Insect identification, sampling and management Erin Hodgson Department of Entomology Iowa State University

2011 Field Crop Scout School, Ames, IA

Outline • Why insects are successful • Important insect ID features

• Sampling and recognizing damage • IPM guidelines • Common field crop insects

2011 Field Crop Scout School, Ames, IA

Why are insects so successful?

Why are insects so successful? Small size Multigenerational Flight Metamorphosis

Wide variety in food choices Wide variety in habitat resources

2011 Field Crop Scout School, Ames, IA

Insect metamorphosis

Complete metamorphosis: egg, larva, pupa, adult

Incomplete metamorphosis: egg, nymph, adult

E.g., beetles, butterflies, flies

E.g., grasshoppers, true bugs 2011 Field Crop Scout School, Ames, IA

How to ID insects: wings

tegmina

elytra

hemelytra

2011 Field Crop Scout School, Ames, IA

2011 Field Crop Scout School, Ames, IA

How to ID insects: mouthparts

Piercing sucking: mosquito

Chewing lapping: honey bee

Siphoning: butterflies, moths

Sponging: house fly

Chewing: grasshoppers, beetles

2011 Field Crop Scout School, Ames, IA

How to ID insects: antennae

2011 Field Crop Scout School, Ames, IA

How to ID insects: legs

2011 Field Crop Scout School, Ames, IA

Easy to confuse…

2011 Field Crop Scout School, Ames, IA

HOW TO SAMPLE AND COLLECT INSECTS 2011 Field Crop Scout School, Ames, IA

Know your system… • What is the plant, what is normal? • Most plant health problems are not caused by biotic (living) factors such as insects and disease • Most plant health problems are a result of non-biological factors (environment, cultural methods, irrigation, plant nutrients, etc.) • Learn about your target insect 2011 Field Crop Scout School, Ames, IA

Key points about scouting • • • • •

Start looking before you expect them Continue sampling regularly Try to cover the field DON’T avoid and DON’T “eyeball” Use a defined walking pattern

2011 Field Crop Scout School, Ames, IA

Regular grid pattern

Regular staggered pattern

Regular circular pattern

Regular zigzag pattern

2011 Field Crop Scout School, Ames, IA

Use the best collecting method • Varies depending on target insect • Estimate density or damage – # insects per plant – % defoliation

• In-field counts, sweep net, shake bucket

2011 Field Crop Scout School, Ames, IA

Common collecting tools • Notebook • Sweep net

• Drop cloth • Hand lens • 5-gallon bucket

• Sticky cards 2011 Field Crop Scout School, Ames, IA

How to sweep net Across two rows

Three feet along a row

2011 Field Crop Scout School, Ames, IA

shake bucket in-field plants

sticky cards/ pheromone traps

black light trap

drop cloth

Other common methods

2011 Field Crop Scout School, Ames, IA

RECOGNIZE INSECT FEEDING AND DAMAGE 2011 Field Crop Scout School, Ames, IA

Recognizing insect damage • Chewing: remove plant tissue, girdle stems, defoliate, skeletonize leaves, or clip pods – Beetles, grasshoppers, caterpillars

2011 Field Crop Scout School, Ames, IA

Percent defoliation is typically over-estimated 2011 Field Crop Scout School, Ames, IA

Recognizing insect damage • Piercing-sucking: feed on phloem and can cause stippling or punctures that result in

discoloration or mottling, honeydew – Aphids, thrips, spider mites, stink bugs

2011 Field Crop Scout School, Ames, IA

2011 Field Crop Scout School, Ames, IA

honeydew

black sooty mold

hopperburn

spider mite damage

USE TREATMENT THRESHOLDS TO MANAGE PESTS 2011 Field Crop Scout School, Ames, IA

What is IPM? • Integrated Pest Management – Multiple, proactive tactics – Suppress pest pressure – Sustainable crop production

• More than biological control!

2011 Field Crop Scout School, Ames, IA

2011 Field Crop Scout School, Ames, IA

Treatment thresholds • Economic injury level: lowest population density that will cause economic damage • Economic threshold: point at which action should take plant to avoid EIL

2011 Field Crop Scout School, Ames, IA

Average # of soybean aphids per plant

800 700

economic injury level

600 500 400 300

economic threshold

200 100 0 29 Jun

6 Jul

13 Jul

20 Jul

27 Jul

3 Aug 10 Aug 17 Aug 24 Aug 31 Aug

2011 Field Crop Scout School, Ames, IA

Why use thresholds? • • • •

Minimize input costs Protect beneficials and pollinators Prevent flares of other pests Prolong insecticide efficacy, aka… delay genetic resistance to MOA

2011 Field Crop Scout School, Ames, IA

Important considerations • Strive for 100% kill with applications • Uniform coverage – Sufficient volume/pressure

• Be aware of pre-harvest intervals later in season (30d, 45d, 60d) • Assess product efficacy (check strip!) • Continue to scout

2011 Field Crop Scout School, Ames, IA

COMMON IOWA FIELD CROP PESTS

2011 Field Crop Scout School, Ames, IA

Common IA corn pests • Corn rootworm, wireworms, Japanese beetle • European corn borer, corn earworm, stalk borers, cutworms

• Aphids, spider mites, leaf miners

2011 Field Crop Scout School, Ames, IA

Corn rootworm (CRW)

Northern corn rootworm

Western corn rootworm

Diabrotica barberi

Diabrotica virgifera virgifera

Leaf beetle (Coleoptera: Chrysomelidae) 2011 Field Crop Scout School, Ames, IA

CRW life cycle

Pupa Larvae (3 instars)

Adult, 5 mm

Eggs*

2011 Field Crop Scout School, Ames, IA

CRW larval injury

2011 Field Crop Scout School, Ames, IA

CRW adult injury

2011 Field Crop Scout School, Ames, IA

European corn borer (ECB) • Ostrinia nubilalis (Lepidoptera: Pyralidae) – 2 generations per year

• Larvae – Pinkish-tan body, 1 cm long – Dark head capsule

2011 Field Crop Scout School, Ames, IA

ECB adults • • • •

Small, tan night fliers 1 cm long Wings in a delta shape Females have thick body and light colored wings

♂

2011 Field Crop Scout School, Ames, IA

ECB damage • 1st gen, window-pane leaves – Deep in the whorl

• 2nd gen, stalk and earshank

2011 Field Crop Scout School, Ames, IA

Japanese beetle (JB) • Popillia japonica (Coleoptera: Scarabaeidae)

2011 Field Crop Scout School, Ames, IA

JB

Eggs

Larvae(3 instars)*

• 1 generation/year • 1.5 cm long, oval

• Highly migratory • Highly aggregated • Wide host range Adult

Pupa 2011 Field Crop Scout School, Ames, IA

JB damage

2011 Field Crop Scout School, Ames, IA

Common IA soybean pests • Soybean aphid • Potato leafhopper • Bean leaf beetle, Japanese beetle

• Green cloverworm, loopers, thistle caterpillar • Spider mites

2011 Field Crop Scout School, Ames, IA

Soybean aphid (SBA) • • • • •

Aphis glycines (Hemiptera: Aphididae) 2 mm long Soft-bodied, pear-shaped Bright lime-green body Dark cornicles

2011 Field Crop Scout School, Ames, IA

Aphids have two forms

apterae alatae

2011 Field Crop Scout School, Ames, IA

Asexual reproduction all spring and summer

Winged forms move to secondary host

Aphids hatch at bud burst on buckthorn

Mate and generate overwintering eggs*

Produce mixture of wingless and winged forms all summer

Winged forms (including MALES) move back to primary host

Soybean aphid host alternating life cycle 2011 Field Crop Scout School, Ames, IA

Aphid feeding damage • Aggregated on plant • Mottling, leafcurl, yellowing, stunting • Honeydew production

2011 Field Crop Scout School, Ames, IA

Black sooty mold

Mold can reduce photosynthesis, eventually impacting yield!

2011 Field Crop Scout School, Ames, IA

Bean leaf beetle (BLB) • Cerotoma trifurcata – leaf beetle (Coleoptera: Chrysomelidae)

• 5 mm long, oval shape • Typically dark yellow with black – orange and red phases possible

2011 Field Crop Scout School, Ames, IA

• 4 black rectangles on forewings (usually) • Black triangle at the base of “neck”

• Long antennae, walking legs, obvious eyes

2011 Field Crop Scout School, Ames, IA

BLB Life Cycle • Generations variable – Multivoltine (3 gen); SE U.S. – Bivoltine (2 gen); IA, IL – Univoltine (1 gen); MN, Canada

• Overwinter as adults in leaf debris

2011 Field Crop Scout School, Ames, IA

Common IA alfalfa pests • Alfalfa weevil • Aphids • Potato leafhopper

2011 Field Crop Scout School, Ames, IA

Alfalfa weevil (AW) • Hypera postica (Coleoptera: Curculionidae) • Dark grey weevils • 5 mm long

2011 Field Crop Scout School, Ames, IA

AW life cycle

Larvae (3 instars)

Eggs Adults*

Pupa 2011 Field Crop Scout School, Ames, IA

AW adult and larval damage • Defoliation, frosting

2011 Field Crop Scout School, Ames, IA

Potato leafhopper (PLH) • Empoasca fabae (Hemiptera: Cicadellidae) • 3 mm long • Lime green, white eyes

• Wedge-shaped head • Roof-like wings

2011 Field Crop Scout School, Ames, IA

PLH damage • 3-4 gen/year • Migrate to IA annually • Cause “hopperburn” • Often confused with disease/nutritional

deficiencies 2011 Field Crop Scout School, Ames, IA

Summary • Use references! (see outline) • Know the target pest – ID, life cycle, biology

• Know how to sample target pest – Recognize damage – Time of year, collection method

• Use IPM to manage pests

2011 Field Crop Scout School, Ames, IA

@erinwhodgson [email protected]

2011 Field Crop Scout School, Ames, IA