Provisioning Australian Seed Carrot Agroecosystems with Non-Floral Habitat Provides Oviposition Sites for Crop-Pollinating Diptera.

The addition of floral resources is a common intervention to support the adult life stages of key crop pollinators. Fly (Diptera) crop pollinators, however, typically do not require floral resources in their immature life stages and are likely not supported by this management intervention. Here, we deployed portable pools filled with habitat (decaying plant materials, soil, water) in seed carrot agroecosystems with the intention of providing reproduction sites for beneficial syrphid (tribe Eristalini) fly pollinators. Within 12 to 21 days after the pools were deployed, we found that the habitat pools supported the oviposition and larval development of two species of eristaline syrphid flies, Eristalis tenax (Linnaeus, 1758) and Eristalinus punctulatus (Macquart, 1847). Each habitat pool contained an average (±S.E.) of 547 ± 117 eristaline fly eggs and 50 ± 17 eristaline fly larvae. Additionally, we found significantly more eggs were laid on decaying plant stems and carrot roots compared to other locations within the pool habitat (e.g., on decaying carrot umbels, leaves, etc.). These results suggest that deploying habitat pools in agroecosystems can be a successful management intervention that rapidly facilitates fly pollinator reproduction. This method can be used to support future studies to determine if the addition of habitat resources on intensively cultivated farms increases flower visitation and crop pollination success by flies.

Crop-pollinating Diptera have diverse diets and habitat needs in both larval and adult stages.

Insects are important pollinators of global food crops and wild plants. The adult and larval diet and habitat needs are well known for many bee taxa, but poorly understood for other pollinating taxa. Non-bee pollinators often feed on different substrates in their larval and adult life stages, and this diet and habitat diversity has important implications for their conservation and management. We reviewed the global literature on crop pollinating Diptera (the true flies) to identify both larval and adult fly diet and habitat needs. We then assembled the published larval and adult diets and habitat needs of beneficial fly pollinators found globally into a freely accessible database. Of the 405 fly species known to visit global food crops, we found relevant published evidence regarding larval and adult diet and habitat information for 254 species, which inhabited all eight global biogeographic regions. We found the larvae of these species lived in 35 different natural habitats and belong to 10 different feeding guilds. Additionally, differences between adult Diptera sexes also impacted diet needs; females from 14 species across five families fed on protein sources other than pollen to start the reproductive process of oogenesis (egg development) while males of the same species fed exclusively on pollen and nectar. While all adult species fed at least partially on floral nectar and/or pollen, only five species were recorded feeding on pollen and no fly larvae fed on nectar. Of the 242 species of larvae with established diet information, 33% were predators (n = 79) and 30% were detritivores (n = 73). Detritivores were the most generalist taxa and utilized 17 different habitats and 12 different feeding substrates. Of all fly taxa, only 2% belonged to the same feeding guild in both active life stages. Our results show that many floral management schemes may be insufficient to support pollinating Diptera. Pollinator conservation strategies in agroecosystems should consider other non-floral resources, such as wet organic materials and dung, as habitats for beneficial fly larvae.

Eristalis flower flies can be mechanical vectors of the common trypanosome bee parasite, Crithidia bombi.

Flowers can be transmission platforms for parasites that impact bee health, yet bees share floral resources with other pollinator taxa, such as flies, that may be hosts or non-host vectors (i.e., mechanical vectors) of parasites. Here, we assessed whether the fecal-orally transmitted gut parasite of bees, Crithidia bombi, can infect Eristalis tenax flower flies. We also investigated the potential for two confirmed solitary bee hosts of C. bombi, Osmia lignaria and Megachile rotundata, as well as two flower fly species, Eristalis arbustorum and E. tenax, to transmit the parasite at flowers. We found that C. bombi did not replicate (i.e., cause an active infection) in E. tenax flies. However, 93% of inoculated flies defecated live C. bombi in their first fecal event, and all contaminated fecal events contained C. bombi at concentrations sufficient to infect bumble bees. Flies and bees defecated inside the corolla (flower) more frequently than other plant locations, and flies defecated at volumes comparable to or greater than bees. Our results demonstrate that Eristalis flower flies are not hosts of C. bombi, but they may be mechanical vectors of this parasite at flowers. Thus, flower flies may amplify or dilute C. bombi in bee communities, though current theoretical work suggests that unless present in large populations, the effects of mechanical vectors will be smaller than hosts.