A sustainable use of functional agrobiodiversity (FAB) providing habitats with suitable floral resources is needed to conserve and improve pest control by natural enemies in organic cropping and other low-input systems. We present an overview on our activities identifying appropriate flowering plants in relation to the antagonists-pest complex and quantifying benefits and limits in lab- and field tests. We have focussed on the control of apple-aphids and cabbage lepidopterean pests in two organic cropping systems. We can show that tailoring the flowering strips to the needs of specific natural enemies within a cropping system is a key issue for successful application of FAB. We found plants as Fagopyrum esculentum, Centaurea cyanus and Vicia sativa enhancing target parasitoids in cabbage, and we found Daucus carota, Carvum carvi, Pastinca sativa, Vicia sepium as promising plants in apple orchards. A successful on-farm application of FAB using flowering strips and companion plants is challenging and needs further analyses of its impact on pest control, considering different scales as plot, farm and landscape

Luka, Henryk

Pfiffner, Lukas

Schärer, Hans-Jakob

English

Organic Eprints

FUNCTIONAL BIODIVERSITY TO IMPROVE PEST CONTROL IN ORGANIC CROPPING SYSTEMS  Lukas Pfiffner1, Hans-Jakob Schärer1 & Henryk Luka1/2 1 Research Institute of organic agriculture (FiBL), Ackerstrasse 21, Postfach 219, 5070 Frick, Switzerland, lukas.pfiffner@fibl.org; www.fibl.org  2 University of Basel, Department of Environmental Sciences, NLU-Biogeography  Abstract: A sustainable use of functional agrobiodiversity  (FAB) providing habitats with suitable floral resources is needed to conserve and improve pest control by natural enemies in organic cropping and other low-input systems. We present an overview on our activities identifying appropriate flowering plants in relation to the antagonists-pest complex and quantifying benefits and limits in lab- and field tests. We have focussed on the control of apple-aphids and cabbage lepidopterean pests in two organic cropping systems. We can show that tailoring the flowering strips to the needs of specific natural enemies within a cropping system is a key issue for successful application of FAB. We found plants as Fagopyrum esculentum, Centaurea cyanus and Vicia sativa enhancing target parasitoids in cabbage, and we found Daucus carota, Carvum carvi, Pastinca sativa,  Vicia  sepium  as  promising  plants  in  apple  orchards.  A  successful  on-farm application  of FAB  using flowering strips and companion plants  is  challenging and needs further analyses of its impact on pest control, considering different scales as plot, farm and landscape.  Key words: functional agrobiodiversity, habitat management, natural enemies, pest control, flowering strips, companion plant, apple, aphids, cabbage, lepidopterea.  Introduction  There is a growing concern that declining biodiversity caused by intensive agriculture affects ecosystem services. Due to landscape fragmentation and loss of suitable habitats natural enemies have been reduced in species diversity and abundance. In consequence this leads to a substantial loss of biocontrol function. Therefore a sustainable use of FAB, providing habitats with suitable floral resources to conserve these functions, is needed (Bianchi et al. 2013). Herbivore populations are regulated by bottom-up control through  food  availability  and  quality  and  by  top-down  control  by  natural  enemies. Land-use dominated by monocultures provides abundant food to specialized herbivores and simultanously has a negativ impact on natural enemies because lacking in adequate food sources (Balmer et al. 2013). We have found insufficient effects of ‘unspecific’ flowering strips, which were based on officially recommended plant mixtures, targeting to increase the overall biodiversity (Pfiffner et al. 2009). Therefore we have tailored the strips in relation to the requirements of the specific complex of natural enemies within a cropping system.   Here we focus on flowering plants as one promising approach to boost pest control within a four-step pest-control strategy (Zehnder et al. 2007). We present an overview on the activities in which we analysed this targeted approach in two cropping systems. The overall objective was (i) to identify appropriate plants in relation to the antagonist-pest complex, (ii) to quantify the benefits and assess the limits under field conditions.      Archived at http://orgprints.org/25470/   Material and methods  We  have  focused  our  activities  on  two  model  crops  as  apple  with  multi-annual flowering strips and cabbage cropping system using annual strips and companion plant. Apple and cabbage  were selected since perennial and annual  crops differ greatly in biology and management and are highly productive and economically relevant.  The use of flowering strips was tested in organic apple and cabbage cropping systems on different farms in low-land of Switzerland (fig. 1). First, based on literature data, we conducted lab-trials to identify selective plant species that would improve the longevity and fecundity of natural enemies (parasitoids, predators) without benefiting the pests and are attractive to natural enemies (olfactory tests). Effects of floral and extra-floral nectar of the plants were analysed in the cabbage crop. Afterwards we investigated the impact of the flowering strips under field conditions, focussing on the control of aphids in apple and lepidopteran pests (Mamestra brassicae (Noctuidae) in cabbage. Weekly visual  observations,  monthly  beating-tray  samples  and  branch  samples  in  winter  on randomly chosen trees were performed to analyse the impact in a low-tree orchard with and without flowering plants. To better understand the plant-parasitoid interaction, we have studied the olfactory attractiveness of five wildflowers (Ammi majus, C. cyanus, F. esculentum, Iberis amara and Origanum vulgare) to Microplitis mediator (Braconidae), a larval parasitoid of the cabbage moth M. brassicae. We conducted choice experiments in a Y-tube olfactometer to test the attractiveness of flowers against air and the relative attractiveness in paired choice tests.  Results and discussion  The most relevant pest species of cabbage in central Europe is M. brassicae. Its primary larval  parasitoid  is  M.  mediator  and  the  main  egg-parasitoids  are  Trichogramma brassicae, T. evanescens (Trichogrammatidae) and Telenomus sp.(Scelionidae).   Beneficial  effects  of  F.  esculentum  (floral  nectar),  C.  cyanus  (floral  and  extrafloral nectar) and non-flowering V. sativa (extrafloral nectar) on parasitoids M. mediator have been found in lab-tests (Geneau et al. 2012). Longevity and fecundity of the pest (M. brassicae) were not increased by the plant species tested. Longevity of M. mediator as well as parasitism rates of M. mediator were significantly increased by the presence of F. esculentum, C. cyanus and non-flowering V. sativa (EFN only). The key parasitoid M.  mediator  parasitized  202.3±29.7  M.  brassicae  larvae  during  its  lifetime  when presented F.esculentum, compared to 14.4±3.4 larvae in the absence of floral resources (Geneau et al. 2012).   The olfactory test of plant attractiveness showed that C. cyanus and I. amara were greatly attractive to the target parasitoid M. mediator. This has shown innate preferences that can be effectively exploited in biological control (Belz et al. 2013).  Our  field  trials  showed  that  the  application  cornflowers  as  companion  non-crop flowering  plant  within  the  crop  can  significantly  increase  parasitism  by  larval parasitoids.  Additionally,  higher  parasitism  and  predation  of  herbivore  eggs  finally reducing crop damage and may increase yield (Balmer et al. 2013). Companion plant presence lead to a significant increase in parasitation of M. brassicae by M. mediator and  had  a  significant  positive  effect  on  cabbage  head  weight  and  the  number  of damaged leaves was also significantly lower in plots with companion plants (Balmer et al. submitted). Furthermore, we found higher abundance and species richness of spiders and carabids in flowering strips compared to adjacent cabbage fields (Dittner et al. 2013). Intersown cornflowers had a positive effect on spider and carabid abundance. Other predators such as syrphids, chrysopids and coccinellids were also detected on these flowering plants. The  species  richness  of  spiders  and  carabids  was  only  weakly  affected  by  this companion plant.  Tab. 1: Impact of FAB using flowering strips on a key-pest and their natural enemies and pest-control function in a cabbage and apple cropping system (refs.1, 2, 4, 5, 8, 9).    lab-test     field test                Increased (parasitoids)   Reduced  Increased   enhanced density of    fecundity   longevity  pest density  parasitism  predation predators parasitoids M. brassicae  +  +  +  + + (larvae)  +   +   o in cabbage1)           +  (egg)          D. plantaginea  o  o  +  -   + +  + +   -  A. pomi  o  o  +  -   +   + +   -  in apple 2)                      Legend: + +: high impact, +: moderate impact, o: not investigated, -: not found Useful plants in 1) F. esculentum, C. cyanus, V. sativa 2) D. carota, C. carvi, C. sepium, L. corniculatus, M. sativa  Apple  orchards  are  in  general  characterised  by  simplified  plant  and  animal communities.  The  soil  below  the  trees  is  often  kept  bare  and  has  a  uniform  flora dominated by grass which is mulched regularly. Using flowering strips in organic apple orchards we found a positive impact in controlling apple key pests (Wyss et al. 2005). The higher numbers of all relevant predator groups (Coccinellids, Chrysopids, Syrphids, Cecidomyiids, Bugs, Spiders, Staphylinids) leads to a better pest control in the plots with  flowering  plants  compared  to  the  control  plots  without  (Wyss  1995).  These predators were able to keep the aphids (Dysaphis plantaginea, Aphis pomi) under the commercially  threshold  In  autumn,  spiders  (i.a.  Araniella  sp.)  were  the  dominant predators of aphids and they were significantly more reduced in the area with flowering strips  compared  to  areas  without  flower  strips.  This  was  mainly  due  to  higher abundance of spiders and more spider webs (Wyss et al. 1995).   Conclusions  An accurate plant screening is essential to achieve plant selectivity and to maximize biological  control.  In  cabbage crop,  F.  esculentum, C. cyanus  and V. sativa  can be recommended as selective plant species to enhance target parasitoids. In orchards it is challenging  to  establish  a  perennial  flower  strip.  Plants  of  the  family  of  Apiaceae (Daucus  carota,  Carvum  carvi,  Pastinca  sativa)  and  others  (Vicia  sepium,  Lotus corniculatus, Medicago sativa) are promising plants.  For a successful practice, the composition of the agro-biodiversity elements needs to be adapted to  the crop, pest  complex, pedo-climatic conditions,  as  well as  to  the farm structure  and  the  farmer.  Suitable  tailored  flowering  plants  can  also  improve  the efficacy of commercially available biocontrol agents. The pest-damage reduction has to be  substantial  within  the  pest-control  strategy  and  the  management  needs  to  be practically and economically feasible.   The  implementation  of  FAB  to  effectively  control  pests  in  the  practice  of  farming systems is a challenge and we are still at the beginning of the development of eco-intensification. We want to find the optimal use of specific biodiversity elements and further  research  is  therefore  needed  to  appropriately  combine  indirect-  preventive measures and direct intervention strategies which are effective in controlling pests and finally pay off for farmers and the environment.  Acknowledgements   We thank E. Belz, C. Géneau, PhD-workers within this project. C. Daniel, O. Balmer and E. Wyss for general support and fruitful discussions. The project was funded by Bundesamt für Umwelt  (BAFU)  and  foundations  as  Bristol, Ernst  Göhner, Parrotia, Werner  Steiger,  Singenberg,  Schöni  Swissfresh  AG,  Stiftung  zur  internationalen Erhaltung der Pflanzenvielfalt, SWO, Gamil and Bank Vontobel.  References 1. Balmer,  O.,  Pfiffner,  L.,  Schied,  J.,  Willareth,  M.,  Leimgruber,  A.,  Luka,  H.  & Traugott, M. (2013): Noncrop flowering plants restore top-down herbivore control in agricultural fields. Ecol and Evol 3(8): 2634-2646. 2. Balmer, O., Géneau, C. E., Belz, E., Weishaupt, B., Förderer, G., Moos, S., Ditner, N., Juric, I. & Luka, H. (submitted): Companion plants increase pest parasitism and yield in cabbage fields: experimental demonstration and call for caution.  3. Bianchi, F.J.J.A., Mikos, C., Brussaard, L., Delbaere, B., Pulleman, M.M. (2013) Opportunities  and  limitations  for  functional  agrobiodiversity  in  the  European context. Review. Environ Sci & Pol 223 – 231. 4. Belz, E., Kolliker, M. & Balmer, O. (2013): Olfactory attractiveness of flowering plants to the parasitoid Microplitis mediator: potential implications for biological control. BioControl 58: 163–173. 5. Géneau, C. E., Wäckers, F. L., Luka, H., Daniel, C. & Balmer, O. (2012). Selective flowers to enhance biological control of cabbage pests by parasitoids. Basic and Appl Ecol 13 (2012) 85–93. 6. Pfiffner L, Wyss E (2004) Use of sown wildflower strips to enhance natural enemies of agricultural pests; Gurr GM, Wratten SD, Altieri MA, editors. Collingwood VIC, Australia: CSIRO Publishing. 165-186 p. 7. Pfiffner,  L.,  H.  Luka,  C.  Schlatter,  A.  Juen,  and  M.  Traugott  (2009):  Impact  of wildflower  strips  on  biological  control  of  cabbage  lepidopterans.  Agri  Ecosys  & Environ 129: 310-314. 8. Wyss E, Luka H, Pfiffner L, Schlatter C, Uehlinger G, et al. (2005) Approaches to pest management in organic agriculture: a case study in European apple orchards. CABI Publishing, pp. 33-36. 9. Wyss E (1995) The effects of weed strips on aphids and aphidophagous predators in an apple orchard. Entomol Exp Appl 75: 43-49. 10.  Wyss, E., Niggli, U. and Nentwig,W. (1995). The impact of spiders on aphid populations in a strip managed apple orchard. Appl Entomol 119: 473–478. 11.  Zehnder  G,  Gurr  GM,  Kühne  S,  Wade  MR,  Wratten  SD,  Wyss,  E.  (2007) Arthropod Pest Management in Organic Crops. Ann Rev Entomo 52: 57-80. Fig. 1 Annual flower strips in organic cabbage crop in Switzerland to boost natural enemies.        

(submitted): Companion plants increase pest parasitism and yield in cabbage fields: experimental demonstration and call for caution.

Approaches to pest management in organic agriculture: a case study in European apple orchards.

Arthropod Pest Management in Organic Crops.

Impact of wildflower strips on biological control of cabbage lepidopterans.

Noncrop flowering plants restore top-down herbivore control in agricultural fields.

Olfactory attractiveness of flowering plants to the parasitoid Microplitis mediator: potential implications for biological control.

Opportunities and limitations for functional agrobiodiversity in the European context.

Selective flowers to enhance biological control of cabbage pests by parasitoids.

The effects of weed strips on aphids and aphidophagous predators in an apple orchard.

The impact of spiders on aphid populations in a strip managed apple orchard.

Use of sown wildflower strips to enhance natural enemies of agricultural pests;

Functional biodiversity to improve pest control in organic cropping systems

Functional biodiversity to improve pest control in organic cropping systems

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