Entomology Measurement Antenna Diptera

Measurement of the length of the first two antennal segments in Choerades

M. J. SMART*

(1998)

[* The author sent this description to Mr. Geller-Grimm - not published]

A problem arieses in the measurement of the length L1 of segment 1 because the outer edge of segment 1 is not perpendicular to the long axis of the segment (in cross section the segment is trapezium-shaped)
It is therefore necessary to define L1 as either:

the minimum length L1a
the maximum length L1b or,
the average of the two = (L1a+L1b)/2

Measurement of the antennal length

A second problem arises because the long axis of segment 2 is not aligned with the long axis of segment 1. Theoretically, L1 should be measured with the microscope graticule in one position and L2 with the graticule of a different angle, so that it is aligned with the long axis of each segment individually. In practice, any movement or adjustment of the microscope between measurements involves introducing baseline and/or parallax errors into the measurements. It is therefore better to make both measurements along the axis of segment 1 - i.e. as M1 and M2, but this will involve a slight underestimation of L2.

For the purposes of the present exercise, I have measured M2 and M1 assuming M1 = (L1a+L1b)/2.
The ratio L1/L2 has been assumed to be equal M1/M2.

Address

Malcolm J. SMART, Southcliffe, Pattingham Road, Wolverhampton WV6 7HD, United Kingdom, malcolm@smart-home.freeserve.co.uk