Intro to Insects Flashcards
How many insects are there?
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
Insect Diversity
Vary in size from sub-milimeter to crow-sized
heaviest extant: 100g
longest extant: 56cm
Habitats: just about everywhere save marine
Sociality
- 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
Common Features
- 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
Classification of Insects
•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
Sub-class Apterygota
• 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)
Subclass Pterygota
- 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
Superorder Exopterygota
(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.
Superorder Endopterygota
- 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
Types of Insect Larvae
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
Eruciform Larvae
(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)
Campodeiform Larvae
OLIGOPOD: Lack abdominal pro-legs; Have functional thoracic legs
• Well sclerotised
• Distinct segmentation
• Dorso-ventrally flattened
• Active predators
Scarabaeiform Larvae
OLIGOPOD: Lack abdominal pro-legs; Have functional thoracic legs
- Well sclerotised head only
- Less distinct segmentation
- slow moving detritivores or phytophages
Apodous Larvae
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
Larval Types by Order
Endopterygote Pupae
Between their last larval instar and their adult form, Endopterygotes enter a pupal stage
Insect Reproduction
- 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)
Oviparity (egg-laying)
•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
The Insect Head
Insect Mouthparts
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)
Mandibulate Mouthparts
Haustellate Mouthparts (aphid)
Haustellate Mouthparts (Housefly)
Mouthparts Glossary
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.
