Bio 367 - behavior & communication, development & life histories

communication

When an action or condition of one organism alters the behavior of another in an adaptive way

Why do insects communicate?

It may be an intraspecific prerequisite for behavior involving participation or cooperation

Adaptive values of communication

recognition of kin, locating members of opposite sex, give directions for food, regulate spacial distribution, antagonistic behavior, deception/mimicry

intraspecific comm.

within species

example of intrasexual comm.

When males are fighting in a lek to attract females

example of intersexual comm.

When males and females are interacting during courtship or parental care

example of interspecific comm.

When a stink bug releases odor or a plant releases a chemical that deters pests

example of food signaling

Honeybees do the waggle dance to signal food

example of food scarcity communication

When a plant is heavily infested and low on nutrients, aphids will pick up on signals to produce a generation of winged aphids for dispursal

example of alarm signaling

Hissing cockroaches will release an alarm pheromone that signals aggression and prompts bugs to quickly hide

example of trail cues

Ants will lay down trail pheromones that other ants can follow to a food source

example of growth and sexual maturation inhibition

Some colonial insects have queens that will produce pheromones that keep females from reaching sexual maturity

example of aggregation communication

When pine beetles find a new tree to feed on they produce an aggregation pheromone that can be sensed by others from a long distance

4 forms of communication

Visual, sound, light, chemical

modified spiracles

Forcing air through spiracles can create a hissing sou

wing vibration

Air can be forced through elytra to create a buzzing sound

stridulation

Process of sound production when insect rubs one part of the body against another part (often done with file and scraper in ants, crickets)

example of percussion communication

Mole crickets tap forelegs or maxillary palps on the ground, and can amplify their sound through a production chamber called a horn

color as a secondary sex character

Can be significant in courtship rituals when males and females differ. Peacock spiders use bright colors and long tufts of setae to attract females

warning colors

aposematic colors, warn of distastefulness, toxicity, venom

example of light production

Lightening bugs have a photic organ (lantern) where a chemical reaction produces bioluminescence. Used in courtship, aposematically, or to mimic prey species

Intraspecific chemical communication

By pheromones, chemicals produced by individuals to be received by individuals of the same species & induces a behavioral or physiological change

Interspecific chemical communication

By kairomones, synomones, allomones

kairomones

Chemicals that benefit the receiver and are disadvantageous to the producer (ex. plant metabolism by products)

synomones

Benefit both the receiver and producer (ex. when a plant is being damaged it releases chemicals to attract predators to attack insects)

allomones

Benefit the producer, not the receiver (ex. allomone plants and kairomone plants will be planted next to each other to deter pests)

molting

Growing a new exoskeleton under the old one and shed off previous, since they are hard and don’t flex with growth

Requirements of molting

Brain responds to stimuli about external env. (temp, daylight), insect has grown enough and has abundant nutrients for next life stage, hormones have been released by neurosecretory system

ecdysone (ECD)

Primary hormone involved in telling an insect it is time to molt

juvenile hormone (JH)

The amount of this hormone tells the insect what life stage its going into. JH high + ECD high= molt to juvenile

Molting step 1

Apolysis: the epidermis separates from cuticle at zone of formation

Molting step 2

Apolysial space (zone of formation) fills with molting fluid, enzymes separate old inner cuticle layer and compounds that begin new cuticle. Epidermis is growing as epidermal cells divide by mitosis

Molting step 3

New outer cuticle layer is formed

Molting step 4

Molting epidermis produces enzymes that dissolve endocuticle of old cuticle

Molting step 5

New cuticle layers continue to be deposited

Molting step 6

Ecdysis: remnants of old cuticle split along endysial line, which is the weaker area along middle of dorsal thoracic nota

Molting step 7

Eclosion: the insect emerges from its old exoskeleton as a teneral adult

exuvium

Old exoskeleton that was shed off

egg

contains developing embryo

juvenile

After egg hatches, before development of wings & sex. reproduction. Nymph or larva

nymph

Juvenile of hemimetabolous insects that resemble adult

larva

juvenile of holometabolous adult

pupa

In holometabolous insects, non feeding stage with no legs or wings

subimago

Has all adult features EXCEPT not sexually mature and they aren’t completely sclerotized, will molt again

teneral adult

Right after they do final molt, not yet sclerotized

Imago

Once completed adult sclerotizes

indeterminate growth

Will continue to molt until they die, found in primitive hexapods (springtails & silverfish)

determinate growth

Have a set number of times they will molt to get to an adult, mostly in winged insects

life cycle

From egg to adult, divided by periods of growth and development

growth stage

Period of development between molts (ex. egg stage, 1st 2nd & 3rd instar larval stage, 1st 2nd & 3rd nymphal stage, pupal stage, imago stage)

stadium

Interval of time between molts

instar

Postembryonic juvenile growth stage (1st instar larva, 2nd instar larva, 3rd instar larve)

ametabolous

egg→nymph→…→adult

In privative hexapods & primitively wingless, overlapping generations means all generations found together

hemimetabolous (“incomplete metamorphosis”)

egg→nymph→…→adult

Juvenile looks like adult but smaller with developing wing pads, in Hemiptera, Odonata, Ephemeroptera. May have overlapping generations

holometabolous (“complete metamorphosis”)

egg→larva→…→pupa→adult

Juvenile is caterpillars, grubs, & maggots with rare overlapping generations. In Coleoptera, Hymenoptera, Lepidoptera, Diptera

polypod larva

have prolegs (unsegmented fleshy abdominal legs) and segmented thoracic legs, “many legs” on caterpillars

polypod larva

oligopod larva

segmented thoracic legs, “few feet” in beetle larva

oligopod larva

apod larva

no legs, in maggots

apod larva

exarate pupae

Have appendages not tightly appressed to the body

decticous exarate pupae

Have articulated mandibles used to cut open cocoon

adecticous exarate pupae

Non articulated mandibles, adult sheds pupal cuticle and used legs and mandibles to escape cocoon

obtect pupae

Enclosed in firm pupal case, cuticle is heavily sclerotized w/appendages tightly appressed to body, adecticous only

puparium

Formed under last larval exoskeleton, pupa forms under this

cocoon

Covering made to cover pupa

puparium

cocoon

chrysalis

What factors affect development?

Life cycle duration and reproductive strategy - Number of times they reproduce and number of eggs produced involves tradeoffs and may maximize survival

voltinism

Number of generations per year, measure of how long life cycle is

univoltive life cycle

egg→adult=1 year

One generation per year, reproduces annually, most insects

biovoltine life cycle

Complete life cycle in one year but lay eggs twice

multivoltine life cycle

Produce more than two generations per year (aphids)

semivoltine life cycle

May take 2-3 years to complete life cycle (cicadas live for 7-13 years)

What factors influence insect development?

Temperature (ectothermic=unstable internal temp influences chemical rxn rate), food availability, pauses in development

aestivation

Long term dormancy in summer, may be from high temp, low water, low food resources

hibernation

long term winter dormancy

torpor

short term dormancy in summer or winter from extreme temperature

quiescence

aestivation, hibernation, or torpor in response to unfavorable conditions w/development resuming after physiological stimulus

diapause

Aestivation or hibernation with adaptive physiological change, development resumes following a stimulus

Obligatory diapause

Occurs at fixed time regardless of varies env. conditions in each generation. (ex. mosquitos lay eggs above water level to diapause until optimal conditions (water cover) reduces oxygen and temp around eggs to resume development)

facultative diapause

Occurs in bivoltine and multivoltine insects when they must survive unfavorable conditions. Pushed development from univoltine to other types.

The speckled wood butterfly is univoltine in the south and bivoltine in the north- Why isn’t it considered obligatory diapause?

It is facultative diapause because this diapause doesn’t occur in every population, only those undergoing cold temperatures in the north

reproductive diapause

A cessation or suspension of reproduction in mature insects so metabolism is redirected to other physiological needs, such as migration, producing cryoprotectants during temp extremes, food