Nutritional composition of larvae of mealworm (Tenebrio molitor L.) and crickets (Gryllus assimilis) with potential usage in feed

The use of insects in animal feed currently presents itself as an alternative to soybean meal since it requires low land and water for its production. The Tenebrio molitor is reported as an easy breeding and maintenance insect due to the low production cost. In addition, these insects have been evaluated both in human food (Costa, 2017) and animal feed (Belforti et al., 2015). Another interesting species is the cricket of the genus Gryllus assimilis, since it has a high rate of reproduction and development at certain time of the year, mainly due to heat, humidity, and the presence of crops such as corn and soybean. Semi-arid Regions, such as the Northeast of Brazil, present low soy production and may, eventually, present a shortage of protein sources for use in animal feed.

The use of insects in animal feed currently presents itself as an alternative to soybean meal since it requires low land and water for its production. The Tenebrio molitor is reported as an easy breeding and maintenance insect due to the low production cost. In addition, these insects have been evaluated both in human food (Costa, 2017) and animal feed (Belforti et al., 2015). Another interesting species is the cricket of the genus Gryllus assimilis, since it has a high rate of reproduction and development at certain time of the year, mainly due to heat, humidity, and the presence of crops such as corn and soybean. Semi-arid Regions, such as the Northeast of Brazil, present low soy production and may, eventually, present a shortage of protein sources for use in animal feed.
Thus, the use of insects can be an alternative to solve this problem. However, there is little information about the chemical composition of different types of insects. In addition, the nutritional composition of insects can be changed depending on their diet (Siemianowska et al., 2013). The aim of the present study was to determine the nutritional composition of Tenebrio molitor larvae and crickets of the genus Gryllus assimilis for usage in animal feed.

MATERIAL AND METHODS
The study was approved by the Ethics Committee in Research with Production Animals Recebido em 25 de agosto de 2020 Aceito em 14 de dezembro de 2020 *Autor para correspondência E-mail: valribjunior@academico.ufs.br (CEPAP) of the Federal University of Sergipe, under protocol number 03/2019. Chemical analyses of insects followed the protocols described by AOAC (Official…, 1990). Samples of Tenebrio larvae and crickets were placed in plastic containers, weighed, and euthanized in a freezer at -6 ° C. Then, the samples were dried in forced circulation ovens at 55 ° C and ground in a ball mill. The dry matter content of the samples was determined according to protocol 934.01. The crude protein (CP) content was determined by the Kjeldahl method (protocol 954.01). The gross energy (GE) was determined using a calorimetric combustion pump (IKAC200).
The content of ether extract (EE) was determined using the Soxhlet method (protocol 955.04). The ash content (Ash) was determined according to the 942.05 protocol. The levels of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined according to protocol 937.18. The content of phosphorus (P) was determined by a colorimetric test (Fiske and Subbarow, 1925). Acid molybdate and reducing solution were added to wet-ash samples to make a phosphorus-molybdenum complex. The color intensity was proportional to the P concentration and was determined with a spectrophotometer using absorbance at 620 nm (SpectraCount, Model # AS1000, Packard, Meridian, CT). The other macrominerals and trace minerals were obtained from dry digestion. (Mn), zinc (Zn) and copper (Cu) were determined by the atomic absorption spectrophotometric method (protocol 968.08) using an atomic absorption spectrometer (AAnalyst 300, Perkin Elmer, Norwalk, CT).

RESULTS AND DISCUSSION
Proximal composition and mineral content of Tenebrio molitor larvae and crickets of the genus Gryllus assimilis are shown in Table 1. In the crickets, the quantified contents were 49.1 g/kg (Ash), 8.30 g/kg (P), 11.6 g/kg (K), 1.10 g/kg (Na), 3.88 g/kg (Ca), 0.82 g/kg (Mg), 96.8 mg/kg (Fe), 23.7 mg/kg (Mn), 18.3 mg/kg (Zn) and 21.7 mg/kg (Cu). Siemianowska et al. (2013) stated that fresh and powdered larvae of mealworm are characterized by high content of minerals containing more phosphorus, magnesium, zinc, iron, cupper, and manganese than Polish conventional meats of animals and eggs. Larvae of mealworm (Tenebrio molitor L.) and crickets of the genus Gryllus assimilis may be alternatives for reducing the use of vegetable protein sources in animal feed.