1985] 
Schmidt & Tarter — Acroneuria carolinensis 
395 
grams were produced for each month. Number of age classes was 
determined based on the distribution of the body length. 
Population range diagrams (Hubbs and Perlmutter, 1942) were 
used to show monthly head width variations between males and 
females. Early instar naiads too small to sex (usually < 6.0 mm) 
were excluded from the analysis. Head width was measured to the 
nearest 0.05 mm using an ocular micrometer in a binocular dissect- 
ing microscope. Head width was used as a size standard because it 
changes least during preservation (Britt, 1953). Monthly growth 
rates were calculated as a percent increase in mean head width from 
one month to the next for males and females. 
An estimation of the number of instars was calculated using the 
Janetschek method (Janetschek, 1967). Head width frequency his- 
tograms were produced for all collections combined. A trend-line 
for population growth was then calculated using a gliding mean 
over five successive class frequencies at a time. Gliding means were 
then subtracted from the frequency for each size class. These peri- 
odic maxima and minima were ploted and positive peaks were 
counted to determine number of instars. 
Sex of naiads was determined by examining the posterior margin 
of the 8th abdominal sternite. A chi-square test was performed on 
72 males and 152 females. Deviation from the expected 1:1 sex ratio 
was tested at the 0.05 confidence level. 
Naiad food preference was determined by examining the contents 
of the foregut. Twelve foreguts were analyzed each month. After the 
foreguts were removed by dissection, contents of the foregut were 
gently scraped onto a glass slide and examined under a binocular 
dissecting scope. Food items were sorted and identified to the lowest 
taxonomic unit possible. Taxa, number of taxa per foregut and 
number of foreguts with the item were recorded. The mean number 
of a particular taxon per foregut and the percentage of foreguts in 
which that taxon occurred (percent frequency of occurrence) were 
calculated on a monthly and seasonal basis. 
Using a Ward ultraviolet light trap (8 watts), an attempt was 
made to collect emerging adults at the study area. On 31 May 1984, 
the trap was set up from 10:00 to 12:00 p.m. During May and June, 
the banks of Panther Creek were searched for exuviae to determine 
the emergence period. Distance of exuviae from the stream bank 
and type of substrate on which they were found were recorded. 
