Geoff Baker

Life history determines biogeographical patterns of soil bacterial communities over multiple spatial scales.

The extent to which the distribution of soil bacteria is controlled by local environment vs. spatial factors (e.g. dispersal, colonization limitation, evolutionary events) is poorly understood and widely debated. Our understanding of biogeographic controls in microbial communities is likely hampered by the enormous environmental variability encountered across spatial scales and the broad diversity of microbial life histories. Here, we constrained environmental factors (soil chemistry, climate, above‐ground plant community) to investigate the specific influence of space, by fitting all other variables first, on bacterial communities in soils over distances from m to 102 km. We found strong evidence for a spatial component to bacterial community structure that varies with scale and organism life history (dispersal and survival ability). Geographic distance had no influence over community structure for organisms known to have survival stages, but the converse was true for organisms thought to be less hardy. Community function (substrate utilization) was also shown to be highly correlated with community structure, but not to abiotic factors, suggesting nonstochastic determinants of community structure are important Our results support the view that bacterial soil communities are constrained by both edaphic factors and geographic distance and further show that the relative importance of such constraints depends critically on the taxonomic resolution used to evaluate spatio‐temporal patterns of microbial diversity, as well as life history of the groups being investigated, much as is the case for macro‐organisms.

Adaptive management of pest resistance by Helicoverpa species (Noctuidae) in Australia to the Cry2Ab Bt toxin in Bollgard II® cotton

In Australia, monitoring Helicoverpa species for resistance to the Cry2Ab toxin in second generation Bacillus thuringiensis (Bt) cotton has precisely fulfilled its intended function: to warn of increases in resistance frequencies that may lead to field failures of the technology. Prior to the widespread adoption of two‐gene Bt cotton, the frequency of Cry2Ab resistance alleles was at least 0.001 in H. armigera and H. punctigera. In the 5 years hence, there has been a significant and apparently exponential increase in the frequency of alleles conferring Cry2Ab resistance in field populations of H. punctigera. Herein we review the history of deploying and managing resistance to Bt cotton in Australia, outline the characteristics of the isolated resistance that likely impact on resistance evolution, and use a simple model to predict likely imminent resistance frequencies. We then discuss potential strategies to mitigate further increases in resistance frequencies, until the release of a third generation product. These include mandating larger structured refuges, applying insecticide to crops late in the season, and restricting the area of Bollgard II® cotton. The area planted to Bt‐crops is anticipated to continue to rise worldwide; therefore the strategies being considered in Australia are likely to relate to other situations.

The abundance and diversity of earthworms in pasture soils in the fleurieu peninsula, south australia

Abstract Earthworms were surveyed in 113 pasture soils in the Mount Lofty Ranges, Fleurieu Peninsula, South Australia, in a region where annual rainfall is 600–1200 mm and the climate is mediterranean. The soils within these pastures included a variety of profile forms (e.g. sandy soils with yellow, brown or red clays in the B horizon; uniform coarse textured sands). The most widespread earthworm species were Aporrectodea trapezoides (found at 95% of sites), Microscolex dubius (61%), Aporrectodea rosea (38%) and Aporrectodea caliginosa (36%). These are all introduced species. The total densities of earthworms varied from 0 to 608 m −2 (mean = 169.2). At most sites (66%), densities were −2 . Native earthworms were present at 40 sites but their total densities exceeded 100 m −2 at only 7 sites. The species richness and diversity of the earthworm communities were low; never more than 5 species were found in any one pasture (mean = 3.1). The abundance of the introduced species (all species combined) varied between soil profile forms, being least in the uniform sands. No such variation was found for native species. Several significant, but weak, correlations were obtained between the numbers and weights of earthworms and other environmental variables (e.g. rainfall, depth of A horizon, % sand, clay. nitrogen and carbon). Stepwise multiple regression of the numbers and weights of introduced species against these environmental variables suggested that % clay was the most important regressor. The potential for increasing the abundance and diversity of earthworms in Australian soils is discussed.

Network analysis reveals that bacteria and fungi form modules that correlate independently with soil parameters

Network and multivariate statistical analyses were performed to determine interactions between bacterial and fungal community terminal restriction length polymorphisms as well as soil properties in paired woodland and pasture sites. Canonical correspondence analysis (CCA) revealed that shifts in woodland community composition correlated with soil dissolved organic carbon, while changes in pasture community composition correlated with moisture, nitrogen and phosphorus. Weighted correlation network analysis detected two distinct microbial modules per land use. Bacterial and fungal ribotypes did not group separately, rather all modules comprised of both bacterial and fungal ribotypes. Woodland modules had a similar fungal : bacterial ribotype ratio, while in the pasture, one module was fungal dominated. There was no correspondence between pasture and woodland modules in their ribotype composition. The modules had different relationships to soil variables, and these contrasts were not detected without the use of network analysis. This study demonstrated that fungi and bacteria, components of the soil microbial communities usually treated as separate functional groups as in a CCA approach, were co-correlated and formed distinct associations in these adjacent habitats. Understanding these distinct modular associations may shed more light on their niche space in the soil environment, and allow a more realistic description of soil microbial ecology and function.

Soil pH preferences and the influences of soil type and temperature on the survival and growth of Aporrectodea longa (Lumbricidae): The 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

The potential of the deep-burrowing earthworm, Aporrectodea longa, to improve the functional diversity of soil communities, soil properties and plant production if introduced in high rainfall pastures in south-eastern Australia has been recognised previously. This paper reports on suitable soil types, pH and temperature regimes for the culturing of A. Tonga and develops predictions as to where A. Tonga might best establish. Laboratory experiments show that A. longa will survive and grow to maturity when reared in the laboratory in a commercially available sand: loam mix, supplemented with sheep dung for food. Survival, development of cocoons and growth of hatchling earthworms was, overall, optimal at 15°C. Few cocoons survived two months in air-dried soil. Earthworms showed a strong aversion to soil pH below 4.5. The development time required for cocoons at soil temperatures likely to be experienced in the field in southern Australia (e.g. 15-20 weeks at 10 °C) is discussed in terms of likely establishment success.

Does the deep-burrowing earthworm, Aporrectodea longa, compete with resident earthworm communities when introduced to pastures in south-eastern Australia?

Pastures in southern Australia are dominated by endogeic earthworms such as Aporrectodea caliginosa (Sav.). Introductions of the anecic earthworm, A. longa (Ude), which is mostly restricted to Tasmania at present, are likely to increase the functional diversity of local communities and thereby enhance plant production and agricultural sustainability. However, the potential impact of A. longa on resident earthworm communities first needs assessing. Glasshouse and field experiments reported here suggested that A. longa can reduce the abundance and biomass of A. caliginosa, but that these effects are likely to be offset by overall increases in worm abundance. There was no evidence to suggest that species richness was reduced by A. longa introduction.

Influence of lumbricid earthworms on yield and quality of wheat and clover in glasshouse trials

Abstract Field surveys have shown that the introduced lumbricid earthworm, Aporrectodea rosea, predominates in fields used for cereal-pasture rotations in South Australia and western Victoria. Another introduced lumbricid, A. trapezoides, also occurs in these fields, but is usually much rarer. A glasshouse experiment investigated the influences of A. rosea and A. trapezoides on wheat and subterranean clover production. The plants were grown in a red-brown earth (Palexeralf), maintained at 60% field moisture capacity with the equivalent of 460 worms m−2. Wheat was grown first and then the soil was re-used for the clover. A. trapezoides increased wheat plant biomass by 39%, grain yield by 35%, grain N content by 14% and straw N content by 19% compared with controls (no worms). A. rosea increased wheat plant biomass by 13%, but had no significant influence on grain yield or grain or straw N content. The biomass of clover herbage was increased by 21% by A. trapezoides, but A. rosea had no effect. Neither earthworm species influenced the N content of the clover or the dry weight of clover roots. The implications of these results for future management of earthworms in cereal-pasture ratations are discussed.

Host distribution, larviposition behaviour and generation time of Sarcophaga penicillata (Diptera: Sarcophagidae), a parasitoid of conical snails.

Host characteristics, hyperparasitism, larviposition behaviour and generation time of Sarcophaga penicillata Villeneuve a parasitoid of the conical snail, Cochlicella acuta Muller (Mollusca: Helicidae) in southern France are described. Only snails which aestivated on vegetation were found to be parasitized by S. penicillata. Sarcophaga penicillata preferred C. acuta which were both significantly higher off the ground and larger in size than the population averages. Of the 2768 snails collected at the study site, 4% (112) were parasitized by S. penicillata , of which 36.6% (41) failed to emerge while 34% (38) were hyperparasitized. The predominant hyperparasite was Novitzkyanus cryplogaster Boucek (Hymenoptera: Pteromalidae) which was responsible for 79% (30) of the hyperparasitism. Larvipositing S. penicillata were observed to fabricate a hole in the epiphragm of resting snails in which they deposited one larva. After larviposition, female S. penicillata remained with the freshly parasitized snail a mean time ± SE of 25.2 ± 10.3 min. It is suggested that this may be an adaptive response to avoid superparasitism. The mean generation time of S. penicillata when reared in the laboratory was 18 days, indicating that more than six generations are possible during summer in the south of France. During winter, S. penicillata enters diapause in the pupal stage within a host snail for up to 6 months. The possible utility of S. penicillata as a biological control agent of introduced conical snails is discussed.

The potential of several species of terrestrial Sciomyzidae as biological control agents of pest helicid snails in Australia

Abstract The seasonality, habitat preference and prey acceptability of the terrestrial sciomyzids, Coremacera marginata Fabricius, Euthycera cribrata Rondani, Trypetoptera punctulata Scopoli, Pherbellia cinerella Fallen, and Dichetophora obliterata Fabricius are described. Four of the species (C. marginata, D. obliterata, T. punctulata and E. cribrata) are univoltine and were most abundant in either riverine forest or low scrubland (garrigue) while one species (Pherbellia cinerella) is multivoltine and was very abundant only in open pasture habitats. All of the species had a wide range of prey acceptability (five to nine species of snails) although they varied widely in their predation efficiency. The potential of the univoltine species as biological control agents for pest pasture snails in Australia can be assumed to be poor due to differences between their preferred habitat and the target habitat. However, the multivoltine, pasture-inhabiting species, P. cinerella may have potential use, if it can be shown that it will not overlap with the habitat of endemic Australian snails.

Method for caging earthworms for use in field experiments

Abstract A method is described for caging earthworms in undisturbed soil in field experiments. The method is applicable to sites which are seasonally dry (e.g. summer in southern Australia). Cages were made from sections of PVC pipe (20 cm long × 30 cm dia) which were driven vertically into the soil beneath a permanent pasture in South Australia during spring when the soil was moist and resident earthworms were active near the surface. During the following summer, when most resident earthworms had burrowed below the depth of the pipes to escape surface aridity, the pipes and the soil within them were lifted from the surrounding soil. Fine curtain mesh was strapped across the bottom edges of the pipes and the resultant “cages” were then replaced in their holes. The mesh isolated the soil within the cages and prevented escape or invasion of earthworms during the subsequent wet season when the desired earthworm species were added. The method was used to compare: (1) the influences of surface-applied lime and sheep dung on the establishment of two earthworm species, Aporrectodea longa (Lumbricidae) and Spenceriella sp. (Megascolecidae); (2) the abilities of the same two earthworm species to bury lime and dung; and (3) the relative influences of A. caliginosa, A. longa, A. rosea, A. trapezoides and Spenceriella sp. on pasture production. The earthworms were caged for 5 months. Survivorship of all species was good (⩾ 50%). Contamination in the cages by undesired species was small ( A. longa (greater numbers and biomass) but not the establishment of Spenceriella sp. The addition of lime did not influence the establishment of either A. longa or Spenceriella sp. A. longa buried lime and dung more readily than did Spenceriella sp. Pasture production was greater in the presence of A. longa and dung than in other treatments.