Review Sheet -- Test 4 (Week 14) Biology 1224 -- Entomology; James Adams
Quick Nervous System review:
Brain, ventral nerve cord(s), segmental ganglia. Integration (refinement) and even simple
modification of behavior (learning?) can take place in ganglia.
Chapter 6, pgs. 139 - 144
Is all insect behavior "hard-wired"? A lot certainly is, but behavior really depends on
three different factors:
1. Genetics -- innate behavior or instinct (reflexive [protective] behaviors are genetic)
2. Learning -- experience
3. Physiological state -- hunger, thirst, molting, etc. (drives)
In insects, learning is much less important than it is for you, but that doesn't mean insects can't
learn a limited number of items, especially those individuals that are long-lived in some life stage.
Control of behavior involves two major systems of the insect (as it does in you): nervous
and endocrine. The nervous system controls moment to moment activity, while the endocrine
system (with its hormones) controls activities taking place over a longer period of time
(development, for instance).
Taxes (plural of taxis)
A taxis is an orientation behavior, typically involving movement of the insect toward
(positive) or away from (negative) a specific stimulus.
Types: geotaxis, phototaxis, anemotaxis, phonotaxis, chemotaxis, astrotaxis,
hydrotaxis, thermotaxis (geo- refers to gravity [the earth], anemo- to wind currents, phono-
to sound, astro- to celestial bodies, hydro- to water, thermo- to temperature)
Examples? You will need to be able to provide examples of these, or recognize examples
that are given.
Taxes are not necessarily rigidly programmed -- insects in many cases may alter their
response to specific stimuli. Some taxes are often tied together, such as negative phototaxis and
positive geotaxis, or the reverse (why?). READ last full paragraph, first column, page 139.
Instincts -- most complex instinctual behaviors are called fixed action patterns: one stimulus
always results in a stereotypical response.
What kinds of behavior would you expect to be instinctual? Many behaviors that are
absolutely vital to life or reproduction are fixed and unchangeable. Feeding behaviors, migratory
behaviors, mating, oviposition, nest building, molting behavior, cocoon building are mostly innate.
Any behavior that can be changed as a result of experience.
Very simple learning may occur in most insects. A good example would be learning to
avoid unpleasant (but not fatal!) stimuli.
Communication is absolutely necessary for any social behavior, and all insects must have the
ability to communicate for at least one (social) behavior -- mating. Communication may be visual,
chemical, auditory or tactile, or a combination of these signals. It may be short-range or long-
range; and may be used in sequence from long-range to short-range (examples?). It may be
intraspecific (such as for mating, aggression/defense [attack in honeybees, for example], or a
wide variety of behaviors in social insects) or interspecific. Interspecific communication can be
divided into those that: 1) benefit sender (warning signals), 2) benefit recipient (predator
avoidance [moth and other insect ears, for instance]), 3) benefit both (mutualistic, such as
flower signals that result in pollination/nectar gathering).
You will need to give examples of or recognize examples of visual, auditory, chemical
and tactile communication in the insect world.
Pheromones -- trail, aggregation (lekking), sex, alarm
Allomones, Kairomones, Synomones
We'll discuss examples of all of the above in class, and,
as indicated, you will be responsible
for knowing both what the terms mean and examples of each (see below as well).
Communication (continued; pages 145-151; also page 169) --
The Honeybee dance: a combination of tactile/auditory/visual/chemical communication
Worker honeybees typically exhibit different behaviors as they get older -- initially, they are
nurses to the brood, then help build new cells inside the hive, then guard the entrance, and finally
act as foragers for nectar and pollen (see page 169). These "new" foragers learn where the best
food sources are by following, and ultimately learning, the honeybee waggle dance.
The waggle dance is done on the vertical surface of a mostly dark hive (the visual
communication here is minimal, though the bees will initially learn to associate the color of the
flower with the food source, as well as learn landmarks and direction of sun in relation to the food
source). Directly up on the surface (negative geotaxis) represents toward the sun; dancing at
an angle on the surface represents the direction to the food at the same angle away from the
sun. Remember that polarized light on mostly cloudy days can indicate where the sun is to a bee.
The dance is called the waggle dance because the bees "waggle" the abdomen while dancing in
the appropriate direction, alternating looping to the left and then to the right, returning each time to
the correct angle and waggling again. Other bees follow the dancer, and touch the dancer with the
antennae (tactile) to get a sense of the direction to the food resource. The followers can pick up
flower odors from the dancer, and the dancer/forager may even present a small amount nectar
from her crop to the followers (chemical). Distance to and quality of the resource is also
communicated. Distance is indicated by the speed of the dance (slower = farther). The waggle
component produces a buzz (auditory), which is lower pitched when slower; the turns are also
done more slowly. The quality is indicated by the length of time the dance persists (longer =
better). Bees can apparently even indicate changing distance to experimental food resources
(weird!). All of this will be clarified in class; you will need to be able to interpret drawn examples
of the dance on the next test (see page 147).
The Sun Clock and Circadian Rhythms
Most insects (indeed most organisms) use the sun as a reference for all sorts of activities.
Different insects are active (and at rest) at different times (matinal [dawn], diurnal, crepuscular
[at dusk (or dawn)], nocturnal). The insects may further divide their active time into foraging
time at peak resource abundance, mating time, oviposition time, molting, etc. All of these
activities will necessarily follow a daily, or circadian, cycle.
For some activities, the cue (light) is the complete stimulus for the behavior. However, for
several behaviors in many insects, there is an internal clock that is partly responsible for the
behavior that is reset each day by the sun. For instance, crickets calling for mates will continue to
do so at approximately 24 hour periods even in total light or dark (see page 150). So, although
the orientation cue is external (the sun), there is an internal component (the clock), which will
continue to run in the absence of the external cue. Exactly how the clock works is not clear.
Using phototaxis as a directional reference to other resources (food, migration to south,
etc.) requires an expectation as to where the sun should be at specific times during the day -- in
other words, an internal clock. For example, the sun should be east in the morning, south at noon
(if you are in the northern hemisphere), and to the west in the evening. So migrating individuals
trying to maintain a constant direction will adjust their response to the sun as the day progresses.
Social Behavior --
We have talked about several groups of insects that have at least some social behavior.
The obvious ones include the termites and many hymenopterans, but we've also mentioned some
dermapterans, embiopterans, roaches, gryllids, psocopterans, and hemipterans (several families,
including some that are social with ants) with some form of rudimentary social behavior.
Furthermore, a number of species in the Diptera, Coleoptera and Lepidoptera are gregarious, or
communal (behavior where groups get together but not for care/rearing of young), particularly
in the larval stages, and so could be considered to exhibit some social activity. Examples include
passalid beetles, tent-building lep larvae, Monarch Butterflies roosting during migration, roosting
groups in Long-Winged Butterflies (check out the Zebra Butterflies [Heliconius charitonius] on
my Georgia Lepidoptera website), and maggots of several fly species.
Subsocial Behavior -- some parental care, but parent leaves/dies before immatures reach
adult stage. This would include dermapterans, some hemipterans/homopterans (14 families),
gryllids, roaches, psocopterans, embiopterans, thrips, beetles (9 families), and some bees/wasps.
Parasocial Behavior -- interactions between adults of the same generation. Many wasps
and bees exhibit parasocial activity, where a nest is inhabited by several females, all of which
provision their own brood cells. The benefits are added protection for all offspring in the nest.
Eusocial Behavior -- characterized by the following: 1) members cooperate in caring for
the young, 2) more than one adult generation overlaps in the colony, and 3) there is a division of
reproductive labor between reproductives (queens and kings/drones) and the non-reproductive
workers. In other words, there is a caste system. True eusocial behavior is exhibited by termites
and by a number of different hymenopteran lineages (wasps, ants, bees). In most cases, the castes
are determined largely by specific semiochemicals released by certain members of the colony.
Termites (pages 158 - 160)
All termites are eusocial. Termites differ from hymenopteran social species by the
following: 1) termite colonies have castes of both sexes; 2) both sexes are diploid; and 3)
termites are hemimetabolous, meaning the similar young instars may actually participate in work.
Castes of termites include: primary reproductives (initially winged after last molt),
supplementary reproductives, workers, soldiers (mandibulate and/or nasute).
Hymenopterans (pages 161 - 169)
Several different lineages of Hymenoptera are eusocial -- ants, at least one lineage of
vespids (a few subfamilies, including the Paper Wasps [Polistes] and the Hornets and
Yellowjackets), one lineage of neotropical sphecids, and several different lineages of bees. They
all differ from termites by the following: 1) they are holometabolous; the larvae are helpless and do
not participate in colony health, 2) nest caretakers are only female; 3) males are haploid (from un-
fertilized eggs), and solely for reproduction. The males often die or are rejected from the nest/hive
after mating (and then die).
Castes typically include the queens and sterile female workers for ants and the highly
social bees in perennial colonies, with several weird exceptions in the ants. New colonies are
established by solitary mated queens in ants, and colony division, or swarming, in the bees.
Within the vespids and social bees that establish new colonies annually, there may be one queen
with sterile (but similar sized) workers, there may be more than one queen, or one dominant
reproductive which one of the other nest caretakers will replace if the original dominant "queen"
is killed. At the end of the year, the nest is disbanded and typically solitary fertilized queens go
into "hibernation" to reestablish new nests the following spring.