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 pesticide treatments to prevent aphid outbreaks in greenhouse lettuce crops. In the laboratory, we determined the susceptibility of three lettuce-infesting 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 obtained in the laboratory indicated that the three aphid species were susceptible to the entomopathogenic fungus, the plant extract, and the soap. Under greenhouse conditions, we assessed the potential of the three pesticides to reduce aphid populations and compared it with that of a synthetic insecticide, the organophosphate Malathion. Greenhouse experiments demonstrated that all three pesticides significantly reduced the population of each aphid species compared with the untreated plants. This study also revealed differences in aphid susceptibility between aphid species and between laboratory bioassays and greenhouse trials. The high initial aphid densities, difficulties to reach the aphids on the undersurface of leaves, stains left by Vertalec on the harvested lettuce, and high cosmetic standards for lettuce mitigated the performance of the insecticides. The potential of using Vertalec, BioNeem, and Safer's soap for. the control of lettuce aphids is discussed in relation to aphid species and crop management.