The Science Behind Larval Wandering…

In response to the comments (Re: The Mysteries of Pupation) in Matthews’ recent ”British Wildlife” journal article, I thought I’d high light a couple of important articles which have already explored this ‘mystery’ in some detail. Links are below:

http://jeb.biologists.org/content/110/1/35.full.pdf+html

http://jeb.biologists.org/content/117/1/45.full.pdf+html

Although the experimental work (mentioned above), was admittedly conducted using Manduca sexta, as stated by the authors, their findings relating to larval wandering behavior are expected to be analogous across other Lepidoptera species. In summary, the take home message from the experimental work conducted by Dominick and Truman appears to be as follows: Similar with the induction of diapause (see my previous “Larval Diapause” purpleempire post, 6th November 2011), pre-pupation larval wandering appears to be induced and controlled by the dose and the duration of release of the insect moulting hormone 20-Hydroxyecdysone (or Ecdysone as it is more commonly referred), in the inverse proportional absence of another insect hormone (Juvenile hormone). Release of 20-Hydroxyecdysone (from the corpus allatum) within the larvae is itself influenced/controlled by photoperiod and occurs in three distinct pulses. The second of these 20-Hydroxyecdysone pulses appears to be highly influenced by the duration of the scotophase (night) cycle, 15 hours prior to the initiation of wandering. Although this initiation trigger is also likely to exist within the Apaturinae, the specifics regarding the duration of the scotophase cycle involved in the trigger are likely to highly species specific.

The experiments performed by Dominick and Truman also showed that the initiation (not stoppage) of wandering in 5th instar larvae could be prevented by the pre-wandering administration of Juvenile hormone. Unfortunately however the administration of Juvenile hormone to these larvae also consequently prevented any subsequent developmental (i.e. pupation) progression.

In light of the comments mentioned within these papers, I suppose that the take home message from these publications, relative to the ‘disappearance’ of mature, pre-pupation iris larvae, is that it is all part of nature taking its natural course and aside from caging specimens, there unfortunately doesn’t appear to be very much that we can do to prevent or stop it. Although certainly not ideal, I suppose the injection of internal, digital tags of some kind (the cogs are still slowly turning with respect to this one) could potentially provide some invaluable insights as to the ultimate wandering locations which are preferentially chosen by these larvae as natural pupation sites. Certainly food for further mental processing…

Mark