1979] Thorpe & Harrington — Seed-Bug Parasitism 
401 
rates of parasitism between the sexes of L. diffusus (summed across 
both collection dates) was not significant at the .05 level. 
Table 1. Rates of parasitism by Catharosia in L. diffusus collected on 2 separate 
dates in 1978 in Wood Co., Wisconsin. 
19 June 22 August 
L. diffusus 
L. diffusus L. diffusus 
L. diffusus 
8 
5 
8 
$ 
Number collected 25 
40 
39 
42 
Numberparasitized 12 
27 
5 
8 
% parasitism 48 
67.5 
12.82 
19.05 
Total % parasitism 60 16.05 
Laboratory reared flies began mating on the day of eclosion. 
There was no apparent, regular courtship ritual. However, males 
appeared to orient visually to females and both sexes frequently 
flicked their wings upward while running, displaying the white apex 
of the wing which contrasts sharply with the darker basal portion. 
This wing flicking behavior may serve in some sort of intraspecific 
visual communication. Copulating males placed their foretarsi over 
the females’ eyes but no special adaptations of the male foretarsi 
were discernible. The duration of copulation ranged from a few 
seconds to several minutes, and copulation was often repeated by 
single pairs at short intervals. 
Examination of female flies revealed an interesting structure 
located on the fourth abdominal sternum (Fig. 1). It consists of 
paired plates on either side of the midline covered by a field of 
spines directed medially and slightly caudad. The presence of this 
structure was previously noted by Lundbeck (1927) who described 
the fourth sternum of Catharosia as “cleft in the middle and covered 
with short spinules.” Although oviposition was not observed during 
our rearing efforts, the needle-like nature of the Catharosia 
ovipositor (or larvapositor) suggests subcutaneous deposition of 
either eggs or larvae into the host. The spined plates probably aid in 
holding the host during oviposition. A similar structure is found on 
tachinids of the genus Celatoria which parasitize beetles in the 
family Chrysomelidae, however the structure in this case is located 
on the apex of a laterally compressed tubercle that extends ventrally 
from the second abdominal segment and opposes the larvapositor 
