When Appearance Misleads: The Role of the Entomopathogen Surface in the Relationship with Its Host

Abstract

Currently, potentially harmful insects are controlled mainly by chemical synthetic insecticides, but environmental emergencies strongly require less invasive control techniques. The use of biological insecticides in the form of entomopathogenic organisms is undoubtedly a fundamental resource for the biological control of insect pests in the future. These infectious agents and endogenous parasites generally act by profoundly altering the host’s physiology to death, but their success is closely related to the neutralization of the target insect’s immune response. In general, entomopathogen parasites, entomopathogenic bacteria, and fungi can counteract immune processes through the effects of secretion/excretion products that interfere with and damage the cells and molecules typical of innate immunity. However, these effects are observed in the later stages of infection, whereas the risk of being recognized and neutralized occurs very early after penetration and involves the pathogen surface components and molecular architecture; therefore, their role becomes crucial, particularly in the earliest pathogenesis. In this review, we analyze the evasion/interference strategies that entomopathogens such as the bacterium Bacillus thuringiensis, fungi, nematocomplexes, and wasps implement in the initial stages of infection, i.e., the phases during which body or cell surfaces play a key role in the interaction with the host receptors responsible for the immunological discrimination between self and non-self. In this regard, these organisms demonstrate evasive abilities ascribed to their body surface and cell wall; it appears that the key process of these mechanisms is the capability to modify the surface, converting it into an immunocompatible structure, or interaction that is more or less specific to host factors.

Susceptibility of Drosophila suzukii larvae to the combined administration of the entomopathogens Bacillus thuringiensis and Steinernema carpocapsae

“…respectively, living in their gut: the third stage of the nematode, also named infective juvenile (IJ) stage, penetrates the insect body and reaches the hemocoel cavity of the host where symbiotic bacteria are released and, due to their proliferation and toxins secretion, affect the physiology of the larvae up to septicemia and death 13 , 14 . The lethality and effectiveness of EPN is closely related to its interaction with the target and the possibility of reproduce itself undisturbed inside the host's body 4 , 15 , 16 .…”

Compatibility between Entomopathogenic Fungi and Egg Parasitoids (Trichogrammatidae): A Laboratory Study for Their Combined Use to Control Duponchelia fovealis

“…These contrasting observations may be due to differences in the conidia concentrations applied, the B. bassiana strains used, or the target organism [ 22 ]. It is possible that T. pretiosum females can recognize the presence of a harmful or repellent substance deposited on the host eggs before parasitizing them [ 22 , 37 ]. Females may be able to recognize whether the host is infected by a fungus by walking back and forth over the eggs, touching them with the gustatory sensilla of their antennae [ 22 , 37 , 38 ].…”

“…It is possible that T. pretiosum females can recognize the presence of a harmful or repellent substance deposited on the host eggs before parasitizing them [ 22 , 37 ]. Females may be able to recognize whether the host is infected by a fungus by walking back and forth over the eggs, touching them with the gustatory sensilla of their antennae [ 22 , 37 , 38 ]. Meanwhile, commercial products may contain carrying substances in their formulations, which could partially explain the stronger effect of these bioinsecticides on the Trichogramma species studied.…”

Antimicrobial Peptides: Novel Source and Biological Function With a Special Focus on Entomopathogenic Nematode/Bacterium Symbiotic Complex

“…Nematodes also serve as a novel invertebrate model to study innate immunity and host-pathogen interactions (Kurz and Tan, 2004;Nicholas and Hodgkin, 2004). EPNs and their associated bacteria have evolved with several defense mechanisms to elude and counteract the host (insect) immune responses Brivio and Mastore, 2020). The nematode Steinernema carpocapsae can produce proteolytic secretions that can interfere with the host immune system in S. feltiae, S. glaseri, and G. mellonella (Balasubramanian et al, 2010;Chaubey and Garg, 2019).…”