a1 Tropical Development and Research Institute, College House, Wrights Lane, London, W8 5SJ UK
In the field in India, most eggs of Chilo partellus (Swinh.) hatched in the morning soon after first light. Laboratory experiments show that in continuous light hatching occurs after 250 hour-degrees of development above 12°C from the time at which the head capsule darkens (blackheading). Hatching may be advanced by a lights-on stimulus or retarded by darkness, and these effects account for the extensive hatching at dawn. Hatching is not entrained by a circadian rhythm. The significance of hatching at this time of day is discussed.
(Received March 29 1983)