Entomopathogenic Nematode Effect on Pickleworm (Lepidoptera: Pyralidae) Under Laboratory and Field Conditions

Abstract

Laboratory and field tests were performed to assess the potential of entomopathogenic nematodes from the genera Steinernema and Heterorhabditis as biological control agents for the pickleworm, Diaphania nitidalis (Stoll). In the laboratory, there were significant differences in virulence among five nematode species, based on the lack of overlap of95% FL of LC50. S. carpocapsae (Weiser) (Mexican strain) had the lowest LC50 and was ≍2, 4, 30, and 38 times more pathogenic than H. bacteriophora Poinar (HP88 strain), S. feltiae (Filipjev), S. glaseri (Steiner), and S. anomali (Kozodoi), respectively. Nematode infectivity (number of nematodes in the host) was positively correlated with mortality. Larval mortality and penetration rate of infective juveniles into the host were positively correlated to host exposure time for S. carpocapsae (Mexican strain), S. feltiae , and H. bacteriophora . Nematode species that were smaller were more infective and induced mortality more quickly. Nematodes did not affect first instars and pupae to the same extent as older larvae and prepupae; pupae were particularly refractory. S. carpocapsae (All strain) applied to squash plants were able to enter blossoms, where they persisted and infected pickleworms. Nematode applications reduced damage to blossoms and fruit and, when applied weekly at 2.5 billion/ha, protected squash fruit at a level equivalent to the insecticide permethrin.