Entomopathogens: Theory and practice

Entomopathogens are the pathogens of insects, in other words those microorganisms or microscopic infectious agents like viruses, capable of causing them a disease possibly leading to their death. Beyond this simple and obvious definition, entomopathogens can be seen as those microbes that evolved with their hosts developing the ability to overcome their immune barriers, successfully exploiting them as useful nutritional resources. While we might agree that a primary ecosystem role of microbials (especially soil microorganisms like bacteria and fungi) is as decomposers of organic matter, we might infer that speciation has led to the establishment of species that became capable of interacting to their own advantage with living organisms for which they became pathogens. Within the multifaceted network of biocenotic relationships in the ecosystem, we can imagine the complexity of interactions between the invisible microbial world and the relatively larger insect world (Douglas, 2009). Only careful observation, supported by the aid of technologies and scientific equipment that have over time become increasingly sophisticated and advanced, has made it possible to study and interpret the mechanisms through which a pathogen interacts with its host, giving a clear glimpse of possible practical applications, especially in the field of pest management. In fact, although in a natural ecosystem we assume the existence of well-established balances between entomopathogens and insect populations, conditions of disequilibrium in favour of the latter typically characterise man-made agro-ecosystems. Accordingly, pest outbreaks in such environments are frequent and, particularly in the population density peak phases, are associated with epidemic phenomena caused by entomopathogenic agents that find ideal conditions to spread and thus act containing pest populations. Beyond these special cases, entomopathogens are always present in the environment contributing to the so-called “environmental resistance” regulating the biotic potential of pest species. Although we can identify these common characteristics, among entomopathogens we find very different living forms such as viruses, bacteria, fungi, microsporidia, and a particular category of nematodes (Tanada and Kaya, 2012). This fascinating world of entomopathogens is also represented by a wide inter- and intraspecific variability that represents considerable opportunities for practical applications. Although numerous studies have been conducted in recent decades by a dedicated scientific community, many aspects still need to be clarified regarding the mechanisms of action and pathogenic processes involving a plethora of proteins and other insecticidal compounds, enzymes and virulence factors. Added to this is the continual discovery of new strains of entomopathogens with previously unknown gene traits that give them special biological properties that can be leveraged for the development of new biosolutions. Hence the industrial interest that has always supported research and development in this area by foreseeing the changing needs of pest management and introducing ever newer and more sophisticated microbial-based products to the market.