Entomology Lecture Notes

Introduction to Entomology

Overview

Course: PLNT2011: Plant & Environmental Health
Instructor: Dr. Anthony Young
Topics: Evolution, diversity, development, functions, identification, anatomy and physiology, human interactions, and management of insects.

Tribute to Dr. Errol Hassan

Vale: Dr. Errol Hassan passed away on June 27, 2022.
Career: Taught entomology at UQ for 34 years.
Contributions: Named multiple insects and had 5 named after him.
Research: Conducted eco-friendly insect control research for over 40 years.
Last taught: PLNT2011 in 2022.
Student feedback: Highly knowledgeable, passionate, easy to understand, thorough, engaging.

Major Points About Insects

Insects are incredibly diverse.
Diversity is driven by specialization of segments.
They occur virtually everywhere on Earth.
Insects are critical to ecosystems.
Insects are critical to humanity.
Insects are subject to extinction.

Defining Insects

Domain: Eukarya
Phylum: Arthropoda
Sub-Phylum: Hexapoda
Class: Insecta
Orders: Approximately 30
Hexapoda: Includes collembolans, proturans, and diplurans.
- Insects are arthropods with 3 body segments.
- Uniramous appendages (typically 6).
- One pair of antennae.
- Usually with wings (=ptera) as adults.

Significance of Segmentation

Segmentation is a key feature in arthropods
Examples include Polychaete worms, Onychophorans, and Insects

Diversity of Insects

Currently ~30 Orders of insects.
Expected to be 5.5 million species (https://www.annualreviews.org/doi/10.1146/annurev-ento-020117-043348).
Differentiated by anatomy and molecular characteristics.
Beetles are the most diverse of insects.
- Approximately 1.5 million beetle species.
- Weevils are the most diverse of beetles.
- Coleoptera: Ptilidae.

Insect Functions

Integral component of food webs.
Pollinators, seed dispersal.
Biocontrol agents of other pests.
Waste removal and nutrient recycling.
Cultural value

Evolutionary Origins of Insects

Emerged in Devonian period after land plants.
Insects have a common ancestor.
Ancestors had multiple segments.
Segmental fusion gave 3 ‘segments’.
Segments then specialised: sensory/dietary, locomotion, reproduction.
Different groups have different development pathways: ametabolous, hemimetabolous, holometabolous.

Insect Development

Ametabolous: nymphs look like adults, no wing development
Hemimetabolous: nymphs look like adults, wing development
Holometabolous: larvae look unlike adults, wing development
Neometabolous: pseudo-pupal stage
Hypermetamorphosis: additional pupa stage; https://doi.org/10.1016/j.jinsphys.2012.02.009

Taxonomy of Insects

Multiple broad scale groupings
Approx. 30 Orders, many families/subfamilies
Genomic molecular systematics is revising our understanding of insect relationships
Molecular clock has insects pre-Silurian
Continued work in this space means taxonomy is fluid; https://www.pnas.org/doi/epdf/10.1073/pnas.1817794116

Classification of Insects

Insects are arthropods that have been on Earth for ~400+ million years
Insects accompanied plants and other arthropods onto land
Ancient insects were (are) wingless
- Archaeognatha (=ancient jaws)
- Thysanura (=fringe tail)
Primitive state is WINGLESS and AMETABOLOUS
Source: Gullan and Cranston (1994) The Insects: An outline of Entomology

Classification: Wings and Metamorphosis

Wings and metamorphosis came later…
PTERYGOTA - Insects with wings
PALEOPTERA
- Ephemeroptera (=temporary wings)
- Odonata (=toothed)
Hemimetabolous and wings do not fold
Both have aquatic nymphs
Previously thought that wings evolved as modified gas exchange organs

Classification: Folding Wings

Folding wings came later
NEOPTERA - new wings
POLYNEOPTERA - many new wings
- Orthoptera (=straight wings)
- Mantodea (=prophets)
- Phasmatodea (=phantoms)
- Blattodea (=cockroaches & termites)
- Plus several others
Folding wings allowed for less wing damage
All hemimetabolous

Classification: True Bugs

Then came the bugs…
True bugs
ACERCARIA → No tails
True bugs
- Hemiptera (=half wings)
- Homoptera (=same wings)
All have specialised sucking mouthparts
Many have ‘neometabolous’ development

Classification: Holometabola

HOLOMETABOLA - Insects with complete metamorphosis
- Coleoptera (=sheath wings)
- Lepidoptera (=scaly wings)
- Siphonaptera (=tube without wings)
- Trichoptera (=hair wings)
- Hymenoptera (=membrane wings)
- Diptera (=two wings)
- Plus others…
Young are larvae (singular: larva)

Physical Structure of Insects

Insects have exoskeletons
Muscles attach inside the exoskeleton
To grow they have to shed their skin then quickly expand
Exoskeletons comprised of chitin (same as fungi)
Insects can also produce silk which is protein based

Basic Insect Structure

Head
Abdomen
Thorax
Circulatory system
Digestive tract
Nervous system
Brain

Insect Communication

Antennae = nose and ears
Tympanum is also an ‘ear’
Sensilla taste sensors on feet, maxillae etc.
Compound eye composed of ommatidia
‘Vocalisation’ via stridulation or tymbals
Use of light, color, physical structures

Insect Feeding

Mouthparts: mandibles, maxillae, labium (fused 2° maxillae), hypopharynx, labrum
All specialised mouthparts derived from same basic plan
Insects can be pests in their own right
Many bugs vector viruses, bacteria and fungi
Most are beneficial and control other pests; https://www.pnas.org/doi/epdf/10.1073/pnas.1817794116

Insect Digestive System

Foregut: Ingestion, storage, grinding and transport of food to midgut
Midgut: Enzymatic (+/- endogenous) breakdown and nutrient absorption
Hindgut: H_2O absorption, salts and other important minerals, discharge of droppings (frass) through anus.

Insect Excretory Systems

Malpighian tubules join mid-hind gut junction
Excrete nitrogenous waste
Uric acid is nitrogenous waste molecule
Crystalline white powder
Uric acid (33%) is not as N rich as urea (47%)
Does not require H_2O for excretion

Insect Circulation

Insects have blood (haemolymph)
Transports nutrients, hormones, enzymes etc., but not O_2
Open circulatory system
Multiple ‘hearts’ that pump haemolymph direct to tissues via dorsal vessel
Wing veins supply sensory organs and other living components

Insect Respiration

Insects take oxygen directly to their cells
O2 enters & CO2 exits via spiracles and trachea
These end directly at cells
This limits the size of insects
Contrast with Carboniferous

Insect Reproductive Systems

Multiple systems exist
Visual, pheromone cues
Males typically heterogametic
Females often possess spermathecae
Males can partake in sperm wars
Others parthenogenetic

Insect Nervous System

Comprised of brain and ventral ganglia
Ganglia are concentrated nervous bundles
Can operate in concert or independently
Many insecticides target the nervous system
- Anticholinesterase compounds
- Imidicloprid

Insect Microbe Interactions

All insects rely on microbes for their proper function
Many of these are inherited maternally
Reduced genomes and functions
Cannot exist outside host
Can impact fertility (e.g., Wolbachia)

Management Strategies

Cultural
- Variety selection
- Land management systems
- Rotation crops
- Burning
- Corridors for enemies
- Smoke
Physical
- Exclusion (netting, screens, newspaper)
- Squishing
- Flooding
- Solarisation

Management Strategies Continued

Biological
- Natural enemies (insects, nematodes, spiders, mites, fungi etc.)
- Endotoxins
- Male sterilisation
- Inundative vs. inoculative
Chemical
- Nervous system
- Digestive system
- Contact
- Systemic
- Different modes of action
- Natural products

Integrated Pest Management (IPM)

Uses an appropriate mixture of different management methods
Based on monitoring, identification, records and economic thresholds
Prevents development of resistance
Accepts some loss to prevent major loss
Maintains natural enemy populations

Conclusions

Insects are among the first land animals
Insects conquered the land and air
Critical services to agroecosystems
Worldwide insect numbers declining
Understanding insects is rewarding in its own right, but can help the environment