Dose-response susceptibility of pest aphids (Homoptera : Aphididae) and their control on hydroponically grown lettuce with the entomopathogenic fungus Verticillium lecanii, azadirachtin, and insecticidal soap

The objective of our research was to identify alternatives to synthetic pes ticide treatments to prevent aphid outbreaks in greenhouse lettuce crops. I n the laboratory, we determined the susceptibility of three lettuce-infesti ng aphid species, Macrosiphum euphorbiac (Thomas), Myzus persicae (Sulzer), and Nasonovia ribisnigri (Mosley), to the hyphomycete Verticillium lecanii (Viegas) (strain Vertalec), the plant triterpenoid molecule azndirachtin ( BioNeem), and an insecticidal soap (Safer's). Estimated LC50 and LT50 obtai ned in the laboratory indicated that the three aphid species were susceptib le to the entomopathogenic fungus, the plant extract, and the soap. Under g reenhouse conditions, we assessed the potential of the three pesticides to reduce aphid populations and compared it with that of a synthetic insectici de, the organophosphate Malathion. Greenhouse experiments demonstrated that all three pesticides significantly reduced the population of each aphid sp ecies compared with the untreated plants. This study also revealed differen ces in aphid susceptibility between aphid species and between laboratory bi oassays and greenhouse trials. The high initial aphid densities, difficulti es to reach the aphids on the undersurface of leaves, stains left by Vertal ec on the harvested lettuce, and high cosmetic standards for lettuce mitiga ted the performance of the insecticides. The potential of using Vertalec, B ioNeem, and Safer's soap for. the control of lettuce aphids is discussed in relation to aphid species and crop management.