A typical insect head possesses a
pair of antennae; eyes; mandibles, labrum, maxillae and labium
(the latter four forming the cluster of "mouth parts", no. 32. in the diagram).
Lying above the oesophagus is the
brain or supraesophageal ganglion, divided into
three pairs of ganglia:
the protocerebrum, deutocerebrum and tritocerebrum from front to back (collectively no. 5 in the diagram).
Nerves from the
protocerebrum lead to the large compound eyes; (hence is sensory and probably equivalent to our midbrain)
deuterocerebrum to the antennae; (our forebrain is also associated with our sense of smell)
tritocerebrum to the labrum and stomatogastric nervous system.
Circum-oesophageal connectives lead from the
tritocerebrum around the gut to connect the brain to the ventral ganglionated nerve cord: (the output of teh brain hence probably equivalent to our cerebellum)
nerves from the first three pairs of ganglia lead to the mandibles, maxillae and labium, respectively
teh protocerebrum is huge in bees. (something like 1,000,000 neurons)
so big that I have trouble believing that its all from one ganglion associated with a single segment
Two very prominent optical lobes are present, and they are responsible for processing the inputs from the eyes. They are attached to the PC, but they’re not part of it.
I think
the reason the protocerebrum (which I think is analogous to our midbrain) is so large is because the animal eventually evolved multiple eyes (just like spiders have 8 eyes. Also just like millipedes have multiple legs) and the ganglia associated with them fused to form the so-called protocerebrum.
I believe that each lens of a compound eye was originally an entire eye with its own ganglia.