Box Tree Moth (Cydalima perspectalis)






The Making Of



Introduction


When the Box Tree Moth invaded my garden in Munich in 2017, I had not previously heard of it and was fascinated by the large caterpillars, although not thrilled by the damage they were doing. After manually removing hundreds of Box Tree Moth caterpillars and pupa from my infested Box Trees, the idea to document them developed. Initially, I decided to try and watch the eclosion and show this to my son. However, soon a plan to document the whole lifecycle developed. I had always wanted to try some macrophotography and this seemed like a great opportunity. The observation and documentation techniques were gradually developed, largely by trial and error, however when it came to captive breeding, I was able to obtain very helpful advice from the Box Tree Moth expert Dr Annette Herz.


The following paragraphs explain how the Box Tree Moth was documented in the different phases of its lifecycle, in particular the collection of specimens, captive larval husbandry and breeding are documented, as are different methods of filming.





Where did the Box Tree Moths used come from?


All film material was obtained using animals filmed in situ in gardens in Munich-Obermenzing, or are "studio" filmed (if you can call my cellar a studio) using animals derived from the same locations.


Caterpillars and pupa can be easily "harvested" from infested Box Trees. The caterpillars can be kept on Box Tree cuttings, although this is rather labor-intensive since twigs need to be frequently replaced, otherwise damaged twigs and the caterpillar faeces beneath start to go mouldy. Transfer of the caterpillars to fresh twigs often needs to be performed manually. Especially for smaller larvae, one needs to pick them up individually with a soft paintbrush. Alternatively one can use whole Box Trees for maintaining the larvae, but it is increasingly difficult to find untreated trees, since garden centers tend to have trees pretreated with chemical pesticides.





The pupa can be suspended by their tail ends in order to allow detailed observation of eclosion (see also dedicated section below). For this purpose, simple HD camcorders with macro functionality (available for under 100 Euros via ebay) were purchased. These were run for days at a time using their plug-in power supplies until eclosion occurred .  Using the moths scurry out of the picture frame once they have emerged, probably in part to avoid the strong light used for filming.





Keeping and Observing the Moths


A simple cage with narrow mesh netting is sufficient for keeping the moths. I made several such cages during the course of the project. To set up a small breeding colony one can simply take about 20 pupa and lay them out on the floor of the cage. Eclosion of healthy moths can take place from a lying position. Generally, similar numbers of males and females emerge. Copulation only seems to occur under cover of darkness. This makes observation very difficult, in particular it was never possible to observe the courtship behaviour (if occurring) prior to copulation. Even low levels of light inhibit breeding. Once copulation has commenced, the moths will not abort the process if subjected to a strong light source.








The moths live for about 2 weeks and should be provided with water or dilute sugar solution during this period. Oviposition can occur on Box Tree cuttings placed in the cage. Oviposition takes place under cover of darkness and will be aborted if the moths are subjected to the light required for filming. The few videos of oviposition obtained are not very satisfactory but were the best that could be achieved after spending several hours per night for a period of weeks, observing the moths in near total darkness and then applying minimal light once oviposition commences.





Observation of Feeding


Although the larvae prefer to avoid direct sunlight, the are certainly prepared to eat in sunlight or under artificial light. Hence, observation of feeding is relatively straightforward. Various cameras were tested for this purpose. It is relatively difficult to get the caterpillars into focus, especially when working at high magnification levels.. Light reflects strongly off the caterpillar, in particular its dark head. Some attempts were made to use polarizing filters but the results were not satisfactory. Since the filters remove as much as two full aperture stops of light, they were no longer used. 




In addition timelapse documentation was used to show how caterpillars damage and defoliate twigs or even whole trees.






Observation of Egg Development


Finding egg clutches in Box Trees is extremely difficult, even for the trained eye. Thus all documentation of the eggs was performed using clutches derived from the moth breeding cage. Standard macro timelapse photography and post-processing to video was performed. Eggs hatch about 5 days after they are laid. Hatching is well synchronized.




Observation of Pupation and Metamorphosis


Box Tree Moth caterpillars do not appear to like to pupate under light conditions suitable for filming. This makes observation of pupation challenging. The caterpillars also tend to spin themselves into a cocoon which hides them from view. This can however be carefully opened or removed, although many caterpillars then abort pupation and appear to start feeding again. After pupation the pupa have a very intense green colour, this later gradually fades. About 1-2 days before eclosion a significant colour change occurs and one can see through the husk of the pupa whether a regular or melanic variant is about to emerge. Standard timelapse methodology can be used to film the metamorphosis. I performed this in a small box since it is otherwise difficult to avoid light fluctuations during the about 14 days the process takes.







Eclosion (Emergence of the Moth)


This is probably the most impressive part of the lifecycle of any moth or butterfly. The colour of the moth is clearly visible through the pupal case, making it possible to distinguish regular and melanic variants about 1-2 days prior to eclosion. The pupa tends to become more restless in the hours leading up to eclosion as it gradually stretches and starts to extend and break open the case at the designated breakpoints. Shortly before eclosion, the moth thrusts downwards several times until its head emerges. About 1-2 minutes later, the moth rapidly emerges. The moth must now rest and slowly pump hemolymph fluid into its wings so that they extend. This process is largely completed in about 6 minutes.


Eclosion is best filmed with camcorders unless one is prepared to sit around for hours to manually start filming at the right time. Predicting the exact timing is difficult and it is possible that the process is delayed by light. Normal cameras with video functionality are not suited for long periods of filming as, at least in Europe, these are limited to half an hour long film files (Situation Jan. 2020). I have observed eclosions happening about 48 hours after I had predicted based on pupal colouration.











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