Consumption of polypropylene by Galleria mellonella (Insecta, Lepidoptera, Pyralidae) larvae did not cause degenerative changes in internal organs

Abstract

Abstract G. mellonella is a promising species for use in the biodegradation of plastics. It is easy to breed and has high resistance to diverse climatic conditions, which is particularly valuable when considering its potential application in the decomposition of plastics. Although it does not pose a direct threat to humans, the greater wax moth is a parasitic species in bee hives, contributing to the population decline of these insects. This species has demonstrated the capacity for biodegradation of the most common types of plastics, such as polyethylene and polypropylene (PP). The microbiome inhabiting the digestive system is responsible for this degradation. However, there reports on whether consumed plastics or their decomposition products will adversely affect the structure and functioning of the internal organs are rather poor. The aim of these studies was to determine whether the consumption of PP by a larger wax moth (G. mellonella) larvae caused any ultrastructural changes in the organs of the animal's body and to evaluate the survival rate of the animals and describe their reproduction. Thus, this study provided a preliminary understanding of histological and ultrastructural changes caused, or not caused, by the PP diet. We investigated whether any degenerative changes appeared in cells of selected organs – midgut, silk gland, and fat body – under PP consumption by G. mellonella caterpillars (7th instar larvae). We also examined whether there was an increase in levels of reactive oxygen species (ROS) in selected organs, as well as the ability of larvae to survive and undergo metamorphosis. The animals were divided into four groups: G0-C, G0-S, G0-24, and G0-48. The research was carried out using transmission electron microscopy (TEM), confocal microscopy, and flow cytometry. Our study on G. mellonella larvae fed with PP bags showed that a diet containing such plastic did not affect internal organs at the ultrastructural level. Cells in the analyzed organs – midgut, silk gland, and fat body – showed no degenerative changes. An increase in the intensity of autophagy and cell vacuolization was noted, but they probably act as a survival pathway. These observations suggest that the final larval stage of the greater wax moth can potentially be applied in PP biodegradation.