Daily Temperature Cycle Induces Daily Hatching Rhythm in Eastern Lubber Grasshoppers, Romalea microptera

In nature, Eastern Lubber Grasshoppers, Romalea microptera, tend to hatch in the morning, thus exhibiting a daily hatching rhythm. They also show high intra-pod hatching synchrony. We tested the hypotheses that both diel-hatching rhythmicity and intra-pod hatching synchrony are elicited by a daily temperature cycle. In the laboratory, we exposed egg pods to either a daily 15:26 °C temperature cycle (12 h at each temperature) or a constant 26 °C temperature regimen. Under the daily temperature cycle, hatching was strongly rhythmic, with peak hatching at 3 h after the beginning of the warm phase. Under the constant temperature, hatching rhythmicity was greatly reduced and eggs hatched throughout the 24-h period. There was little intra-pod hatching synchrony under either treatment. We propose that in nature both daily hatching rhythm and intra-pod hatching synchrony are controlled by a thermal threshold for hatching.