Abstract
The interactions between entomopathogenic fungi and insects serve a classic example of a co-evolutionary arms race between pathogens and their target host. The cuticle, site of the first contact between insects and entomopathogenic fungus, is an important defensive barrier against pathogens. It is covered by a layer of lipids that appears to play a key role in these processes and cuticular free fatty acid (FFA) profiles are consider as a determinant of susceptibility, or resistance, to fungal infections. These profiles are species-specific. The cockroaches Blattella germanica (Blattodea: Blattidae) and Blatta orientalis (Blattodea: Ectobiidae) are unsusceptible to the soil fungus Conidiobolus coronatus (Entomophthorales: Ancylistaceae) infection, therefore we studied the profiles of FFAs in order to understand the defensive capabilities of the cockroaches. The fungus was cultivated for three weeks in minimal medium. Cell-free filtrate was obtained, assayed for elastase, N-acetylglucosaminidase, chitobiosidase and lipase activity, and then used for in vitro hydrolysis of the cuticle from wings and thoraces of adults and oothecae. The amounts of amino acids, N-glucosamine and FFAs released from the hydrolysed cuticle samples were measured after eight hours of incubation. The FFA profiles of the cuticle of adults, and the wings, thoraces and oothecae of both species were established using GC-MS and the results were correlated with the effectiveness of fungal proteases, chitinases and lipases in the hydrolyzation of cuticle samples. Positive correlations would suggest the existence of compounds used by the fungus as nutrients, whereas negative correlations may indicate that these compounds could be engaged in insect defence.
Highlights
Insect populations are regulated in part by the activity of entomopathogens
The aim of the present work was to identify any relationships between the cuticular free fatty acid (FFA) profiles of two cockroach species, B. orientalis and B. germanica, and the efficiency of fungal enzymes in hydrolysing the insect cuticle
Chemical pesticides are among the most popular methods of controlling cockroach infestations, their disadvantages have spurred the search for new strategies, including the use of entomopathogenic fungi [34,37,38]
Summary
Insect populations are regulated in part by the activity of entomopathogens. Entomopathogenic fungi are proposed as an eco-friendly alternative to chemical insecticides and as model organisms to study insect infection [1,2,3,4]. Since the cuticle is the first point of contact between the insect and fungus, it is the first and most decisive defence mechanism in insects, and its composition varies greatly according to the species and the developmental stage [9,10,11,12,13]. This complex structure is covered by a waxy layer rich in lipids which play a key role in resistance to entomopathogenic fungi [8,14]. Many cuticular lipids have antimicrobial properties, other stimulate the germination process, growth and virulence of fungi; and variations in lipid profiles between species are reflected in differential susceptibility to infection [15,16,17,18,19,20,21]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have