1. INSECT GROWTH & METAMORPHOSIS
Unit 3 - Internal Features of Insects
INSECT GROWTH & METAMORPHOSIS
ADULT
NYMPH
EGG
ENT063 - Spring 2006

2. All insects develop from eggs
Unit 3 - Internal Features of Insects
All insects develop from eggs
Lady beetle egg masses
German cockroach with ootheca
Most hatch from an egg after it has been laid
Some are born alive from eggs that developed inside the female (e.g., Madagascar hissing roach)
Some insects lay their eggs singly, others lay their eggs in masses
Some insects, such as the cockroach, lay their eggs in a capsule (ootheca)
Some insects, such as the grasshopper and the June beetle, lay their eggs in the ground
Plant-feeding insects lay their eggs on plants and parasitic insects lay they eggs on or in the body of the host.
Parasitic wasp laying egg in caterpillar
Grasshopper laying egg in ground
ENT063 - Spring 2006

3. Unit 3 - Internal Features of Insects
Insect Growth
With few exceptions (e.g., silverfish), only immature insects grow.
In order to grow, an insect must molt:
shed their old cuticle
form a new cuticle
The growth of an insect in each stage is limited by the space available to it within its external skeleton. So in order to grow, an insect must molt. As the insect develops, it lays down a new skeleton directly beneath the old one. The old body wall splits down the back, and the next stage emerges and expands to a larger size before the skeleton hardens again. This process is repeated 4 – 8 times in the average insect before it reaches adulthood. Some species, however, may have as many as 20 or more molts.
ENT063 - Spring 2006

4. Unit 3 - Internal Features of Insects
Hormones
HORMONE - a chemical formed in an organ or body tissue that travels through the body and causes some effect on another body part.
The primary hormone controlling molting is ecdysone.
Juvenile hormone (JH) is also involved in the molting process.
In insects, the molting process involves numerous, complex interactions between hormones, enzymes, cell, and organs. Therefore, a detailed discussion is beyond the scope of this presentation. The primary hormone controlling molting is ecdysone. Ecdysone induces activation or production of the enzymes associated with molting.
At high levels, JH keeps the insect in the juvenile stage. When it’s time to molt, JH levels decrease and molting begins.
Other hormones (e.g., eclosion hormone) are associated with the process of shedding the old cuticle, and the formation and sclerotization (or hardening) of the new cuticle.
ENT063 - Spring 2006

5. Unit 3 - Internal Features of Insects
Hormone Production
Some insecticides mimic these hormones - prevent the insect from molting or maturing or cause it to become an adult too quickly.
Insect growth regulators (IGR’s) are chemicals that are currently used in pest management. Methoprene is an IGR that prevents immature insects from molting by mimicking JH. This type of IGR is referred to as a juvenile hormone analog.
ENT063 - Spring 2006

6. Unit 3 - Internal Features of Insects
REMEMBER: The outer layer of the exoskeleton is called the cuticle. The cuticle contains the chemical chitin.
Cuticle
Approximately 50% of the dry weight of an insect’s exoskeleton is chitin. So, anything that depletes the formation of chitin will have a negative impact on the structural integrity of the exoskeleton. Some IGRs disrupt the laying down of new during new cuticle formation. These IGRs are called chitin synthesis inhibitors (CSIs). CSIs include hexaflumuron/noviflumeron (the AI in Sentricon, the termite bait) and lufenuron (the AI in Program).
ENT063 - Spring 2006

7. Unit 3 - Internal Features of Insects
Insect Growth
ENT063 - Spring 2006

8. Unit 3 - Internal Features of Insects
ENT063 - Spring 2006

9. Unit 3 - Internal Features of Insects
Insect Metamorphosis
Metamorphosis refers to a change in form.
Insects go through different life stages during metamorphosis.
ENT063 - Spring 2006

10. Terms Used in Metamorphosis
Unit 3 - Internal Features of Insects
Terms Used in Metamorphosis
Stage - a distinct period in development of an insect.
Instar – the insect’s form in between molts. Usually designated by numbers (e.g., 3rd instar). The instar number is one more than number of times it has molted (e.g., a 3rd instar insect has molted twice)
Knowing the instar of the pest may be important for control (older larvae may be harder to kill).
ENT063 - Spring 2006

11. Unit 3 - Internal Features of Insects
ENT063 - Spring 2006

12. Unit 3 - Internal Features of Insects
Insect Life Stages
Egg - most insects deposit their eggs singly or inv clusters. Some insects (e.g., aphids) deposit live immatures.
Immatures - young, nymphs or larvae. Usually the destructive stage of an insect.
Adults - primary purpose is reproduction.
ENT063 - Spring 2006

13. Types of Insect Metamorphosis
Unit 3 - Internal Features of Insects
Types of Insect Metamorphosis
ENT063 - Spring 2006

14. Unit 3 - Internal Features of Insects
No Metamorphosis
Primitive wingless insects
Little change in appearance (mostly change in size)
Adults can molt
Example - silverfish
Adults of insects that don’t undergo metamorphosis are like their young in many ways. They share similar food, environmental, and habitat preferences, meaning that all stages of development will be found together in a structure.
Unit 3
ENT063 - Spring 2006

15. Gradual Metamorphosis
Unit 3 - Internal Features of Insects
Gradual Metamorphosis
Egg
Adult
Nymph
Gradual change in appearance
Immatures (nymphs) and adults usually have the same food preferences.
Most adults have wings; older nymphs have wing buds
Adults do not grow or molt.
Examples – cockroaches, termites, bed bugs, crickets, aphids
Immature and adults share similar habits, food preferences, and body form, but the development into the adult stage is more distinctive. Reproductive organs and wing pads do not begin to develop until the later instars of the nymph and neither become functional until the insect reaches the adult stage. The adult stages does not molt.
ENT063 - Spring 2006

16. German Cockroach Life Stages
Unit 3 - Internal Features of Insects
German Cockroach Life Stages
ENT063 - Spring 2006

17. Complete Metamorphosis
Unit 3 - Internal Features of Insects
Complete Metamorphosis
Distinct changes in the insect’s appearance.
Immature = Larvae
usually look very different from adults
usually have different food preferences from adult.
Examples – ants, wasps, fleas, flies, mosquitoes, butterflies & moths
Egg
Adult
Pupa
Larva
Insects with complete metamorphosis have four distinct life stages: egg, larva, pupa, and adult.
The impact of these factors on urban pest management are many. For some species, the larva itself could be the only stage that does economic damage (e.g., with some moths – Indianmeal moth). Or it could be a stage that has little to no impact on a person (as with fleas). If the larvae and adults do not share the same habitats, finding both habitats may be crucial to control, even if the non-damaging stage may not be noticed.
ENT063 - Spring 2006

18. Unit 3 - Internal Features of Insects
Indianmeal moth larva
Indianmeal moth adult
Ladybeetle adult
Ladybeetle larva
Unit 3
ENT063 - Spring 2006

19. Complete Metamorphosis
Unit 3 - Internal Features of Insects
Complete Metamorphosis
Pupal stage serves as a transition stage from larval form to the adult form
Most adults have wings; larvae do not have wing pads.
The pupal stage is also an important consideration. For some species, it can provide protection from pesticides and environmental conditions and hamper control efforts. For insects with a delayed emergence from the pupal stage, there exists the potential for a new infestation long after the problem appears to be under control.
When an adult emerges from the pupal case, it may or may not become a pest. The adult clothes moth, for example, does no damage; the larvae does all the damage. But with grain beetles, both the adult and larval stage feed on stored food products.
ENT063 - Spring 2006

20. Modified Metamorphosis
Unit 3 - Internal Features of Insects
Modified Metamorphosis
Ticks and mites
Larva - 6 legs Nymphs & adults - 8 legs
Larvae, nymphs and adults may have different host preferences
ENT063 - Spring 2006

21. Modified Metamorphosis
Unit 3 - Internal Features of Insects
Modified Metamorphosis
ENT063 - Spring 2006

22. Unit 3 - Internal Features of Insects
Questions?
ENT063 - Spring 2006