Investigations on the presence of an infectious proportion amongst populations of Steinernema feltiae (Site 76 strain) infective stages

Abstract

SUMMARYExperimental studies were conducted on the proportion of Steinernema feltiae Filipjev (Site 76 strain) infective stages that infected Galleria mellonella L larvae, in sand tube assays. A full statistical analysis of the sand assay tubes was also undertaken. The analysis showed that the sand tubes were not a significant source of variation. Consequently the observed behaviour of the infective stages was considered to be due to a biological effect. The study shows that the proportion of infective stages that became parasitic did not increase with increases in the density of applied infective stages, nor did the proportion increase with an increase in the number of hosts. It is argued that these findings are consistent with the presence of a proportion of individual infective stages that are capable of causing infection.

Behavioral ecology of entomopathogenic nematodes

“…This calls into doubt the existence of phased infectivity sensu Bohan and Hominick in these species (or at least the strains tested). However, the temporal changes in infectivity reported by Bohan and Hominick (1996) may represent more subtle changes in infectivity-i.e., phased infectivity sensu GriYn (1996). GriYn (1996) reported an increase in the infectivity of H. megidis IJs stored at 20°C, reaching a peak after 3 weeks.…”

Phased activity in Heterorhabditis megidis infective juveniles

“…However, for the entomopathogenic nematodes, both heterorhabditids and steinernematids, changes in infectivity occur prior to the eventual decline associated with starvation (Fan & Hominick, 1991 ;Curran, 1993 ;Ishibashi, Wang & Kondo, 1994 ;Griffin, 1996 ;Bohan & Hominick, 1997). Two hypotheses have been proposed to explain this so-called ' phased infectivity '.…”

“…Campbell et al (1999) found evidence of a temporarily non-infectious proportion in Heterorhabditis bacteriophora, but not in 3 Steinernema species. An alternative hypothesis of phased infectivity proposed by Griffin (1995Griffin ( , 1996 assumes that the infectious individuals are not all physiologically and behaviourally identical, but that they vary in their infectivity (probability of penetrating a host per unit time). Fluctuations in the infectivity of a population may reflect underlying changes in the infectivity of individuals -either their ability or motivation to infect an insect.…”

“…For H. megidis, an increase in infectivity occurred during the second or third week after emergence from the host cadaver when IJs were maintained at 20 mC and tested in an assay with restricted access to hosts (Griffin, 1996 ;Boff, Wiegers & Smits, 2000). Griffin (1996) proposed that low infectivity of these nematodes was associated with a lower likelihood of each IJ infecting within the time-period of the assay, and that the observed increase in infectivity of the population represented an increase in infective capabilities rather than a switch from non-infectious to infectious status.…”

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…Detection by baiting gives an indication of the "killing power" of the soil, which is what matters in biocontrol; it can be argued that this is what matters in an ecological context also, as IJs that are not infective cannot reproduce. However, baiting may underestimate the persistence of ecologically relevant IJs if part of the population is temporarily non-infective (Bohan & Hominick, 1996, 1997Griffin, 1996).…”