David M wrote: ↑Sun Jul 26, 2020 7:58 pm
You should thank your lucky stars you don't live near me, Pauline!
Right back at you David
![Smile :)](./images/smilies/icon_smile.gif)
. The weather here is foul today so I thought it was about time for one of my mini summaries. I have chosen the Duke rearing as the shots I have previously posted have been very fragmented so I thought I would pull it all together a little .... and add a few initial thoughts on what I have learned:
Rearing the Duke of Burgundy has been a fascinating and insightful experience. It has been a challenge recording every individual transition but I wanted to get a complete and detailed understanding of the lives of these insects.
1. Eating shed skin but only in first instar.
It would seem that this is the first time that this has ever been recorded. I photographed this occurrence several times to ensure that it wasn’t just a one-off.
2. Colour changes prior to shedding skin
I was initially alarmed at the dramatic colour changes of each instar as they prepared to shed their skin but they were very consistent in that the colour drained from them for 3 days prior to the event leaving them looking very pallid. The day before a remarkable colour change came about as they turned an almost jet black. At this point the shedding of skin would happen within hours.
3. Length of time for transition from one instar to the next
Given that this took between 3-4 days (mostly 4 days) I have to wonder if the colour change and transition time is linked. The larva is obviously very vulnerable during these 3-4 days lying quite torpid on the underside of a leaf or stem of the food plant. The first time I witnessed this I thought that the larva had died. It looked dead – black and shrivelled. Likewise, when white it looked very insipid. I believe that this may be a survival mechanism to avoid predation whilst spending such a long period of time in this state. Over the life cycle of an immature stage that accounts for approximately 16 days or about 25%.
4. Difference in development times of individuals in identical conditions
Even allowing for the difference in timings of when the eggs were laid it was clear from the beginning that even as early as 1st instar the development of some individuals was much faster than others despite being kept in identical conditions. This difference appeared to widen as development progressed through the instars and I am still waiting for the last larva to pupate (although that looks imminent). Like the transition from one instar to the next, the 4th instar settles down close to the plant for about 3 days before actually pupating.
5. Behavioural changes between early and late instars
a. Mobility
In 1st and 2nd instar the larva do not stray far, mostly staying on the same leaf as where they hatched from the egg. This is also apparent in the wild, these being the easiest instars to track for that very reason. It is easy to locate them in the wild as at this stage they pepper the leaf with little holes where they have fed. They also seem unconcerned by gentle interference and monitoring. Conversely, 3rd and 4th instar roam much wider and their increased appetites leave their leaf in a skeleton form in very few hours. This increase in food intake may explain their increased mobility.
b. Camouflage
Their inclination to roam is not the only factor which causes difficulty in tracking and monitoring. Like many insects they become masters of camouflage and the slightest interference causes them to fall to the ground, similar to many other species. For the first time ever this year I have been able to find 3rd and 4th instars in the wild and this is wholly as a result of the rearing experience.
Conclusion
These are my initial thoughts. It has been an educational experience rearing these Dukes over the last 10 weeks or so and one I won’t forget. At times it has been enjoyable but there have been times when it has been mind-numbingly boring, when hours, if not days, have been spent just watching and waiting for whatever was going to come next. It is a great relief that to date it has been successful and I am very much looking forward to the Spring when (fingers crossed) the Dukes can be returned to Noar Hill.