Life History of Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae) in Oklahoma

Abstract

The life history of Helicopsyche borealis was compared for 13 months in two Oklahoma streams that have different thermal regimes. Densities of H. borealis were usually higher in the thermally constant stream. The species was multivoltine with overlapping generations in the thermally constant stream and univoltine in the thermally fluctuating stream. INTRODUCTION Larvae of Helicopsyche (Trichoptera: Helicopsychidae) are unusual in that their sand-grain cases superficially resemble snail shells. In fact, the genus was first described as a snail based on the shape of the case alone (Lea, 1834). There are five species of Helicopsyche in North America N of Mexico (Wiggins, 1977; Denning and Blickle, 1979). Helicopsyche borealis (Hagen) is the most common species occurring in clear running water, springs and the littoral zone of lakes, and has been found in thermal springs exceeding 34 C (Wiggins, 1977). Mackay and Wiggins (1979) reported the occurrence of H. borealis in streams receiving domestic sewage and this species also tolerates petroleum-related pollution (Bugbee and Walters, 1973). The life history of Helicopsyche borealis has only been partially described. Ross (1944) and Williams and Hynes (1974) reported continual emergence of adults from spring to early autumn followed by an egg diapause of 5-6 months in Illinois and Ontario, respectively. Bane and Lind (1978) studied H. borealis in a tributary of the Rio Grande in Texas. Biomass was highest in the spring and lowest in the winter. Adults were found only in April. I collected Helicopsyche borealis from two Oklahoma streams with different thermal regimes for 13 months. I report on life history patterns of H. borealis in these two streams and present new information on egg masses and early case-building behavior. METHODS Study area and sampling method. -Pennington Creek is a second-order, spring-fed, thermally constant stream in the Arbuckle Mountains of S-central Oklahoma. Caney Creek is a third-order, thermally variable stream in the Ozark Mountain foothills of northeastern Oklahoma (Fig. 1). Helicopsyche borealis densities were sampled in each of these streams at monthly intervals from May 1981 through May 1982. A modified quadrat sampling technique was used. Stratified random samples of the substratum were collected with a 95 cm2 cylinder to a depth of 3 cm. The H. borealis were removed from the substratum, counted and assigned to an age class (see below for technique). Fifty samples per month were collected from each stream from May through August 1981, and 25 thereafter for the remainder of the sampling period. Temperature was measured with an Extech meter (model 651). Development. -The development of 20 egg masses was followed in the laboratory from the time they were laid through pupation of the resulting larvae. Egg masses were obtained from adults reared from pupae collected from Pennington Creek in July and August 1982. Adults were reared in 76-L artificial streams with screen cage tops. Floating pieces of styrofoam were provided as oviposition surfaces. Observations on hatching and early case-making were made in 8 x 2 cm glass finger bowls under a dissecting microscope. Larvae were reared in 3.8-liter glass aquaria. Cases of Helicopsyche borealis were measured to determine the range of sand particle sizes used in the