Aphid Infestation in Field Grown Lettuce and Biological Control with Entomopathogenic Fungi (Deuteromycotina: Hyphomycetes)

Abstract

ABSTRACT The objective of this study was to identify the most common aphid species infesting field grown lettuce in Sweden and to evaluate the use of entomopathogenic fungi to suppress aphid infestations. Colonization of aphids to lettuce fields at two locations was monitored during two seasons. Aspects of the host specificity and pathogenicity of fungal isolates from different genera were tested under laboratory conditions on Macrosiphum euphorbiae (Thomas) and Nasonovia ribisnigri (Mosley) followed by field trials on the use of a bioinsecticide Vertalec® (Lecanicillium longisporum) against aphids. In the laboratory, a single exposure dose assay for each isolate was conducted, followed by a dose mortality assay on the most pathogenic isolates. Vertalec was included as a standard in all assays. The field trial had four treatments: untreated control, control treated with Confidor (Imidacloprid) and two Vertalec application treatments at different doses. In both seasons N. ribisnigri was the most commonly found aphid on lettuce. In bioassays, one Lecanicillum sp. isolate for M. euphorbiae and three Lecanicillium spp. isolates for N. ribisnigri were more pathogenic than the Vertalec isolate. Vertalec was pathogenic in the laboratory and caused a higher mortality than controls among the nymphs at one of the field sites, but neither Vertalec nor Confidor reduced total aphid population. This study identified pathogenic fungi that might be promising to use as bioinsecticides. However, in order to evaluate the usefulness of the identified pathogenic isolates as well as Vertalec as microbiological control agents in field grown crops, more studies in laboratory on abiotic factors as well as field studies over several seasons are necessary.