Presence of Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) Populations in Sweet Corn and their Susceptibility to Insecticides in Puerto Rico

Corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), are important pests in sweet corn. Our objectives were to assess the occurrence of the Lepidopteran species affecting sweet corn in Puerto Rico, and to evaluate the efficacy of 9 insecticides to control larvae of corn earworm and fall armyworm. Spodoptera frugiperda was observed in all plant stages, whereas H. zea and Diatraea saccharalis (F.) (Lepidoptera: Crambidae) affected only ears. Larvae of corn earworm and fall armyworm were susceptible (mortality > 80% at 96 h) to Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae) + oil and to methomyl, respectively, whereas both species were susceptible to chlorpyrifos. The LC50 values for chlorpyrifos was 248 ppm, whereas 312,500 S. carpocapsae nematodes per L + 625 ppm of rapeseed oil caused 53% of larval mortality at 120 h post-treatment for corn earworm larvae.