Solanaceae Glycoalkaloids Disturb Lipid Metabolism in the Tenebrio molitor Beetle

Abstract

Glycoalkaloids (GAs) are produced naturally by plants and affect insect survivability and fertility. These compounds can be considered potential bioinsecticides; however, the mechanisms and effects of their action remain undiscovered. As lipids are essential molecules for the proper functioning of an insect organism, this research aimed to determine the effects of GAs on the lipid metabolism of the Tenebrio molitor beetle. Solanine, chaconine, tomatine, and tomato leaf extract were applied to larvae by injection at two concentrations, 10−8 and 10−5 M. Then, the tissue was isolated after 2 and 24 h to determine the levels of free fatty acids, sterols and esters using the GC–MS technique. Moreover, the triacylglyceride level and the activity of the key β-oxidation enzyme, 3-hydroxyacyl-CoA dehydrogenase (HADH), were measured. The results indicate that GAs affect the content and composition of lipid compounds in the beetles’ haemolymph and fat body. The effects depend on the GA concentrations, incubation time, and kind of tissue. Moreover, the tested compounds decrease HADH activity, especially in the fat body, which may affect energy production. To our knowledge, this is the first study concerning lipid metabolism in T. molitor after GA application. Our results provide some insights into that topic.

Analysis of glycoalkaloid distribution in the tissues of mealworm larvae (Tenebrio molitor)

“…Thus, GAs can alter fat body structure. Moreover, SOL, CHA, and tomatine affect lipid metabolism 19 . Despite GA delivery by injection through the cuticle, the compounds were also detected in the gut tissue.…”

“…PHL80075) (Sigma‒Aldrich, Merck, Darmstadt, Germany) were used in experiments at a concentration of 10 −5 M. The insects were injected with 2 μL of GA solution, which corresponds to 69.45 ng of SOL or 68.17 ng of CHA per sample composed of 4 larvae (with a dosage ranging from 0.12–0.14 ng/mg body mass). This concentration was selected based on the literature, the content of the plant extract, and our previous studies showing that it leads to different metabolic and developmental disorders 15 , 16 , 18 , 19 . The tested compounds were administered to larvae by injection using a microsyringe (Hamilton).…”

“…Sublethal effects of GAs, such as disturbed development, food intake, and reproduction, were observed in T. molitor after the addition of pure GAs and S. nigrum fruit extract to food 18 . The injection of GAs and tomato leaf extract into T. molitor larvae affects lipid metabolism 19 ; in turn, the administration of S. nigrum fruit extract modulates insect immune system activity 20 in this species.…”