Methods and Markers for Synchronizing Maturation of Fifth-Stage Larvae and Pupae of the European Corn Borer, Ostrinia nubilalis (Lepidoptera: Pyralidae)1

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Abstract
Techniques for monitoring development in European corn borer, Ostrinia nubilalis (Hübner), fifth-stage larvae and pupae are described. About 90% of larvae left the medium before pupation. Larvae in the process of gut emptying exuded tan fluid, whereas those that had completed gut emptying exuded white fluid. Gut emptying occurred ca. 4 days later in diapause-bound than in non-diapause-bound larvae, even though both groups developed at the same rate until the 5th instar. Ocellar retraction marked pharate pupal formation. During the next 6 to 8 h, the pigment mass that was previously behind the ocelli migrated posteriorly and then ventrally coming to rest just above the base of the head capsule. Ecdysis to the pupa occurred ca. 4 h later. In insects reared under a photoperiod of LD 16:8 and 30°C, the ocellar pigment became diffuse and disappeared during the first 24 h of the pupal stage. Pharate adult formation occurred on day 3. By day 4, the future compound eyes looked like very dark spheres. Dark bands on the wings were observed on the day preceding adult eclosion. Eclosion occurred primarily during the scotophase and was characterized by a sexual dimorphism, in that females tended to eclose 1 day earlier than males.