Life History and Case-Building Behavior of Culoptila cantha (Trichoptera: Glossosomatidae) in the Brazos River, Texas

Abstract

The life history of Culoptila cantha (Ross) in the Brazos River, northcentral Texas, was studied from January 1995 to December 1997. The several thousand larvae, pupae, and adults sampled from a large riffle indicated a predominately trivoltine cycle during both years. The overwintering generation spanned 6–7 mo; most larvae recruited from August and September eggs grew to 4th instar by November, resumed growth to 5th instar in February, and pupated and emerged during March. Growth of the warm-season generations was less synchronized with probable cohort spreading and overlap, and occurred steadily during respective development periods of 2–3 mo. Water temperature thresholds of 22–24 and 27–29°C appeared to synchronize emergence of overwintering and 1st warm-season generations, respectively, whereas the later warm-season generation emerged asynchronously. Emergence occurred near dusk, and adults were nocturnally active within an air temperature range of 15–30°C. Mean fecundity was highest in March and decreased throughout the summer and fall. Larvae and pupae aggregated on the downstream undersides of clean cobbles (10–20 cm diameter) in the head of the riffle. Case reconstruction progression and behavior of larvae removed from field cases were observed and videotaped; larvae constructed emergency cases of loosely attached sand particles in the first 0.5 h, and subsequently modified these into typical cases when placed overnight in a laboratory stream. Emergence success was not affected by forcing 5th instars to construct these new cases. This study provides the 1st comprehensive life history of a species of Protoptilinae.