Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2015
Publication Date: 7/17/2015
Citation: Morales Ramos, J.A., Rojas, M.G. 2015. Effect of larval density on food utilization efficiency of Tenebrio molitor (Coleoptera: Tenebrionidae). Journal of Economic Entomology. 108:2259-2267.
Interpretive Summary: The yellow meal worm is produced commercially in the U.S. and sold for many purposes including as foods for captive mammals, birds, reptiles, and amphibians and as fish bait. Increasing production capabilities could open new possibilities for commercial applications of meal worm protein, such as animal feed and production of biological control agents. Current methods of production are rudimentary limiting the volume of meal worm production. Producers have the tendency of crowding meal worm larvae in rearing trays to save space and optimize production. Some previous reports have found that crowding meal worm larvae may increase development time and mortality. Our objectives were to determine if the density of larvae in rearing trays could have an effect on the efficiency of food conversion by the meal worms. Food conversion can be measured as mg of insect biomass produced per gram of food consumed or also as the percentage of food converted to insect biomass. We measure food conversion efficiency of meal worms at different larval densities in four 3-week period intervals. Our results showed that increasing the number of larvae per unit of area impacts the efficiency of food conversion in a negative way. As larval density increases, less insect biomass is produced per gram of food. Our results show that meal worm production efficiency can be increased by reducing crowding in the rearing trays. In addition, density expressed as meal worm mass per area had a higher impact than density as number of larvae per area. This means that as meal worms grow density increases and conversion efficiency drops. These results could be valuable to improve meal worm rearing conditions in ways that optimize insect biomass production.
Technical Abstract: Rearing conditions, particularly the crowding of larvae, may have a significant impact on production efficiency of some insects produced commercially, such as Tenebrio molitor L. (Coleoptera: Tenebrionidae). Although larval densities are known to affect developmental time and growth in T. molitor, no reports were found on the effects of crowding on food utilization. The effect of larval density on food utilization efficiency of T. molitor larvae was studied by measuring efficiency of ingested food conversion (ECI), efficiency of digested food conversion (EDC), and mg of larval weight gain per gram of food consumed (LWGpFC) at increasing larval densities (12, 24, 36, 48, 50, 62, 74, and 96 larvae per dm2) over 4 consecutive 3-week periods. Individual larval weight gain and food consumption were negatively impacted by larval density. Similarly, ECI, ECD, and LWGpFC were negatively impacted by larval density. Larval ageing, measured as 4 consecutive 3-week periods, significantly and independently impacted ECI, ECD, and LWGpFC in a negative way. General linear model analysis showed that age had a higher impact than density on food utilization parameters of T. molitor larvae. Larval growth was determined to be responsible for the age effects as measurements of larval mass density (in grams of larvae per dm2) had a significant impact on food utilization parameters across ages and density treatments (in number of larvae per dm2). The importance of mass versus numbers per unit of area as measurements of larval density and the implications of negative effects of density on food utilization for insect biomass production are discussed.