The influence of wet feed distribution on the density, growth rate and growth variability of Tenebrio molitor

Mealworm larvae have the potential to be a future food and feed. One of the difficulties in rearing mealworms efficiently, is their need for both dry and wet feed. Extensive research has been done on dry feed and distributing this feed is easy with the existing technology. However, the wet feed (frequently chopped up vegetables) comes with several challenges. The nature of the wet feed (neither solid nor liquid) complicates automation, making manual feeding still the norm in many farms. This may result in an unequal distribution of the wet feed. The goal of this study was to assess the influence of distance to the wet feed (substituted by agar) on density, growth rate and growth rate variability of mealworm larvae. The entire larval growth stage was assessed from less than 1 mg up to more than 100 mg, as differences in mobility were expected for different sized larvae. The results indicate that the distribution of the agar plays a major role in the distribution and growth of the larvae, with less larvae and a decrease in growth rate observed when the agar was more than 5 to 10 cm away from the larvae. Few mealworms were found more than 15 cm from the agar, and their growth was inhibited resulting in a biomass up to 150 times lower than near the agar. The effects were mainly observed in larvae weighing less than 30 mg, heavier mealworms were mobile enough to crawl to and from the agar. Based on the results, and in order to ensure that all larvae sizes grow equally well and are well distributed in the crate, we strongly advise against distances of 10 cm or more and we recommend the placement of wet feed within 5 cm from the larvae.