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Understanding beneficial insect behaviour

Commercial scale on-farm trials at AHDB Cereals and Oilseed’s Strategic Farms results days gave growers a taste of new approaches to cutting costs and boosting yields that they can try on their own farm businesses.

Variations in species diversity and abundance of pests and beneficials from field to field can make management practices challenging, but by getting to know how different species interact and behave, pest pressure can be reduced.


This is according to Mark Ramsden, entomologist at ADAS, who speaking at the Strategic Farm East results day said: “A lack of pest thresholds, or faith in existing thresholds has made control of pests harder, leading to dependence on pesticides to avert risk. However, this trend is changing.”

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Regardless of whether the threshold is known or not, growers should aim to reduce pest pressure in the first place, by focusing on mortality rates to decrease population growth rates.


He said: “We don’t necessarily need to shrink the population growth rate, but just make sure they’re growing at a rate that isn’t going to get to a damaging level.”


For example, hoverfly larvae - legless maggots found on the leaf of cereals - will consume hundreds of aphids from hatching to pupation, he said.


“However, the important thing to remember for hoverflies is the adults don’t eat aphids at all. They need completely different resources to the larvae, which are quite happy in the crop if aphids are there. The adults need floral resources like nectar and pollen.


"On the whole, farming landscapes are not great at providing those extra resources, not just for hoverflies but for beneficials that require that nectar and pollen to complete their life cycle.”




Adult hoverflies are capable of moving kilometres between crops, but this depends on how pollen and nectar resources are distributed across the farm, he said.


“When you go into a crop, you get a drop-off of natural enemies the further you move away from field margins, but that is very dependent overall on what resources are spread around.


“If you’ve got a simple landscape with not much resource around the crop, and you add in one floral margin, you get an attractant scenario where natural enemies do very well next to those resources but they’ve got nowhere else to go so they tend to stick around there.”

This is likely to result in a big drop off of beneficial numbers in the crop because they will not move away from available resources.



“Conversely if you’ve got a landscape with loads of resources, they’re so attracted to those areas they don’t go into the crop as much for additional food supply. We’re trying to get a balance of resources across the landscape so they’re moving around and getting into the crop. They are looking for colonies of aphids to lay their eggs next to. This also tends to be the case for ladybirds.”


Parasitic wasps – thought to feast on CSFB - tend to move much more with the aphids because they do not migrate, but they will not necessarily move from field to field, he added.


“Again, they’re looking for their prey. Its very related to the individual natural enemy and there’s no single strategy that will work for everything which is why it is so challenging.”


Pests and natural enemies will be explored further at the Strategic Farm West in 2020.

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