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A while ago, I wrote about Why do frogs need vitamins:

Animals also need a range of minerals, one of the main ones being calcium (for bones and the nervous system). Insects don't have bones, and compared with vertebrates, they have a reversed calcium:phosphorus ratio, i.e. they contain more phosphorus than calcium, whereas in animals, it's the other way round. Most insects are therefore a poor source of calcium, although soil arthropods such as springtails and woodlice may contain reasonable amounts.

On Frognet recently, Ed Kowalski pointed at an interesting scientific paper I hadn't seen before, in which scientists kept Drosophila melanogaster on low and high calcium diets to see if this increased the calcium content of the flies. To cut a long story short, the answer is no:

Flies were raised on the standard calcium diet and then transferred to either the high calcium or low calcium diet within 24 h of emergence. Calcium contents of whole flies and tubules were measured for 10 days after transfer, and calcium contents of whole flies of the resulting F1 generation were determined at intervals for 15 days after emergence. The flies maintained a calcium content of ~4.4 nmol/fly for 10 days after emergence; there was no increase in calcium content with time after transfer to high calcium diet.

However, they did find that:

Although larvae weighed 2X as much as adult flies, they contained 3–4X as much calcium.

Unfortunately, these amount of calcium are low, probably not enough to satisfy frog's needs. When the levels of calcium are high enough to ensure a positive calcium to phosphorus ratio of at least 1:1 and ideally closer to 1.5 to 1, the mortality of the insects increases rapidly. So we still need to supplement feeder insects with calcium (and other minerals and vitamins).

Related: Tip of the Day: Feeding Drosophila larvae

Calcium homeostasis in larval and adult Drosophila melanogaster. 2000 Archives of Insect Biochemistry and Physiology
44: 27-39

Calcium homeostasis in Drosophila melanogaster was examined in response to the challenges imposed by growth, reproduction and variations in dietary calcium content. Turnover time for calcium, calculated as the time for Ca to accumulate to half the steady state value of 3.46 nmol/fly, was 3.3 days. Although larvae weighed 2X as much as adults, they contained 3–4X as much calcium. Anterior Malpighian tubules (MTs) contain much more calcium than posterior MTs, accounting for 25–30% of the calcium content of the whole fly. In response to a 6.2-fold increase in dietary calcium level, calcium content of whole flies increased only 10%. Hemolymph calcium concentration (~0.5 mM) was similar in males and females and in animals raised on diets differing in calcium content. Fluid secretion rate, secreted fluid calcium concentration, and transepithelial calcium flux in tubules isolated from flies raised on high and low calcium diets did not differ significantly. Malpighian tubules secrete calcium at rates sufficient to eliminate whole body calcium content in 0.5 and 3 days for tubules secreting fluid at basal and maximal rates, respectively. It is suggested that flies absorb high quantities of calcium from the diet and maintain homeostasis through the combined effects of elimination of calcium in fluid secreted by the Malpighian tubules and the sequestration of calcium in granules, especially within the distal segment of the anterior pair of Malpighian tubules.

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