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Summary
Neck-ligated and thorax-ligated post-feeding (day 4) (last instar larvae of Spodoptera mauritia were treated with ecdysterone alone or in combination with a juvenile hormone analogue, hydroprene. The effects of these treatments on larval-pupal transformation were studied.
Sixty three pecent of neck-ligated and 84% of the thorax-ligated larvae injected with ecdysterone (4 μg/larva) (moulted into larval-pupal intermediates. Eighty percent of neck-ligated larvae injected with 4 μg ecdysterone and simultaneously treated with 5 μg hydroprene transformed into headless pupae. By contrast, treatments of same doses of ecdysterone and hydroprene to thorax-ligated larvae induced 60% of the larvae to moult into larval-pupal intermediates only.
These results indicate that in S. mauritia the presence of juvenile hormone late in the last instar of larval development is crucial for the successful larval-pupal transformation. Furthermore, since hydroprene and ecdysterone induced pupation is observed only in neck-ligated larvae which possess the prothoracic glands, it is suggested that these glands might be the source of ecdysteroids with critical morphogenetic roles in pupal development.