Animal Pests in Arable Crops

1

Animal pests in arable crops – biology and control

AgroEcosystem Analysis and Management at Farm Scale

2013

Annie Enkegaard, AU

Annie EnkegaardAarhus University, Science & Technology,

Department of Agroecology, Research Centre Flakkebjerg

This lecture

• Pest biology

• Preventive methods

• Exercise

• Behaviour modifying methods

• Biological control

• Chemical control

• Integrating methods

• Exercise

2

What is an animal pest?

• An animal which has characteristics

which people regard as injurious or

harmful - damages to crop, domestic

animals, our houses, ourselves …

• = defined from a human point of view

3

• Ideal conditions for pests

• Monocultures

• Large areas of food

• Improved plant quality

• Very homogeneous

• Low diversity

• few competitors

• few natural enemies

Pests in agricultural crops

4

Groups of animal pests

5

• Vertebrates

• Nematodes

• Slugs, snails

• This lecture:

insect and mites = arthropods

Types of damage

• Direct damage

• leaves, flowers, fruits, roots

• Indirect damage

• honey dew – sooty mould

• wounding – diseases

• virus vectoring

6

2

Consequences

• Consequences

• direct yield losses

• cosmetic damages = reduced crop quality

Soybean aphid

7

Pest biology

8

• What we need to know to evaluate

• Pest potential

• How to prevent or control

Life cycle, niches of stages

9

large larva

eggssmall larvae

overwintering pupa

Large white butterfly

adult

Life cycle, niches of stages

28

large larva

eggssmall larvae

overwintering pupa

Large white butterfly

adult

egg on the groundWine weevil

pupa in soillarvae in soil

larvae in soil

adult

overwintering

Feeding type

11

• Monophagous – 1-few plant species

• Polyphagous – many plant species

• Oligophagous – in between (e.g. one plant family)

Strawberry tortrix

Western flower thrips

Cabbage root fly 12

Population increase

upper ºC thresholdlower ºC threshold

Biological activity, e.g. development

Biological activity, e.g. development

• What is the potential for population increase?

• fertility, mortality, generations per year

• Influence of abiotic factors

• temperature, humidity, soil moisture etc.

• lower and upper thresholds; optimum

Low Medium High ºC

optimal ºC

near lethal ºC

suboptimal ºC

temperature

3

Overwintering, spread

• Spread

• by itself, passively (wind, water, soil, humans,

tools, international plant trade)

• how far?

• Overwintering / survival of dry / hot season

• which stage, where (in or outside field)

• Host plant shift during the season …

13 14

Host plant shift - aphids

Winged females

Wingless females need mating

Winged males

Migrationspring

Egg stage

Summer hosts –cereals, maize, grasses

Winged females

Several wingless generations Local

dispersal to other plants

Winged females

Migration, fall

Several wingless generations

Wingless stem mother

1-3 wingless generations

SUMMER

bird cherry trees

WINTERBird-cherry-oat aphid


15


Migrationspring

Egg stage

Migration, fall




WINTER

Winged females



SUMMER

cereals, grasses

bird cherry trees

Winged females

Bird-cherry-oat aphid


16


Migrationspring

Egg stage

Migration, fall




WINTER

Winged females



SUMMER

cereals, grasses

bird cherry trees

Winged femalesWinged

females

Winged males

Bird-cherry-oat aphid

• Wild and cultivated cabbage species

• rather monophagous (= the cabbage family)

17

Example: Cabbage root fly

• Adult flies emerges in spring; adult live in hedges; fly back

and forth to fields; egg-laying at stem base

• Bi (tri) voltine – 2-3 generations/year

• Good fliers - local migration to and from fields to hedges +

more distant migration (1-2 km) to seek other fields

eggs at based of stem

larvae

adult

Overwinter in soil

pupa

2-3 generations / year

egg to pupa 4-5 weeks

18

Cabbage root fly

4

• Damage:

• Larval feeding inhibits uptake of water and nutrients;

• growth slowed, wiltering and death

• on cabbage heads – fungal infections become possible

=> extensive yield losses

19

Cabbage root fly

slower development – 2 generations

higher mortality – smaller population sizes

fast development – 3 generations

low mortality – large population sizes

20

• Fecundity important (150 eggs/female)

• Development time and juvenile mortality important

• the faster development the larger the risk for 3 generations

• the lower mortality the larger the size for following generations

• Winter mortality important

Cabbage root fly

Pest management

21

Management of pests in arable crops

• Traditionally – pest destruction

Insecticides

Exploit natural enemies

Prevention

4.

3. 2.1.

22

Management of pests in arable crops

• A more solid and intelligent approach – not pest

destruction but pest management

Insecticides (in organic production: only some; only at imminent danger)

Release natural enemies

Conservation biocontrol

Trap plants, intercropping, cover crops

Resistant varieties

Planting / harvesting time

Tillage, watering, limit access

Rotation, sanitation

4.

3.

2.

1.

23 24

Two types of methods in plant protection

• Prevention

• Cultural and physical methods

• Behavioural methods

• Biological methods

• … to limit access to crop, reduce pest survival

• Direct control when needed

• Biological and chemical methods

5

Physical and cultural preventive methods

25

Rotation

• Growth of different crops in sequence

• instead of growing the same crop in the same

field from year to year

• Each crop has it specific pest complex

• Changing between crops attempts to ensure

that the pest complex of Year1-crop can not

attack Year2-crop

26

Rotation

• Against mono-/oligophagous species with

limited dispersal abilities

• Example:

• Brassica pod midge -pest of oilseed rape

• overwinter as larvae in soil of last years field

• in spring, new adult emerge

• new non-host crop on former year’s field =>

adults must fly to new oilseed rape fields

• poor flyers => many will die

27

Brassica pod midge

Cabbage field, last year –pupae in the soil

Oviposition in cabbage

Cabbage root fly

Feeding in hedges

Spring – pupae develop to adults

1-2 km

28

Cabbage field, this year

Limit access, netting

Floating row cover

Feeding in hedges

Cabbage field, this year

29

X

Cabbage field, last year –pupae in the soil

Spring – pupae develop to adults

Cabbage root fly

Limit access, netting Choice of cultivar

• Partially resistant varieties may be available

• Act by

• discouraging colonisation (antixenosis)

• e.g. reduced attractiveness for oviposition

• toxic action (antibiosis)

• e.g. increased mortality of the stage feeding on the plant

• Examples:

• corn earworm

• cabbage root fly

• carrot fly

• lettuce aphid

Cabbage root fly

Lettuce aphid

30

Corn earworm

Carrot fly

6

several larval stages –

1) small larvae hides beneath soil surface; emerge few times a day to feed on leaves

2) larger larvae most active at night – feed on leaves and roots

fully grown larvae

Turnip moth

pupa in soil

2-3 generations / yearadult

eggs on a stem

overwintering31

Increase mortality, water

several larval stages –

1) small larvae hides beneath soil surface; emerge few times a day to feed on leaves

fully grown larvae

irrigation aimed at young larvae -

forces them from the soil => exposed to enemies and environment

increase mortality among young larvae

32

Increase mortality, water

Exercise, introduction

• Trap crops and pollen beetles

• Trap crops

• preventive tactic based on plants that are

more attractive than the crop

• placed adjacent to the crop

• divert pests from the crop

Green stink bug

Trap crop

Soybean

33

Exercise

• Discuss in groups

• Answer questions – 15-20 minutes

• Plenum discussion on answers

34

35

Behavioural methods

36

• The exercise – an example of manipulation of pest

behaviour as a preventive tactic

• General possibilities to manipulate behaviour

• host location, host acceptance (for egg laying, for

feeding), mating behaviour

• Through methods aimed at

• vision

• olfaction

Manipulation of pest behaviour

Buckeye butterfly

Dock bug

7

Vision-based tactics

37

Sticky apple for mass-trapping adult apple maggot flies emerging from overwintering

• Mass-trapping

• many insects are attracted to specific colours

• sticky traps may catch a large proportion of a pest

• can limit influx to crop

• Reflective mulches

• prevent some insects from landing on the crop

• perhaps because they think it is the sky …

Mediterranean fruit fly

Olfaction-based tactics

• 1. Allelochemicals

• communication between species, e.g. between plants and

insects; between different insect species (predator and

prey)

• Plant attractants - attractive to insects; used in host

plant location

• Plant repellents - repel insects; used as plant defence

38

Rose chafer

• Push-pull strategy

• push the pest away from the crop – pull it

somewhere else

• Example – the maize stalk borer

• pest of maize, sorghum, sugarcane

• damage caused by larvae – feed on young leaves

and later enter the stem

Using allelochemicals

Maize stalk borer

Larvae

Damaged maize

39

Push-pull

maize

Desmodium - repellent

• Intercropping maize with repellent plant (push) –

masking host stimuli

• Attractive plant as borders (pull)

Napier grass - attractive

40

• 2. Pheromones

• communication within species; e.g. where to

hibernate; is a predator approaching (alarm

pheromone); calling for mate

41

Olfaction-based tactics, cont.

Convergent ladybeetle

Convergent ladybeetle

New Forest burnet moth

Using pheromones, attract-and-kill

• Attract-and-kill

• lure the pest to a site where it is killed

• Example – the cotton boll weevil

• pest of cotton

• damage caused mainly by larvae – feed on flowers

and inside the boll

Cotton boll weevil

Larvae in boll

Damaged boll Healthy boll

42

8

• Device aimed at adults emerging from hibernation

• To catch and kill before they enter the cotton and

lay eggs

• Put out in cotton field

• Green colour attractive

• Contains aggregation pheromone - attracts

• Cotton oil (attracts) mixed with insecticides (kill)

on the side

43

Using pheromones, attract-and-kill Using pheromones, mating disruption

• Mating disruption

• exploiting the fact that many pests use pheromones

for finding mates

44

• Mating disruption

• large-area application of pheromone saturates an

area and prevents/reduces chance of male finding

the real females

• species specific =>

• important to treat large areas – otherwise

immigration of mated females 45

Using pheromones, mating disruption

46

Biological methods

Definition

• Biocontrol is NOT biologically-based non-chemical

methods such as pheromones, insect hormones,

repellents/attractants, pest-resistant crops, botanicals,

biopesticides containing only microorganism toxins, ….

47

The use of living organisms to

suppress the population of a specific pest organism

making it less abundant or less damagingthan it would otherwise be

(Eilenberg et al., 2001)

Basic principle

Time

Pes

t (or

ben

efic

ial)

pop

ula

tion

size

Carrying capacity

EIL

ET

New GEP

Original GEP

Biocontrol agent introduced

A B

Lag phase

Time

equilibrium after control

damage thresholds

equilibrium prior to control

• Biocontrol involves use of populations of natural enemies

to suppress pest populations to lower densities

• permanently or temporarily

48

9

49

Types of natural enemies for control of arthropods

• Entomopathogens (=virus, bacteria, fungi)

• Insect pathogenic nematodes

• Predators

• Parasitoids

• Collectively called “beneficials”

Predatory arthropods

Predatory adults and juveniles Predatory larvae; adults eat nectar, pollen

Parasitoids

51

• Parasitoid = the immature stage parasitise other insects; the

adult is free living as adult; host is killed

• Endoparasitoids

Aphidius ervi, a parasitoid of aphids

Endoparasitoid life cycle

Parasitoids

Cotesia glomerata, a parasitoid of caterpillars

52

• Parasitoid = the immature stage parasitise other insects; the

adult is free living as adult; host is killed

• Endoparasitoids and ectoparasitoids

Larva of large white butterfly parasitised by Cotesia glomerata

• Conservation biocontrol

• a preventive tactic

• - making use of naturally occurring beneficials

• Augmentative biocontrol

• direct control through releases

• Classical biocontrol

53

Biocontrol strategies Conservation biocontrol

• Native natural enemies are

• 1) conserved

• by minimising harmful factors

• preserve the natural enemies already present in or

around a crop

54

10

Minimise harmful factors - pesticides

• Many pesticides are harmful to natural enemies

• Differences exists

• in toxicity – from non-toxic to highly toxic

• in persistence – from a few days to many weeks

• Different species react differently to the same pesticide

• Essential to select the least harmful pesticides

• - or apply the harmful ones protectively

• e.g. spot-treatment, reduced dose, avoid key activity periods

• Many pesticides screened for toxicity to natural enemies

and for their persistence

55

Minimise harmful factors - pesticides

• Beware of pesticide drift

• may not land where intended

• In non-target areas

• direct effects – kill beneficials

• indirect effects – kill flowers/prey or

hosts …

56

• Preserve landscape elements

57

Preserve natural enemies Preserve natural enemies

58

• Avoid harming activities here

Enhance natural enemies

• Native natural enemies are

• 1) conserved

• 2) enhanced

• by increasing factors that will stimulate presence,

survival, population increase

59

To enhance

• Flower strips

• more microhabitats

• increased access to nectar/pollen/hosts/prey

• Beetle banks

• non-cultivated areas in the field

• permanent habitat within the field

• overwintering site for e.g. ground beetles

• Resting / nesting places

60

11

Other enhancing possibilities

• Trap crops

• Cover crops

• Intercropping

• Hedges = non-cropped areas surrounding the crop;

undisturbed by agricultural practise

61

Other enhancing possibilities

• Increased landscape diversity

• reduced distance from overwintering sites to field

• especially important for attracting natural enemies to

annual crops

• No conservation tactic must create/increase

problems with pests/diseases

• Plant species used must not have the potential to

become weeds in the crop

62

Augmentative biocontrol

• Active releases of biocontrol agents

• An effect from released organisms wanted and

from their off-spring, if possible

• When …

• no beneficials present

• beneficials present but are too few/too late to exert

control

63

Augmentation

• Many beneficials are commercially available

• Much used in greenhouses

• Also in field crops especially in warmer regions

• mainly nematodes and entomopathogens

• mainly in high value crops (fruit, vegetable)

• problems outdoor

• – variable climate

• – dispersal from release site

64

Chemical methods

65

Insecticides

• Non-living substances capable of killing insects

• May have different origin

• from plants = botanicals

• from other organisms = biopesticides

• chemical substances

• inorganic

• organic

66

12

Insecticides, advantages

• May control where no other means available

• May be less expensive

• May require less knowledge of pest biology and

agroecosystem processes

• Often rapid

• Less planning compared to preventive tactics

• Relatively predictable level of control

67

• Effect on non-targets in and outside field, e.g.

• pollinators, natural enemies, alternative prey/hosts

• May be expensive

• Residues in harvest products,

pollution of environment

• Hazard to farm workers, consumers, wildlife

• The three ’s of the pesticide treadmill

• pest esurgence ... higher pest densities when pest

population recover (natural enemies and competitors

killed)

• pest eplacement ... a new pest arise (formerly

controlled by natural enemies)

• pest esistance

Insecticides, disadvantages

68

Intelligent use of insecticides

• Do not use as a routine

• Only apply when necessary

• - when the stage that can be controlled is present

• or

• - when pest density is approaching damaging levels

69

When is the pest there?

• Detect by monitoring = looking for pests or symptoms

• = traps, sweeps, scouting

• Predict from models for e.g. emergence from

overwintering

• = models based on knowledge on lower thresholds for

development and development time in relation to weather

conditions

• = models used in decision support systems

70

When is damaging levels approached?

• Models on relationship between pest density and yield reduction

• Determination of damage threshold = max level of pest below

which no yield loss occur

71

pest density

Damage threshold

yie

ld

max yield value


• Combined with models on pest population development

in relation to climatic conditions

72

0

20

40

60

80

100

120

140

1 6 11 16 21 26

Days

Ap

hid

per

str

aw

18 C

15 C

12 C

days

aphid density

13


• When should we do something to prevent yield loss?

• Economic Injury Level (EIL): pest density where losses becomes

bigger than cost for control

• Action Threshold (AT – also called Economic Threshold): pest

density where actions must be taken to prevent economic losses

73

time

pest density

AT

Integrating methods

74

The intelligent approach to pest management

• Decision making

• only apply measures when needed

• monitoring/scouting important

• Preventive and control measures

• Physical methods

• Cultural methods

• Biological methods

• Behaviour-modifying methods

• Chemical methods

• = Integrated Pest Management - IPM

1

2

3

4

5

75

physical

behavioralcultural

chemical

biological

IPM concept

• Management of pest populations using all relevant preventive

and control practices in a complimentary manner, so that the

pest will be maintained below the economic injury level and there

is minimal adverse effects on the environment

76

Chemical Behavioural

CulturalPhysical

Biological

77

• Continuum from chemically to biologically intensive programs

• Chemically intensive IPM

• pesticide treatments are made according to monitoring /

scouting (i.e. not as calendar spraying)

• perhaps other elements added

• still the most common IPM-type

Behav

CultPhys

Biol

Chemical

Component-based IPM-systems Component-based IPM-systems

• Continuum from chemically to biologically intensive programs

• Biologically intensive IPM

• reliance on host plant resistance, cultural and physical methods

and biocontrol

• pesticides are used as the last resort

PesticideBehavioural

CulturalPhysical

Biological

78

14

Target-based IPM-systems

• Continuum from single-organism targeted to multiple-

organism targeted programs

• single- to few-organism targeted programs still the most

common

• For multiple-organism targeted programs, integration may

focus on one pest category

• IPM of weeds / plant pathogens / arthropods

• still more common IPM-type compared to

• or be more holistic addressing all pest categories

• IPM of weeds + plant pathogens + arthropods

79

Holistic and biologically intensive IPM programs

• High degree of complexity

• Methods must be selected so that they do not interfere

with each other

• Prioritised order of target pests

• sometimes control of e.g. an arthropod pest must be

sacrificed to achieve sufficient control of e.g. weeds

• Applied measures must be economically (including

labour-saving) feasible

80

Exercise

• Plant protection at a pea farm

• Work in groups

• Answer questions – ca. 35 min

• Plenum discussion on answers

81

Maize 2013

Wheat 2013

Wheat 2013

Wheat 2013

Grass 2013

Grass 2013

Maize 2013

1 km

S N

naboers arealer

Exercise

82

• Where to place the pea field

in 2013

• in relation to last year’s

crops

• in relation to the

surroundings

• Which management tactics

can be applied (and when)

against expected problems

with defined pest species

Exercise

• 1) read the red-marked additions about the pests

• 2) read about the natural enemies on the farm

• 3) discuss and answer question 1


• a quick time-overview of pest phenology may help … don’t use

too much time on this


March April Mai June July August

Pea aphid

Pea moth

Pea thrips

Mice

Pigeons

sowing harvest

crop phenology

pest phenology

Documents

Animal Pests in Arable Crops