Assessing immunocompetence in red palm weevil adult and immature stages in response to bacterial challenge and entomopathogenic nematode infection

Abstract

Parasites and pathogens can follow different patterns of infection depending on the host developmental stage or sex. In fact, immune function is energetically costly for hosts and trade‐offs exist between immune defenses and life history traits as growth, development and reproduction and organisms should thus optimize immune defense through their life cycle according to their developmental stage. Identifying the most susceptible target and the most virulent pathogen is particularly important in the case of insect pests, in order to develop effective control strategies targeting the most vulnerable individuals with the most effective control agent. Here, we carried out laboratory tests to identify the most susceptible target of infection by infecting different stages of the red palm weevil Rhynchophorus ferrugineus (larvae, pupae, male, and female adults) with both a generic pathogen, antibiotic‐resistant Gram‐negative bacteria Escherichia coli XL1‐Blue, and two specific strains of entomopathogenic nematodes (EPNs), Steinernema carpocapsae ItS‐CAO1 and Heterorhabditis bacteriophora ItH‐LU1. By evaluating bacterial clearance, host mortality and parasite progeny release, we demonstrate that larvae are more resistant than adults to bacterial challenge and they release less EPNs progeny after infection despite a higher mortality compared to adults. Considering the two EPN strains, S. carpocapsae was more virulent than H. bacteriophora both in terms of host mortality and more abundant progeny released by hosts after death. The outcomes attained with unspecific and specific pathogens provide useful information for a more efficient and sustainable management of this invasive pest.

Altered feeding behavior and immune competence in paper wasps: A case of parasite manipulation?

“…As a measure of general immune competence, we used a standard approach for insects that consists in quantifying the ability of a specimen to remove bacterial cells from the haemolymph [31,32]. Wasps were infected through injection with the tetracycline-resistant strain XL1 Blue Escherichia coli (Stratagene, La Jolla, California), an immune elicitor not found in P. dominula and commonly used to test antibacterial activity in insects [33][34][35][36][37][38][39].…”

Evaluation of entomopathogenic nematodes against red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae)

“…The S. carpocapsae caused maximum mortality of 96.4% in the last instar larvae of red palm weevil. In previous studies, the entomopathogenic nematodes have been found most pathogenic against larvae of red palm weevil compared to pupae or adult weevils [45]. This trend of pathogenicity has also been documented against pine weevil, Hylobius abietis [41].…”

Immunity of honeybee guards reflects their transition from house bees to foragers

“…To evaluate the workers' ability to remove bacteria from their haemolymph (i.e. bacterial clearance), we challenged workers with the Gram-negative bacteria Escherichia coli, an immune elicitor not naturally found in A. mellifera, to exclude its presence prior to experimental infection, already used in previous studies testing immunocompetence in insects (Yang & Cox-Foster 2005;Manfredini et al 2010;Cappa et al 2015;2019). Injection of live bacteria induce the activation of the organism immune system (Charles & Killian 2015) and subsequent bacterial clearance evaluation provide an integrative view of workers immunity being linked to other parameters used to assess insects' immune response (Gillespie et al 1997).…”

“…Among the different task specialization of honeybee workers, guards represent a peculiar behavioral phenotype, being intermediate between house bees working inside the nest and foragers collecting resources outside (Moore et al 1987). Workers become guards after performing in-hive duties but before foraging: they patrol the colony entrance, inspecting incoming bees and excluding foreign individuals (Breed et al 2004;Cappa et al 2014Cappa et al , 2016Cappa et al , 2019. Only a small proportion of the colony worker population (about 10%) performs guarding activities (Breed et al 2004), usually middle-aged workers, between 7 and 22 days post-emergence (Moore et al 1987).…”