Crop variety in agriculture has a positive impact on the natural enemies of aphids. Farmers can use this insight to keep aphids at bay and cut down on pesticides.
The greater the diversity of crops grown in agricultural landscapes is, the better natural enemies are able to control pests on wheat fields. This is because a varied landscape provides better living conditions for the aphids' natural enemies than a never-ending series of monocultures.
Measuring natural pest control (from left): a closed cage without predators, a set-up which all predators can access and a semi-open cage that allows all predators in except for birds.
Where wheat is grown on huge areas, ladybirds, spiders, hoverfly larvae and other enemies of aphids don't have enough food in spring, as the pest begins to populate the wheat fields not before May when they start to reproduce. Therefore, the enemies move on to places farther away where there is more abundant supply of food. When pest infestation occurs, the aphids thus encounter ideal conditions since their enemies are low in numbers.
The situation looks different if a variety of different crops grows around a wheat field: Since the natural enemies are around anyway, they are quick to devour the aphids. This effect is all the more pronounced the more diverse the landscape is in a 500 m radius around the field. This is what Sarah Redlich writes in the "Journal of Applied Ecology"; she is an ecologist and a PhD student of Professor Ingolf Steffan-Dewenter at the University of Würzburg in Bavaria, Germany.
18 landscapes around Würzburg investigated
For her study, the scientist picked 18 landscapes in the greater Würzburg area that exhibited a maximum crop diversity. The landscapes were six kilometres in diameter and each had a winter wheat field at its centre. "We chose fields in low-diversity landscapes and fields with high landscape-level crop diversity," Sarah Redlich explains. For this purpose, the abundance and area of up to 12 crop plant groups in the landscape were calculated, both in a small radius (up to 500 metres) and in a larger radius (3000 metres) around the fields.
She set up two cages each containing 100 aphids on each winter wheat field. The wheat in one of the cages was completely inaccessible. "This cage was designed to keep out all predators. I wanted to know how quickly the aphids reproduce in this case," Redlich says.
The other cage was coarse meshed, denying only birds access but no other enemies. "I used this set-up to determine the influence birds have on regulating the aphid population in wheat," the scientist explains.
Thirdly, she demarcated an area that was fully accessible to all predators and again put out 100 aphids there. "I let nature take its course here," Redlich explains. She then counted the aphids and their enemies at five-day intervals for around two weeks.
After this time, she compared the aphids' population development in the environments with predators to that in predator-free cages. She found that the more varied the landscape around the wheat field is, the fewer aphids thrive on the wheat plants. And what is more, birds proved to be irrelevant as natural enemies of aphids on wheat in the crop system under investigation.
Benefit for farmers
Farmers can also capitalize on this finding: "If they cultivate their fields accordingly, namely increase crop diversity, they may be able to cut down on pesticides which after all damage the natural enemies, too," the ecologist says. "The fact that the biggest impact of crop diversity was found in a radius of 500 metres around the fields adds further advantages. Often, the adjacent fields are owned by the farmers, leaving them free to decide for themselves which crops to grow there. Within the three-kilometre radius, they would have to agree with their neighbours which crops to grow, which would be more difficult but still feasible," says Redlich.
Moreover, the finding could help the farmers implement a regulation of the EU Common Agricultural Policy that has been in force since 2014. It stipulates that a greater crop diversity must be grown within the scope of "greening" efforts. This means that farmers need to cultivate "plants that are more diverse in terms of structure and food availability," says Sarah Redlich. This would require the farmers to create fields of sunflower, rapeseed, beet or similar crops around a field of winter wheat to establish a mix of plants in the landscape that sustains as many enemies of aphids or other pests as possible throughout the year.
Sarah Redlich, Emily A. Martin, Ingolf Steffan-Dewenter: Landscape-level crop diversity benefits biological pest control, Journal of Applied Ecology, DOI: 10.1111/1365-2664.13126
Sarah Redlich, Chair of Animal Ecology and Tropical Biology (Zoology III), T.: +49 931 31-82129, email@example.com
Prof. Ingolf Steffan-Dewenter, Chair of Animal Ecology and Tropical Biology (Zoology III), T.: +49 931 31-86947, firstname.lastname@example.org
Emily Martin, Chair of Animal Ecology and Tropical Biology (Zoology III), T.: +49 931 31-83876, email@example.com
Corinna Russow | Julius-Maximilians-Universität Würzburg
Nanocages in the lab and in the computer: how DNA-based dendrimers transport nanoparticles
19.10.2018 | University of Vienna
Less animal experiments on the horizon: Multi-organ chip awarded
19.10.2018 | Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS
Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.
Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...
Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles
Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...
When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.
We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...
Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...
Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...
17.10.2018 | Event News
16.10.2018 | Event News
02.10.2018 | Event News
22.10.2018 | Physics and Astronomy
19.10.2018 | Life Sciences
19.10.2018 | Physics and Astronomy