Relationships between the lucerne flea, Sminthurus viridis (L.) (Collembola: Sminthuridae), and damage to lucerne

Abstract The effect of lucerne flea, Sminthurus viridis , on plant growth (stem length and leaf number) and damage (percentage of leaves damaged and the percentage reduction in leaf area in the top, mid and lower thirds of stems) was considered at 2-weekly intervals in three consecutive lucerne growth cycles, each with a different mode of attack. The data were analysed to progressively determine relationships leading to a proposal for plant-based thresholds for lucerne flea control. Lucerne flea affected each factor measured, with damage considered more appropriate for making control decisions than plant growth. Damage increased from the base of plants upwards and its effect on yield was carried over into subsequent growth cycles. Damage was significantly related to lucerne flea numbers ( P  < 0.001) in two growth cycles and was higher when large nymphs or adults were dominant in one of these cycles. Yield was closely and best related to the percentage of the total number of leaves damaged ( R ² = 81.3%). The percentage of leaves damaged was also related to loss of final yield estimated at 2 ( R ² = 81.3%), 4 ( R ² = 78.9%) and 6 ( R ² = 66.6%) weeks into the first growth cycle only. Direct damage in the other two cycles did not result in yield loss. The percentage of leaves damaged (± confidence intervals) equating to 5% increments in yield loss were estimated at 2, 4 and 6 weeks into the first growth cycle. These are proposed as damage or treatment thresholds for testing.     

Population dynamics and diapause response of the springtail pest Sminthurus viridis (Collembola: Sminthuridae) in southeastern Australia

The springtail, Sminthurus viridis (L.) (Collembola: Sminthuridae), is an important agricultural pest across southern Australia. We investigated the seasonal abundance patterns and summer diapause response of S. viridis in southeastern Australia by using field and shadehouse (a greenhouse that offers seedlings shade) experiments. Seasonal activity patterns of S. viridis were largely consistent with previous studies, with the pest active from autumn to spring. In addition, the timing and pattern of the summer-diapausing egg stage was established, with multiple generations probably producing diapause eggs. A strong relationship between soil moisture and temperature with autumn emergence also was observed. These results suggest that S. viridis autumn pest pressure can be predicted and indicate that late-season spraying strategies currently used for a sympatric agricultural pest are unlikely to be as effective against S. viridis.     

A novel method of self-righting in the springtail Sminthurus viridis (Insecta: Collembola)

Photographic evidence shows that the ventral tube can be used as a tentacle-like mechanical aid for self-righting from an inverted position. It is proposed that the extraordinary length of the vesicles of the ventral tube in globular springtails has been evolved in order to combat postural instabilities resulting from spherical symmetry of body form.     

The scolopidial organs in the first antennal segment in Allacma fusca (Collembola,Sminthuridae)

Summary The proprioceptors of the musculature moving the second antennal segment in the collembolan Allacma fusca were examined with the electron microscope. There are five muscles, the most important of which appear to be a levator and a depressor muscle. Only these two muscles are monitored by proprioceptors. These proprioceptors, the scolopidia, are referred to here as the levator (l-) and the depressor (d-) scolopidium. The former contains two, the latter one sensory cell.Both scolopidia deviate from the usual pattern in that they have unmodified dendritic outer segments (no dilatations, no electron-dense material) and are enveloped by only one cell. But l- and d-scolopidia also differ from one another. The dendritic inner segments of the l-scolopidium are branched to an h-shaped pattern, with one branch ending on the levator muscle and the other running to the antennal nerve where the perikarya are located. In the d-scolopidium a muscle fiber of about 1 m diameter (140–320 myosin filaments) accompanies the scolopidium for a distance of about 0.5 m.On the basis of the structural features it is hypothesized that (1) the mechanical forces possibly act on the membranes of the dendritic inner segments, (2) the small muscle parallel to the d-scolopidium is a receptor muscle, and (3) both scolopidia are highly derivative.Dedicated to Professor Dietrich Burkhardt on the occasion of his 60th birthday     

Does Bdellodes lapidaria (Acari: Bdellidae) have a role in biological control of the springtail pest, Sminthurus viridis (Collembola: Sminthuridae) in south-eastern Australia?

Throughout southern Australia, the lucerne flea, Sminthurus viridis (Collembola: Sminthuridae), is an important pest of a variety of winter grain crops and pastures. The predatory mite, Bdellodes lapidaria (Acari: Bdellidae), co-occurs with S. viridis and is reported to be a biological control agent of this pest. Using laboratory bioassays and field experiments, we assessed the susceptibility of B. lapidaria to several pesticides and investigated its impact in controlling S. viridis. In the laboratory, B. lapidaria was found to be susceptible to the synthetic pyrethroids, α-cypermethrin and bifenthrin, but relatively tolerant to the avermectin, abamectin, and organophosphorous chemicals, omethoate and chlorpyrifos. In field experiments, B. lapidaria was not adversely affected by applications of either bifenthrin or omethoate. Despite strong intraspecific interactions, we found no detectable impact of B. lapidaria on S. viridis numbers in the field. These results indicate that B. lapidaria has a relatively high tolerance to several pesticides, perhaps partly through behavioural avoidance, but little impact as a biological control agent on S. viridis in south-eastern Australia.     

沿海拔高度松突圆蚧热耐受性的变化

为了解松突圆蚧Hemiberlesia pitysophila Takagi对海拔的热适应性, 通过极端温度暴露试验和过冷却点测定, 比较了不同海拔梯度（80～725 m）上冬季松突圆蚧1龄若虫、2龄性分化前若虫和雌成虫的热耐受性。结果表明: （1）不同海拔松突圆蚧的热耐受性具有显著差异, 主要表现为海拔391 m 区域2龄性分化前若虫和雌成虫的耐寒性, 以及雌成虫的耐热性均显著较强; 除2龄性分化前若虫的耐寒性外, 该虫的热耐受性未表现出随海拔升高而显著增强的趋势。这一结果不支持气候变化假说, 但说明海拔是限制松突圆蚧种群扩张和地理分布的重要因素。（2）海拔梯度上, 1龄若虫和2龄性分化前若虫中耐寒性与耐热性的相关性均不显著, 但在雌成虫中呈显著正相关, 说明海拔梯度上松突圆蚧耐寒性和耐热性的关系与其发育阶段有关。（3）海拔梯度上, 雌成虫的过冷却点与其致死中低温的相关性未表现出显著水平。本文结果有助于深入理解松突圆蚧的热适应性和地理分布特征。     

Genotypes of lucerne (Medicago sativa L.) show differential tolerance to manganese deficiency and toxicity when grown in bauxite residue sand

The physical and chemical characteristics of bauxite residue sand (BRS) affect the availability of a number of nutrients to plants, especially manganese (Mn). Lucerne (Medicago sativa L.) has been chosen as a BRS revegetation species because of its deep-rooting habit and tendency to tolerate moderately alkaline and saline soils, even though it is still prone to Mn deficiency stress. Sixteen commercially available lucerne genotypes were grown in BRS after addition of 5, 50 or 500 g Mn g^–1 BRS in a glasshouse. Manganese deficiency and toxicity symptoms were observed in 5 and 500 g g^–1 treatments, respectively. Symptom expression varied in severity between genotypes. Relative tolerance to Mn deficiency was defined by shoot dry weight at 5 g Mn g^–1 as a percentage of shoot dry weight at 50 g Mn g^–1. Salado, a genotype tolerant to Mn deficiency, and Sirosal, a genotype intolerant to Mn deficiency, were then grown with 0, 10, 20, 50, 100, 200 or 800 g Mn g^–1 BRS and found to have critical shoot Mn concentrations of 17.7 (Salado) and 26.6 g g^–1 (Sirosal). The use of genotypes with high relative Mn deficiency tolerance is recommended to help improve sustainability of BRS revegetation as well as to improve productivity on Mn-fixing agricultural soils.     

Feeding Life Style of Redlegged Earth Mite, Halotydeus Destructor (Acari: Penthaleidae), in pastures and the role of broad-leafed weeds

Redlegged earth mite, Halotydeus destructor, is a major pest of pastures and crops in Australia, and also feeds on lower plants on the soil surface. Feeding behaviour is reviewed, and the role of Arctotheca calendula, capeweed, in determining occurrence and abundance in pastures is investigated. Mites fed more and produced more progeny on Trifolium subterraneum (subclover) than on capeweed in non-choice experiments. In pastures with mixed species three times more mites were feeding on subclover than on capeweed foliage. However, twice as many mites were found on the soil surface under pasture patches consisting mainly of capeweed than of subclover. Patches were selected on the basis of pasture height, irrespective of plant composition. Twice as many mites were found in populations under patches of tall than short pasture. The daytime relative humidity was higher in tall than short patches, and the temperature slightly lower, making tall patches a more favourable niche for these mites. Ninety per cent of H. destructor were on the soil surface, while 10% were feeding on the upper canopy of pasture. The proportion of each population that was feeding was greater on subclover than capeweed, and subclover was a more suitable food. In Australia H. destructor occurs in regions with mixed pasture species, grown in rotation with grain crops. The ability of H. destructor to utilize foliage of a range of plant species of differing suitability for food, while living mostly on the soil surface in niches favourable for survival, has enabled it to become very abundant.     

Establishment and seasonal variation in abundance of the European rabbit flea,Spilopsyllus cuniculi (Dale), on wild rabbits in Australia

Observations on the establishment, and seasonal variations in the number, of the European rabbit flea, Spilopsyllus cuniculi (Dale), on wild rabbits in Australia.     

Internal proprioceptive organs of the distal antennal segments in Allacma fusca (L.) (Collembola : Sminthuridae): Proprioceptors phylogenetically derived from sensillum-bound exteroceptors

The internal proprioceptive organs of the distal antennal segments of Allacma fusca (Collembola : Sminthuridae) were examined with light, scanning, and transmission electron microscopy. There are 2 such organs, each belonging to the sensory equipment of a sensory peg. These pegs are part of the sensory organs of the 3rd antennal segment (SO - AIII), and show characteristics of both hair sensilla and chordotonal organs. They have 5 sensory cells of which 4 can be regarded as chemoreceptors, because the walls of the pegs are pierced by pores. The 5th cells are the proprioceptors. Their dendritic outer segments are connected to the base of the SO - AIII peg but show no specializations. Their dendritic inner segments are distally joined to a thecogen cell containing a scolopale. Proximally, they span the hemolymph space within the antenna. The perikaryon of one of the organs is located on a muscle that deflects the 3rd antennal segment (IP - AIII). The perikaryon of the other is attached to the antennal nerve near a point where it is connected to a muscle that deflects the 4th antennal segment (IP - AIV). There is a conspicuous membrane system, associated with microtubules and a prominent ciliary rootlet within the dendritic inner segment of the IP - AIII. The cytological features of the organs are discussed with reference to 2 problems, the phylogeny of chordotonal organs and the process of mechanosensory transduction.     

The response of lucerne (Medicago sativa L.) to sodium sulphate and chloride salinity

Sodium and sulphate-dominated salinity is a serious environmental problem occurring in soils and groundwater in many parts of the world. The effect of Na2SO4 and NaCl, at electrical conductivity levels ranging from 2 to 17 dS m-1, on the growth and tissue ion concentrations of 16 lines of lucerne (Medicago sativa L.) was examined in the greenhouse over a 2 month period. Averaged across all lines, plants grown at 17 dS m-1 produced 66% of the dry matter of plants grown at 2 dS m-1. However there were significant differences among lines in relative salt tolerance (as defined by the slope of the reduction in dry matter) versus electrical conductivity. Dry matter production was negatively correlated with shoot concentrations of Na+, Cl- and S2- and generally lines that were more tolerant to salinity had lower concentrations of those ions in the shoots. We conclude that lucerne is moderately tolerant to Na2SO4 -predominated salinity, and that the degree of intraspecific variation that exists within this species will allow more tolerant lines to be selected for establishment in conditions where sulphate salinity is a problem.Collaborator