Hormonal regulation of pupation in the codling moth, Laspeyresia pomonella

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Abstract
According to the different reactions to the juvenoid Altosid®, the last larval instar (L5) of Laspeyresia pomonella (L.) (Tortricidae) reared under ‘long day’ conditions (constant light) was subdivided into three sensitive phases: an additional larval instar, a larval–pupal intermediate, or a pupa. Under short day conditions, the prothoracotropic effect of juvenile hormone (JH) in L5, which have a continuous high titre of JH during the whole instar, indicated that it is not a particular titre of JH but a rise in the titre that can induce the production of moulting hormone. Neck‐ligation experiments showed that JH acts not directly on the prothoracic glands but via the head, probably via the neurosecretory system. The meaning of the JH‐peak in mature L5 reared under long days was determined either by injections with the anti‐JH, precocene II, in combination with applications of Altosid, or by forcing precocene‐treated larvae to a precocious moult by injecting them with ecdysterone. Precocene delayed, and JH accelerated pupation if administered 4.5 days after the L5 ‐moult. JH was also found to stimulate the growth and differentiation of the imaginal discs. Moulting hormone in long‐days reared insects was detected one day after the larvae had spun their cocoon, with a maximum on the second day after spinning. The hormone was also present in freshly moulted pupae. Neck‐ligation of mature larvae indicated that the delay between activation of the prothoracic glands and the production of an effective amount of moulting hormone is less than one day.