American cockroaches Periplaneta americana are unique insects. First, they are the most ancient insects in the world. Second, these large (up to four centimeters long) red creatures are the fastest among all land insects.
In 1991, a world record was registered: a Periplaneta americana cockroach ran at a speed of 5.4 km/h. That means that for one second, the champion cockroach overpassed a distance 50 times greater than the length of its body.
To achieve a similar result, a man of average height would have to run at a speed of 330 km/h.
S.A.Shukolyukov and V.S.Saakov, researchers from the Sechenov Institute of Evolutional Physiology and Biochemistry, St. Petersburg, have found that American cockroaches are not only good sprinters. These insects are capable of synthesizing beta-carotene in their body. So far, this capability has not been found in other animals.
Carotinoids, including beta-carotene, are vitally important substances. They are precursors of chromophore of rhodopsin, visual pigment. When mosquitoes or butterflies were fed on a carotinoid-deficient diet, they became almost blind.
But the American cockroaches are not so feeble.
In the experiment, the researchers compared cockroaches fed on carotene-deficient diet and those which got additional carrot juice. Regardless of the diet, cockroaches of both groups had enough beta-carotene in their eyes, whereas 13 times more carotene was found in the guts of the cockroaches that got carrot juice.
The researchers, amazed, prolonged the experiment up to three years. For this period, no fewer than four cockroach generations changed (they live about a year). Despite the lack of carotene in the food, all the insects had enough of it in their bodies.
To prove that the American cockroaches can synthesize beta-carotene, the researchers injected radioactively labeled pyrophosphate of mevalonic acid (beta-carotene precursor) into the insects' bodies. On the next day, the labeled beta-carotene was found in the insects.
The researchers have not yet learned how the American cockroaches manage to synthesize beta-carotene. Maybe they have special enzymes, or some microorganisms living in the insects' bodies provide the synthesis.
In any case, Periplaneta americana has two mechanisms for maintaining the level of beta-carotene in the eyes. The first way is accumulation of carotinoids in reserve; the second way -- synthesis of these substances de novo -- takes place when they are lacking in the diet.