releases of H. axyridis were made in Oregon, but it was recorded in Oregon for the first time when one larva was recovered in Kaiser, Marion Co during October, 1991. (R. Westcott, Oregon Department of Agriculture, personnel communication). By early spring of 1993 this species was very abundant on aphid-infested trees and shrubs in Corvallis, Benton Co., OR (Authors, personal observation).
The release of generalist predators for biological control programs has been the subject of debate based on: 1) inconsistent and long-delays between release and establishment (e.g. Angelet, 1979); 2) possible displacement of other guild members (see Rosenheim et al., 1994); and 3), impacts on nontarget species (Howarth, 1991). The occurrence of H. axyridis in Oregon provided an opportunity to record baseline data on certain aspects of its behavior and ecology during a phase of population expansion into a new environment. The objectives of this study were to: 1) document the occurrence and distribution of H. axyridis in Oregon in 1993 and 1994, including different color forms; 2) assess guild composition of semi-arboreal, aphidophagous coccinellids between March and October of 1994; 3) document the phenology of all life-stages and overwintering; 4) record host plant and prey associations; and 5), document parasitism of larvae, pupae, and adults.
Harmonia axyridis has established in the Pacific Northwest of North America. Ten years occurred between the intentional release of beetles and the first observation of an individual on July 18, 1991, in Kings Co., Washington. The beetle was extremely abundant in western Washington and Oregon throughout 1993-94, where the species ranged from mid-eastern Washington, south to just north of the California / Oregon border, east to an elevation of 1371 m in the Cascade Mtns. and west to the Pacific Coast. Field sampling confirmed the habits and habitats of H. axyridis as a generalist, semi-arboreal, aphidophagous predator. Our records associate H. axyridis with 17 aphid prey species on 17 plant hosts. In western Oregon, H. axyridis co-occurs with 11 species of native and 2 species of exotic aphidophagous coccinellids on trees and shrubs. In arboreal habitats, 70% of individual lady beetles and 82% of live adult coccinellid mass was represented by H. axyridis, while comprising only 4% of the coccinellids in alfalfa, clover, and peppermint. Adult H. axyridis dispersed to feeding sites from overwintering aggregations, which formed the preceding October, during March. At least two generations, with a partial to complete third generation, occur per year. Parasitism of field-collected adult beetles by Dinocampus coccinellae (Schrank) was less than 1%.