What is Ametaboly?
These insects hatch from the egg in a form resembling adult but lacking genitalia (primitive developmental pattern) e.g.
What is Hemimetaboly?
Incomplete metamorphosis
- Juvenile stages are called nymphs
- In all but the youngest instars, wings (or wing buds) are visible externally
What is Holometaboly?
Complete metamorphosis during pupal stage
- Juvenile stages prior to pupation are called larvae
- Wings and other structures are present internally in juvenile stages as groups of undifferentiated cells
What are some features of the egg stage in insect development?
- Eggs can be laid singly, in clusters, or in oothecae
- A lot of insects spend winter/dry season as eggs (diapause)
What are immature holometabolous insects called?
Larvae or pupae
What are immature hemimetabolous insects called?
Nymphs
Why might holometaboly be beneficial?
- Reduces competition between adults and juveniles for the same food source
- Allows for developmental plasticity (e.g. adults and nymphs may occupy different ecological niches)
What are three different types of larvae?
- Oligopod larvae: 3 pairs of thoracic legs
- Polypod larvae: 3 pairs of thoracic legs + abdominal prolegs
- Apod larvae: no legs
When does metamorphosis between instars occur and what controls metamorphosis
- Onset of metamorphosis between instars generally occurs due to the insect reaching a certain size
- Metamorphosis is under the control of hormones (e.g. juvenile hormone)
What are the two main processes in pupa (holometabolous insects)?
- Pupation is the moult into the pupal stage
- Eclosion is the process of emerging from the pupae
What are the main features of the adult (imago) stage?
- Adult stage is defined by sexual maturity after the final moult, can be triggered by environmental changes. Reproduction is the major goal of the imago
- Newly emerged adults have a soft cuticle, they swallow air to increase haemolymph pressure and expand
What is voltinism?
The number of generations per year
What are the three different types of voltinism?
- Univoltine (one generation per year)
- Bivoltine (two generations per year)
- Mutlivoltine (many generations per year)
- Semivoltine (less than one generation per year) e.g. cicadas take 13 or 17 years to mature
What are some of the environmental (abiotic and biotic) factors that effect development (growth rate)?
- Temperature, moisture
- Type and amount of food
- Presence of environmental signals
- Mutagens/toxins can lead to fluctuating symmetry/developmental abnormalities
- Other organisms including competitors and predators (e.g. influence on food availability)
What is diapause? And what are some environmental cues that could cause diapause?
The delay in development in response to adverse environmental
- Physiological shanges before diapause: storage of lipids, proteins and carbs, accumulation of anti-freeze polyhydric alcohols (winter diapause)
- During diapause, the metabolism is lowered and development stops
Environmental cues (e.g. photoperiod, temperature, food quality) alter levels of juvenile hormone and diapause hormone, triggering diapause.
What are the different types of water based on their oxygen supply, and how does this affect aquatic insects?
- In lentic (standing) water, oxygen diffuses through water slowly. Insects may have to live in low oxygen conditions for long periods
- In lotic (flowing) water, oxygen diffuses with currents and turbulences and is less limiting.
How do the aquatic insects exchange system differ from terrestrial insects, and what limitations does this pose?
- Exchange systems depend upon oxygen diffusion. In the majority of terrestrial insects, trachea open to atmosphere via spiracles
- For some small aquatic animals, oxygen can easily permeate the body wall
- Larger insects require augmentation of gaseous exchange:
1. Oxygen uptake with a closed tracheal system
2. Oxygen uptake with an open spiracular system
3. Behavioural ventilation
Why might a closed tracheal system in aquatic insects be advantageous?
Aquatic insects have a closed tracheal system, where air is trapped in a network of tubes (tracheae) and brought directly to the cells, because it allows them to efficiently extract oxygen from the water and maintain a higher oxygen concentration gradient. This is important because oxygen is less abundant in water than in air.
The closed tracheal system prevents the loss of oxygen to the surrounding water, ensuring that oxygen reaches the tissues where it is needed for respiration. Additionally, this system helps prevent the entry of water into the tracheae, which could disrupt gas exchange and buoyancy control in aquatic insects.
What type of aquatic insect has an open tracheal system, and how does it manage to keep ventilating?
Diving beetles
What structure is present in aquatic insects with closed tracheal systems, and what does it help to increase?
The role of gills is to increase the gaseous exchange surface area
What is behavioural ventilation?
Insects moving their gills to increase gaseous exchange
Why might aquatic insects choose certain environments?
- Due to the flow > if the flow is higher this maximises the insects oxygen uptake
What characterises lotic systems (streams, rivers)? And what might the velocity of flowing water have an effect on?
Lotic systems:
- Unidirectional, fluctuating flow
- Unstable channel and bed morphology
The velocity of flowing water is a major influence on:
- Substrate type and size
- Transport of fine particles (food or other)
- Maintenance of high oxygen
What are the two sources of food for stream invertebrates?
- Autochthonous (from within the stream e.g. algae)
- Allochthonous (from surrounding vegetation e.g. leaves from tree)
