Amino acid diet improves frozen fly survival

For many people, the humble fruit fly is a pest that competes with us for the ripest fruit, but to many biologists, the pesky insect has become a fount of knowledge since the development of powerful molecular tools that allow scientists to answer fundamental biological questions. However, Vladimír Koštál from the Czech Republic's Institute of Entomology explains that presently it is not possible to store the genetically modified insects by freezing in the way that scientists routinely store cells and bacteria. ‘Current practice relies on continuous rearing of Drosophila flies. This is very tedious, expensive and risky’, Koštál explains. So, in a bid to develop a technique to preserve the insects at an earlier stage of development, Koštál and his colleagues designed a protocol to freeze larvae in which they washed the insects, wrapped them in a ball of moist cellulose and then added an ice crystal to trigger ice formation in the larvae's bodies down to –5°C. Then, having thawed the larvae, the team monitored the insects as they developed into adults and found that they could improve survival from 0.7% to an impressive 12.6% by cooling the larvae slowly. But could they find a dietary additive that would improve the insects’ survival still further?

Systematically feeding the larvae diets fortified with individual amino acids and other amine compounds before freezing and testing their survival, the team was impressed to find that the survival of the adult flies improved dramatically to 50.6% and 42.1% when the larvae had been fed a diet including either 25 mg g⁻¹ arginine or 50 mg g⁻¹ proline. Discussing possible mechanisms that may allow the two amino acids to protect structures and prevent damaged proteins and lipids from forming destructive aggregations in cells, the team is optimistic that their evaluation of the impact of different amino acids on freeze tolerance will eventually contribute to the development of a successful protocol that will allow researchers to store valuable insect strains for extended periods at low temperatures.