"The transformation of a caterpillar to a butterfly is one on nature's great mysteries," says William E. Connor of the Oregon Health and Science University in Portland. "Powerful chemical mediators are necessary to produce this transformation. We hypothesized that considerable energy would be necessary for metamorphosis to occur. It appears as though the larva is sleeping, and one might think that very little energy would be required in hibernation, but the reverse must be true since a great deal of metabolic activity is occurring in the butterfly chrysalis."
Because of this energy expenditure, Connor and his colleagues surmised that butterflies experience a great loss in body fat during metamorphosis. Using the Blue Morpho butterfly from the Butterfly Farm in Belize, the scientists analyzed the fatty acid composition and content of the butterflies, their diet, and their larva. They were able to do this easily because the larva feed solely on the leaves of the rain forest tree Pterocarpus, on which the butterfly lays its eggs.
On a daily basis, they measured the food consumption of the larva and then analyzed the fatty acid composition and content of the diet as well as the larva. Once the larva had transformed into butterflies, the researchers examined the fatty acid composition and content of the butterfly.
They found that both the diet and the tissues of the larva and butterfly had a high concentration of polyunsaturated fatty acids. However, the larva had a much higher total fatty acid content than the butterfly, indicating that the transformation from larva to butterfly drastically reduced the total fatty acid content.
"We were parti cularly impressed with how the caterpillar concentrated these polyunsaturated fatty acids and then transferred them to the butterfly," says Connor. "The polyunsaturated fatty acids can act as precursor substances for prostaglandin and other ferments that may be very necessary in the health of both the larva and the butterfly and, in particular, the transformation during metamorphosis. The mantra is that every organism has a specific dietary pattern which is important for its maturation and survival. Human beings are much in the same category."
Hoping to build on these initial findings, Connor and his colleagues are planning on looking at the Monarch butterfly next. Monarch larva feed exclusively on milkweed, and Connor has already started growing milkweed and analyzing it for this purpose. "It has very high polyunsaturated fatty acid composition, much like the leaves in Belize which the Blue Morpho caterpillar feeds on," explains Connor.