4.2 Predation experiments
Grasslands and cereal crops showed no difference in predation rates, but
new grasslands increased ant activity compared to cereal crops. This
suggests that new grasslands embedded in agricultural landscapes are
able to provide a consistent amount of biological control services.
Further, we could show that vegetation density influenced the outcome of
sticky card experiments more than habitat type and that predation of
experimentally exposed fruit flies as a proxy for pest control is
generally lower on sites with higher vegetation density, such as newly
established and old grasslands. These findings support the assumption
that in new and old grassland transects predatory arthropods were less
dependent to feed on experimentally exposed fruit flies, as the high
vegetation density of these habitats likely provided a higher supply of
food resources
(Kruess
& Tscharntke, 2002; Siemann, 1998) compared to cereal crops.
For the management of pest control it is important to consider that
biocontrol services are not provided solely by ants, but by a diverse
assemblage of ground-dwelling arthropod predators in the agricultural
matrix
(Meyer,
Heuss, Feldhaar, Weisser, & Gossner, 2019). Carabids, spiders and wasps
were also able to access fruit flies glued to sticky cards and their
contribution, which was not assessed in this study, is most likely the
reason for the lack of a correlation between predation rate and ant
activity. Nevertheless, the results of the predation experiment are
relevant because ants are among the most abundant predatory arthropods
in certain agricultural landscapes and account for a significant part of
the arthropod biomass
(Wills
& Landis, 2018).