UC Riverside

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 and attraction was evident for 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. Two fungal species, Aureobasidium pullulans and Cladosporium cladosporioides, were repeatedly isolated from field-collected honeydew samples. House flies were attracted to odors from A. pullulans cultures but not to those of C. cladosporioides. Gas chromatography-electroantennogram detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS) identified possible active compounds from pea aphid on faba bean plants, whitefly on navel orange, and whitefly on grapefruit leaves. 10 different compounds were identified from honeydew aeration samples that elicited a house fly antennal response. 4 of these compounds were identified from honeydew produced by whiteflies on navel orange and whiteflies on Marsh grapefruit plants, while one compound was identified from these two whitefly honeydews samples as well as honeydew from a laboratory colony of pea aphids. Two of these compounds were attractive to house flies in a blend and individually. These compound blends and single compounds were compared to fermented vinegar compounds previously found to be attractive to house flies. This dissertation presents the first study of house fly attraction to honeydew and specific honeydew odors. It contributes materially to our understanding of house fly responses to honeydew volatiles and demonstrates that insect honeydew is attractive to house flies, supporting our hypothesis that honeydew production by sucking insects infesting food crops may contribute to attraction of house flies to food crops.