Environmental factors affecting Adelina in the Burdekin region : final report CE004

Abstract

The project aimed to determine why the canegrub pathogen Adelina does not infect a significant proportion of the canegrub population in the Burdekin Delta area. It examined the effect of physical characteristics of soil (pH, sodicity and composition) and three other environmental parameters (temperature, relative humidity and compaction) on retention of oocyst infectivity for larvae over periods corresponding to one and two cycles of grub infestation of crops in the field. In addition, the project raced the establishment and persistence of Adelina infection in two experimentally inoculated field plots in the Burdekin canegrowing area. A ‘sentinel larva’-based bioassay that allows examination of the effect of various environmental factors on the retention of infectivity of Adelina was developed. Results of such a bioaasay showed no differences between the three types of soils tested, despite one soil coming from a region where the pathogen is very common (Bambaroo), and another from a region where it is quite rare (Burdekin Delta). The test did clearly show that drying conditions can be highly detrimental to retention of infectivity of the pathogen. Extrapolation from these results would suggest that field locations where there are prolonged periods of dry soil conditions would be at a relative disadvantage as regards maintenance of high levels of the pathogen in grub populations. Under field conditions in the Burdekin, Adelina did survive at levels sufficient to cause infection in the following generation of canegrubs in some areas and in one of two years; in the other plots and year, there was no subsequent infection. These results thus show that while oocysts of protozoan pathogens such as Adelina have robust external walls, they are, nevertheless, susceptible to the influence of adverse environmental conditions. Under field conditions, where exposure to any potential inoculum is likely to be more transient, the influence of an adverse environmental factor is even more acute. Improved understanding of the physical tolerances of the infective stages of Adelina has assisted in the design of crop-management strategies that maximise the impact of the pathogen on canegrub populations. These strategies have been incorporated into the GrubPlan program that has been successful in reducing the impact of greyback canegrub.