Improved understanding of the damage, ecology, and management of mirids and stinkbugs in Bollgard II

In recent years mirids and stinkbugs have emerged as important sucking pests in cotton. While stinkbugs are causing damage to bolls, mirids are causing damage to seedlings, squares and bolls. With the increasing adoption of Bollgard II and IPM approaches the use of broad-spectrum chemicals to kill Helicoverpa has been reduced and as a result mirids and stinkbugs are building to levels causing damage to bolls later in crop growth stages. Studies on stinkbugs by Dr Moazzem Khan revealed that green vegetable bug (GVB) caused significant boll damage and yield loss. A preliminary study by Dr Khan on mirids revealed that high mirid numbers at later growth stages also caused significant boll damage and that damage caused by mirids and GVB were similar. Mirids and stinkbugs therefore demand greater attention in order to minimise losses caused by these pests and to develop IPM strategies against these pests to enhance gains in IPM that have been made with Bt-transgenic cotton. Progress in this area of research will maintain sustainability and profitability of the Australian cotton industry. Mirid damage at early growth stages of cotton (up to squaring stage) has been studied in detail by Dr Khan. He found that all ages of mirids cause damage to young plants and damage by mirid nymphs is cumulative. Maximum damage occurs when the insect reaches the 4th and 5th nymphal stages. He also found that mirid feeding causes shedding of small and medium squares, and damaged large squares develop as ‘parrot beak’ bolls. Detailed studies at the boll stage, such as which stage of mirids is most damaging or which age boll is most vulnerable to feeding, is lacking. This information is a prerequisite to developing an IPM strategy for the pest in later crop growth stages. Understanding population change of the pest over time in relation to crop development is an important aspect for developing management strategies for the pest which is lacking for mirids in BollgardII. Predators and parasitoids are integral components of any IPM system and play an important part in regulating pest populations. Some generalist predators such as ants, spiders, damsel bugs and assassin bugs are known to predate on mirids. Nothing is known about parasitoids of mirids. Since green mirid (GM), Creontiades dilutus, is indigenous to Australia it is likely that we have one or more parasitoids of this mirid in Australia, but that possibility has not been investigated yet. The impact of the GVB adult parasitoid, Trichopoda giacomelli, has been studied by Dr Khan who found that the fly is established in the released areas and continues to spread. However, to get wider and greater impact, the fly should be released in new locations across the valleys. The insecticides registered for mirids and stinkbugs are mostly non-selective and are extremely disruptive to a wide range of beneficial insects. Use of these insecticides at stage I and II will minimise the impact of existing IPM programs. Therefore less disruptive control tactics including soft chemicals for mirids and stinkbugs are necessary. As with soft chemicals, salt mixtures, biopesticides based on fungal pathogens and attractants based on plant volatiles may be useful tools in managing mirids and stinkbugs with less or no disruption. Dr Khan has investigated salt mixture against mirids and GVB. While salt mixtures are quite effective and less disruptive, they are quite chemical specific. Not all chemicals mixed with salt will give the desired benefit. Therefore further investigation is needed to identify those chemicals that are effective with salt mixture against mirids and 3 of 37 GVB. Dr Caroline Hauxwell of DPI&F is working on fungal pathogen-based biopesticides against mirids and GVB and Drs Peter Gregg and Alice Del Socorro of Australian Cotton CRC are working on plant volatile-based attractants against mirids. Depending on their findings, inclusion of fungal-based biopestcides and plant volatile-based attractants in developing a management system against mirids and stinkbugs in cotton could be an important component of an IPM approach.

DAQ00083 Integration of biopesticides into IPM against sucking pests

Develop and evaluate novel fungal biopesticides.

Comparative studies on the invasion of cattle ticks (Rhipicephalus (Boophilus) microplus) and sheep blowflies (Lucilia cuprina) by Metarhizium anisopliae (Sorokin).

Microscopic investigations over time were carried out to study and compare the pathogenesis of invasion of ticks and blowflies by Metarhizium anisopliae. The scanning electron microscope and stereo light microscope were used to observe and record processes on the arthropods' surfaces and the compound light microscope was used to observe and record processes within the body cavities. Two distinctly different patterns of invasion were found in ticks and blowflies. Fungal conidia germinated on the surface of ticks then hyphae simultaneously penetrated into the tick body and grew across the tick surface. There was extensive fungal degradation of the tick cuticle, particularly the outer endocuticle. Although large numbers of conidia adhered to the surface of blowflies, no conidia were seen to germinate on external surfaces. A single germinating conidium was seen in the entrance to the buccal cavity. Investigations of the fly interior revealed a higher density of hyphal bodies in the haemolymph surrounding the buccal cavity than in haemolymph from regions of the upper thorax. This pattern suggests that fungal invasion of the blowfly is primarily through the buccal cavity. Plentiful extracellular mucilage was seen around the hyphae on tick cuticles, and crystals of calcium oxalate were seen amongst the hyphae on the surface of ticks and in the haemolymph of blowflies killed by M. anisopliae isolate ARIM16.

Corymbia leaf oils, latitude, hybrids and herbivory: a test using common-garden field trials

Foliar oils, particularly monoterpenes, can influence the susceptibility of plants to herbivory. In plants, including eucalypts, monoterpenes are often associated with plant defence. A recent analysis revealed an increase in foliar oil content with increasing latitudinal endemism, and we tested this pattern using three eucalypt taxa comprising a latitudinal replacement cline. We also examined the relative concentrations of two monoterpenes (alpha-pinene and 1,8-cineole), for which meta-analyses also showed latitudinal variation, using hybrids of these three taxa with Corymbia torelliana. These, and pure C. torelliana, were then assessed in common-garden field plots for the abundance and distribution of herbivory by four distinct herbivore taxa. Differing feeding strategies among these herbivores allowed us to test hypotheses regarding heritability of susceptibility and relationships to alpha-pinene and 1,8-cineole. We found no support for an increase in foliar oil content with increasing latitude, nor did our analysis support predictions for consistent variation in alpha-pinene and 1,8-cineole contents with latitude. However, herbivore species showed differential responses to different taxa and monoterpene contents. For example, eriophyid mites, the most monophagous of our censused herbivores, avoided the pure species, but fed on hybrid taxa, supporting hypotheses on hybrid susceptibility. The most polyphagous herbivore (leaf blister sawfly Phylacteophaga froggatti) showed no evidence of response to plant secondary metabolites, while the distribution and abundance patterns of Paropsis atomaria showed some relationship to monoterpene yields.

Laboratory-rearing Techniques for Tephritid Fruit Flies in the South Pacific

Laboratory colonies of 15 economically important species of multi-host fruit flies (Diptera:Tephritidae) have been established in eight South Pacific island countries for the purpose of undertaking biological studies, particularly host status testing and research on quarantine treatments. Laboratory rearing techniques are based on the development of artificial diets for larvae consisting predominately of the pulp of locally available fruits including pawpaw, breadfruit and banana. The pawpaw diet is the standard diet and is used in seven countries for rearing 11 species. Diet ingredients are standard proportions of fruit pulp, hydrolysed protein and a bacterial and fungal inhibitor. The diet is particularly suitable for post-harvest treatment studies when larvae of known age are required. Another major development in the laboratory rearing system is the use of pure strains of Enterobacteriaceae bacterial cultures as important adult-feeding supplements. These bacterial cultures are dissected out of the crop of wild females, isolated by sub-culturing, and identified before supply to adults on peptone yeast extract agar plates. Most species are egged using thin, plastic receptacles perforated with 1 mm oviposition holes, with fruit juice or larval diet smeared internally as an oviposition stimulant. Laboratory rearing techniques have been standardised for all of the Pacific countries. Quality control monitoring is based on acceptable ranges in per cent egg hatch, pupal weight and pupal mortality. Colonies are rejuvenated every 6 to 12 months by crossing wild males with laboratory-reared females and vice versa. The standard rearing techniques, equipment and ingredients used in collecting, establishment, maintenance and quality control of these fruit fly species are detailed in this paper.

A phylogenetic and taxonomic re-evaluation of the Bipolaris - Cochliobolus - Curvularia Complex

Three genera, Cochliobolus, Bipolaris and Curvularia form a complex that contains many plant pathogens, mostly on grasses (Poaceae) with a worldwide distribution. The taxonomy of this complex is confusing as frequent nomenclatural changes and refinements have occurred. There is no clear morphological boundary between the asexual genera Bipolaris and Curvularia, and some species show intermediate morphology. We investigated this complex based on a set of ex-type cultures and collections from northern Thailand. Combined gene analysis of rDNA ITS (internal transcribed spacer), GPDH (glyceraldehyde 3-phosphate dehydrogenase), LSU (large subunit) and EF1-α (translation elongation factor 1-α) shows that this generic complex divides into two groups. Bipolaris and Cochliobolus species clustered in Group 1 along with their type species, whereas Curvularia species (including species named as Bipolaris, Cochliobolus and Curvularia) clustered in Group 2, with its generic type. The nomenclatural conflict in this complex is resolved giving priority to the more commonly used established generic names Bipolaris and Curvularia. Modern descriptions of the genera Bipolaris and Curvularia are provided and species resolved in this study are transferred to one of these genera based on their phylogeny. © 2012 Mushroom Research Foundation.

A review of the Ustilago-Sporisorium-Macalpinomyces complex

The fungal genera Ustilago, Sporisorium and Macalpinomyces represent an unresolved complex. Taxa within the complex often possess characters that occur in more than one genus, creating uncertainty for species placement. Previous studies have indicated that the genera cannot be separated based on morphology alone. Here we chronologically review the history of the Ustilago-Sporisorium-Macalpinomyces complex, argue for its resolution and suggest methods to accomplish a stable taxonomy. A combined molecular and morphological approach is required to identify synapomorphic characters that underpin a new classification. Ustilago, Sporisorium and Macalpinomyces require explicit re-description and new genera, based on monophyletic groups, are needed to accommodate taxa that no longer fit the emended descriptions. A resolved classification will end the taxonomic confusion that surrounds generic placement of these smut fungi.

Diversity and abundance of fungivorous thrips (Thysanoptera) associated with leaf-litter and bark across forest types and two tree genera in subtropical Australia

Leaf-litter thrips were much more common and diverse in dry sclerophyll forest than in wetter forest types in subtropical southeast Queensland, Australia. In dry sclerophyll forest, the species composition of thrips in leaf-litter was strongly differentiated from the thrips fauna associated with bark of the trees Eucalyptus major and Acacia melanoxylon (4 of 34 species in common). The species composition of bark-dwelling thrips was similar across the two tree species and also across two eucalypts with different bark types, Eucalyptus major (flaky) and Eucalyptus siderophloia (rough). The diversity of thrips from the leaf-litter was not differentiated across all of these tree species. Virtually all thrips collected were Phlaeothripidae, subfamilies Idolothripinae and Phlaeothripinae. Idolothripinae were associated almost exclusively with leaf-litter, but Phlaeothripinae were in leaf-litter and bark. The association of fungal-feeding thrips with dry sclerophyll forest raises questions about their ecological requirements and the role they play in nutrient cycling. © 2012 Copyright Taylor and Francis Group, LLC.

Recent emergence of the wheat Lr34 multi-pathogen resistance: insights from haplotype analysis in wheat, rice, sorghum and Aegilops tauschii

Spontaneous sequence changes and the selection of beneficial mutations are driving forces of gene diversification and key factors of evolution. In highly dynamic co-evolutionary processes such as plant-pathogen interactions, the plant's ability to rapidly adapt to newly emerging pathogens is paramount. The hexaploid wheat gene Lr34, which encodes an ATP-binding cassette (ABC) transporter, confers durable field resistance against four fungal diseases. Despite its extensive use in breeding and agriculture, no increase in virulence towards Lr34 has been described over the last century. The wheat genepool contains two predominant Lr34 alleles of which only one confers disease resistance. The two alleles, located on chromosome 7DS, differ by only two exon-polymorphisms. Putatively functional homoeologs and orthologs of Lr34 are found on the B-genome of wheat and in rice and sorghum, but not in maize, barley and Brachypodium. In this study we present a detailed haplotype analysis of homoeologous and orthologous Lr34 genes in genetically and geographically diverse selections of wheat, rice and sorghum accessions. We found that the resistant Lr34 haplotype is unique to the wheat D-genome and is not found in the B-genome of wheat or in rice and sorghum. Furthermore, we only found the susceptible Lr34 allele in a set of 252 Ae. tauschii genotypes, the progenitor of the wheat D-genome. These data provide compelling evidence that the Lr34 multi-pathogen resistance is the result of recent gene diversification occurring after the formation of hexaploid wheat about 8,000 years ago.

Short-range resource location by Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) demonstrates a strong preference for fungi associated with cotton seed

Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is a common stored grain pest for which a wide range of suitable resources has been recorded. These beetles are facultatively fungivorous and their resource range may extend to fungi associated with non-grain resources (e.g. cotton seed) and other decaying plant matter. Little is known with respect to fungi in terms of resource location by these beetles in the field. We, therefore, conducted a series of experiments in laboratory arenas, glasshouse cages and the field to determine how beetles respond to grain resources in relation to cotton seed (together with its lint stubble and associated fungal flora). Results from the tests conducted in relatively small arenas and cages in the laboratory and glasshouse reveal that the responses of T. castaneum adults to food resources were twice as strong when walking as when flying (as measured by the proportion of the released beetles that were trapped). Also, a clear preference for linted cotton seeds was evident in walking T. castaneum, especially in small-scale arenas in the laboratory, where at least 60% of beetles released preferred linted cotton seeds over wheat and sorghum. Similarly, in cages (1 m3) they responded five times more strongly to linted cotton seed than to conventional grain resources. However, this pattern was not consistent with those obtained from field trapping over 20 m and the beetles did not show any particular preference to any of the resources tested above. Our results suggest a focus on walking beetles in trapping studies for population estimations and, for developing effective food-based trapping lures, the potential use of active volatiles from the fungi associated with linted cotton seed. © 2012 Elsevier Ltd.

Responses of tribolium castaneum to olfactory cues from cotton seeds, the fungi associated with cotton seeds, and cereals

We tested, in an olfactometer, whether or not Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) responds preferentially to the volatiles that emanate from the fungi associated with cotton [Gossypium hirsutum L. (Malvaceae)] seed over those that emanate from cereals, because cereals are usually portrayed as the primary resources of these beetles. Pairwise comparisons were conducted between cotton seed, wheat (Triticum aestivum L.), and sorghum [Sorghum bicolor (L.) Moench] (both Poaceae); volatiles were tested from intact seeds and from both water and ethanol extracts. The results demonstrate that T. castaneum is attracted more strongly to cotton seeds with its lint contaminated with fungi, than to the conventional resources of this species (i.e., wheat and sorghum). Further tests prove that it is the fungus on the lint that produces the active volatiles, because the beetles did not respond to sterilized cotton lint (i.e., without the fungi typically associated with it when cotton seed is stored). Tests with five fungal cultures (each representing an unidentified species that was isolated from the field-collected cotton lint) were variable across the cultures, with only one of them being significantly attractive to the beetles. The others were not attractive and one may even have repulsed the beetles. The results are consistent with the beetles having a strong ecological association with fungi and suggest it would be worth investigating the ecology of T. castaneum from this perspective. © 2012 The Netherlands Entomological Society.

Earthy-muddy tainting of cultured barramundi linked to geosmin in tropical northern Australia

Tainting of outdoor pond-reared barramundi Lates calcarifer by muddy-earthy off-flavours is frequently reported across tropical Australia. To investigate the possible causes and effects of off-flavour tainting, we analysed water samples from outdoor rearing ponds for the presence of geosmin (GSM) and 2-methylisoborneol (2-MIB), 2 microbial metabolites often associated with tainting episodes. We then conducted controlled dose-effect experiments which measured the accumulation of tainting metabolites in the flesh, and the impact tainting had on taste and flavour attributes. GSM was deemed to be the compound most likely responsible for off-flavour tainting, persisting at moderate (similar to 1.00 mu g l(-1)) to extreme levels (similar to 14.36 mu g l(-1)), while 2-MIB was never detected during the study. Controlled experiments revealed that the accumulation of GSM in the flesh of market-sized barramundi was directly related to GSM levels of the holding water (0 to similar to 4 mu g l(-1)), with higher levels resulting in significant increases in undesirable taste and flavour attributes, particularly muddy-earthy flavour and weedy aftertaste. We identified the sensory detection threshold for GSM in farmed barramundi to be <= 0.74 mu g kg(-1), similar to estimates for GSM detection in rainbow trout Oncorhynchus mykiss (similar to 0.9 mu g kg(-1)) and for 2-MIB in channel catfish Ictalurus punctatus (0.7 mu g kg(-1)). Quantitative estimation of flesh-bound GSM using gas chromatography-mass spectrometry (GC-MS) agreed well with human sensory assessment scores and highlights the reliability of chemical analysis of GSM in barramundi flesh while also indicating the value of GC-MS analysis in predicting the impact of GSM on the sensory properties of farmed barramundi.

Microbial indicators related to yield and disease and changes in soil microbial community structure with ginger farm management practices

TRFLP (terminal restriction fragment length polymorphism) was used to assess whether management practices that improved disease suppression and/or yield in a 4-year ginger field trial were related to changes in soil microbial community structure. Bacterial and fungal community profiles were defined by presence and abundance of terminal restriction fragments (TRFs), where each TRF represents one or more species. Results indicated inclusion of an organic amendment and minimum tillage increased the relative diversity of dominant fungal populations in a system dependant way. Inclusion of an organic amendment increased bacterial species richness in the pasture treatment. Redundancy analysis showed shifts in microbial community structure associated with different management practices and treatments grouped according to TRF abundance in relation to yield and disease incidence. ANOVA also indicated the abundance of certain TRFs was significantly affected by farming system management practices, and a number of these TRFs were also correlated with yield or disease suppression. Further analyses are required to determine whether identified TRFs can be used as general or soil-type specific bio-indicators of productivity (increased and decreased) and Pythium myriotylum suppressiveness.

Consequences of Corymbia (Myrtaceae) hybridisation on leaf-oil profiles

The present study examines patterns of heritability of plant secondary metabolites following hybridisation among three genetically homogeneous taxa of spotted gum (Corymbia henryi (S.T.Blake) K.D.Hill & L.A.S.Johnson, C. citriodora subsp. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson and C. citriodora (Hook.) K.D.Hill & L.A.S.Johnson subsp. citriodora (section Maculatae), and their congener C. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson (section Torellianae)). Hexane extracts of leaves of all four parent taxa were statistically distinguishable (ANOSIM: global R = 0.976, P = 0.008). Hybridisation patterns varied among the taxa studied, with the hybrid formed with C. citriodora subsp. variegata showing an intermediate extractive profile between its parents, whereas the profiles of the other two hybrids were dominated by that of C. torelliana. These different patterns in plant secondary-metabolite inheritance may have implications for a range of plant-insect interactions.