Is there any evidence that aphid alarm pheromones work as prey and host finding kairomones for natural enemies?

1. The aphid alarm pheromone (E)‐β‐farnesene (EBF) is often considered to be used by natural enemies as a prey/host finding kairomone. However, studies show opposing results, some appear to confirm an attraction of aphid natural enemies by EBF whereas others do not provide any evidence for the kairomone function of EBF. 2. To clarify if aphid natural enemies are attracted by the amounts of EBF naturally emitted by aphids, the existing literature was reviewed about EBF attractiveness to aphid natural enemies with consideration of the amounts of EBF used in the studies. 3. Thirty‐one publications that investigated the ability of EBF, aphid cornicle secretion, and attacked aphids, to attract aphid natural enemies were found. Several studies showed an attraction by EBF, but these used much higher amounts of EBF than usually emitted by aphids during a predator attack. Studies investigating EBF amounts similar to what is emitted by aphids are rare and failed to show attraction. Only two studies document an attraction of natural enemies by attacked aphids. 4. As EBF is emitted in very low amounts, not very stable, and only present after an attack, we suggest that aphid‐derived EBF is not a suitable kairomone for most natural enemy species, especially when they are able to use alternative cues. As EBF, amongst other volatiles, is also emitted by herbivore‐induced plants, we propose that natural enemies might use plant‐derived EBF as a synomone to identify aphid‐infested plants via an altered plant volatile bouquet.     

Duthieeae,a new tribe of grasses (Poaceae) identified among the early diverging lineages of subfamily Pooideae: molecular phylogenetics,morphological delineation,cytogenetics and biogeography

The phylogeny of Pooideae, one of the largest subfamilies of grasses, has been intensively studied during the past years. To investigate the early evolutionary splits in Pooideae we used a broad sample of genera with uncertain placement, some of which have not been studied in molecular phylogenetics before, complemented by representatives from other lineages of this subfamily. Morphological, cytogenetic and biogeographical analyses were added to the molecular sequence work on chloroplast matK–3’trnK and nuclear ITS. According to chloroplast DNA data, a new and well-supported lineage was identified among the early branches. It consisted of Phaenosperma and a larger group of genera encompassing Anisopogon, Danthoniastrum, Duthiea, Metcalfia, Pseudodanthonia (inclusion resting on ITS and morphology), Sinochasea and Stephanachne. Based on structural characters we suggest to keep Phaenosperma under the monotypic tribe Phaenospermateae and to accommodate the other genera under a new tribe Duthieeae, which is morphologically well-defined by synapomorphic spikelet features. Megalachne and Podophorus were not part of the early diverging Pooideae lineages but belong to the Aveneae/Poeae complex. Morphological characteristics of Duthieeae are discussed with respect especially to Stipeae and reveal consistent differences between both tribes. The genera of Duthieeae and the major lineages of Stipeae are keyed. A cytogenetic survey of exemplary taxa corroborates high chromosome base numbers as prevailing within the early diverging lineages of Pooideae, but chromosome sizes are more highly varied than previously reported. Ecogeographical analyses point to warm and humid conditions as the ancestral bioclimatic niche of Phaenosperma and Duthieeae, whereas adaptation to cold and drought occurred only in a part of Duthieeae but was obviously less successful than in the widespread and much more species-rich tribe Stipeae. The distribution of Duthieeae with species-poor or monotypic genera in mountains of the northern hemisphere and Anisopogon as an outlier in Australia suggests relict character.     

Disposition of ribosomal DNAs in the chromosomes of perennial oats (Poaceae: Aveneae)

The chromosomal loci of 5S and 45S ribosomal DNAs (rDNAs) and the activity of nucleolar‐organizing regions (NORs) were analysed in perennial oats of the genera Ammophila, Amphibromus, Arrhenatherum, Avena, Deschampsia, and Helictotrichon s.l. (Poaceae: Aveneae) using fluorescence in situ hybridization, staining with chromomycin/4′,6‐diamidino‐2‐phenylindole (DAPI), and silver impregnation. All chromosomes with a secondary constriction were nucleolar active. In chromosomes without a secondary constriction, NORs corresponded exclusively to broad bands of 45S rDNA with chromomycin‐positive, DAPI‐negative, and silver‐positive stainability. Additional minor bands of 45S rDNA showed no nucleolar activity. 5S rDNA was localized mostly in loci different from the nucleolar‐active 45S rDNA. If both rDNAs occurred within the same chromosome, they were at largely corresponding distances from the centromere, irrespective of their particular localization in either the same chromosome arm or in opposite arms. In the latter case, 5S rDNA was never more distal to the centromere than 45S rDNA. A new model was devised to explain this non‐random distribution of both rDNAs in nucleolar‐organizing chromosomes, which identified the Rabl orientation of chromosomes as ensuring a spatial proximity of 5S to 45S rDNA in interphase nuclei, even if they were localized in opposite arms. The possible role of the Rabl orientation in determining the spread and accumulation of 5S rDNA sequences in further chromosomes of the genome was discussed. B chromosomes were devoid of 5S rDNA, but most contained 45S rDNA and were nucleolar active. In some large groups of species, the number and arrangement of 5S and 45S rDNA sites in the chromosomes were remarkably uniform, especially in Helictotrichon subgenus Helictotrichon and Helictotrichon subgenus Pratavenastrum. Such distribution patterns have survived many speciation processes and have also remained widely unchanged in polyploids. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 193–210.     

Attachment forces of pea aphids (Acyrthosiphon pisum) on different legume species

1. Sympatric populations of insects adapted to different host plants are good model systems not only to study how they adapt to the chemistry of their food plant, but also to investigate whether morphological modifications evolved enabling them to live successfully on a certain plant species. 2. The pea aphid, Acyrthosiphon pisum (Harris) encompasses at least 11 genetically distinct sympatric host races, each showing a preference for a certain legume species. The leaflet surfaces of these legumes differ considerably in their wax coverage. 3. It was investigated whether the attachment structures of three pea aphid genotypes from different host races are adapted to the different surface properties of their host plants and whether they show differences in their attachment ability on the respective host and non‐host plants. 4. The surface morphology of plants and aphid tarsi was examined using SEM (scanning electron microscopy). The ability of the aphids to walk on specific surfaces was tested using traction force measurements. 5. The presence of wax blooms on the leaflets lowers the aphids' attachment ability considerably and diminishes their subsequent attachment on ‘neutral’ surfaces like glass. The pea aphid host races differ in their ability to walk on certain surfaces. However, the genotype from the adapted aphid host race was not necessarily the one with the best walking performance on their host plant. All aphids, regardless of the original host plant, were most efficient on the neutral control surface glass. The general host plant Vicia faba was the plant with the most favourable surface for all aphid host races.     

Entomopathogenic fungi stimulate transgenerational wing induction in pea aphids,Acyrthosiphon pisum (Hemiptera: Aphididae)

1. Aphid natural enemies include not only predators and parasitoids but also pathogens, of which fungi are the most studied for biological control. While wing formation in aphids is induced by abiotic conditions, it is also affected by biotic interactions with their arthropod natural enemies. Wing induction via interactions with arthropod natural enemies is mediated by the increase in their physical contact when alarmed (pseudo‐crowding). Pathogenic fungi do not trigger this alarm behaviour in aphids and, therefore, no pseudo‐crowding occurs. 2. We hypothesise that, while pathogenic fungi will stimulate maternally induced wing formation, the mechanism is different and is influenced by pathogen specificity. We tested this hypothesis using two entomopathogenic fungi, Pandora neoaphidis and Beauveria bassiana, an aphid specialist and a generalist respectively, on the pea aphid, Acyrthosiphon pisum Harris. 3. We first demonstrate that pea aphids infected with either pathogen and maintained in groups on broad bean plants produced a higher proportion of winged morphs than uninfected control aphids. We then show that, when maintained in isolation, aphids infected with either pathogen also produced higher proportions of winged offspring than control aphids. There was no difference between P. neoaphidis and B. bassiana in their effects on wing induction in either experiment. 4. Unlike the effect of predators and parasitoids on pea aphid wing induction, the effect of pathogens is independent of physical contact with other aphids, suggesting that physiological cues induce wing formation in infected aphids. It is possible that aphids benefit from wing induction by escaping infected patches whilst pathogens may benefit through dispersion. Possible mechanisms of wing induction are discussed.