Biology Reference
In-Depth Information
(
Waddell and Quinn 2001
). Molecular-genetic methods may allow us to local-
ize and identify some of the individual genes among the “many” involved in
determining the interesting and complex behaviors exhibited by insects (
Doerge
2002
). Perhaps the most significant advance in the study of behavior has been
the sequencing of whole genomes of insects other than
Drosophila
. This has
allowed novel and detailed studies of behavior in a variety of insects and prom-
ises to provide exceptional new insights.
Analyses of insect behavior use techniques from several disciplines includ-
ing anatomy, biochemistry, ecology,
ethology
(study of animal behavior in the
natural environment), genetics, psychology, physiology, and statistics (
Matthews
and Matthews 1978, Hay 1985, Bell 1990, Holman et al. 1990, Via 1990, Barton
Browne 1993, Heisenberg 1997, Doerge 2002
). These disciplines are required
because an insect perceives the environment through its sensory systems. The
external sensory stimuli are transduced into electrical information, which is
then processed and decoded, leading to a behavioral response. Behavior can be
divided into several sequential steps:
stimulus recognition
,
signal transduction
,
integration
, and
response
or motor output.
11.3 The Insect Nervous System
The insect brain contains
≈
10
5
-10
6
neurons. It consists of three main divisions,
the
protocerebrum
,
deutocerebrum
, and
tritocerebrum
. In each division, differ-
ent
neuropil
regions are located; a neuropil is a dense network of interwoven
axons and dendrites of neurons and neuroglial cells in the central nervous sys-
tem and parts of the peripheral nervous system.
In the protocerebrum, centers are present that are associated with vision and
other sensory receptors (the mushroom bodies and central complex). The supe-
rior protocerebrum, with the pars intercerebralis, contains sets of neurosecre-
tory cells that supply neurohemal organs in the corpora cardiaca and corpora
allata, which are located in the head or prothorax in insects. The optic lobes
flanking the protocerebrum contain the most well organized neuropiles in the
brain.
Mushroom bodies in the brain are associated with olfactory pathways, includ-
ing olfactory learning (
Figure 11.1
). Among the insects, mushroom bodies dif-
fer greatly in size and shape, with the number of cells ranging from 2500 in
Drosophila
to 50,000 in the cricket
Acheta
, 170,000 in the honey bee, and
200,000 in the cockroach
Periplaneta
(
Heisenberg 1998, Strausfeld et al. 1998
).
The antennal centers are found in the deutocerebrum. In the tritocerebrum,
neurosecretory neurons and neurons associated with the control of feeding and
