How to Control Soil Insects with Beneficial Nematodes

Ed Lewis Department of Entomology and

Nematology University of California, Davis

Using Microbials in IPM •  Do not have to change everything

about crop management

•  Many microbial insecticides fit into current production plans with minimal effort and change

•  They require specialized information about their use

Insect pathogens can be effective

• Naturally occur – Even in intensively managed

systems • Have an impact on insect

populations at natural levels

Necessary information: Products

•  Shelf life •  Storage conditions •  Resting stage? •  Viability in field •  Host range •  Time to kill •  What does an infected insect look like?

Recognized Species of Entomopathogenic Nematodes H. bacteriophora H. brevicaudis H. hawaiiensis H. indica S. kraussei S. arenarium S. bicornutum S. carpocapsae S. caudatum S. ceratophorum S. cubanum S. feltiae S. glaseri S. intermedium S. affine

H. marelatus H. megidis H. zealandica H. argentinensis S. karii S. kushidai S. longicaudum S. monticolum S. neocurtillae S. oregonense S. puertoricense S. rarum S. riobrave S. ritteri S. scapterisci

Infective Juveniles

•  Resistant to Environmental Extremes •  Only Function is to Find A New Host •  No Feeding •  No Development •  No Reproduction •  Only Life Stage Outside the Host

Infective Stage Juvenile Steinernema carpocapsae

Bacterial Chamber

Symbiotic Bacteria Released

Mating for Steinernema spp.

Two to three generations occur in a single host. About 6 days after the original infection, this is the appearance

New Infective Juveniles in 10 Days

Entomopathogenic Nematodes Can Control:

•  Weevils: Diaprepes root weevil, Diaprepes abbreviatus Blue green weevils, Pachnaeus spp. Otiorhynchus spp. Bill bugs

•  Fungus gnats: e.g., Sciaridae

Entomopathogenic Nematodes Can Control:

•  Scarab larvae: e.g., Japanese beetle, Popillia japonica, Chafers, etc.

•  Lepidoptera: Black cutworm, Agrotis ipsilon Codling moth, Cydia pomonella Leafminers, Liromyza spp. Banana moth, Opogona sacchari Navel Orangeworm, Amyelois transitella

•  Other: fleas, mole crickets

Some Things to Remember About Entomopathogenic

Nematode Products

Products Can Be Deceiving

• Infective Stage is NOT a Resting Stage

Live Infective Stage Nematodes

Infective Stage Survival

H. bacteriophora

S. carpocapsae

S. glaseri

Formulation Shelf-life (storage method)

Sponge 2 Months (Refrigerated)

Vermiculite 3-5 Months (Refrigerated)

Dispersable Granule 2-5 Months (Room Temperature)

How Long Do They Last?

How Do We Figure Out Where and When to Use them?

•  Climate •  Soil Types

Special considerations for applying microbials

•  Not chemical pesticides – Storage – Application

•  Special habitat requirements •  Realistic expectations

– Kill slower than chemicals – Will not (usually) completely eliminate

pests

Case Study •  Entomopathogenic

nematodes to manage Diaprepes abbreviatus (citrus root weevil) in Florida and California

Citrus Root Weevil Adult

Diaprepes Damage

Southport Grove, Osceola County, FL

What makes Diaprepes difficult to control?

•  270 known host plant species •  asynchronous, complex, variable life

history •  high fecundity, protected egg masses •  many pesticides are ineffective against

soil-dwelling larvae •  many natural enemies have limited,

patchy distributions

Diaprepes abbreviatus Life Cycle

Adults

Eggs

Neonates

Larvae Pupae

Perc

ent m

orta

lity

Sand Sandy Clay Loam 0

20

40

60

80

100 + S. riobrave

Untreated Field Experiment

Nematodes Most Effective in Coarse Sandy Soils

(Duncan et al., unpublished)

What to do in California?

•  Soil type has major impact on efficacy •  Soils in California much more diverse than

in Florida

Objective

•  Develop methods to determine whether or not entomopathogenic nematodes will be effective biological control agents of citrus root weevils in CA citrus

Column Assay Units

Num

ber o

f S. r

iobr

avae

(±S

E)

Soils

0

200

400

600

800

1000 10 cm

0

100

200

300

400 25 cm

0

100

200

300

400 50 cm

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15

16 17 18 19

20 21 22 23 24

25 26 27 28 29 30 31 32 33

S. riobrave – Efficacy Bioassay

8

9

11 10 12 13

7

4 24

25

26

6 5 3

1 2

23

22

21 14

15 16

17 18

19 20

28

27

31 30

32

34

35

33

36

29

S1

S2

S3

S4

S5

Silt

C

lay

pH

EC

MR

A

B

C

D O

M

Cluster analysis: grouped similar soils based on physical and chemical characteristics

Med

ian

Num

ber o

f Nem

atod

es (±

25t

h per

cent

ile )

Efficacy of EPNs in different clusters

600

0

100

200

300

400

500 (a)

0

20

40

60

80

100

120 25cm

0

10

20

30

40

50

60

A B C D

Cluster

(b)

(c)

10cm

50cm

a a

b c

a b

c

d

a

b b

c

Using This Information

Can soilless media be constructed to enhance persistence and efficacy of microbial insecticides?

Foraging of S. riobrave in Soilless Media Components

0

2

4

6

8

10

Sand Peat Moss Cedar/PineBark

RecycledPlant

Material

Redw oodSaw dust

(w /o bark)

Redw oodSaw dust(w /bark)

Perlite Vermiculite

Dis

tanc

e tr

avel

led

(cm

)

02550

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ab

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bcde

deff

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eff

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Foraging of S. riobrave in Soilless Media Components

0

2

4

6

8

10

Sand Peat Moss Cedar/PineBark

RecycledPlant

Material

Redw oodSaw dust

(w /o bark)

Redw oodSaw dust(w /bark)

Perlite Vermiculite

Dis

tanc

e tr

avel

led

(cm

)

02550

a

ab

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bcde

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eff

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How to Make EPNs Work?

•  Product quality •  Product suitability

•  Application rates •  Application timing

•  Environmental conditions •  Substrate conditions