Date Published: May 22, 2013
Publisher: Blackwell Publishing Ltd
Author(s): Dörte Goertz, Gernot Hoch.
The behaviour of predators can be an important factor in the transmission success of an insect pathogen. We studied how Calosoma sycophanta influences the interaction between its prey [Lymantria dispar (L.) (Lepidoptera, Lymantriidae)] and two microsporidian pathogens [Nosema lymantriae (Microsporidia, Nosematidae) and Vairimorpha disparis (Microsporidia, Burellenidae)] infecting the prey.Using laboratory experiments, C. sycophanta was allowed to forage on infected and uninfected L. dispar larvae and to disseminate microsporidian spores when preying or afterwards with faeces.The beetle disseminated spores of N. lymantriae and V. disparis when preying upon infected larvae, as well as after feeding on such prey. Between 45% and 69% of test larvae became infected when C. sycophanta was allowed to disseminate spores of either microsporidium.Laboratory choice experiments showed that C. sycophanta did not discriminate between Nosema-infected and uninfected gypsy moth larvae. Calosoma sycophanta preferred Vairimorpha-infected over uninfected gypsy moth larvae and significantly influenced transmission.When C. sycophanta was allowed to forage during the latent period on infected and uninfected larvae reared together on caged, potted oak saplings, the percentage of V. disparis infection among test larvae increased by more than 70%. The transmission of N. lymantriae was not affected significantly in these experiments.Beetles never became infected with either microsporidian species after feeding on infected prey.We conclude that the transmission of N. lymantriae is not affected. Because no V. disparis spores are released from living larvae, feeding on infected larvae might enhance transmission by reducing the time to death and therefore the latent period.
Arthropods and their natural enemies are embedded in a complex web of interactions. Two species can be directly involved in a trophic interaction, indirectly by competing for a joint resource or in a combination of both. Intraguild predation describes a situation when predators, parasitoids or pathogens share a host and are also engaged in a trophic interaction (Rosenheim et al., 1995), possibly resulting in the release of the host from regulation and therefore the interruption of biological control (Meyling & Hajek, 2010). Other direct or indirect antagonistic interactions can arise when the population density of the host species is decreased to a point where transmission of a pathogen is interrupted, or when the nutritional quality of an infected host is altered, resulting in lower longevity, fecundity or the death of a parasitoid or predator (Hochberg et al., 1990; Ruberson et al., 1991; Brooks, 1993; Rosenheim et al., 1995; Sajap et al., 1999). By contrast, benefits for at least one of the interacting enemies of a host species may arise when parasitism enhances the susceptibility of the host to predation or when the action of a predator or parasitoid enhances the transmission of a pathogen by defecation of environmental stable life stages or vectoring the pathogen to susceptible hosts (Carpinera & Barbosa, 1975; Brooks, 1993; Roy & Pell, 2000; Castillejos et al., 2001; Down et al., 2004).
Although there are a number of studies that consider the interactions of microsporidian pathogens and parasitoids sharing a host (Brooks, 1993), very few studies have investigated the interactions between predators and microsporidia feeding on the same host species (Van Essen & Anthony, 1976; Down et al., 2004). When Nosema (= Anncaliia) algerae was fed to predators of mosquitoes, one of the nine tested predatory species, Notonecta undulate (Hemiptera), became infected (Van Essen & Anthony, 1976). In a more extensive study, Down et al. (2004) reported that the spined soldier bug Podisus maculiventris disseminated spores of Vairimorpha necatrix on tomato plants with their faeces, thereby causing the reduced survival of Lacanobia oleracea and Spodoptera littoralis larvae by 61% and 75%, respectively. They concluded that P. maculiventris is a very effective disseminator of V. necatrix and might be useful for introducing this pathogen into a pest population and for enhancing the effectiveness of this biological control agent. The present study shows that a predator such as C. sycophanta can influence the host–pathogen interaction of L. dispar and its microsporidia at a small scale and that C. sycophanta itself is not infected by the microsporidian pathogens.