Interaction of a newly established immigrant, soybean looper Thysanoplusia orichalcea and the indigenous green looper Chrysodeixis eriosoma (Plusiinae: Noctuidae) in New Zealand

Abstract

Soybean looper Thysanoplusia orichalcea (Plusiinae: Noctuidae) moths were first intercepted in New Zealand in 1984 by light trapping that was being used as a surveillance tool for new lepidopteran pests; in particular, noctuid species from Australia. This prompted studies on larval infestations to separate the impact of T. orichalcea caterpillars from that of the closely related indigenous green looper, Chrysodeixis eriosoma. Subsequent studies described here show that the establishment phase took place over c. 3 years and that, rather than replacing the resident green looper, soybean looper added to the population density of plusiine caterpillars in several field crops, especially lucerne, parsley, soybeans, brassicas, and lettuce. The increases in larval populations caused by T. orichalcea in soybeans were documented from 1980 to 1989, with total plusiine populations reaching c. 46/m of row compared with c. 10/m of row for C. eriosoma. Light trap catches of moths confirmed the increasing abundance of T. orichalcea. By 1990 it represented 87% of the plusiine moths trapped at Pukekohe. This case history supports the use of light traps as a surveillance tool to provide biosecurity warnings and to initiate establishment and impact surveys for incursions of new noctuid pests.