Insect Pests

Economic importance of insect pests

• Can cause direct damage to crops• Can be vectors of plant pathogens

Direct Damage• Decrease photosynthetic ability

o Defoliationo Leaf miningo Leaf curling

• Stunting, yellowing, distorted growth, and honeydew• Lodging in some crops

o Bore into stems

• Feed on roots• Damage to harvested plant parts

What is an insect?• Phylum Arthropoda

o Means “jointed foot”o Largest phylum in the world

• Insects, crustaceans, spiders, centipedes, millipedes

• Insects1. Possess an exoskeleton made of chitin

• Encases internal organs2. Body is divided into three distinct regions

• Head, thorax, abdomen3. Three pairs of jointed legs, attached to the thorax4. Compound eyes5. One pair of antennae

• Absence of a backbone makes the hard exoskeleton crucial to life on land

• Insect body divided into a head, thorax, and abdomen

External Anatomy of an Insect

• Composed of numerous plates o Plates are called scleriteso Fused together to form a solid capsule

• Bears:o One to three simple eyeso Two compound eyeso One pair of antennaeo Mouthparts

• Houses the braino Nerve cord runs from brain down the body on the ventral surface

The Head

• Divided into three segmentso Prothorax, mesothorax, metathorax

• Each segment is made up of four scleriteso Upper (dorsal) sclerites are called the notumo Lower (ventral) surface is the sternumo Side (lateral) regions called the pleura

• Can combine these terms to define a region (e.g., pronotum)

• One pair of legs is attached to each segment near the bottom of the pleura• If present, wings can be on:

o mesothorax alone o both the mesothorax and metathorax

The Thorax

• Softer and more flexible than the head or thorax

• Devoid of appendageso Exceptions are cerci and genitaliao Ovipositor

• Houses the tracheal systemo Must expand and contract

The Abdomen

• How insects breathe• Insects take in and expel air through spiracles

o Openings on each side of the abdomeno One pair of spiracles per abdominal segment (11 pairs)

• Each spiracle leads to air tubes (tracheae) and air sacs• Oxygen flows through these tubes and sacs to all organs and

tissues throughout the body

The Tracheal System

• Mouthparts tell us about insect feeding habitso Tells us more about life cycle and ecological relationships

• Types of Mouthpartso Chewing

• Chewing• Chewing-lapping

o Sucking• Piercing-sucking• Siphoning

o Sponging

Mouthparts and Feeding

• Most commono Dragonflies, grasshoppers, crickets, katydids,

beetles, ants, wasps, caterpillar larvaeo Damage includes leaf mining, defoliation, boring of

tissues, root damage

o Labrum• Upper lip

o Mandibles• Toothed jawlike apparatus adapted for cutting,

crushing, grindingo Maxillae

• Smaller but also jawlike and adapted for grasping

o Labium• Lower lip• Hypopharynx – tonguelike appendage that rests

on the labium

Chewing Mouthparts

• Chewing-lappingo Beeso Elongated labium helps lap nectar

Chewing Mouthparts

• Insects ingest only liquid food

• Piercing-suckingo Aphids, leafhoppers, fleas,

sucking lice, mosquitoso Modified mouthparts

• Proboscis (beak)o Elongated labium that

sheaths slender mandibles and maxillae

o These are called stylets• Stylets do the

piercingo Can also transmit pathogens,

inject toxins

Sucking Mouthparts

• Siphoningo Butterflies and mothso Proboscis is coiled

and extends when insect wishes to feed on nectar

Sucking Mouthparts

• Most flies• Have a fleshy labium on

the tip of the proboscis that acts like a spongeo Soaks up liquids and food

particles

• Also called rasping-slurping

Sponging Mouthparts

• Insects start as eggs, go through metamorphosis

• No metamorphosiso Emerge from eggs as miniature adultso Silverfish, springtails

• Incomplete metamorphosis (hemimetabolous)o Nymphs emerge from eggs and gradually develop

complete adult features and sizeo Aphids, leafhoppers, grasshoppers

• Complete metamorphosis (holometabolous)o Four separate life stages

• Egg, larva, pupa, adulto Butterflies, cutworms, stem borerso Larval and adult stages are damaging to crops

Life Cycles

• Nymphs eat the same food as the adults• The stage preceding each molt is called an instar• Each succeeding instar more closely resembles the adult stage

Incomplete Metamorphosis

Incomplete Metamorphosis Example(hairy chinch bug)

egg 1st 2nd 3rd 4th 5th shortwing normal wing instar instar instar instar instar adult adult

Egg Nymphal AdultStage Stage Stage

• Egg hatches to larva• Larva do not resemble adults, worm-like instead

o Has simple eyes onlyo Chewing or chewing-sucking mouthpartso Short antennaeo Up to three pairs of true legs, possibly other appendages that resemble legso Larvae molt several times to accommodate growth (also called an instar)

• Pupa emerges from final larval molto Pupa do not eato Tissues differentiate, compound eyes form, wings, antennae, mouthparts, etc. o Can last 4 days to several months

• Adult emerges, on a mission to mate and lay eggs

Complete Metamorphosis

Complete Life Cycle Example(northern masked chafer)

egg 1st 2nd 3rd pupa adult instar instar instar

Egg Larval Pupal AdultStage Stage Stage Stage

• Sexualo Males transfer species to a female and sperm are stored in a special sac in her

abdomeno Egg-laying females (oviparous) have ovipositors as abdominal appendages

• Deposit eggs in suitable sites• As eggs are laid, they meet sperm on the way out of the female

o Non-egg laying females (viviparous) house eggs until they hatch

• Asexualo Parthenogenesis

• An unfertilized egg develops into an adulto Social bees, wasps

Reproduction

• Insects smell with their antennae

• Segmented, flexible, and covered in tiny hairs (setae) that sense chemicals, touch, taste, sounds, etc.

• A variety of configurations

Antennae