Complex and Diverse Drivers of Parasite Loads in a Cosmopolitan Insect

Loop-mediated isothermal amplification identifies nematode Leidynema in the hindgut of non-pest cockroach

Cockroach microbiome studies generally focus on pest cockroach species belonging to the Blattidae and Ectobiidae families. There are no reports characterizing the gut microbiome of non-pest cockroach species Blaberus discoidalis (family Blaberidae), which is commonly used as a food source for insectivorous animals. We discovered the parasitic nematode Leidynema appendiculata in the B. discoidalis hindgut during initial work characterizing the gut microbiome of this organism. To determine the proportion of the B. discoidalis colony that was colonized by L. appendiculata, 28 S rDNA was amplified using two Methods: endpoint polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP). B. discoidalis colonies were raised on three diet types (control, high fibre, and high fat and salt) for 21 days before dissection. Each individual was sexed during dissection to identify potential sex-based effects of colonization. Data collected were analysed to determine if diet and sex impacted parasite colonization patterns. LAMP detected a higher proportion of parasite positive samples when compared to endpoint PCR. No sex- or diet-based differences in L. appendiculata colonization were found. This study adds to the limited existing knowledge of the B. discoidalis gut microbiome.

From trees to fleas: masting indirectly affects flea abundance on a rodent host

Mast seeding causes strong fluctuations in populations of forest animals. Thus, this phenomenon can be used as a natural experiment to examine how variation in host abundance affects parasite loads. We investigated fleas infesting yellow-necked mice in beech forest after two mast and two non-mast years. We tested two mutually exclusive scenarios: (1) as predicted by classical models of density-dependent transmission, an increase in host density will cause an increase in ectoparasite abundance (defined as the number of parasites per host), vs. (2) an increase in host density will cause a decline in flea abundance ("dilution", which is thought to occur when parasite population growth is slower than that of the host). In addition, we assessed whether masting alters the relationship between host traits (sex and body mass) and flea abundance. We found a hump-shaped relationship between host and flea abundance. Thus, the most basic predictions are too simple to describe ectoparasite dynamics in this system. In addition, masting modified seasonal dynamics of flea abundance, but did not affect the relationship between host traits and flea abundance (individuals with the highest body mass hosted the most fleas; after controlling for body mass, parasite abundance did not vary between sexes). Our results demonstrate that pulses of tree reproduction can indirectly, through changes in host densities, drive patterns of ectoparasite infestation. This article is protected by copyright. All rights reserved.