OBSERVATIONS ON A POPULATION OF SIALIS ITASCA ROSS IN WEST VIRGINIA ( MEGALOPTERA : SIALIDAE )

ruin and Tarter (1973), Pritchard and Leischner (1973), Tarter and Woodrurn (1973), Tarter (1973), Tarter et al. (1976), and Tarter et al. (1978) have reported on the taxonotny, distribution, life history, and ecology of several Sialis spp. Other authors, including Roback and Richardson (1969), Warner (1971), Nichols and Bulow (1973), Tarter and Woodrutn (1972) and Woodrutn and Tarter (1973), have noted the extretne tolerance of Sialis to acid mine drainage. The prirnary objectives of this investigation were: (1) to rnake observations on the life history and ecology of the alderfly S. itasca in a srnall farrn pond and (2) to determine the pH tolerance of this population under laboratory conditions.


Psyche
[June-Septenber mud and debris in the net.The larval alderflies were collected and preserved in 70 percent ethanol.
Temperatures were taken with a Taylor rnaxinun-nininurn thernometer placed on the pond botton 0.5 neter below the water surface.They were recorded in degrees Celsius once per month at the time benthic samples were taken.Water chenistry tests were perforned in the field with a Hach chemical kit, Model AL-36- WR.All tests were conpleted within one hour.Hydrogen-ion concentration (pH) was neasured colorinetrically.Dissolved oxy- gen, carbon dioxide, hardness (nagnesiurn and calciun), phenol- phthalein and nethyl orange alkalinity, free acidity, and total acidity were neasured and recorded in ng/1.
Size classes were determined by length frequency distributions arranged in nn length groups.Total length (exclusive of the caudal filanent) was measured under 7 magnification with calipers and a plastic ruler (nearest 0.5 rnn).Head width was neasured with an ocular micrometer between the inner edges of the eyes (nearest 0.01 nn).Differences in head width of 124 larvae were determined to show the mean range and standard deviation.
A total of 84 foreguts were examined to deternine food habits.
The head was renoved and the abdomen was split open to renove the intestine.The contents of the intestine were removed and exanined under a dissecting nicroscope and a conpound nicro- scope to identify their contents.The percent frequency of occur- rence of each item was deternined, and the nonthly and seasonal averages and various sizes were conpared.
For the pH tolerance test, forty mature larvae collected from the pond in April were taken to the laboratory for acclinatization over a 24 hr period.The larvae were placed in groups of 10 in 4 finger bowls.One bowl was filled one-third of the way with pond water.A one molar solution of potassium dihydrogen phosphate (KH2PO4) was diluted approxinately into the other three bowls, to set pH values at 5.5, 4.0, and 2.5.The p H value of the control was 7.0.A Model 5 Corning Scientific pH meter was used to determine pH values.Oxygen was constantly supplied with air stones.The tenper- ature did not change significantly during the experiment and averaged 12 C.The 96 hour TErn (nedian tolerance linit) test (APHA, 1965) was used to neasure the effect of low pH.The pH value at which 50 percent of the alderfly larvae died after 96 hours was determined by straight-line graphical interpolation.
Fifteen larvae were collected in April and returned to the laboratory for rearing in vials containing pond water.These vials were connected to vials containing sand by a short section of rubber tubing (Pritchard and Leischner, 1973).Wire mesh and strips of foam rubber were placed in the vials and rubber tubing to enable the larvae (one per vial) to move freely between the vials.The vials were kept at roon tenperature which was approximately 70 F.
Fecundity was determined by a direct count of ovarian eggs under a compound microscope.The ovaries of 3 adults were renoved and a total of 1616 eggs were counted.The diameters of 90 eggs were measured to the nearest 0.01 nn with an ocular nicroneter using a Bausch and Lonb conpound nicroscope.

Pond Environment
Temperature.
The average annual temperature for the pond was 18.1 C. The extreme monthly temperatures were 0.5 C in February and 35.0 C in August and September.
Water Chemistry.

Larval Stage
Development.
Length-frequency histograms indicated that the population of S. itasca contained one size class (Fig. 1).Hatching occurred at the end of May.There were 18 egg masses located in the field at the end of May.The egg masses were found on the leaves of hornbeam and buckeye trees.Three egg masses which were returned to the laboratory hatched within 2 days.In July all the egg tnasses were empty but no larvae were located.The earliest and smallest larvae were collected on August 2, 1975.Their average length was 6.45 rnrn, and their average head width was 1.02 rnm.The last and largest larvae were collected on April 6, 1976.Their average length was 13.67 rnrn, and average head width was 1.59 rnm.
Head width was used to show the monthly variation in growth rate and the percent increase in growth rate (Fig. 2).Due to the Length-frequencies at monthly intervals of S. itasca larvae from a farm pond near Shoals, W. Va.The number of larvae is given for each month.
small sample size (4) in August, no statement can be made concerning the growth rate from August to September.An eighteen percent increase in growth rate was recorded from October to November.There was a decrease in growth rate in December.Small sanple sizes in January (2) and February ( 6) prevented any growth rate information.There was a six percent growth rate from March to April.The largest mean head width was measured in April at 1.59 rnrn and ranged between 0.95 and 1.86 rnrn September and November, respectively.No larvae were located in May, June and July.
Woodrurn and Tarter (1973) also found a decrease in growth during the winter months in S. aequalis.Azarn and Anderson (1969)   found a decrease in the growth rate for S. rotunda and S. californica during the winter months.This population of S. itasca was found to feed alsnost exclusively on the ostracod, Cyclocypris sp.The only other food itesns were 3 snidges, Chironomus sp., which were found on 3 different occasions.Of the 84 foreguts analyzed, 21 percent were esnpty and 79 percent contained food.Ostrocods were found in 71 percent of the foreguts, and snidges were found in 4 percent of the foreguts.
Excluding the snonth of August when a very ssnall sasnple size (4) was used, the largest nusnber of esnpty foreguts occurred in January (50%).The percent of esnpty foreguts increased again in April supporting the findings of Woodrusn and Tarter (1973) in S.
aequalis that the larvae probably do not feed just before pupation.
Azasn and Anderson (1969) reported S. rotunda and S. cali- fornica to be indiscrisninate feeders and reported cannibalissn to be frequent.Woodrusn and Tarter (1973) found S. aequalis to be snore restricted in its feeding due to the lisnited choices of organissns found in the acid snine streasn in which they were located.They also reported cannibalissn to occur to a lesser extent.The S. itasca in this investigation were found to be snore restrictive feeders preying alsnost exclusively on ostracods while having an abundant supply of other organissns upon which they could feed.Cannibalissn was observed in the laboratory when larvae were confined for three days without food. Predation.
The stosnachs of 18 odonates and 10 sunfish were exasnined.No alderfly resnains were found in the sunfish and only one alderfly head was found in the odonates.Schwiebert (1973) noted that the hellgramsnite and trout are predators of the alderfly.
The 96 hour TLm value for S. itasca was found to be 3.1.All ten larvae survived the 96-hour period at pH values of 7.0 and 5.5, 70 percent survived in a pH of 4.0, and 30 percent survived at a pH of 2.5.Tarter and Woodrusn (1972) found S.
aequalis frosn an acid mine streasn to have a TLm value of 2.1.These values would indicate that S. itasca and S. aequalis are quite tolerant of low pH.Sialis spp.have been noted to be tolerant to low p H conditions in western Pennsylvania streasns (Roback and  Richardson, 1969), Roaring Creek in eastern West Virginia (Warner, 1971), and in the East Fork of the Obey River in Tennessee (Nichols  and Bulow, 1973).
Pupal Stage Larvae placed in the laboratory rearing chambers moved to the sand for pupation within 2 to 4 days.The pupal stage lasted for approxitnately 2 weeks.The adults etnerged during the night.No pupae could be located in the bank of the pond.
Azatn and Anderson (1969) reported S. rotunda and S. californica to pupate during April, May and June.Pritchard and Leischner (1973) reported that S. cornuta pupated from May to mid-June.Woodrun and Tarter (1973) found S. aequalis to crawl 1.5 to 5 tn out of the water onto a moist sandbank when the water temperature reached 11 to 13 C and pupated in an earthen cell to 7 crn below the surface.They found the pupae to respond to a disturbance but otherwise remained rather dormant.

Adult Stage
Number and Size of Eggs.
Fecundity of 3 adult alderflies showed a range of 454 to 587 eggs per fetnale; the average was 539 eggs.The eggs were cylindrical, rounded on the ends, had a curved tnicropylar tubercle on one end, and averaged 0.31 rntn in length by 0.14 ntn in width.The nutnber of eggs found in S. itasca was similar to those of S. aequalis (657) (Woodrun and Tarter, 1973), S. rotunda (300-500) and S. californica (400-700) (Azatn and Ander- son, 1969), and S. cornuta (615) (Pritchard and Leischner, 1973).Egg tnasses of S. itasca were found on the underside of hornbeatn and buckeye leaves 0.5 to 3 rn above the water surface.The eggs are laid in rows in a nearly vertical position tnuch like those of S. rotunda (Azan and Anderson, 1969). Mating.
Although copulation was not observed, a courtship behavior was observed in the laboratory tnuch like that described by Azatn and Anderson (1969) for S. rotunda and by Woodrurn and Tarter (1973) for S. aequalis.

Longevity.
Adults in the laboratory lived for 4 to 6 days.Only one adult was captured in the field on 3 May 1975.Sialis rotunda was first seen in mid-April and reached their peak in May (Azan and Anderson, 1969) while S. californica was seen in May but did not peak until nid-June (Azatn and Anderson, 1969).Sialis aequalis was observed in the field between April 21 and May 4 (Woodrutn Figure1.Length-frequencies at monthly intervals of S. itasca larvae from a farm pond near Shoals, W. Va.The number of larvae is given for each month.

Figure 2 .
Figure 2. Monthly variation of the head width in S. itasca larvae.Vertical lines ranges, horizontal lines means, open rectangle one standard deviation, numbers sample sizes, and dotted lines temperature (C).