The Effect of Temperature and Diet on the Larval Growth of Glossosoma Nigrior

The effects of diet and temperature were investigated on the growth of Glossosoma nigrior (banks) larvae. Early instars were collected from a 3rd and 1st order stream in Southern Michigan. The 3rd order stream appeared visibly rich in periphyton food resources and had warmer mid-summer water temperatures. Instars collected from this stream were larger in weight than instars from the first order stream and the respective estimated larval growth curves were significantly different, with instars from the 3rd order stream showing larger individual weights and faster growth. Experiments were conducted investigating the relative importance of diet and temperature on larval growth. Larvae collected from the first order stream were reared on their natural periphyton diet and on periphyton removed from the 3rd order stream, at temperatures of 10°, 15° and 20°C for four weeks. Results indicated that diet was not significant in effecting weight gains. Temperature, however, significantly (P < 0.001) increased larval growth rates, increasing mean total growth from 0.074 ±.02 mg per larva at 10°C to 0.13 ±.07 mg per larva at 20°C after 4 weeks. The direct affects of temperature on larval growth may therefore be more important than diet affects in many streams.