The problem

Controlling insect pests on crops is essential if we are to increase our food

provision for a population predicted to reach 9 billion people by 2050.

Crop pests are traditionally controlled using insecticides. However, loss of

control due to the emergence of resistance to key insecticides, along with fears

over their impact on farmland biodiversity, means we must seek alternative

control strategies.

It is therefore imperative that we develop a range of techniques to control

insect pests that are compatible with other innovations to increase yield and

that are beneficial to farmland biodiversity.

Science-led solutions:

Integrated Pest Management (IPM)

IPM involves applying an understanding of the insect’s life cycle, its interactions

with its host plant and its natural enemies, to create conditions where the pest

is unable to thrive and/or cause economic damage. IPM programmes are

based on the use of preventative methods, monitoring of pest

numbers/damage and guidelines for thresholds when control action is needed.

Biological control. Controlling pests using their natural enemies — predators,

parasites & pathogens. Conservation biocontrol encourages populations of our native

natural ememies through careful landscape management.

Cultural, Mechanical and Physical controls. Reducing pest

establishment, reproduction and survival using methods such as crop rotation, trap

crops, intercropping, trapping and exclusion barriers.

Semiochemical control. Using airborne chemicals naturally derived from

plants or insects to influence the behavior of the pest and/or its natural enemies.

Examples include pheromones used in traps, repellents and antifeedants.

Chemical control. Spraying synthetic insecticides in IPM occurs only when

needed and in combination with other approaches for more effective, long-term control

which minimizes their possible harm to people and the environment.

Optimizing field margins for biodiversity and

conservation biological control

Petals vs Pests: the use of petal colour and

scent in IPM strategies

IPM pest control methods:

The importance of IPM in the crop protection armoury has never been

greater. At Rothamsted Research we are optimising IPM strategies to

ensure sustainable protection against the major pests of arable crops.

Our results can often be applied to horticultural and garden situations.

Pollen beetles (Meligethes aeneus) are major pests of oilseed rape (OSR)

(Brassica napus) crops which are grown for cooking oil and as biofuel. Insecticides

are applied to control pollen beetles but over-use has led to resistance and

alternative control strategies are required.

Controlling by colour

The attraction of pollen beetles to the yellow petals of OSR can be exploited in

trap cropping strategies in which pollen beetles are attracted to small areas of

early-flowering turnip rape (Brassica rapa) planted around the edge of a later-

flowering OSR crop. Pest infestation and the need for insecticides are therefore

reduced in the OSR crop.

What if the flowering OSR crop wasn't yellow? We explored the possibility of

reducing infestation of OSR by pests by making it less attractive by changing the

petal colour. Using an experimental line of OSR with white petals, we dyed the

petals red, blue and yellow using food colouring which was taken up by the roots

of potted plants. Pollen beetle infestation was greater on plants with yellow and

white flowers while blue and red flowers were least preferred.

Do pollen beetles have a sense of smell? We measured the response of

beetles' antennae to different components of the floral scent released by OSR and

determined that a compound (phenylacetaldehyde), released from the petals, is

particularly attractive and important for locating host plants.

This knowledge helped to explain why some brassica plants such as turnip rape

are more attractive to pollen beetles than others when developing trap crops.

We used this scent to bait a monitoring trap which enables farmers to easily

assess the numbers of pollen beetles in the crop and inform their management

decisions; helping to save unnecessary insecticide sprays.

Scent from non-host plants can be used to repel or mask the attractive scent of

host plants. We found that the essential oil from lavender flowers (Lavendula

anguistifolium) is highly repellent to pollen beetles and was particularly successful

in reducing pollen beetle numbers when used in conjunction with a trap crop.

Field margins are commonly found at the edge of crops, planted by farmers

as part of Government agri-environment schemes. They range from simple

grassy borders to strips of wild flowers containing dozens of plant species.

Aside from adding beauty to an otherwise functional environment, field

margins also provide resources that can enhance farmland biodiversity.

These include pollen and nectar for invertebrates and winter food for

farmland birds.

Field margin mixes that contain flowering plants provide significantly more

resources than simple grassy borders and therefore support greater

biodiversity. While margin mixes have been designed to provide resources

for birds and pollinators, they are also capable of supporting natural

enemies of crop pests such as ladybirds, parasitic wasps, ground beetles

and spiders. These species can perform important biological control

services. We therefore believe that field margins are an essential

component of IPM schemes.

However, most current margin mixtures do not contain the variety of plant

species required to support the diversity of natural enemies required to

control pests on all crop types. For example, brassica plants are needed in

margin mixes to support the specialist natural enemies of OSR pests. Our

mixtures therefore contain cereal, brassica and legume species to support

high numbers of natural enemies of all crops types. We are assessing

which margin mixes are utilised by most natural enemies, designing mixes

that flower for longer periods of the season and comparing the relative

benefits of perennial and biennial wildflower margin mixes.

Petals & PestsPetals & Pests

Flower-powered IPM: Understanding and

applying the attraction of flowers to insects

To facilitate pollination, flowers produce brightly coloured petals, sweet-

smelling scents and food resources in the form of pollen and nectar to attract

and reward insect pollinators. These include bees and butterflies.

However, some insects that visit flowers may cause more damage than good to

the plant and are classed as pests. Examples include the pollen beetle, which

feeds on the pollen of brassica plants and lays its eggs inside developing flower

buds resulting in reductions in seed yield, and aphids which infest the stems

and leaves of flowers and cause damage through feeding and virus

transmission.

In contrast, some insects provide a useful role in controlling pests and are

classed as natural enemies. For example, predatory insects such as ladybirds

visit flowering plants to feed on pest insects while lacewings and hoverflies use

the pollen and nectar from flowers as food and the plants themselves as egg-

laying sites.

At Rothamsted Research we are gaining an understanding of insect attraction

to flowers and their role in providing resources for natural enemies and

applying it to develop novel and effective IPM strategies.

Petals & PestsPetals & Pests

RESEARCHROTHAMSTED

®

RESEARCHROTHAMSTED

®

Using flowers

to minimise insecticide use

and

enhance biodiversity

Rothamsted Researchwhere knowledge grows

Rothamsted has been providing the world with

independent, cutting edge research for over 170 years.

We continue to develop innovations that benefit our

health, agriculture and the environment.

Rothamsted Research

West Common, Harpenden, Herts. AL5 2JQ

Telephone: +44 (0)1582 763133

Further information

Scientific lead at Rothamsted, Dr Sam Cook,

Department of AgroEcology

www.rothamsted.ac.uk/field-margins

http://www.rothamsted.ac.uk/science-stories

Petals & PestsPetals & Pests