The present study showed that the eggs of the desert locust, Schistocerca gregaria, and the migratory 28
locust, Locusta migratoria, responded to photoperiod by hatching when placed on sand in the laboratory. 29
S. gregaria mainly hatched during the dark phase and L. migratoria during the light phase. The importance 30
of light as a hatching cue depended on the magnitude of the temperature change during the ther- 31
moperiod; photoperiod played a more important role in the control of hatching time in both species 32
when the magnitude of the temperature change was small. In addition, the eggs of the two species that 33
were covered with sand did not respond to photoperiod and hatched during both the light and dark 34
phases, indicating that light did not penetrate through the sand. Because locust eggs are normally laid 35
as egg pods and a foam plug is deposited between the egg mass and the ground surface, we tested a 36
possibility that naturally deposited eggs perceived light through the foam plug. The eggs that were 37
deposited and left undisturbed in the sand hatched during the light and dark phases at similar frequen- 38
cies. These results suggest that the eggs of both locust species responded to light and controlled their 39
hatching timing accordingly but would not use light as a hatching cue in the field. The evolutionary sig- 40
nificance of the ability of eggs to respond to light in these locusts was discussed