Investigations of host preferences in haematophagous insects, including Culicoides biting midges (Diptera: Ceratopogonidae), are critical in order to assess transmission routes of vector-borne diseases. In this study, we collected and morphologically identified 164 blood-engorged Culicoides females caught in both light traps and permanent 12-m high suction traps during 2008-2010 in Sweden. Molecular analysis of the mitochondrial cytochrome c oxidase subunit I (COI) gene in the biting midges was performed to verify species classification, discern phylogenetic relationships and uncover possible cryptic species. Bloodmeal analysis using universal vertebrate cytochrome b primers revealed a clear distinction in host selection between mammalophilic and ornithophilic Culicoides species. Host sequences found matches in horse (n = 59), sheep (n = 39), cattle (n = 26), Eurasian elk (n = 1) and 10 different bird species (n = 18). We identified 15 Culicoides species previously recorded in Scandinavia and four additional species haplotypes that were distinctly different from the described species. All ornithophilic individuals (n = 23) were caught exclusively in the suction traps, as were, interestingly, almost all mammalophilic species (n = 41), indicating that many biting midge species may be able to cover long distances after completing a bloodmeal. These results add new information on the composition of Culicoides species and their host preferences and their potential long-distance dispersal while blood-engorged.

No abstract

The use of logistic regression is proposed as a method of verifying and calibrating disease risk algorithms. The logistic regression model calculates the log of the odds of a binary outcome as a function of a linear combination of predictors. The resulting model assumes a multiplicative (relative) relationship between the different risk factors. Computer programs for performing logistic regression produce both estimates and standard errors, thus permitting the evaluation of the importance of different predictive variables. The use of receiver operating characteristic (ROC) curves is also proposed as a means of comparing different algorithms. An example is presented using data on Sclerotinia stem rot in oil seed rape, caused by Sclerotinia sclerotiorum.

No abstract

Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing's fixed effect model analysis. An open field experiment was conducted in 2004/ 2005 to investigate heterosis for fourteen traits in 66 F 1 hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (H b 2 ) for fruit traits were more than 60% and with wide gap from narrow sense heritability (h n 2 ) for most of the important traits like number of fruit per plant (H b 2 = 88.3% and h n 2 = 46.0%), days to maturity (H b 2 = 87.2% and h n 2 = 23.1%) and dry fruit yield per plant (H b 2 = 72.6% and h n 2 = 14.6%). Maximum heterosis over mid-parent and betterparent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (-29.8, -31.5 and -23.6%).

No abstract

Wheat dwarf virus (WDV) causes disease in wheat ( Triticum aestivum ) and barley ( Hordeum vulgare ) in many parts of Europe. The host range also includes many species of the family Poaceae. WDV is only transmitted by the leafhopper Psammotettix alienus . During a five-year period (2001)(2002)(2003)(2004)(2005), grass samples were collected in central Sweden in the vicinity of fields with WDV-infected winter wheat. Screening with ELISA and PCR identified WDV in a low number of samples (8/1098) from only three grass species: Apera spica-venti , Avena fatua and Poa pratensis . In addition, triticale was found to be positive. Fourteen WDV isolates from Avena fatua , Apera spica-venti , Triticum aestivum , Lolium multiflorum , Poa pratensis , triticale and the insect vector Psammotettix alienus , were partially sequenced ( ca. 1200 nucleotides), providing the first published WDV sequences from the insect vector. All isolates belonged to the wheat strain of WDV and the genetic diversity was low. Phylogenetic analyses showed no clear grouping according to geographical location or host species. The results suggest that the same WDV genotypes are infecting both wheat and grasses in Sweden. Interestingly, one group of isolates (subtype B) formed a distinct clade in the phylogenetic tree. Subtype B was always found in mixed infection with the main genotype. Complete sequencing of a subtype B isolate showed that it was 98·6% identical to a typical wheat isolate from the same plant.

The sequence variability of Barley yellow dwarf virus-PAV (PAV) and Barley yellow dwarf virus-MAV (MAV) was studied by comparing 502 nucleotides from the coat protein-encoding region of six isolates from Latvia and four from Sweden. The diversity within MAV was low (>97% sequence identity), also when compared to isolates from USA and China. In contrast, the variability among PAV isolates was greater and phylogenetic analysis including isolates of a wide geographic origin detected two major clusters, of which both contained isolates from Latvia and Sweden. A new distinct variant of BYDV-PAV was discovered in Latvia, and because of the sequence difference it is proposed to belong to a new species (BYDV-OYV).