Читать книгу The Disappearance of Butterflies - Josef H. Reichholf - Страница 18

My dissertation also dealt with the details of the skin structure and its changes during the period when the caterpillar stops breathing through its skin and starts to breathe oxygen using the system of trachea that is typical of insects. This required imaging with an electron microscope, which the University of Munich was able to arrange. But what was truly exciting for me was – and remains – the lives of these moths with their adaptations to the water plants that sustain them and their life in the water. Why did they come to inhabit this environment? What advantages does it offer them?

The discovery that would be of greatest importance in addressing this issue did not even occur to me at first: nearly all my attempts to breed caterpillars were successful and produced moths. Indeed, nothing could happen to them in my small aquarium, except perhaps damage through my own carelessness. All the pupae that I collected outdoors (together with their underwater leaf cases) in order to watch the emergence process emerged successfully. Without giving it any thought, I assumed that all the caterpillars in their various stages that I had collected for my research would continue to develop without any problems, pupate and produce moths. The penny only dropped, as the saying goes, years later, when I had already become involved with a quite different type of species, the small ermine moth. There is a separate chapter devoted to them. Through them, the advantage of life in the water became suddenly apparent: I had had no losses, because the caterpillars and pupae of my aquatic moths had not been attacked by parasites. For practically all the butterflies and moths that live on dry land, parasites are among the main factors that determine their abundance and their development from one stage to the next. With around 96–98 per cent of 694 caterpillars from several breeding groups, the hatching success of my aquatic moths was phenomenally high. I only recorded higher losses for the eggs. I did not discover who or what caused the losses under outdoor conditions, but I considered the egg-eating water mites and the rotting sludge build-up in the heavily silted pools to be the likely causes. With 100 or more eggs per clutch and per female moth, such losses prevent the caterpillars from consuming all the available floating leaves too soon, which can easily happen where brown china-marks exist in large numbers.

This was why the gardeners in the Botanical Gardens in Munich placed their hopes in my research into the aquatic moths when I first encountered the little nymphs. Over the following years and decades, I definitively established that the female brown china-mark will leave the pool from which she emerged if the floating leaves of the water plants have been overconsumed. She will examine the edges of the floating leaves quite thoroughly before laying her eggs, and for good reason. If there is extensive feeding damage, she will leave and search for other waters with better conditions. A tendency to disperse would already be expected, since such small bodies of water are normally only temporary. Under natural conditions, they arise through inundation of the floodplains. New ponds will last a couple of years or a few decades, depending on how large or small they are when they form, and gradually disappear again through sedimentation and plant succession. Species that colonize an environment that is by its nature unstable must seek alternatives in good time.

The dispersal behaviour of the aquatic moths is therefore very particular. As insects, they probably belong to the group of pioneering species that is familiar to us through many land-based plants and that quickly colonizes newly created environments. On the other hand, maybe we are dealing with specialists that need a specific, longer-lasting ‘life zone’: that of floating leaves at the edges of large bodies of still water. Closer to the centre of the body of water there are plants that grow entirely under water, described by specialists as ‘submerged’. The moths seek out shore plants that stand in the water but protrude above it, away from the centre of the pool. These are plants that are ‘emerged’ (in the ecological sense). In order to understand my aquatic moth and to be able to place it properly among its relatives, I would need to deal with the environment of small waterbodies and shores in far greater detail. Was it a pioneer species or was it specially adapted to the specific environment of bodies of water?