J Ireson

Worth the risk? Introduction of legumes can cause more harm than good: an Australian perspective

Weeds are serious threats to Australias primary production and biodiversity conservation. For example, a recent Australia Bureau of Statistics survey found that 47% of farmers across Australia have a significant weed problem. A literature review revealed that legumes represent a significant proportion of the national weed problem and most serious Australian legume weeds are exotic thicket-forming species that were deliberately introduced for their perceived beneficial properties, such as for shade and fodder, or even quite trivial reasons, such as garden ornamentals. The low economic value of the rangelands most of these species infest, compared with control costs, hinders chemical and mechanical control of these weeds, such that biological control, which takes time, is expensive to implement and has no guarantee of success, may represent the only economically viable alternative to abandoning vast tracts of land. We argue that, because the behaviour of an introduced species in a novel environment is so hard to forecast, better predictive techniques should be developed prior to further introductions of plant species into novel environments. We also discuss the potential of legumes currently being promoted in Australia to become weeds and suggest the recent trend of exporting Australian Acacia spp. to semiarid regions of Africa risks history repeating itself and the development of new weed problems that mirror those posed by Australian Acacia spp. in southern Africa.

Biology and key to the Australian species of Hypogastrura and Ceratophysella (Collembola: Hypogastruridae)

The family Hypogastruridae is represented by nine genera in Australia, three of which: Mesogastrura Bonet, Hypogastrura Bourlet and Ceratophysella Börner, consist only of species that have been probably introduced from Europe within the last 250 years, with the exception of a new species described here. All species in these three genera are typical of, and abundant in, disturbed habitats. The 11 species currently recorded from Australia in Hypogastrura and Ceratophysella are C. communis (Folsom, 1897), C. denticulata (Bagnall, 1941), C. gibbosa (Bagnall, 1940), C. succinea (Gisin, 1949), Hypogastrura assimilis (Krausbauer, 1898), H. distincta (Axelson, 1902), H. manubrialis (Tullberg, 1869), H. purpurescens (Lubbock, 1867, H. vernalis (Carl, 1901) and H. viatica (Tullberg, 1872), and a new species C. pauciseta sp. nov. Ceratophysella communis was misidentified in some published literature as C. engadinensis Gisin, 1949. Although C. communis is confirmed as occurring in Australia, there now seems to be no evidence that C. engadinensis occurs here, and the name H. denticulata may include more than one species. An illustrated dichotomous key and description is given here for all Australian species of Hypogastrura and Ceratophysella, and their distributions and habitats documented. Their value as indicators of disturbed habitats in Australia is discussed. Collembola in general have been shown to have a positive influence on nutrient cycling. It is not known what contribution Hypogastrura and Ceratophysella make to Australian arable and grazing systems in this respect, but it may be considerable because of their abundance.

Pre-adult development of Phytoseiulus persimilis on diets of Tetranychus urticae and Tetranychus lintearius: implications for the biological control of Ulex europaeus.

Predation by the phytoseiid mite, Phytoseiulus persimilis, is considered a major threat to the effectiveness of biological control of gorse, Ulex europaeus, using Tetranychus lintearius. To assess this threat and to determine if the impact of P. persimilis on T. lintearius populations is comparable to its impact on T. urticae populations, its development and predator : prey generation time ratios were assessed. The pre-adult mortality and development time of two populations of P. persimilis fed on two diets, T. urticae and T. lintearius, were determined at two temperatures, 14 and 24°C. There were no significant differences in either mortality or development time between the two populations of P. persimilis at these temperatures. There is therefore no evidence that the two tested populations of P. persimilis are behaving as different strains. Similarly, diet had no significant effect on either mortality or development time at these temperatures. At 14°C the mortality of P. persimilis was significantly higher and development was significantly longer than at 24°C. Using pre-adult development as a surrogate for generation times, predator : prey generation time ratios were calculated between P. persimilis and both T. urticae and T. lintearius using data from this and other studies. The predator : prey generation time ratios between P. persimilis and T. lintearius were lower than those between P. persimilis and T. urticae. These results indicate that the impact of P. persimilis on T. lintearius populations is likely to be comparable to its impact on T. urticae populations. This provides further evidence that predation by P. persimilis is having a deleterious effect on T. lintearius populations and therefore reducing its effectiveness as a biological control agent for gorse.

The influence of host plant genotype on variation in population densities of the gorse thrips, Sericothrips staphylinus (Thysanoptera: Thripidae), and its consideration in relation to release strategies

Abstract Large variations in population densities of Sericothrips staphylinus were observed between gorse bushes at a field site in an earlier Tasmanian study. A replicated potted plant experiment was conducted to assess whether genetic variation between gorse bushes could affect densities of S. staphylinus. There were significant differences in the number of S. staphylinus recovered from the individual bushes sampled within sites and individual bushes across all sites. This provides evidence that genetic variation between gorse bushes is at least partly responsible for the observed variability in field populations. The result validates the current release strategy used for the field establishment of S. staphylinus in south-eastern Australia. This strategy involves making multiple small releases (ca. 250 adults per bush per site) instead of a small number of large releases (ca. 1000 per bush per site), thereby reducing variation in numbers due to genetic affects. Genetic variation between individual plants of the same species and associated effects on herbivore densities should be considered when devising release strategies for biological control agents.

Survival of larvae of the ragwort flea beetle, Longitarsus flavicornis (Coleoptera: Chrysomelidae), in water-logged soil

Abstract Water-logged soil could be a major factor affecting populations of the ragwort biological control agent, Longitarsus flavicornis, in Australia. Survival of L. flavicornis larvae in potted ragwort plants after inundation with water for up to 264h (11days) was compared to larval survival in control plants not exposed to inundation. Probit analysis indicated that 35.6% mortality of the larval population occurred after 24h inundation and 50.4% after 72h. As high mortality was recorded at periods of inundation known to occur in the field, it is concluded that winter flooding is likely to be detrimental to populations of L. flavicornis.

Desiccation and egg viability of the ragwort flea beetle, Longitarsus flavicornis (Coleoptera: Chrysomelidae).

Abstract A study was conducted to investigate the effect of desiccation on the survival of eggs of Longitarsus flavicornis. Eclosion of L. flavicornis eggs in laboratory trials decreased with increasing desiccation time between 0 days (93% hatching) and 42 days (no egg hatching) at 50±2% relative humidity and 23±2°C. Probit analysis indicated that 25, 50 and 99% mortality of L. flavicornis eggs occurred after 5.7, 9.3 and 50.4 days desiccation, respectively. Egg development varied between a minimum of 8 days at 7 days desiccation to a maximum of 15 days at 28 days desiccation. Hatching span did not differ between treatments with all eggs hatching within 12 days of each other. A relative humidity of 88–100% was measured under ragwort rosettes in non-drought field conditions. This would be expected to facilitate successful egg eclosion. However, the occurrence of summer drought could be detrimental to egg survival.