Abstract
House flies are of major concern as vectors of food-borne pathogens to food crops. House flies are common pests on cattle feedlots and dairies, where they develop in and feed on animal waste. By contacting animal waste, house flies can acquire human pathogenic bacteria such as Escherichia coli and Salmonella spp., in addition to other bacteria, viruses, or parasites that may infect humans and animals. The subsequent dispersal of house flies from animal facilities to nearby agricultural fields containing food crops may lead to pre-harvest food contamination with these pathogens. We hypothesized that odors from honeydew, the sugary excreta produced by sucking insects feeding on crops, or molds and fungi growing on honeydew, may attract house flies, thereby increasing the risk of food crop contamination. House fly attraction to honeydew-contaminated plant material was evaluated using a laboratory bioassay. House flies were attracted to the following plant-pest-honeydew combinations: citrus mealybug on squash fruit, pea aphid on faba bean plants, whitefly on navel orange and grapefruit leaves, and combined citrus mealybug and cottony cushion scale on mandarin orange leaves. House flies were not attracted to field-collected samples of lerp psyllids on eucalyptus plants or aphids on crepe myrtle leaves. Fungi associated with field-collected honeydews were isolated and identified for further study as possible emitters of volatiles attractive to house flies. Two fungal species, Aureobasidium pullulans and Cladosporium cladosporioides, were repeatedly isolated from field-collected honeydew samples. Both fungal species were grown in potato dextrose enrichment broth and house fly attraction to volatiles from these fungal cultures was evaluated. House flies were attracted to odors from A. pullulans cultures but not to those of C. cladosporioides. Identification of specific honeydew odors that are attractive to house flies could be valuable for the development of improved house fly baits for management of this pest species.
Highlights
Food-borne pathogens including Escherichia coli, Salmonella spp., and Campylobacter spp. are persistent and widespread problems in food production and preparation [1,2], and the PLOS ONE | DOI:10.1371/journal.pone.0124746 May 13, 2015
Similar methods were used for host plant materials from citrus mealybug and pea aphid colonies, except that 8 week-old butternut squash infested with citrus mealybugs and clean butternut squash controls were gently washed with 30 mL of dH2O and the runoff was collected
House fly attraction to volatiles of fungi isolated from honeydewcontaminated plants Aureobasidium pullulans and C. cladosporioides were identified in higher concentrations from most of the field collected honeydew samples relative to the corresponding uninfested plant material
Summary
Food-borne pathogens including Escherichia coli, Salmonella spp., and Campylobacter spp. are persistent and widespread problems in food production and preparation [1,2], and the PLOS ONE | DOI:10.1371/journal.pone.0124746 May 13, 2015. Subsequent studies in the region where the contaminated spinach originated resulted in the capture of filth flies carrying this pathogen on leafy greens (spinach and lettuce) in field crops adjacent to a cattle pasture [6]. Filth flies are not typically associated with leafy green crops, and flies that typically develop in crop waste would not be expected to harbor human or animal pathogens such as E. coli O157:H7. Within a field of leafy greens, filth flies are more abundant where honeydew-producing insects are present [6]. House fly dispersal behavior is poorly understood, but odors from honeydew and/or fungi growing on honeydew-contaminated crop plants may attract flies. 2. To assess house fly attraction to odors produced by cultures of two fungi repeatedly isolated from field-collected honeydew
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