Vitamin C or ascorbic acid is important to us for the integrity of our connective tissue, but why do vegetarian insects need ascorbic acid in food? They need her in another role. This molecule is necessary for building their normal exoskeleton
By Amos Navon, former senior researcher in entomology at the Agricultural Research Administration
Vitamin C or ascorbic acid is important to us for the integrity of our connective tissue, but why do vegetarian insects need ascorbic acid in food? They need her in another role. This molecule is necessary for building their normal exoskeleton. Symptoms of ascorbic acid deficiency in the vegetarian insect are only detected when the larva is grown on a synthetic food substrate that does not contain this molecule. Man and a limited number of mammals and vegetarian insects have lost the ability to synthesize ascorbic acid. Regarding the person, it is important that the food include vegetables and fruits, and if necessary then also provide vitamin C as a nutritional supplement.
Vitamin C in humans
The discovery of scurvy, a vitamin C deficiency disease, began with sailors during the period of land discovery, mainly by Columbus, Vasco da Gama and Magellan. The sailors' food did not contain it and they did not know that it was a deficiency of ascorbic acid. The disease manifested itself in death from hemorrhages in the gums and the rest of the body, loss of teeth and death from infections and starvation. Those who did not die, suffered from a weakness that did not allow them to function. This was then considered an occupational disease. The sailors discovered that the natives in the countries they reached showed no signs of vitamin C deficiency, because they were fed plant foods. Later we will learn the need to add citrus fruits to the seafarers' food basket. The British Navy issued a regulation that transoceanic voyages must be equipped with citrus fruits. This regulation allowed Great Britain to take control of the continent of Australia and New Zealand. After many years of medical research, it became clear that scurvy is a disease of damage to the connective tissue and the role of ascorbic acid is to serve as a restoring molecule in the hydroxylation of lysine and proline - amino acids typical of the collagen protein. Today in the diet of the western world, scurvy does not pose a threat to humans because our food contains vitamin C amounts above the requirement.
The evolution of ascorbic acid consumption in mammals
Over the years it became clear that apart from humans, those who need ascorbic acid are apes (primates), voles (rodents) and species of fruit-eating bats (there are other animals that I will not mention here). What these animals have in common is that the abundance of ascorbic acid in their natural food led to the loss of the ability to synthesize this molecule. In the process of evolution, the dependence on this ascorbic acid probably passed from the primate monkeys to humans. In the voles, this dependence happened due to being a definite vegetarian, while other rodents, for example mice that feed on seeds, did not need this molecule in their diet. The mammals that depend on ascorbic acid in their diet have lost the ability to synthesize the enzyme golonolactone oxidase, the last enzyme in the biosynthetic chain of ascorbic acid. This mutation probably happened in the Middle Paleolithic period (several tens of thousands of years ago), when the human diet was based on hunting and eating plants and fruits (hunter-gatherers). There is a possibility that the loss of the ability to synthesize ascorbic acid happened later, during the agricultural revolution (10,000 years ago) when man began to grow domesticated agricultural crops that served as a food source for man and the vegetarian insect.
The research on ascorbic acid spans many years and on a huge scale. It was done by researchers from various fields in the natural sciences and medicine, and in the pharmaceutical industry. The basic research of ascorbic acid reached the identification of the difference in the DNA sequence that codes for the creation of the final component in the biosynthesis of ascorbic acid.
The difference is in the genetic difference between the nitrogenous bases in the genome in comparison between a mouse that is not a consumer of ascorbic acid and the human:
CTTCTGGCTGCTGTTAAC mouse
TTTCTGACTCCTGTTTGC A person
Evolution and physiological effect on prodenia"
The association between caterpillars and higher plants began tens of thousands of years ago. The vegetarian insects became agricultural pests in the agricultural revolution because the domestication of plants such as grains and legumes made it possible for insects and humans to feed on annual plants. The record of cotton as a surrogate of the prodania is mentioned in papyri from the second millennium BC. The name of this insect in English is The Egyptian Cotton Leaf worm. The damage from the prodonia (vernacular name) to cotton in Egypt is still a problem today. The desert locust, which is unable to synthesize ascorbic acid, is mentioned in the Bible as one of the plagues of Egypt, and is known as the worst pest of agricultural crops. The insects that develop on flours and seeds do not need ascorbic acid in their food, for example the pink lactic acid, whose larvae feed on the cotton seeds inside the lactic acid. Another insect is the desert locust. The aforementioned vegetarian moths also include the silkworm whose cultivation in nature and under artificial conditions is done obligatorily on the leaves of a mulberry tree.
In order to study the effects of ascorbic acid on the vegetarian insect, it was necessary to assemble an artificial food substrate that does not contain even traces of this molecule. The number of entomologists who have done this is not many, and I am among them. For the purpose of studying the effects of ascorbic acid deficiency in Prudenia, Spodoptera littorualis (scientific name), I assembled a synthetic substrate based on an agar-agar gel. It contained vitamin-free casein, soy hydrolyzate, sucrose, cholesterol, wheat germ oil, a mixture of group B vitamins, choline chloride and a salt mixture. The source of the larvae for research on ascorbic acid was the mass rearing of the insect on artificial food soil that contained ascorbic acid.
The physiological and biochemical study
The study was done as part of my doctoral thesis as well as during a sabbatical year with the late Prof. Herbert Lipke at the University of Massachusetts-Boston, funded by the Israel-USA Fund for Agricultural Research (BARD). The findings were published in the leading journals of insect physiology and biochemistry.
Physiological effect of ascorbic acid deficiency in the synthetic food substrate, the Prodania larva was used as a model insect of ascorbic acid dependence in food. Initially, under conditions lacking this molecule the larva grew slowly and weighed less. He was still growing on the reserves of ascorbic acid he had in the egg. In the last stages of the larva a dramatic process happens. The caterpillar failed to drop the weevil. In an extreme situation, the old head box does not fall forward from the head but remains close to the head box and the skin of the skin does not fall off the body either, as you can see in the picture below.
The failure to shed the skin of the body will mean that the caterpillar cannot stick to the surface on which it is supposed to stand. In the less extreme situation, the damage is "postponed" to the embodiment phase. As seen in picture 2.
The biochemical effect of ascorbic acid
Insects do not have connective tissue which is internal tissue in mammals, but a hard sclerotinic armor in the vegetarian larva will exist mainly in the head box and the pupal box. The puberty is done under the supervision of the youth hormone and the puberty hormone. In the healthy larva, a distance is formed between the old cuticle and the one that develops below it, and the space between the two cuticles is filled with exfoliation fluid secreted by the epidermal cells. The function of this fluid is to digest with enzymes the chitin and protein in the old cuticle. The larva digests the liquid by swallowing to recover the enzymatic breakdown products of chitin and protein. Also, the larva uses the molting fluid as a hydrostatic force in shedding the molting skin.
Ascorbic acid and the enzyme phenoloxidase are found in the exfoliation fluid and their full role requires further study. Ascorbic acid plays a role in the sclerotization process by controlling the rate of sclerotin formation. The lack of this repeating molecule will cause early sclerotization and its biological manifestation will be failure of the larva to expand the head box and wing pockets in the pupa. In the larva, the jaws that are attached to the smaller head box will press on the swallow house. As a result, the upper jaws will be pushed forward and the larva will not be able to bite the food. Due to the technical difficulties in operating the jaws, the larva will enter a state of starvation in which the body components needed to carry out the full pupation will be missing, and the larva will die of starvation within a day or two. Following a partial lack of ascorbic acid in the food substrate, the incarnate larva will not be able to expand the wing pockets to the correct dimensions (photo 2). The damage to the moth emerging from the cocoon will manifest itself in damaged wings in such a way that it will not be able to fly and reproduce.
Ascorbic acid in the vegetarian insect - summary
The number of insect species in the world is estimated between 1-2 million. Not all were discovered. Of these, the vegetarian insects make up about half a million species. Therefore, the "evolutionary accident" of dependence on ascorbic acid in the vegetarian insect is a minority among the insect world. In my research, it was discovered by deliberately growing the larva on a synthetic food substrate devoid of this molecule. The metamorphosis process is an "Achilles heel", both in fully metamorphosed (holometabolic) species, for example in Prudania, and in semi-metabolic (hemimetabolic) species, including the desert locust. Also, it is also present in the arthropod system, in which the number of species is lower than that of the insect class. It should be noted that hatching in an insect is one of the most complex processes in the animal world. In humans, growth is done by adding cells to the body, including connective tissue, on the other hand, in insects, the larva must molt several times to increase the volume of the body until it morphs. This execution is done while activating a complex enzymatic system and a high energy capacity and execution in a very short time, to avoid predators. The compensation for this is the enormous reproduction rate of ascorbic acid consuming insects which are the majority of agricultural pests.
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