Ecdysis, larval-pupal

Diet preparation and rearing procedures were as described in (26). ILPE = Incomplete Larval-Pupal Ecdysis. 

Ecdysone induces the larval-pupal metamorphosis in the absence of JH or a JH-active insecticide, but the presence of active compounds leads to a new larval stage at ecdysis, or to the development of larval-nymphal, larval-pupal, or larval-adult intermediates that are unable to give rise to normal adults. Treated pupae (e.g., tobacco cutworms treated with pyriproxyfen) may develop into normal adults. However, the females are unable to deposit eggs because a substance that induces oviposition behavior after mating is not released in the hemolymph. Other physiological and behavioral effects of JH-active insecticides are also observed. 

Larvae of Inoplnatus emerge as major sequestrators of cardenolides primarily because their hemolymph, which is present in a relatively large volume, effectively sequesters high concentrations of polar cardenolides (26). Cardenolide excretion largely reflects loss of these steroids as components of the larval exuviae, the concentration of these compounds becoming relatively stable after pupal ecdysis. These steroids are ubiquitously distributed in the adult moth, having been derived primarily from the rich cardenolide pool in the larval blood. 

To verify in vitro results, we have also developed an in vivo assay for L. dispar PTTH (52, Thyagaraja et al, in preparation). This assay is comparable to larval assays develop for Af. sexta (56 and B. mori (58) and uses last instar female larvae. Neck ligation prior to day 7, the day when a small pre-peak in hemolymph ecdysteroid titer appears, blocks further development. Injection of PTTH-containing extracts posterior to the ligation, including post-embryonic egg extract, reinitiates development and subsequent pupation. Attempts to develop an in vivo assay comparable to the pupal-adult B. mori assay (5B were unsuccessful, since brain removal as close as 15 min post-pupal ecdysis failed to block L. dispar female adult development (Thyagaraja et a/., unpublished results). 

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