Date Published: February 7, 2019
Publisher: Public Library of Science
Author(s): Michalina Kazek, Agata Kaczmarek, Anna Katarzyna Wrońska, Mieczysława Irena Boguś, Fabio S. Nascimento.
The evolutionary success of insects is arguably due to their ability to build up a complex, highly-adaptable and very effective defense system against numerous pathogens, including entomopathogenic fungi. This system relies on the humoral immune system and cellular defense reactions. The first line of defense against biological pathogens is a cuticle formed of several layers. The cuticular lipids may contain hydrocarbons, free fatty acids (FFA), alcohols, waxes, glycerides, aldehydes and sterols. Cuticular fatty acids may also play a role in defending against fungal invasion. Our present findings show that the diet of insects can have a significant effect on their sensitivity and defense response to pathogens; for example, while G. mellonella larvae fed on beeswax had a similar appearance to those reared on a semi-artificial diet, they possessed a different cuticular free fatty acid (FFA) profile to those fed on a semi-artificial diet, and were less sensitive to Conidiobolus coronatus infection. It is possible that the presence of heneicosenoic acid (C21:1) and other long-chain free fatty acids (C22:0, C24:0, C26:0), as well as Brevibacillus laterosporus bacteria, on the cuticle of larvae fed on beeswax, plays a protective role against fungal invasion. Insect pests represent a global problem. An understanding of the basic mechanisms underlying the fungal infection of insects might provide a clearer insight into their defenses, thus allowing the design of more effective, and environmentally-friendly, means of controlling them. The greater wax moth is an excellent model for the study of immunology resistance. Knowledge of the influence of diet on pathogen resistance in insects can be also useful for creating a model of human diseases caused by pathogens, such as Candia albicans.
Insects comprise the most numerous and widespread class of animals. Their importance to life on earth is huge: they play an important role in the circulation and distribution of organic matter, participate in plant reproduction by pollination and form part of the diet of many vertebrate animals. However, despite the benefits some species bestow, many others are considered pests or vectors of various diseases [1–3].
The present work clearly shows that differences exist in the cuticle components of G. mellonella larvae reared on various diets. It is important to emphasize that no differences in appearance, behavior, duration of development and fecundity were seen between the two groups of insects. No differences in the weights of 5DL7 larvae were observed either. Both the larvae fed on beeswax and those reared on the Sehnal diet were similar in appearance and were in good condition, indicating that both diets were energetically equivalent.