Influence of antibiotic ceftriaxone on the development of the yellow mealworm beetle (Tenebrio molitor L.)

Antibiotics can enter the soil with waste and affect insects in their natural habitat, moreover they are often found in feed for farm animals, which is also used for rearing insects for food and feed. In addition, the possibility of bioconversion of agricultural waste with larvae is currently being widely studied. Such waste may contain significant amounts of antibiotics, which affect the growth, development and microbiota of insects used to process it. Ceftriaxone is a third-generation cephalosporin antibiotic. The influence of cephalosporin antibiotics on insects is little studied, while it depends on both the insect species and the type of antibiotic. The yellow mealworm beetle is an ediable insect and a pest of grain products, most often found in the bins of flour warehouses, bakeries, mills, and feed. In this work, the effect of different concentrations of the ceftriaxone on the weight and survival rate of the T. molitor larvae, several parameters of larvae composition, as well as metamorphosis and the number of offspring was shown. The ability of T. molitor to consume the feed substrate or process waste containing ceftriaxone was demonstrated for the first time. The aim of this work was to study the effect of the antibiotic ceftriaxone on the growth, development and reproductive performance of the yellow mealworm. The experiments were carried out in the insectarium of the All-Russian Research Institute for Food Additives (St. Petersburg, Russia) from July to October 2022. Before the experiment, the insects were reared at 25±2 °C and relative humidity of 50±10 %. A diet for yellow mealworm were composed of wheat bran (16.0 g proteins, 4.0 g fats, 65,0 g carbohydrates per 100 g of the product) and carrot as a source of water. The effect of ceftriaxone (Biosintez, Russia) on insects at concentrations of 0, 0.1, 1, 10, and 100 mg/kg of feed (wheat bran) dry weight was studied. To obtain the feed with certain antibiotic concentration the following procedure was carried out: ceftriaxone solutions with required concentration were added to wheat bran in a 1:1 ratio and thoroughly mixed, then the feed was dried in a convection dryer UF110plus (Memmert GmbH & Co.KG, Germany) at 40 °C for 24 h. The experiment included three stages: the study of the growth rate of larvae, the calculation of the number of pupated and turned into adult insects, and the assessment of the number of T. molitor offspring. Feed conversion ratio (FCR) and efficiency of conversion of digested food (ECD) were calculated. FCR and ECD were calculated given wet feed (bran + carrots) and for bran weight only. The water content of the larvae was determined by drying a sample in the Vacuum Oven OV-12 (Jeio Tech, Korea) at 40 °C. To determine the ash content of the larvae, dried samples were placed in crucibles calcined to constant weight and burned in a SNOL 8.2/1100 muffle furnace (Umega Group, AB, Lithuania) using the following calcination regime: 60 min at 250 °C + 6 h at 550 °C. The fatty acid composition was determined by gas chromatography with mass spectrometry detection on a gas chromatograph Varian 450-GC GC (Varian Chromatography Systems, Netherlands) with a mass spectrometer detector Varian 240-MS (Varian, Inc., USA). Methylation and extraction of fatty acids from samples dried in the Vacuum Oven OV-12 at 40 °C was carried out using a 15 % solution of sulfuric acid in methanol and chloroform. The results of the study showed that the addition of ceftriaxone to the diet of the yellow mealworm beetles at a concentration of 100 mg/kg led to the acceleration in weight gain by the larvae (p = 0.029). No relationship was observed between T. molitor larval survival rate and antibiotic concentration (p > 0.05). In addition, no statistically significant differences were found between the fatty acid composition, feed conversion ratios, ash content and water content of the larvae fed on wheat bran with different ceftriaxone concentrations (p > 0.05). There was no relationship between the antibiotic content (0-100 mg/kg) and the productivity of the yellow mealworm, and no changes were found in the processes of pupation and transformation into imago when the antibiotic was added to the feed (p > 0.05). Therefore, T. molitor can be reared on a diet containing ceftriaxone while maintaining the vitality and basic characteristics of insects necessary for their further use. In addition, these results mean that ceftriaxone does not adversely affect the large mealworm beetles as a pest of grain crop products.