A Test of Immune Priming in the Kissing Bug Rhodnius pallescens (Hemiptera: Reduviidae) against the Entomopathogenic Fungus Beauveria bassiana (Hypocreales: Cordycipitaceae) in Panama1

Abstract

The assumption that the invertebrate immune system lacks memory and specificity has changed over time: many studies now indicate that a primary exposure of the host to a pathogen increases its resistance to a subsequent lethal challenge, a phenomenon known as immune priming. One group of insects in which immune priming has been little investigated is the hematophagous triatomine bugs. Herein, we tested the capability of the kissing bug Rhodnius pallescens Barber (Hemiptera: Reduviidae; hereafter kissing bugs), the vector of Chagas disease, to resist entomopathogenic fungi. Laboratory kissing bugs free of Wolbachia and Trypanosoma spp. as well as kissing bugs collected from the wild were used for tests with the entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae). Against laboratory kissing bugs, the fungus remained virulent for 94 d, indicating long-term viability. Kissing bugs collected from the wild that were exposed to a nonlethal dose of the fungus did not show increased survival against a lethal dose compared with controls inoculated with the lethal dose. However, kissing bugs inoculated with a nonlethal dose had higher levels of total phenoloxidase than control kissing bugs. Although the fungus activates the immune system of the kissing bugs, other variables may influence survival in the face of infection. Moreover, the lethality of the same strain was lower against wild kissing bugs, suggesting that the presence of symbionts or parasites influence the fungus–triatome (host) interaction. This work is one of the few studies that have investigated the fungus–host interaction in terms of immune priming in a hematophagous insect of public health importance. Implications are discussed.