Murray J. Fletcher

Toward an optimal sampling protocol for Hemiptera on understorey plants

There are no standardised sampling protocols for inventorying Hemiptera from understorey or canopy plants. This paper proposes an optimal protocol for the understorey, after evaluating the efficiency of seven methods to maximise the richness of Hemiptera collected from plants with minimal field and laboratory time. The methods evaluated were beating, chemical knockdown, sweeping, branch clipping, hand collecting, vacuum sampling and sticky trapping. These techniques were tested at two spatial scales: 1 ha sites and individual plants. In addition, because efficiency may differ with vegetation structure, sampling of sites was conducted in three disparate understorey habitats, and sampling of individual plants was conducted across 33 plant species. No single method sampled the majority of hemipteran species in the understorey. Chemical knockdown, vacuum sampling and beating yielded speciose samples (61, 61 and 30 species, respectively, representing 53, 53 and 26% of total species collected). The four remaining methods provided species-poor samples (<18 species or <16% of total species collected). These methods also had biases towards particular taxa (e.g., branch clipping and hand collecting targeted sessile Hemiptera, and sticky trapping were dominated by five species of Psyllidae). The most time-efficient methods were beating, sweeping and hand collecting (200 minutes of field and laboratory time yielded >7 species for each technique). By comparison, vacuum sampling, sticky trapping, branch clipping and chemical knockdown yielded <5 species for the same period. Chemical knockdown had further disadvantages; high financial cost and potential spray drift. The most effective methods for a standardised sampling protocol to inventory Hemiptera from the understorey are beating and vacuum sampling. If used in combination, these methods optimise the catch of understorey hemipteran species, as their samples have high complementarity.

The current distribution and geographical origin of the scale insect pest Ceroplastes sinensis (Hemiptera: Coccidae)

Ceroplastes sinensis Del Guercio is a pest of commercial citrus in Australia and has been recorded from New Zealand, southern Europe, northern Africa, North America and Mexico. Its distribution is mainly temperate and it is more restricted climatically than previously believed. Uncertainty concerning the place of origin of C. sinensis has thwarted previous attempts at biological control. In the present study, a novel and cost-effective approach using cladistic estimates is demonstrated to determine the place of its origin. Cladistically derived phylogenies are commonplace for many organisms, but the method has not been used before to predict the area of origin of a cosmopolitan pest. Cladistic analysis of the wax scales predicts a native range for C. sinensis within Central or South America. This prediction appears to have been confirmed by the recent discovery of heavily parasitized individuals of C. sinensis in Argentina. The cladistic analysis also allows prediction of the geographical origin of three other widespread wax scale speries: Ceroplastes ceriferus (Fabricius) may be of Neotropical origin, C. rubens Maskell and C. rusci (Linnaeus) are probably native to the Afrotropical region. The approach used has wide implications because the native areas of many other economically important pests are still unknown or uncertain.

Reducing the immigration of suspected leafhopper vectors and severity of Australian lucerne yellows disease

Three newly-sown lucerne stands in the mid Lachlan Valley region of New South Wales, Australia, were sampled, over 50 weeks, for Australian lucerne yellows disease symptom distribution and severity. Leafhopper populations were also monitored. Symptoms developed in all 3 stands within 32 weeks of sowing. There were statistically significant spatial differences in the density of symptomatic plants for 2 dates at this and another site. Two possible insect vectors, Austroagallia torrida and Batracomorphus angustatus were more numerous in some sections of crop margins at 2 sites. These 2 species and a third possible insect vector Orosius argentatus each had a statistically significant spatial and temporal correlation with symptomatic plant numbers for at least 1 site date. Two subsequent border treatment experiments evaluated the effect of crop-margin treatments on leafhopper movement into and from the stand. The second border treatment experiment examined also the treatment effect on Australian lucerne yellows disease symptomatic plant numbers. Treatment with insecticide or herbicide significantly reduced the overall movement of leafhoppers. In addition, the insecticide treatment lowered the incidence of disease expression in adjacent lucerne. Results suggest that there is scope for management of this plant disease by reducing immigration of leafhopper vectors into lucerne from non-crop vegetation.

Multi-scale patterns in the host specificity of plant-dwelling arthropods: the influence of host plant and temporal variation on species richness and assemblage composition of true bugs (Hemiptera)

The influence of temporal variation in the host specificity of invertebrates to estimates of biodiversity is rarely considered. While patterns at large spatial scales have stimulated much attention, such comparisons are constrained for southern-hemisphere biomes because the patterning of invertebrates on plants is largely unknown. Here, we analyse variation of plant-dwelling Hemiptera from 15 understorey plant species over 18 months in the south-west Australian biodiversity hotspot. Analyses showed significant interactions in species composition between sampling period and plant species. Fauna that were “effectively specialized” (host-specificity index) to plants changed with season, although this was also related to the number of singletons and overall species richness. Sampling from a single season also overestimated the degree of host specificity by 52% and underestimated the perception of species richness when an outbreak of a particular herbivore occurred. High host-specificity values (12.7 hemipteran species per plant) support the case for high estimates of global arthropod richness.

Occurrence and severity of lucerne yellows disease in Australian lucerne seed crops.

Production of lucerne seed is one of the most important seed industries in Australia. Anecdotal reports suggested that the disease lucerne yellows was having a marked impact on the industry, but no firm data existed on its occurrence and severity. An interview-based survey obtained detailed information from eight seedhouse ofices and a telephone-based survey equivalent data from 62 individual growers. Only two of the 36 growers surveyed in New South Wales (NSW) and four of the 26 growers from South Australia (SA) had not observed the disease in their crops. In one instance the incidence of lucerne yellows was reported to be as high as 50–75 percent of plants but the majority of interviewees estimated the incidence to be less than five percent. Responses from farmers in NSW did not indicate a significantly greater severity for the disease than was apparent in SA. The results from the seedhouses support those from individual growers in showing that lucerne yellows disease occurs widely in both States and that its severity is such that significant economic losses are likely.

Structure–Property and Structure–Function Relations of Leafhopper (Kahaono montana) Silk

Kahaono montana Evans (Insecta: Hemiptera: Cicadellidae), an endemic Australian leafhopper, is unique among the insect order Hemiptera in producing a silk. In this study, the secondary structure of the protein comprising leafhopper silk, and the surface stretching mechanical properties of this biopolymer, were investigated using Fourier-transform infrared microscopy and atomic force microscopy, respectively. The curve-fitted amide I and amide III bands revealed a composition of 13.1% α-helix, 23.8% β-sheet, 25.5% random coil, and 37.6% aggregated side chains. The molecular stretching behaviour of raw and cleaned silk fibres differed markedly. Analysis of the AFM force curves showed an adhesive property of the raw silk, while the pure fibre showed only the presence of protein. These findings suggest that the silk fibres act as a structural support for other leafhopper secretions and together form a hydrophobic barrier that may protect the insects from rain and natural enemies. This is the first time such a use of silk has been found in a biological system.

Determining putative vectors of the Bogia Coconut Syndrome phytoplasma using loop-mediated isothermal amplification of single-insect feeding media

Phytoplasmas are insect vectored mollicutes responsible for disease in many economically important crops. Determining which insect species are vectors of a given phytoplasma is important for managing disease but is methodologically challenging because disease-free plants need to be exposed to large numbers of insects, often over many months. A relatively new method to detect likely transmission involves molecular testing for phytoplasma DNA in sucrose solution that insects have fed upon. In this study we combined this feeding medium method with a loop-mediated isothermal amplification (LAMP) assay to study 627 insect specimens of 11 Hemiptera taxa sampled from sites in Papua New Guinea affected by Bogia coconut syndrome (BCS). The LAMP assay detected phytoplasma DNA from the feeding solution and head tissue of insects from six taxa belonging to four families: Derbidae, Lophopidae, Flatidae and Ricaniidae. Two other taxa yielded positives only from the heads and the remainder tested negative. These results demonstrate the utility of combining single-insect feeding medium tests with LAMP assays to identify putative vectors that can be the subject of transmission tests and to better understand phytoplasma pathosystems.

Phytoplasmas and Their Insect Vectors: Implications for Date Palm

Phytoplasmas are transmitted chiefly by insects, most commonly planthoppers and leafhoppers. Molecular genetic analyses have improved the understanding of phytoplasma taxonomy, and also enhanced the ability to identify phytoplasmas detected in hosts and insect vectors. Date palm is affected by Al-Wijam disease in Saudi Arabia and molecularly indistinguishable phytoplasmas (16SrI group) were recovered from affected palms and from Cicadulina bipunctata, an insect commonly found on the palms. The phytoplasma that is associated with the lethal yellowing disease in coconut palm (16SrIV-A) can also infect date palm. In the Americas lethal yellowing is likely to be transmitted by Haplaxius crudus (formerly Myndus crudus). Texas phoenix decline is reported from warm regions of South-East USA and may be transmitted by two species of Derbidae. Phytoplasmas belonging to the 16SrIV-F and 16SrXIV groups have also been identified from date palm growing in the USA and Africa respectively, though vectors have not been identified. Preventing spread in infected vegetative planting material and of vectors is key to limiting the impact of phytoplasma diseases. Management in affected areas can use antibiotics on high value trees, but this is not economical for extensive crops. In these situations, vector control by insecticide use or habitat management can be useful, but the long lifespan of individual palms means that even low vector pressure can lead to infection over successive years. The development of resistant varieties and replanting is the most effective long-term approach developed so far for phytoplasma disease management in this plant species.

Bionomics and feeding impact of Ctenarytaina eucalypti (Hemiptera: Psylloidea: Aphalaridae) on Eucalyptus globulus (Myrtaceae) in the central tablelands of New South Wales

Ctenarytaina eucalypti is considered a key pest of Eucalyptus plantations, especially E. globulus, in different parts of the world. In this study different levels of response of E. globulus to oviposition and feeding by C. eucalypti are reported. The responses in the juvenile E. globulus leaf tissues to oviposition include subcellular damage with the accumulation of callosic material superimposed by lignin‐like polymers in cells proximal to the oviposition site, indicating the earliest response of stress signals in E. globulus to wounding. The feeding action of the first‐ and second‐nymphal instars on the mesophyll cells inflicts both mechanical and chemical damage and manifests newly developed apoplastic spaces between cell walls and plasma membranes, poorly differentiated primordial‐palisade cells, and autolysed protoplast. The phloem‐feeding third‐, fourth‐, and fifth‐nymphal instars induce changes in phloem parenchyma, which occur as actively dividing cells and including autophagic vacuoles. Leaf cells fed by adults also include hypertrophied mitochondria, degenerating cytoplasm and secondary metabolic compounds. The arrangement of antennal sensilla of C. eucalypti varies among nymphs and adults. The adults and nymphs of C. eucalypti appear to prefer specific leaf parts, suggesting that the levels and quality of nutrients vary in the same leaf. Growth in C. eucalypti is allometric, and the total body and antennal lengths show similar patterns in growth rates when compared with other sclerotised parts.

Entomopathogenic fungi of the oil palm pest, Zophiuma butawengi (Fulgoromorpha: Lophopidae), and potential for use as biological control agents

Oil palm, Elaeis guineensis Jacq., is an important cash crop in Papua New Guinea. Production is currently under threat from Finschhafen disorder caused by the planthopper Zophiuma butawengi (Heller), a native pest of coconut. The need for a non‐chemical strategy to manage Z. butawengi is high because the industry is committed to sustainable production. One possible option is the development of biological control using entomopathogenic fungi, and this study aimed to assess the scope for such a technology. Field collections extending over three regions of West New Britain in the 2010 monsoon season yielded 38 mycosed cadavers. Only three yielded entomopathogenic fungi: two of Hirsutella citriformis Speare and one each of Metarhizium flavoviride var. minus Rombach, Humber and D.W. Roberts, and Purpureocillium lilacinum (Thom) Luangsa‐ard, Houbraken, Hywel‐Jones and Samson. The pathogenicity of each isolate to Z. butawengi was confirmed in a laboratory study. M. flavoviride var. minus killed Z. butawengi significantly more rapidly over the course of a 15‐day period, and day 7 mortality was significantly greater than in water or nil control treatments. Given this pathogenic fungus was readily culturable and congenerics are used in other biological control treatments, it merits further investigation as a potential inundative entomopathogenic agent against Z. butawengi.