Date Published: March 8, 2018
Publisher: Public Library of Science
Author(s): Anna Katarzyna Wrońska, Mieczysława Irena Boguś, Emilia Włóka, Michalina Kazek, Agata Kaczmarek, Katarzyna Zalewska, Juan J Loor.
The entomopathogenic fungus Conidiobolus coronatus produces enzymes that may hydrolyze the cuticle of Galleria mellonella. Of these enzymes, elastase activity was the highest: this figure being 24 times higher than NAGase activity 553 times higher than chitinase activity and 1844 times higher than lipase activity. The present work examines the differences in the hydrolysis of cuticles taken from larvae, pupae and adults (thorax and wings), by C. coronatus enzymes. The cuticles of the larvae and adult thorax were the most susceptible to digestion by proteases and lipases. Moreover, the maximum concentration of free N-glucosamine was in the hydrolysis of G. mellonella thorax. These differences in the digestion of the various types of cuticle may result from differences in their composition. GC-MS analysis of the cuticular fatty acids isolated from pupae of G. mellonella confirmed the presence of C 8:0, C 9:0, C 12:0, C 14:0, C 15:0, C 16:1, C 16:0, C 17:0, C 18:1, C 18:0, with C 16:0 and C 18:0 being present in the highest concentrations. Additional fatty acids were found in extracts from G. mellonella imagines: C 10:0, C 13:0, C 20:0 and C 20:1, with a considerable dominance of C 16:0 and C 18:1. In larvae, C 16:0 and C 18:1 predominated. Statistically significant differences in concentration (p≤0.05) were found between the larvae, pupae and imago for each fatty acid. The qualitative and quantitative differences in the fatty acid composition of G. mellonella cuticle occurring throughout normal development might be responsible for the varied efficiency of fungal enzymes in degrading larval, pupal and adult cuticles.
Insect populations are naturally regulated by entomopathogenic fungi. At present, in the literature there are data indicating the possibility of using entomopathogenic fungi to control insect pests [1,2]. Their mode of entry into the insect body is based around two mechanisms: penetration of the cuticle by the growing hyphae or specialized infectious structures like appressoria or penetrant tubes, and by the enzymatic degradation of major cuticle components, including proteins, chitin and lipids [3,4]. The species-specific nature of the exoskeleton seems to be a decisive factor governing the sensitivity or resistance of various insect species to fungal infection . The composition of the cuticle strongly influences conidial adherence and germination, resulting in the susceptibility to a fungal pathogen varying between species [4, 6, 7, 8].
Entomopathogenic fungi are considered to play a vital role as biological control agents of insect populations. Although chemical pesticides are very specific in their action, most do not preserve biodiversity . In contrast, a highly diverse array of fungal species is known to infect insects, and several commercial bio-insecticides based on entomopathogenic fungi have been developed. Although a number of studies have examined improvements in the production, formulation and practical application of these pesticides, much work is still needed before their final implementation. The use of entomopathogenic fungi is unavoidable as it is an fundamental part of integrated pest management programs in many ecological zones. Therefore, it is necessary to understand their underlying mechanisms of action .