Nutrient contents of the yellow mealworm larvae tenebrio molitor L. reared on four different substrates

Abstract

With an increased demand for alternative, inexpensive and sustainable protein sources, there is an increasing interest in edible insects around the world. Tenebrio molitor, the yellow mealworm a species of darkling beetle, which belongs to the family Tenebrionidae, order Coleoptera, is one of those insects’ species of interest due to its cosmopolitan distribution, low rearing requirements and rich nutritional value. The mealworm’s life cycle is completed within close constant contact with their food, stored grains, which is known as a substrate. Both the adult beetles and larvae feed on these stored grains where they are pests. The most common substrate on which to rear mealworms artificially is wheat bran. However, wheat bran is expensive and not readily available for small holders in developing countries. Therefore, this thesis was initiated to seek for cheaper, alternative and readily available substrates for rearing nutritious mealworms. Mealworms were reared on three alternative substrates to wheat bran: wheat flour, maize flour and Lucerne pellets. These substrates were selected due to their long shelf-life, availability in South Africa; both maize flour and wheat flour are found in supermarkets and lucerne pellets can be found in most pet stores. The first part of this thesis evaluated the yield, weight, fecundity of mealworms reared on these four substrates over two generations (Chapter 2). For the first generation, wheat bran and wheat flour produced a higher number of individuals,with individuals reared on wheat bran heavier than those from the other three substrates. Individuals produced from the second generation from all four substrates were similar in yield, weight and fecundity. The second part of this thesis (Chapter 3) evaluated the nutrient contents of both generations of mealworms reared on the four substrates. The protein contents per 100g of Tenebrio molitor larvae from the first generation was between 28 – 36% varying according to the rearing substrates in the following order Lucerne > wheat bran > wheat flour > maize flour. A similar trend was also found in the protein contents of larvae from the second generation but with protein contents in the range of 29 – 35%. The larvae from both the first and second generations reared on all substrates contained the following minerals calcium, phosphorus, sodium, magnesium, copper, manganese, potassium, zinc and iron. They also were rich in oleic (56.67%), linoleic (18.46%) and palmitic acids (13.38%). This study was able to show the potentials of alternative and cheaper substrates for rearing the yellow mealworm and the possibility of rearing over two generations using the same substrate. Results showed there were differences in weight, yield, and fecundity between mealworms reared on the four substrates for the first generation, this was not the case for the second generation. Larvae from both generations and from all substrates were rich in protein, minerals and fatty acids. Indicating the sustainability and cost effectiveness of rearing over generations, an added advantage for subsistence and low-scale mealworm farmers and other end users like small holder poultry farmers.