Mean exsheathment ratio of the different larval populations ± SD (n ≥ 6). Larvae were incubated either in PERL chambers or with or without serum, and with or without CO2 (for detailed overview of populations refer to Table 1). The percentage of exsheathed larvae was determined after 24 h and 48 h, respectively. For each setup, at least 50 larvae were examined. *: statistically significant difference (p ≤ 0.05); n.s.: not significant; †: no data since most of the larvae died.