Intro to Insects

Question 1

How many insects are there?

Answer 1

Estimated 10^18 insects alive at any one time

Over 1,000,000 described species

Constitute ~50% of all known species

Estimates range from 2-30 million species in total

Question 2

Insect Diversity

Answer 2

Vary in size from sub-milimeter to crow-sized

heaviest extant: 100g

longest extant: 56cm

Habitats: just about everywhere save marine

Question 3

Sociality

Answer 3

• Solitary: e.g. preying mantis, locust, bees
• Gregarious (act as individuals but aggregate in groups): e.g. locust, collembola, bees•

Sub-social (most primitive level of interaction involving parents and offspring): e.g. wasps, bees

•Highly social (complex social “caste” system): e.g. ants, bees, termites

Question 4

Common Features

Answer 4

• Body divided into: head, thorax, abdomen
• Head: One pair of antennae and mandibles; 2 pairs of maxillae
• Thorax: 3 pairs of legs; usually 2 pairs of wings
• Abdomen: no locomotory appendages; genital opening usually at posterior end
• Post-embryonic development requires metamorphosis

Question 5

Classification of Insects

Answer 5

•All insects are in the class ‘Insecta’

•There are two sub-classes:
1.Apterygota 2. Pterygota

•The sub-class Pterygota has two divisions:
i) **Exopterygota** ii) **Endopterygota**

•These two divisions also known as:
Hemimetabola Holometabola

Question 6

Sub-class Apterygota

Answer 6

• No wings – a primitive feature
• Metamorphosis slight or absent (nymphs/young are effectively miniature adults (can’t reproduce)
• One (or more) pairs of pre-genital appendages on abdomen
• Adult mandibles articulate with head capsule at single point
Contains orders: Collembola (springtails) and Thysanura (silverfish)

Question 7

Subclass Pterygota

Answer 7

• Winged (sometimes secondarily wingless)
• Metamorphosis occurs
• Adults have no pre-genital abdominal appendages
• Adult mandible articulates with head capsules at two points
• Contains all the ‘important’ orders

Question 8

Superorder Exopterygota

Answer 8

(aka hemimetabola)

• Simple metamorphosis
• Immature stages are nymphs – increasingly resemble adult
• Pupa rarely present
• Wings develop externally
• Nymphs (called naiads if aquatic) and adults often feed on same food resources
• Includes: dragonfly, termites, cockroaches, greenfly.

Question 9

Superorder Endopterygota

Answer 9

• Metamorphosis complex
• Immature stages are larvae – differ from adults in form and function (and often diet)
• Larva assimilates food
• Pupa present: does not feed, tissues ‘re-organised’
• Wings develop internally
• Contains: flies, butterflies and moths, bees, wasps, ants and beetles

Question 10

Types of Insect Larvae

Answer 10

Larva(e) is a generalised term that refers to all endopterygote orders (and sometimes to exopterygote orders)
Most larvae can be grouped into one of five categories based on physical appearance

Question 11

Eruciform Larvae

Answer 11

(Caterpillars!)

•Well defined segmentation with abdominal prolegs
•Each thoracic segment has a pair of segmented legs
•Well developed head capsule with biting mouthparts
•Head strongly sclerotized; antennae present
•Peripneustic arrangement of spiracles (prothorax and abdominal sections 1-8)
Abdominal prolegs on segments 3, 4, 5, 6 and 10 (in Lepidoptera)

Question 12

Campodeiform Larvae

Answer 12

OLIGOPOD: Lack abdominal pro-legs; Have functional thoracic legs
• Well sclerotised
• Distinct segmentation
• Dorso-ventrally flattened
• Active predators

Question 13

Scarabaeiform Larvae

Answer 13

OLIGOPOD: Lack abdominal pro-legs; Have functional thoracic legs

• Well sclerotised head only
• Less distinct segmentation
• slow moving detritivores or phytophages

Question 14

Apodous Larvae

Answer 14

Larvae without legs – e.g. vermiform larvae of diptera, which are often classified based on head capsule characteristics.

• Eucephalous – well sclerotised head capsule.
• Hemicephalous – reduced (retractable) head capsule.
• Acephalous – without a head capsule

Question 15

Larval Types by Order

Answer 15

Question 16

Endopterygote Pupae

Answer 16

Between their last larval instar and their adult form, Endopterygotes enter a pupal stage

Question 17

Insect Reproduction

Answer 17

• Parthenogenesis (development from an unfertilised egg)
• Can be obligatory or facultative
• Virtually all orders have at least one asexual representative
• Highly successful means of rapidly exploiting favourable conditions
• Female only eggs = thelytokous e.g. aphids
• Male only eggs = arrhenotokous e.g. Hymenoptera (male drones)
• Male and female eggs = amphitokous e.g. Hymenoptera
• Hermaphroditism (male and female reproductive organs)
• Polyembryony (two or more embryo’s from one egg)

Question 18

Oviparity (egg-laying)

Answer 18

•Ovoviviparity

EGG + YOLK -> LAID -> HATCH

•Pseudoplacental viviparity

EMBRO (PLACENTA-FED) -> LAID/HATCH ~SIMULTANEOUSLY

•Hemocoelus viviparity

EMBRYO IN HAEMOLYMPH

•Adenotrophic viviparity

LARVA HATCHES IN FEMALE – MILK FED -> LAID -> PUPARIATION

Question 19

The Insect Head

Answer 19

Question 20

Insect Mouthparts

Answer 20

Good example of diversity in form and function:
•Specific mouthparts have been adapted to feed on different substrates
•In some cases. Different mouthparts have been modified to feed on the same type of food, e.g. liquids
•Two broad categories:
•mandibulate (chewing)
•haustellate (piercing-sucking, sponging, and siphoning)

Question 21

Mandibulate Mouthparts

Answer 21

Question 22

Haustellate Mouthparts (aphid)

Answer 22

Question 23

Haustellate Mouthparts (Housefly)

Answer 23

Question 24

Mouthparts Glossary

Answer 24

Labrum: articulates with the lower margin of the insect’s “face” (the clypeus), concealing some or most of the mandibles.

Mandibles: positioned between the labrum and maxillae. Largest mouthparts of chewing insects - used to masticate (cut, tear, crush, chew) food.

Maxillae: (paired) situated beneath the mandibles, manipulate food during mastication, have hairs and “teeth” along their inner margins.

Labium: single structure, although formed from two fused secondary maxillae. Described as ‘floor’ of the mouth.

Proboscis: siphoning mouthpart, e.g. in Lepidoptera.

Stylet: elongated piercing mouthpart, e.g. in Aphids.

Labellum: sponge-like feeding organ with pseudotrachae, e.g. house fly.

Question 25

Order Collembola

Answer 25

ancient order – now actually considered to be separate Class within Super-Class Hexapoda.

Apterygote – without wings, no metamorphosis

Two main groups (sub-orders): elongate and globular.

Habitat: soil and leaf litter (100, 000 ind/m3)

Diet: detritus

One of the most abundant macroscopic animals

Question 26

Leg Morphology (Specifically Bees)

Answer 26

• Distinct modifications of leg segments for pollen collection and transport.
• Pollen is collected by spines on first tarsal segment and transferred to the tibia of opposite leg – the pollen ‘basket’ for transport back to hive.
• A spur at the base of tibia on middle leg dislodges pollen masses from the basket.

Question 27

Click Beetles

Answer 27

(true beetles)

• Function: to regain normal walking position when tipped over or fall from plants onto back (and deter predators if on back).
• A ‘spine on ventral surface projects back into cavity on the mesothorax.
• Spine pushes quickly into cavity (click noise) and beetle ‘rolls’ to one side and can move onto legs.

Question 28

Fleas

Answer 28

Division Holometabola, Order Siphonaptera

• Tube-like mouth-parts adapted to feeding on the blood of their hosts.
• Bodies are laterally compressed permitting easy movement through the hairs or feathers.
• Legs are long, the hind pair well adapted for jumping (around 200 times their own body length)
• Body is hard, polished, and covered with many hairs and short spines directed backward, which also assists its movements on the host.
• Tough body is able to withstand great pressure, likely an adaptation to survive scratching etc

Question 29

Social Structures in Insects

Answer 29

Most insects are entirely solitary in life style
• In Exopterygote insects (Hemimetabola), only strongly social insects are the Order Isoptera - TERMITES

• In Endopterygote insects (Holometabola), social insects are in the order Hymenoptera – BEES, WASPS ANTS

Question 30

Order Isoptera

Answer 30

Termites - important pest in tropical areas

Highly social insects: Large colonies in mounds – TERMITARIUM
• Up to 4-5m high (several million individuals)
4 Castes

Primary reproductives (eventually become King and Queen)

winged adults (♂ and ♀) (swarmers)

Roles: establish colony

• Secondary (supplementary reproductives if either primary dies)

wingless adults (♂ and ♀) or reduced wings

• Workers – wingless and sterile

Roles: foraging, food storage, brood/nest maintenance
• Soldiers – wingless and sterile

FUNCTIONAL MORPHOLOGY: mandibulate and nasute

Roles: defense

Question 31

Termite Feeding

Answer 31

Two main feeding habits

• Wood (rotten or sound), grass, fungi

Normal diet of workers

• Prepared diet
• stomodaeal – salivary secretion and regurgitated intestinal contents
• proctodaeal – droplets from the rectal pouch taken from anus after tactile stimulation

PREPARED DIETS ARE SOLE DIET OF SOLDIERS

Question 32

Biology of Termites

Answer 32

• New colonies founded by primary reproductives – leave in a swarm from an existing colony.
• Fly short distance, shed wings, excavate small chamber, mate.
• Reproduction – in year 1 primary Queen may produce 15-50 eggs. Mature queens produce several thousand eggs per day.
• Reproductive forms live for ~50 years; strerile castes for 2-4 years, supplementary reproductives develop if primary Queen dies.

Question 33

Family Vespidae

Answer 33

Wasps!

• New colonies established each spring
• New Queens emerge from dying colonies in Autumn, mate and overwinter.
• In spring queens leave hibernation sites feed on nectar and scout for nest site
• Queen scrapes wood fibres, mixes with saliva to form a pulp to build nest.
• Eggs are laid in the first cells, Queen collects nectar and insect prey to feed larvae.
• Emerging wasps are workers, which extend nest and collect food for subsequent generations.
• Mature nests may contain 12,000 cells
• In Autumn, males and potential Queens are produced (gynes) – fed by workers.
• When old queen dies, colony declines rapidly – gynes leave nest, workers flight, larvae neglected.
• Gynes mate and overwinter.

Question 34

Family Apidae

Answer 34

Bees!

• New colony established when old one becomes too crowded.
• Founder Queen departs with a swarm of workers.
• Workers build nest cells from wax – malleable at nest temperature 35°C – produced from wax glands.
• Cells in honey bee hive vary in size: small workers; larger drones
• Later in life of nest, elongate cells are produced containing new queens.
• Collected pollen and honey are stored separately in nest.
• Honey bees feed exclusively on plant fluids, and larvae are fed on honey and pollen.
• No animal prey = key difference with wasps.
• Honey bees do not hibernate – reduce activity and feed on stored honey

Question 35

Familae Formicidae

Answer 35

• All ants are social
• Two female castes: Queen and workers
• Workers can exist in different size classes
• New queens and males have wings, lost after mating – male dies.
• Complex genetics depending on species: workers may be sterile or egg laying, produce only males from unfertilised eggs.
• Queen exerts strong influence over workers