Arrangement of setae

3. CHAETOTAXY

4. Insect chaetotaxy is the study of the arrangement , number and types of hairs also
called setae on the body of insects
These setae are found on various parts such as the antennae,legs,wings and
abdomen .
The arrangement of setae and number of setae can be specific to certain body
segments and species
The study of chaetotaxy requires specialized equipment and techniques such as
scanning electron microscopy.
INTRODUCTION

5. IMPORTANCE
• Insect chaetotaxy is used for
identification and classification of insects ,
as different species have different
classification.
• Chaetotaxy also provides insights on
evolutionary relationships between
different insect groups, as the pattern of
setae can indicate common ancestry.
• In addition to that it is useful to
understand the functions of setae

6. Chaetotaxy in Trichoplusia ni

7. Head : There are 11 pairs of
setae on the head portion
• Seta i on the top level with
the top of the epicranial
suture and situated further
away from the suture than
Setae ii,which is near the top of
the frons.
• Seta ii in level of iii and much
above top of the frons;
• Seta iii centre of epicranial lobe

8. • Seta iv placed before ocelli
above level of 5th ocellus;
• Seta v behind ocelli, and
situated near and above 6th
ocellus, nearly equidistant from
iv and xi; vi and vii;
• Seta viii in front of ocelli, in
level of and close to 4th
ocellus,being nearer to iv than ix.
Setae ix, xi
• while seta x is behind ocelli as a
whole and below level of vi.

9. • Seta iv placed before ocelli
above level of 5th ocellus;
• Seta v behind ocelli, and
situated near and above 6th
ocellus, nearly equidistant from
iv and xi; vi and vii;
• Seta viii in front of ocelli, in
level of and close to 4th
ocellus,being nearer to iv than ix.
Setae ix, xi
• while seta x is behind ocelli as a
whole and below level of vi.

10. Thorax - Prothorax (fig. 3):
• Cervical shield slightly curved on
lateral bears four pairs of setae: i, ii,
iii and iv.
• The bisetose va is borne on the same
tubercle, which is situated above the
level of the spiracle, near the
curvature of the cervical shield and
just ectad to iv,v,vi, vii and viii.Which
is anterior and close to spiracle.
• vii being bisetose.

11. Meso and meta thorax :
Setae identical in positions both on
meso- and metathoraces;
i, ii and iii all in a straight line and
equidistant from one another; iv
smallest
and placed on a dark tubercle ,
va moderately developed and
directly caudal of v and vb which
are borne by one tubercle;
vii unisetose and in a line with i, ii
and iii, while vi-ii (Forbes) is small
and occupies the usual place.

12. Abdomen.-
First eight abdominal segments (figs. 5-12):
• Setae i, ii and iii above the level of the spiracle, while iv
is posterior to and in a level with or ventral of the
spiracle
.
• Below the spiracle and above the base of the leg or in
that level in the legless segments are setae v, and vi, the
latter being unisetose.

13. • Seta vii trisetose in the first six
segments,
• viia and viib being on the same
tubercle and ,Viic on separate
ones in the 1st to 4th segments,
• In the 4th segment viic situated
very close to viia and viib; viii
comparatively smallerin size
and situated on inner side of leg
in the leg bearing segments or
near the mid-ventral line in
others.

14. • but all three ( i.e.viia ,viib
, viic) being separate in
5th and 6th segments
• but unisetose on 7th and
8th segments.

15. The positions and general relations of
the
setae to one another are the same in all
the segments as in P. orichalcea, except
in the case
of vii which differs in the 1st, 2nd and
4th segments.
In the 1st segment vii, instead of being
trisetose, is bisetose-viia and vii c being
borne on separate tubercles, while viib
is
not traceable
. In the 2nd segment vii is trisetose, but
all three setae are situated on separate
tubercles.
In the 4th segment vii is bisetose and
viib wanting.

16. Ninth and Tenth segments (fig. 13):
As usual, the 9th segment bears only six pairs of
setae :
P. oricholcea.
• Ninth segment devoid of spiracle and bears only
six pairs of setae. i, ii and iii situated as in first eight
segments, iv and v not traceable ;
• vi and vii both unisetose, forming a straight line with viii,
which is near the mid-ventral
P.ni
i, ii and iii maintain the same positions as in P. orichalcea, but
iii appears weakly
developed and comparatively smaller in size; vi in a line with
vii and Viii and placed as
far from vii as vii is from viii; vii and viii occupy the same
positions as in

17. Tenth segment aborted on lateral sides
and bears only four pairs of setae, viz.
i, ii, iii and iv;
• i near mid-dorsal line and very
near posterior margin;
• ii at a slightly higher level than i
and just on posterior margin of
segment;
• iii placed on posterior margin of
segment, below level of i and
nearly equidistant from iand ii,
while iv is situated near posterior
margin of segment, anterior most in
position and placed twice as far
away from iii as iii is from i.

18. Workers on the study of the setal arrangement in the immature forms of
the order Lepidoptera are divided in their opinions, forming two opposing
groups. Workers with extensive experience-like Dyar, Forbes, Fracker,
Hinton, etc.-all agree that the system of chaetotaxy is scientifically adequate
in its practical application in classifying the order into families and genera
from the immature stages.
As all the regions, viz. head, thorax and abdomen, show differences when
compared with the setal distribution of the respective regions in other species,
classification can be based on this factor either of one part or preferably of a
combination of all the regions of the body.
Conclusion

19. THANK YOU