Population genetics and ecology of the lucerne flea, Sminthurus viridis, with applications for control

© 2010 Dr. John Michael Kenneth RobertsThe lucerne flea, Sminthurus viridis (Collembola: Sminthuridae), is a major pest of broadacre grains and pasture throughout southern Australia. Current control methods for this pest rely heavily on the prophylactic use of broad spectrum pesticides and are unlikely to be sustainable. Development of an integrated pest management (IPM) strategy is needed. However, this requires a greater understanding of the biology, ecology and genetics of S. viridis. This thesis aims to address this by examining the population genetics and life-cycle of this pest, as well as investigating chemical and biological control methods. Laboratory pesticide bioassays were used to compare the response of S. viridis with the redlegged earth mite (Halotydeus destructor) to six broad spectrum pesticides. Sminthurus viridis displayed significantly higher pesticides tolerance than H. destructor and the tolerance differences were greater for the synthetic pyrethroids than the organophosphorous pesticides. This indicates that application rates for S. viridis should be greater than H. destructor and that organophosphates are likely to provide the most effective control of this pest. Seasonal abundance patterns and summer diapause response of S. viridis in southeastern Australia were investigated using field and shade-house experiments. The seasonal activity agreed with previous studies and parameters predicting autumn emergence were defined. A summer-diapausing egg stage was also confirmed, with diapause eggs accumulating across the season. These results suggest autumn emergence of S. viridis can be predicted for target control strategies, but late-season spraying strategies may be difficult to implement. The species status, mode of reproduction and population genetics of S. viridis were examined using microsatellite markers I developed, together with allozymes and a mitochondrial DNA marker. A single, sexually reproducing species was found with limited gene flow between Australian populations. Genetic similarity between some distant populations was also shown, indicating that wind or human-mediated longdistance dispersal occurs. These findings suggest that management strategies may be more effective when locally developed and need to consider the effects of humanmediated dispersal. The impact of the predatory mite, Bdellodes lapidaria, for controlling S. viridis and its susceptibility to several pesticides were assessed using laboratory and field experiments. Bdellodes lapidaria was more susceptible to the synthetic pyrethroids in the laboratory, but was not affected by pesticide applications in the field. In addition, no detectable predator-prey relationship was found between these species. These results indicate that B. lapidaria is not strongly susceptible to pesticides in the field and may not be an effective predator of S. viridis. Overall, this thesis contributes important knowledge of the pesticide tolerance, lifecycle, population genetics and biological control of S. viridis. These findings highlight ways to improve the effectiveness and sustainability of control methods and bring closer the development of an integrated pest management strategy for S. viridis