Abstract
A lot of studies focusing on the effect of agricultural landscapes demonstrate that many arthropod species are influenced by landscape structure. In particular, non–crop areas and landscape diversity are often associated with a higher abundance and diversity of natural enemies in fields. Numerous studies focused on the influence of landscape structure on ground beetles, spiders and ladybeetles but few on other natural enemies or different functional groups. Thus, the objective of the present study was to determine the influence of landscape structure on the functional groups, i.e., active-searching predators, furtive predators and parasitoids of aphidophagous guilds. Natural enemies were sampled on milkweed infested with aphids, growing along the borders of ditches adjacent to cornfields. The sampling occurred weekly from June to September in 2006 and 2007, in the region of Lanaudière (Quebec, Canada). The landscapes within a radius 200 and 500 m around each site were analyzed. The abundance, richness and species composition (based on functional groups) of natural enemies were related to landscape structure. The results indicated that landscape structure explained up to 21.6% of the variation in natural enemy assemblage and confirm the positive effects of non-crop areas and landscape diversity. A lower influence of landscape structure on species composition was observed (6.4 to 8.8%) and varied greatly among the functional groups. Coccinellidae and furtive predators were the group most influenced by landscape structure. In conclusion, the influence of landscape varied greatly among the different species of the same functional group.
Highlights
The aphidophagous guilds are composed of an array of different species that may control aphids in the field
The milkweed aphid is parasitized by Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae), a generalist koinobiont endoparasitoid whose parasitism rate depends on aphid density (Helms et al 2004)
In 2006, 7 sites were not included in the analyses because of the absence of natural enemies on milkweed infested with aphids
Summary
The aphidophagous guilds are composed of an array of different species that may control aphids in the field. Active-searching predators, such as ladybeetles (Coleoptera: Coccinellidae), lacewing larvae (Neuroptera: Chrysopidae and Hemerobiidae) and hoverfly larvae (Diptera: Syrphidae), do not necessarily live within or close to aphid colonies and search actively for their prey. Their hunting behaviour is composed of extensive and intensive search (Ferran and Dixon 1993) and usually induces a strong defensive response from aphids, such as walking, dropping or swiveling (Dixon 1958; Losey and Denno 1998). Coccinellidae are voracious predators that actively search for prey, along the edges of leaves or by following surface irregularities (veins), where aphids are most likely to occur (Dixon 1959; Marks 1977). Active-searching predators, furtive predators and aphid parasitoids can be used to control aphids in fields
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