Responses of <Emphasis Type="Italic">Phradis</Emphasis> parasitoids to volatiles of lavender, <Emphasis Type="Italic">Lavendula angustifolia</Emphasis>—a possible repellent for their host, <Emphasis Type="Italic">Meligethes aeneus</Emphasis>

Hymenopterous parasitoids of herbivorous insects can be useful biocontrol agents in integrated pest management strategies. However, the potential effects on these beneficials of new components in such strategies are often neglected. Essential oil of lavender, Lavendula angustifolia (Miller) (Lamiaceae), has recently been identified as a potential repellent in new control strategies being developed for the pollen beetle Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a major pest of oilseed rape, Brassica napus L. (Brassicaceae). We tested the electrophysiological and behavioural responses of two common parasitoids of M. aeneus: Phradis interstitialis (Thomson) and P. morionellus (Holmgren) (both Ichneumonidae) using coupled gas chromatography-electroantennodetection (GC-EAD) and olfactometry techniques. Both species elicited electrophysiological responses to lavender oil volatiles, including two compounds known to be repellent to M. aeneus. However, the parasitoids gave no significant responses to the odours of lavender oil in behavioural bioassays and there was no evidence to suggest that lavender-treated oilseed rape plants would reduce host habitat location by parasitoids of the target pest.     

Cubic exact solutions for the estimation of pairwise haplotype frequencies: implications for linkage disequilibrium analyses and a web tool 'CubeX'

Background  

The frequency of a haplotype comprising one allele at each of two loci can be expressed as a cubic equation (the 'Hill equation'), the solution of which gives that frequency. Most haplotype and linkage disequilibrium analysis programs use iteration-based algorithms which substitute an estimate of haplotype frequency into the equation, producing a new estimate which is repeatedly fed back into the equation until the values converge to a maximum likelihood estimate (expectation-maximisation).     

Distribution of transfer RNA genes in thePisum sativum chloroplast DNA

Purified chloroplast tRNAs were isolated fromPisum sativum leaves and radioactively labeled at their 3′ end using tRNA nucleotidyl transferase and α³²P-labeled CTP. Pea ctDNA was fragmented using a number of restriction endonucleases and hybridized with thein vitro labeled chloroplast tRNAs by DNA transfer method. Genes for tRNAs have been found to be dispersed throughout the chloroplast genome. A closer analysis of the several hybrid regions using recombinant DNA plasmids have shown that tRNA genes are localized in the chloroplast genome in both single and multiple arrangements. Two dimensional gel electrophoresis of total ct tRNA have identified 36 spots. All of them have been found to hybridize withPisum sativum ctDNA. Using recombinant clones, 30 of the tRNA spots have been mapped inPisum sativum ctDNA.     

Insect-damaged fossil leaves record food web response to ancient climate change and extinction

Plants and herbivorous insects have dominated terrestrial ecosystems for over 300 million years. Uniquely in the fossil record, foliage with well-preserved insect damage offers abundant and diverse information both about producers and about ecological and sometimes taxonomic groups of consumers. These data are ideally suited to investigate food web response to environmental perturbations, and they represent an invaluable deep-time complement to neoecological studies of global change. Correlations between feeding diversity and temperature, between herbivory and leaf traits that are modulated by climate, and between insect diversity and plant diversity can all be investigated in deep time. To illustrate, I emphasize recent work on the time interval from the latest Cretaceous through the middle Eocene (67-47 million years ago (Ma)), including two significant events that affected life: the end-Cretaceous mass extinction (65.5 Ma) and its ensuing recovery; and globally warming temperatures across the Paleocene-Eocene boundary (55.8 Ma). Climatic effects predicted from neoecology generally hold true in these deep-time settings. Rising temperature is associated with increased herbivory in multiple studies, a result with major predictive importance for current global warming. Diverse floras are usually associated with diverse insect damage; however, recovery from the end-Cretaceous extinction reveals uncorrelated plant and insect diversity as food webs rebuilt chaotically from a drastically simplified state. Calibration studies from living forests are needed to improve interpretation of the fossil data.     

Physical and chemical cues influencing the oviposition behaviour of Aphidius ervi

The oviposition behaviour of the aphid parasitoid Aphidius ervi Haliday is influenced by both chemical and physical cues. Oviposition attack responses were elicited by paint pigments sealed into the tip of a glass capillary tube. Parasitoids reacted to yellow pigments with repeated oviposition attack responses, but they did not react to green pigments. The spectrum of reflected light from the yellow pigments was very similar to that from the `green' natural host Acyrthosiphon pisum (Harris), with a high proportion of the total radiation energy being emitted in the yellow-orange wavebands (580–660 nm). Pea aphid cornicle secretion also elicited oviposition attack responses, which were not exclusively induced by its pale yellow-green colour. In fact, the oviposition attack response to capillary tips coated with cornicle secretion remained evident under red light conditions, which, in contrast, nearly completely suppressed the response to yellow pigments. Chemical compounds from cornicle secretion do not appear to be involved in parasitoid orientation, even though they stimulate intense oviposition attack responses. Olfactometer experiments showed that the putative kairomone involved acts only at very short range or on contact. Host exuviae, which also elicited strong and persistent oviposition reactions from A. ervi females, appear to be a good alternative source of ovipositional kairomone(s). This work confirms the existence of an aphid cuticular kairomone.     

Structural basis of RNA binding discrimination between bacteriophages Qbeta and MS2

Sequence-specific interactions between RNA stem-loops and coat protein (CP) subunits play vital roles in the life cycles of the RNA bacteriophages, e.g., by allowing translational repression of their replicase cistrons and tagging their own RNA genomes for encapsidation. The CPs of bacteriophages Qbeta and MS2 each discriminate in favor of their cognate translational operators, even in the presence of closely related operators from other phages in vivo. Discrete mutations within the MS2 CP have been shown to relax this discrimination in vitro. We have determined the structures of eight complexes between such mutants and both MS2 and Qbeta stem-loops with X-ray crystallography. In conjunction with previously determined in vivo repression data, the structures enable us to propose the molecular basis for the discrimination mechanism.     

Revealing pancrustacean relationships: Phylogenetic analysis of ribosomal protein genes places Collembola (springtails) in a monophyletic Hexapoda and reinforces the discrepancy between mitochondrial and nuclear DNA markers

Background  

In recent years, several new hypotheses on phylogenetic relations among arthropods have been proposed on the basis of DNA sequences. One of the challenged hypotheses is the monophyly of hexapods. This discussion originated from analyses based on mitochondrial DNA datasets that, due to an unusual positioning of Collembola, suggested that the hexapod body plan evolved at least twice. Here, we re-evaluate the position of Collembola using ribosomal protein gene sequences.     

Correlations of climate and plant ecology to leaf size and shape: potential proxies for the fossil record

The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.     

Novel Insect Leaf-Mining after the End-Cretaceous Extinction and the Demise of Cretaceous Leaf Miners,Great Plains,USA

Plant and associated insect-damage diversity in the western U.S.A. decreased significantly at the Cretaceous-Paleogene (K-Pg) boundary and remained low until the late Paleocene. However, the Mexican Hat locality (ca. 65 Ma) in southeastern Montana, with a typical, low-diversity flora, uniquely exhibits high damage diversity on nearly all its host plants, when compared to all known local and regional early Paleocene sites. The same plant species show minimal damage elsewhere during the early Paleocene. We asked whether the high insect damage diversity at Mexican Hat was more likely related to the survival of Cretaceous insects from refugia or to an influx of novel Paleocene taxa. We compared damage on 1073 leaf fossils from Mexican Hat to over 9000 terminal Cretaceous leaf fossils from the Hell Creek Formation of nearby southwestern North Dakota and to over 9000 Paleocene leaf fossils from the Fort Union Formation in North Dakota, Montana, and Wyoming. We described the entire insect-feeding ichnofauna at Mexican Hat and focused our analysis on leaf mines because they are typically host-specialized and preserve a number of diagnostic morphological characters. Nine mine damage types attributable to three of the four orders of leaf-mining insects are found at Mexican Hat, six of them so far unique to the site. We found no evidence linking any of the diverse Hell Creek mines with those found at Mexican Hat, nor for the survival of any Cretaceous leaf miners over the K-Pg boundary regionally, even on well-sampled, surviving plant families. Overall, our results strongly relate the high damage diversity on the depauperate Mexican Hat flora to an influx of novel insect herbivores during the early Paleocene, possibly caused by a transient warming event and range expansion, and indicate drastic extinction rather than survivorship of Cretaceous insect taxa from refugia.