Sown Wildflower Strips Research Articles

Structural heterogeneity of wildflower strips enhances fructose feeding in parasitoids

The use of wildflower strips to provide carbohydrate resource for parasitoids and enhance pest regulation is widely recommended in agriculture. However, how the management of wildflower strips affects resource availability and utilisation by parasitoids has never been studied. Using orange orchards as a model system, three experimental alleyway management treatments were investigated: a control treatment where naturally occurring vegetation in the alleyways between rows of trees was managed under standard farm practice; a standard management wildflower treatment in which sown wildflower strips in alleyways were managed by cutting once a year; and an active management wildflower treatment, in which the wildflower strips in alleyways was managed by cutting three times a year. Wildflower strips under standard management prevented the seasonal decline of nectar, supporting fructose feeding in parasitoids across all three seasons. The abundance of floral and hemipteran honeydew carbohydrate resources in the orchard alleyways and citrus canopy was consistently greater with the standard management treatment than the control or the active management treatments. In turn, this treatment was associated with twice the abundance of primary parasitoids than with the control and active management treatments in both summer and autumn. In addition, in autumn, parasitoids were more likely to have recently fed on carbohydrate in the standard management treatment than in the other two alleyway treatments. Finally, greater carbohydrate feeding in parasitoids was associated with increased structural heterogeneity of vegetation within the orchard alleyways. This study demonstrates that the nutritional status of parasitoids in a perennial cropping system can be improved using wildflower strips, which could enhance pest regulation, and emphasises the importance of studying the management of wildflower strips when targeting specific resource requirements.

Sown wildflower strips as overwintering habitat for arthropods: Effective measure or ecological trap?

Wildflower strips (WFS) are increasingly commonly adopted measures to promote biodiversity in agro-ecosystems. While their effectiveness in providing floral and other food resources for pollinators and natural enemies has been relatively well studied, much less is known about the value of different types of WFS as overwintering habitat for different functional arthropod groups. Here, we examined arthropod overwintering in WFS of different age compared to winter wheat fields. Moreover, we addressed the largely unexplored question to what extent non-permanent WFS may act as sink or ecological trap, if they attract high numbers of overwintering arthropods but only a low proportion of them survive and successfully emerge due to ploughing of strips during overwintering.Overwintering of all studied arthropod groups including potential pest natural enemies spiders, carabid beetles, staphylinid beetles and different families of pollinating flies was higher in WFS compared to winter wheat crops. Overwintering increased in WFS compared to wheat fields irrespective of WFS age, except for 4 year old WFS in the case of carabid beetles and 1 year old WFS in the case of spiders. While WFS age positively affected spider overwintering, numbers of overwintering pollinating flies and staphylinid beetles did not change significantly with WFS age. Moreover, carabid beetles tended to decline in the four years old WFS compared to younger ones. Ploughing of annual WFS during overwintering significantly reduced the number of successfully emerging arthropods by 59% on average. Detrimental effects were strongest for carabid beetles and spiders (reductions by 67% and 69%, respectively) to their numbers in ploughed WFS being similar to winter wheat fields. Reductions were less severe for pollinating flies and staphylinid beetles (both 47%), with higher numbers emerging from annual WFS compared to winter wheat fields even after ploughing of WFS.We conclude that perennial WFS are valuable overwintering habitats for a range of arthropod taxa across functional groups in arable cropping systems. Distinct responses of different arthropod taxa to WFS age highlight the importance of managing perennial WFS of various successional stages in order to promote overwintering of a broad variety arthropods in agro-ecosystems. Our study raises concerns, however, that annual WFS ploughed during the overwintering period are poor overwintering habitats for arthropods and may even act as ecological traps.

Landscape greening and local creation of wildflower strips and hedgerows promote multiple ecosystem services

Abstract The explicit and implicit aims of creating ecological focus areas (EFAs) and implementing greening measures in European agro‐ecosystems include the promotion of regulatory ecosystem services (ES) to sustain crop production in conventional cropping systems. However, the extent to which these goals are achieved with current policy measures remains poorly explored. We measured insect‐mediated pollination and natural pest control service provisioning in 18 winter oilseed rape fields as a function of the independent and interactive effects of local EFA establishment─sown wildflower strips and hedgerows─and landscape‐scale greening measures within a 1 km radius around focal fields and quantified their contribution to crop yield. Insect pollination potential and pest predation increased on average by 10% and 13%, respectively, when landscape‐scale greening measures share was increased from 6% to 26%. For pollination, the increase was stronger in fields adjoining an EFA (14%) than in fields without adjacent EFA (7%). Agricultural management practices were the main drivers of crop yield. Neither insect pollination potential or natural pest control (pest predation and parasitism) nor adjacent EFAs and landscape‐scale greening significantly affected crop yield in addition to agricultural management. Synthesis and applications. Local establishment of perennial, species‐rich wildflower strips and hedgerows, combined with landscape‐scale greening measures in agricultural landscapes, can promote multiple ecosystem services (ES) in conventional production systems. Benefits may be maximized when local and landscape measures are combined. However, enhanced pollination and natural pest regulation seem to contribute relatively little to final crop yield compared to local agricultural management practices in the high‐input conventional production system studied. Further research is needed to better understand how to improve the effectiveness of ecological focus areas and other greening measures in promoting regulatory ES. Potential improvements include minimising trade‐offs while promoting synergies between ES provision, food production and biodiversity conservation.

Different response of two Hemiptera species groups to sown wildflower strips: True bugs and leafhoppers

Sown wildflower strips should promote the species diversity of several insect groups in order to be an effective tool for the compensation of biodiversity loss in agricultural environments. We studied the responses of two herbivorous insect groups, Heteroptera (true bugs) and Auchenorrhyncha (leafhoppers), to the properties of wildflower strips in a three-year (2008–2010) study in southern Finland. The experiment was replicated in six reed canary grass fields. The insect groups showed opposite responses; the abundance of Auchenorrhyncha was lower while the abundance and species richness of Heteroptera was higher in wildflower than control strips. During succession, both species richness and abundance of Auchenorrhyncha increased unlike Heteroptera. This difference could largely be explained by dietary differences. Auchenorrhyncha, including several grass feeders, could not take advantage of the increasing dicot species richness like Heteroptera species. This was also a likely reason for the unexpected finding that only Heteroptera species richness depended on the placement of the strip, being higher near field margins than in mid-field. We conclude that the optimal planning and implementation of wildflower strips call for the definition of clear goals, the knowledge of the requirements of target species as well as considering the cropping system involved.

Can pollination services, species diversity and conservation be simultaneously promoted by sown wildflower strips on farmland?

Sown wildflower strips have been used to mitigate against the loss of farmland biodiversity e.g. as a part of agri-environmental schemes. In this four-year field experiment, conducted on six field parcels, the ability of wildflower strips to simultaneously promote the availability of pollination services (using bumblebee abundance as a proxy), species diversity (total species richness of bumblebees, butterflies and diurnal moths) and conservation (abundance of habitat specialist butterflies) was evaluated. The results showed that the first two indicators increased strongly and rapidly in wildflower strips until the third year of the experiment. The conservation indicator increased more slowly and this response was related to the forest cover of the surrounding landscape. Furthermore, the benefits of wildflower strips were largely independent of experimentally varied strip properties. It is concluded that wildflower strips are a flexible mitigation tool to promote different biodiversity targets in agricultural systems. Pollination services and species diversity can be promoted in different kinds of landscapes by ensuring local habitat quality. In the promotion of habitat specialists, landscape matrix quality is more critical.

Butterflies and bumblebees in greenways and sown wildflower strips in southern Sweden

Greenways have recently been established in some intensively farmed areas of South Sweden in order to enhance recreation opportunities and biodiversity, but the effects of these green structures on biodiversity have not yet been determined. In this study, greenways and experimental sown wildflower strips were investigated for butterfly and bumblebee diversity. In total, 1,769 butterflies of 18 species and 1,216 foraging bumblebees of eight species were recorded. Sown wildflower strips proved to support much higher abundances and species numbers of butterflies and bumblebees than greenways, with 86% of all butterflies and 83% of all bumblebees being observed in the sown flower strips. However, in both types of green structure mostly common species were found. Counts of flower visits showed that Knautia, Centaurea and Cirsium were the most commonly visited plant species. The greenways studied did not seem to fulfil their function of enhancing biodiversity—at least not for butterflies and bumblebees. However, these greenways could easily be improved for common bumblebee and butterfly species by sowing wildflower strips along their margins.

Dispersal and persistence of mass released Trichogramma brassicae (Hymenoptera: Trichogrammatidae) in non-target habitats

Field studies were carried out to evaluate whether inundative releases of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) against the European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), can have negative effects on the indigenous arthropod fauna in adjacent non-target habitats. Emigration of released T. brassicae from maize fields into non-target habitats was monitored, and its persistence in non-target habitats was assessed throughout the season. For this purpose, sticky traps were installed on metal sticks along transects from the inside of T. brassicae treated maize fields into sown wildflower strips and a natural common reed stand. In addition, cards with host eggs were used to monitor Trichogramma within potential overwintering sites. Although the highest numbers of released parasitoids were trapped within maize, a considerable amount of T. brassicae moved into non-target habitats. We found a significant transient increase of T. brassicae in both wildflower strips and reeds and no consistent decrease in numbers of trapped wasps up to 40 m from the maize field borders, when monitored directly following mass releases. Indigenous Trichogramma species were present both in the wildflower strip and reeds, and T. brassicae represented only a minor part of the overall Trichogramma population therein, except for a few days after release. However, a few T. brassicae persisted in non-target habitats throughout the season and were still present prior to releases in the subsequent year. These low numbers are not expected to seriously affect populations of native Trichogramma or non-target host species.

The role of different slug species in damage to oilseed rape bordering on sown wildflower strips

Summary.Damage caused by different slug species on above and below ground parts of young oilseed rape bordering on sown wildfower strips was studied. Slug densities and damage were recorded in the field and damage rates for each slug species were measured in the laboratory. Severe slug damage was observed in rape areas 1 m from the wildflower strips. Damage rates of slug species feeding above ground were distinctly higher than those feeding below ground. The estimated damage caused by above‐ground feeding in all four study fields ranged between 72% and 89 % and was always distinctly higher than damage caused by below‐ground feeding (11% to 28 %). The estimated damage caused by Arion lusitanicus above ground was between 54% and 69 %, followed by Deroceras reticulatum (3% to 26 %). Thus A. lusitanicus was responsible for the majority of damage in the rape crops studied.

Slug damage and numbers of the slug pests, Arion lusitanicus and Deroceras reticulatum, in oilseed rape grown beside sown wildflower strips

In 1994 and 1995, slug damage and numbers of the most abundant slugs, Arion lusitanicus and Deroceras reticulatum, were estimated in sown wildflower strips and adjacent rape fields. Slug damage was estimated using an index of defoliation, and slug numbers were measured using bait traps that did not kill the slugs. Investigations began as soon as rape seedlings appeared above ground and lasted for five weeks. In both years, slug damage to rape plants 1 m from the wildflower strips was significantly higher than at greater distances from the strips. Within a distance up to 2 m from the wildflower strips, complete crop losses occurred. In field areas where metaldehyde pellets were used, slug damage was distinctly lower and in these areas complete crop losses near the wildflower strips never occurred. In both years, A. lusitanicus appeared to be responsible for the main damage near the wildflower strips because it was very abundant in the wildflower strips and at 1 m into the crop but was scarcely observed at greater distances from the strips. Results showed that the numbers of the most abundant slug species were related to the amount of slug damage and that severe damage close to the wildflower strips could be prevented by broadcasting a recommended dose of 5% metaldehyde pellets at 8 kg/ha.