a handbook of the mosquitoes of north america - Systematic Catalog ...

6 MOSQUITOES OF NORTH AMERICA
The Thorax
The thorax is distinctly wedge-shaped, the base uppermost.
The sides of the wedge form the pleura while the apex bears
the legs. The spiracles appear as prominent black-rimmed
apertures. Th e various sclerites composing the sides of the
thorax bear stiff setae or hairs which are arranged in rather
definite groups. The arrangement of these hairs and the ab-
sence or presence of certain groups form land marks for the
placing of our northern species in their respective genera with
comparative ease (Plates I and II). These setal groups are
as follows: (1) P YO t/ zoracic group, a varying number of
setae massed on the prothoracic lobes. (2) PTostema,l
group, a single strong setae or a dense mass of them located
on the proepisternum. (3) Pronotal group. This character-
istic group is located just in front of a ridge on the posterior
margin of the pronotum and consists of one or several stout
setae arranged more or less in a row. (4) Spiracztlnr group.
These are located in front of the anterior spiracle and behind
the pronotal ridge. They are usually arranged in a row and
must be looked for with care. (5) Post-spiracdar group.
These, when present, are situated on the upper portion of the
mesepisternum and behind the anterior spiracles. (6) Pre-
alar gr0u.p. A small group on the dorso-posterior projection of
the mesepisternum and directly in front of the point of attach-
ment of the wings. (7) Stenzo-pleural group. This group
consists of a variable number of setae located on the posterior
half of the mesepisternum. In most of our northern genera
it consists of a transverse row arising below the pre-alar group
and then extending ventrally as a more or less dense row along
the posterior margin of this sclerite. In some cases the setae
are located near the centre (Megarlzinxs), near the ventral
margin (Wyeomyia), or they may be scattered (Orthopo-
do?nyia). (8) upp er mesepimeral group. These are located
on the upper portion of the mesepimeron. (9) L ozwer ‘k12esepirneral
group. This group consists of one to several setae lo-
cated usually on the lower half of the mesepimeron.