|Campbell, James - Jim|
|Shapiro Ilan, David|
Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2006
Publication Date: 5/30/2007
Citation: Ramos-Rodriguez, O., Campbell, J.F., Christen, J.M., Shapiro Ilan, D.I., Lewis, E.E., Ramaswamy, S.B. 2007. Attraction behavior of three entomopathogenic nematode species towards infected and uninfected hosts. Parasitology 134: 729-738. Interpretive Summary: Nematodes that attack insects and their associated bacteria are biological control agents for many species of insect pests, but their effectiveness when applied in large numbers for insect control may be limited due to their preference for already infected hosts. The process of host selection and the nature and source of the cues used are not well understood. In this study, we investigated the attraction of three species of nematodes to two species of insects that were previously parasitized by nematodes of the same species to determine how attraction to a host insect is influenced by the stage of its ongoing infection. Level of response to the infected hosts tended not to change with time after infection and to be similar to the uninfected host, except in one nematode/host combination where response to infected host tended to be lower. These results suggest that any influence of host infection status on nematode infective stage behavior leading to preference for already infected hosts is occurring at other steps in the host-infection process than host attraction. This research provides a foundation from which to identify the important steps and cues used in host selection. Ultimately, these cues may be used to manipulate nematode behavior to enhance their ability to control insect pest populations.
Technical Abstract: Entomopathogenic nematodes bridge the gap between hosts by producing infective stage juveniles that search for, and infect, insects. Infective juveniles are likely to encounter both uninfected and already infected host insects, which will differ in their quality as a host. Here we tested the attraction response of three entomopathogenic nematode species (Steinernema carpocapsae, S. glaseri, and S. riobrave), that have different foraging strategies, to infected and uninfected insects (Galleria mellonella and Tenebrio molitor). Infected hosts were tested at 24 h intervals from start of infection to the emergence of infective juveniles from the depleted host. Steinernema glaseri was highly attracted to both uninfected and infected hosts, whereas S. riobrave and S. carpocapsae showed no significant attraction to hosts, with the latter moving away from them in some cases. Level of response to the infected hosts tended not change with time after infection and to be similar to the uninfected host, except for S. glaseri infected T. molitor which tended to be less attractive to S. glaseri infective juveniles than uninfected hosts. At each tested time point after infection, hosts were dissected to determine the number and stages of the nematodes present. Previous studies have shown changes in the production of CO2 from infected hosts over time. In this study, infective juvenile response to hosts was unchanged even though the quality of the host as resource was changing, as measured by the status of the infection, and the cues given off by the host were changing. These results suggest that any influence of host infection status on infective juvenile behavior is occurring at other steps in the host-infection process than host orientation.