3.0024 UNUSUAL CASE BUILDING BEHAVIOR OF HYDROPSYCHE OCCIDENTALS LARVAE (TRICHOPTERA: HYDROPSYCHIDAE) 1 JOHN (). MECOM -During the course of an investigation of tlie distribution and productivity of Trichoptera larvae in a Colorado mountain stream unusual case building behavior was noted in the net-spinning larvae of Hydropsyche occidentalis (Banks). Over 700 larvae of this .species were hand picked from tin-substrate of the St. Yrain River in Moulder County. Colorado at elevations of 1750-2050 m (T3X, K71\V. S2f (T2X. R71\Y. Sf from June. l<>r,S. to May, 1969. From late May to late October the larval case of Hydropsyche occi-dentalis consisted of a loosely woven tube 7-12 mm in length .supported by small pebbles and vegetable matter. A net was spun by this species in front of the case to aid in the capture ot lood. \\ith the onset of colder temperatures in November, H . occidentalis remained inactive in a highly modified overwintering case or hibernaculum. The food net was not present and the case was reinforced with larger pebbles to form a dense, more convex house rarely exceeding 7 mm in length. Pupal cases were found infrequently in late spring and early summer and consisted of an elongate tube in which large anchoring stones were utilized at the lateral margins. Authors such as Ilynes (1 ( 'M) have reported the seasonal habits oi Trichoptera larvae and Copeland and Crowell (1937), Fankhauser and Keik (l ( M5i. and Milne il'MSi have investigated the case building behavior of many species. Flliott ( l ( 'oS) reports that some genera over-winter as fifth instar "resting larvae" but no special case modifications art-present. It is difficult to speculate on the adaptive value of the hibernaculum of H \drops\c1ic occidentalis but such a structure could aid in resisting ice 1 Tliis is contribution number 5S of tin-I'niviTsity of Coloiado Limnology Labora-tory. Final preparation of the manuscript \va> made tbron.ub tin-facilities oi Soullu-rn Mrtbodist L'nivc-rsity. Accrpti-d for publication. February h, 1 ( '7<). 2 ACKNOWLEDGMENTS. ] am indebted to Dr. Robert IVnnak i I niversit\ ('olorado) for bis lK-l])ful su.u.m-stioiis. and to Dr. II. II. Ross (University of ( ieoi for his identification of tin-larvai-of Hydropsyche occiticiittilis. 3 Department of I'.iolouy. Soutbcrn Methodist t'nivrrsity. Dallas. Texas 75 _'_'_' 33
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