Preference by the Nymphs of Americabaetis alphus Lugo-Ortiz & McCafferty, 1996 (Baetidae: Ephemeroptera) for Feeding substrate and Food Size Under Laboratory Conditions.

Feeding by mayflies is influenced by resource availability, and their feeding preferences can vary acrossdevelopment stages. Studies assessing food preferences can therefore provide insights into the functional role of a species. The aim of this study was to evaluate the feeding preferences of Americabaetis alphus nymphs on periphyton growing two different substrates and two sizes of particulate organic matter. Experimental units were composed of acrylic and stainless steel substrates; the control contained no nymphs. The substrate preference was determined by the presence or absence of nymphs on the substrates. Bacterial density and chlorophyll-a concentration were measured to evaluate food intake, and the frequency of microbial taxa adhering to the substrates was calculated. Salix humboldtiana leaves were processed into two categories, fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM). In each experimental unit, 25 mg of FPOM and 25 mg of CPOM were provided. Food intake was estimated by the difference between the initial and final weights of FPOM and CPOM. The highest bacterial and chlorophyll-a intake was observed on the stainless steel substrates. The taxonomic composition differed between the substrates, with stainless steel showing a higher frequency of diatoms. In the second experiment, the weights of FPOM and CPOM were reduced after the feeding period, with a greater reduction observed in FPOM. It is important to evaluate resource preferences in a combined manner, as well as to assess other Baetidae species, given the scarcity of information on the topic for the family.