1980] 
Morris, Chaffee, & Tarter — Baetisca 
45 
Other recognizable diatoms were Fragilaria sp., Meridion sp., 
Cocconeis sp. and Achnanthes sp. Diatom abundance was greatest 
during April and May and October-December. The nymphs collected 
during May had the largest amount of filamentous algae. One desmid 
was found in the study ( Straurastrum sp.). 
Pescador and Peters (1974) conducted a similar study on B. rogersi 
and the results corresponded with those in this study. However, it 
must be pointed out that their particles were counted on the basis of 
number present and not on the area of small grid squares covered. 
The nymphs of B. bajkovi are detritivorous with almost two-thirds 
(65.3%) of the diet composed of plant and leaf detritus (Chaffee and 
Tarter, 1979). 
Habitat Preference .—The preference was for the sand, gravel and 
small stone substrate during all light or all dark conditions. A slight 
preference for sand and leaf litter over sand only was shown. When 
the light was directed to one substrate only, the majority of nymphs 
moved to that substrate. 
Pescador and Peters (1974) reported similar results for B. rogersi. 
Lehmkuhl (1972) found that B. bajkovi preferred a stony or grassy 
substrate to a sand only substrate. 
ADULT STAGE 
Rearing Observations .—Nymphs were reared in the laboratory 
beginning April 23 and emerged from May 7 to the end of May. All 
subimagos emerged betwen 10 AM and 2 PM and all imagos emerged 
approximately 24 hours later. 
Emergence of B. bajkovi adults occurred in the laboratory from 
May 2 to May 26 (Chaffee and Tarter, 1979). All subimagos emerged 
betwen 9 AM and 7 PM with the imagos emerging 13 to 25 hours 
later. Emergence data for other members of the genus Baetisca were 
reported by Traver (1931 and 1937), Berner (1940 and 1955) and 
Pescador and Peters (1974) found that duration of the subimago 
stage of B. rogersi is dependent on water temperature. The warmer 
temperatures produce a shorter subimago stage. 
Fecundity .—Egg counts for B. berneri ranged from 1001 to 2375; 
the mean number of eggs per female was 1899. Egg counts were 
reported for B. rogersi (Pescador and Peters, 1974). The range was 
from 1500 to 2727 eggs; the mean number of eggs per individual was 
2168. Ovarian egg counts for B. bajkovi ranged from 1508 to 3158; 
the mean was 2361 (Chaffee and Tarter, 1979). 
