What are some of the most diverse orders of insects?
Coleoptera (beetles), Diptera (flies), Hemiptera (true bugs), Lepidoptera (butterflies and moths), Hymenoptera (ants, bees and wasps)
Where is the most insect diversity found?
- Tropical species richness much higher than temperate areas
- Few in arctic areas
- Predominantly found on land or in freshwater
What is the taxonomic classification of insects and what features define them at each taxonomic level?
Phylum Arthropoda - Hard exoskeleton with jointed legs
Superclass Hexapoda - Six legs, three segments (head, thorax and abdomen)
Class Insecta - Simple eyes (ocelli) and compound eyes usually present, legs with at least six segments, exposed mouthparts (ectognathus)
Order (approx. 30)
Families (approx. 1000)
Why are insects important (as keystone species)?
- Nutrient recycling
- Plant reproduction
- Maintenance of plant communities
- Maintenance of animal communities
Why are there so many insects?
- Small size
- Versatile exoskeleton
- Highly organised sensory and neuromotor systems, allowing fro high specialisation
- Coevolution between insects and other organisms (e.g. plant mutualisms, parasitism)
- Short generation time allowing fast genetic adaptation and high genetic diversity
- Successful evolutionary strategies: flight (dispersal abilities), metamorphosis, sociality
Why are insects under threat?
- Habitat loss
- Pesticides, pollution
- Introduced species
- Climate change
What is the oldest class of insects?
Oldest fossil hexapods are Collembola (‘springtails’)
How are we able to observe Hexapod evolution?
- Insects in amber provide a historical record
- Many specimens are virtually identical to today’s species
What were the key periods of species radiation in the evolution of Hexapods?
- Extensive radiation in the Carboniferous period (360-300 mya)
- Subsequent radiation associated with seed plants (gymnosperms) in the Permian
- Lepidoptera and Diptera are the most recently evolved of the “big five”
insect orders, arising in the Triassic (250-200 My BP) - Blattodea (cockroaches) and Isoptera (termites) two of the most recent
lineages to “emerge” in the Jurassic
What are the two theories for insect wing evolution?
- Paranotal theory: Wings might be derived from rigid, lateral lobe-like expansions of the thoracic terga (dorsal region), Consistent with terrestrial ancestors
- Pleural theory: Wings are derived from articulated lateral extensions from the
pleuron (lateral thoracic/abdominal region), Consistent with aquatic ancestors
What is the difference between direct and indirect flight?
Direct flight: muscles directly attached to wings - greater control and mobility
Indirect flight: muscles attached to thorax cuticle - faster wing beating (using asynchronous muscles)
What is an example of insects that have secondarily lost their wings/ability to fly? And why might this have occurred?
- Atherimorpha latipennis: females are wingless, males have wings. Evolutionary trade-offs with different contrains in males versus females.
- Flight is an adaptive advantage, but it is also potentially costly
What is metamorphosis?
The process of animal development involving a conspicuous and abrupt change in body structure through cell growth and differentiation
- Indivuduals moult between instars, from eggs to imago (adult).
What are the three types of metamorphosis? Provide a description of each.
- Ametaboly: No metamorphosis - Egg > Young Nymph > Later Nymph > Adult
- Hemimetaboly: Incomplete metamorphosis
- Holometaboly: Complete metamorphosis - Egg > Larvae > Pupa > Adult
What are the main parts of insects external anatomy?
Segmented: generally 6+3+11 segments
- Head (compound eye, antenna, mouthparts)
- Thorax (fore leg, wings, middle leg)
- Abdomen (spiracles, hind leg, cersus, external genitalia)
What are some of the specific parts of the insect head, and what are they used for?
- Frons, Gena, Clypeus, Labrum
- Compound eye
- Ocelli(us)
- Antenna (scape, pedicel, antenna)
- Mandible
- Maxilla, Maxillary palp and labial palp
