Field boundaries as barriers to movement of hover flies (Diptera: Syrphidae) in cultivated land

Abstract

Field boundaries play an important role as refuges, food sources and corridors for invertebrates and vertebrates, and increasing farmland fragmentation impacts on these functions. However, hedgerows and other structures can also impede dispersal by flying insects. The current work uses the pollen of Phacelia tanacetifolia in hover fly guts as a marker to assess hover fly movement in farm landscapes. In the United Kingdom and New Zealand, Phacelia pollen was found in the guts of Ephisyrphus balteatus and Metasyrphus corollae (United Kingdom) and Melanostoma fasciatum (New Zealand) at distances up to 200 m from the source, when there were no barriers between the flowers and the traps used to catch the flies. The rate of decline over distance in the proportion of flies containing pollen was similar for the two countries. The extent to which four replicated field boundary types impeded hover fly movement was tested using post-and-wire fences, lines of poplars (Populus spp.) with gaps, dense poplars and controls (no potential barriers). Phacelia was planted on one side of each boundary, and along the centre of the control plots. The relative presence of the pollen in flies on both sides of the barriers showed that both types of poplar boundary restricted the movement of the flies, but the fence had no effect. In a separate experiment, gravid females of M. fasciatum were captured at a greater height on a shade-cloth fence than were non-gravid females and males. The implications of this work include the functioning and persistence of metapopulations and the influence of field boundaries on population recovery of beneficial invertebrates following pesticide-induced mortality. If field boundaries contribute to a temporal asynchrony between pest and natural enemy populations, this needs to be considered along with the well-established roles of boundaries as refugia for, and sources of, beneficial arthropods.

Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

“…Note that a multivariate logistic mixed effects model was used (see Methods); however, the trend line for a logistic regression model for just one explanatory variable on each panel was used to illustrate the direction of relationship between variables. Log scale used on x axis of both panels structures like buildings and roads in cities may make insect dispersal problematic, and present an obstacle for breeding and foraging (Wratten et al 2003;Raupp et al 2010;Peralta et al 2011). On the other hand, vegetated areas bordering roads, pavements and streets may serve as biological corridors, particularly those that maintain higher plant diversity and density (Haddad et al 2003;Peralta et al 2011).…”

Hoverfly (Diptera: Syrphidae) community of a cultivated arable field and the adjacent hedgerow near Debrecen, Hungary

“…Trees and shrubs in the hedgerow provide physical protection against wind and rain (Tuzet & Wilson 2007), but they function partly as barrier in the distribution of hoverflies (Wratten et al 2003). In addition shadow results in poor herbaceous vegetation and less foraging resources for flower-visiting hoverflies (Tóth 2008).…”

“…The insect-pollinated shrub and herb species in the hedgerows provide pollen and nectar resources for pollinator insects, increasing local biodiversity and enhance crucial ecosystem services such as pollination within the agricultural landscape (Kleijn & Langevelde 2006;Rands & Whitney 2010;Kovács-Hostyánszky et al 2013). Furthermore, hedgerows are important over-wintering and nesting habitats for hoverflies (MacLeod 1999;Wratten et al 2003;Sarthou et al 2005;Garratt et al 2011).…”

Do flower mixtures with high functional diversity enhance aphid predators in wildflower strips?

“…This trait has been extensively studied because many natural enemies need pollen and nectar at certain stages in their development (Lu et al, 2014;Van Rijn et al, 2016). Other morphological traits, such as colour and ultra-violet (UV) refl ectance, are involved in host plant recognition and, thus, fl ower attractiveness (Chittka et al, 1994;Campbell et al, 2010), while plant height might affect their fl ight (Wratten et al, 2003). Finally, phenological traits, such as the month of the onset and duration of fl owering, might be important, because the food pro- …”