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Public Science Insights: Hypermetabolic Production of Water by Insects Fed on Dry Food

Posted Thu, Feb, 02,2017

The larvae of certain insects such as meal moths, clothes moths, wax moths, carpet beetles, cockroaches, and many others, can grow and thrive on absolutely dry food. In order to increase their body mass, these larvae need to raise their internal  water content. During millions of years of insect evolution,  these insects have acquired the ability to manufacture large amounts of water through the total metabolic catabolism of certain nutrients (lipid, carbohydrate). Under conditions of common metabolic rates, however, the yield of metabolically produced water is relatively small. It may be perhaps used to compensate for respiratory water loss, but the amount of water produced during common respiratory metabolism cannot cover the large water demand of larval somatic growth. There have been assumptions that larvae fed on dry food could possibly be absorbing some water from the environment, but this has never been experimentally confirmed. An obstacle to this theory is the fact that the integument of terrestrial insects is coated all over by lipid oil, wax or lipophilic hydrocarbons, which effectively prevents trans-integumental water transport in both directions. 
 
Extensive studies on the metabolic effects of insect juvenile hormone (JH), revealed a surprisingly high stimulation of respiratory metabolism in the larvae of a carpet beetle (Dermestes vulpinus Fabr). When related to the unit of living mass, the enormous increase of oxygen consumption (10 to 20-fold) caused by JH in these larvae, surpassed the previously recorded metabolic rate of any living organism on the planet. The phenomenon was reminiscent of a moderately regulated biological burning process and was referred to as hypermetabolism.  In the carpet beetle, hypermetabolism  was strictly dependent on presence of a lipid in the food (dried calf viscera).  The delipidated food was consumed without the hypermetabolic response.  Another insect species fed on dry food and exhibiting a strong hypermetabolic responses to JH was the greater wax moth (Galleria mellonella). We found that the breeding jars containing the JH-treated wax moth larvae were always warmer by 10°C  or even more in comparison with similar jars containing the untreated specimens. This suggested that the hypermetabolic responses to JH were associated with the formation of endogenous heat dissipated into the environment. Somewhat later, we used a thermovision camera for an easy identification of the hypermetabolic specimens by their increased body temperature. Latest evidence of the JH-induced hypermetabolic process indicates that it is a very special, hitherto mostly ignored epigenetic biochemical process, which is based on the hormonally regulated uncoupling of oxidative phosphorylation from oxidation. The process is associated with the total metabolic combustion of a dietary lipid or carbohydrate, yielding CO2, essential amounts of metabolic water, and large amounts of endothermic energy that is dissipated as heat. Possible use of the hypermetabolic principle in insect thermogregulation and water production (overwintering honey bees) has been envisioned.      
 

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