The incidence and distribution of the armyworms Mythimna convecta (walker) and Persectania spp. (Lepidoptera: Noctuidae) and their parasitoids in major agricultural districts of Victoria, south-eastern australia

Abstract

AbstractField studies of Mythimna convecta (Walker), Persectania ewingii (Westwood) and P. dyscrita Common, and their associated parasitoids, were conducted in cereals and pastures in Victoria, Australia, in 1980–83. The study included a survey of the armyworm fauna in the major agricultural districts, detailed phenological studies within five oat crops, and ultraviolet-light trapping of adults. M. convecta was the most abundant species in cereals and was found more commonly in the warmer months of spring and summer in all districts. Larval development in oat crops during spring was preceded by little moth activity in light traps. P. ewingii was common in the southern districts and in the cooler months from May to September. It was the most prevalent armyworm species in pastures and rarely occurred in barley. P. dyscrita was the least abundant species and occurred mostly in the drier inland areas, particularly in the west. Light-trap catches of P. ewingii and P. dyscrita suggested there were two generations, one in spring and one in the autumn. Regular sampling in oat crops showed that M. convecta developed faster and was usually more abundant than P. ewingii during seed development and ripening, and hence had the potential to inflict more crop damage. Of the 17 species of parasitoids reared from field-collected larvae, the wasp Campoletis sp. was the most abundant. In 1980–82, average parasitism ranged from 13 to 16% but fell to 2% after the drought of 1982.