Effects of mode of delivery of Beauveria bassiana GHA on infectivity in bed bugs and German cockroaches

                Fungal entomopathogens include diverse taxa primarily in the orders Hypocreales and Entomphthorales. Hypocrealean fungi often have a wide host range, whereas Entomphthoralean fungi are more host specific. The ability of an entomopathogen to infect an insect host depends on a variety of host and environmental factors, as well as characteristics inherent to the fungal strain. An insect’s ability to prevent a fungal infection is dependent on the biology and evolutionary history of the insect. Synanthropic pests have adapted to thrive in the indoor environment, yet they arose from divergent evolutionary lineages and occupy different feeding guilds. Thus, the hematophagous bed bug (Cimex lectularius L.) and omnivorous German cockroach (Blattella germanica L.) are highly successful in the indoor environments, but have evolved different physiological and behavioral adaptations for the human-built environment. We tested the ability of Beauveria bassiana (Balsamo) GHA, a fungal entomopathogen with a wide host range, to infect both insects using different exposure techniques, including injection, feeding, topical application, and contact with conidia. Bed bugs were more susceptible to infection by B. bassiana and the speed of infection was dependent on the mode of delivery. The German cockroach was highly resilient to infection, requiring high doses of conidia delivered by injection into the hemocoel. These findings highlight the great variety of host-microbe interactions, even within the seemingly homogeneous indoor environment. They will guide our future research on susceptibility on indoor pests to entomopathogens.