Landscapes, orchards, pesticides–Abundance of beetles (Coleoptera) in apple orchards along pesticide toxicity and landscape complexity gradients

Abstract

Landscapes, orchards, pesticides-Abundance of beetles (Coleoptera) in apple orchards along pesticide toxicity and landscape complexity gradients. -Agriculture, Ecosystems and Environment, 247, AbstractLandscape composition may influence biodiversity and ecosystem services in agricultural fields.Hitherto, most studies have focused on annual crops and the available information on the impacts of landscape structure in orchards is sparse. In this study, we evaluated the effects of pesticide use as cumulative toxicity on pest and predatory beetle (Coleoptera) assemblages in the canopy of apple orchards surrounded by different proportion of semi-natural vegetation, crop fields and settlements in Hungary. Laboratory data suggest that increasing pesticide toxicity negatively affects predators (coccinellids), but we did not find such a pattern. Supposedly, the effect of pesticides was masked by the continuous recolonisation of orchards from the surrounding landscape. On the contrary, for the less mobile pest species [Anthonomus pomorum, Phyllobius oblongus (Curculionidae)] we did find a decline in abundance along the gradient of increasing pesticide toxicity. Landscape composition around the orchards significantly influenced the abundance of predatory, fungivorous and tourist species, but had no effect on pests. Contrary to expectations, however, semi-natural habitats had a minor effect compared to arable fields, orchards and settlements which habitat types had various effects on the abundance of different coleopteran groups and species. For example, Harmonia axyridis (Coccinellidae) abundance was positively affected by its overwintering sites, i.e. human settlements in spring, seminatural forests in summer, and arable fields in autumn. The mass immigration of other predatory, fungivorous and tourist species from the surrounding arable fields into the orchards started from July with senescence and harvesting of arable crops. These results suggest that arable fields, other orchards and settlements might be more important sources of colonisation for natural enemies in orchards than certain semi-natural habitats.

Mixed effects of landscape complexity and insecticide use on ladybeetle abundance in wheat fields

“…We used habitats (woodlots and fallow lands) that have positive effects on ladybeetle abundance to define landscape complexity in order to provide a more accurate measure of the effects of landscape complexity on ladybeetles in the studied region . Our results indicated that ladybeetle abundance was significantly lower in wheat fields exposed to higher insecticide pressure, regardless of how complex or simple the landscape was, even though previous studies have suggested that a large positive contribution by non‐crop habitats in a complex landscape can provide more abundant resources and refuges for ladybeetles, and would be able to better mitigate the negative effects of insecticide use in crop fields . Although complex landscapes promoted ladybeetle occurrence in wheat fields, the negative effects of higher insecticide stress on ladybeetles, which have a high dispersal ability and can escape insecticides and recolonize wheat fields easily, were not fully offset even in the complex landscape.…”

“…Insecticide use can lower ladybeetle abundance directly due to pesticide side effects, which greatly increase ladybeetle mortality, and also indirectly through cascading effects induced by lower prey densities. However, Markó suggested that the strength of the response of arthropod abundance to insecticide use in an agricultural landscape also depends on arthropod dispersal abilities, which are much stronger for less mobile species . For highly mobile natural enemy guilds, the continuous recolonization of such mobile species from surrounding habitats after insecticide applications may be able to compensate for the mortality contributed by in‐field pesticide spray.…”

“…In our study, we used the cumulative percentage of woodlots and fallow lands to define landscape complexity rather than the proportion of the whole non‐crop area. In an agricultural landscape, not all non‐crop habitats have effects on ladybeetle abundance, and the functions of these habitats also vary over time . We used habitats (woodlots and fallow lands) that have positive effects on ladybeetle abundance to define landscape complexity in order to provide a more accurate measure of the effects of landscape complexity on ladybeetles in the studied region .…”

“…In agricultural landscapes, non‐crop habitats (especially natural and seminatural habitats) have a pivotal role in the life cycles of natural enemies, because crop habitats are typically ephemeral and highly disturbed . Non‐crop habitats enhance natural enemies by providing overwintering refuges, shelter from insecticides, and alternative or complementary food sources . A landscape dominated by non‐crop habitats is usually characterized by a higher abundance of natural enemies, and different non‐crop habitats in a landscape may serve varied functions for natural enemies at one or several times of the year .…”

“…[6][7][8] Non-crop habitats enhance natural enemies by providing overwintering refuges, shelter from insecticides, and alternative or complementary food sources. 6,[9][10][11] A landscape dominated by non-crop habitats is usually characterized by a higher abundance of natural enemies, 2,12,13 and different non-crop habitats in a landscape may serve varied functions for natural enemies at one or several times of the year. 10,11,14,15 In recent decades, natural habitats in agricultural ecosystems have been degraded worldwide, with a corresponding reduction in the biological control services provided by natural enemies, leading to the need for increased agricultural input to control pests.…”