Application of a reverse dot blot DNA–DNA hydridization method to quantify host‐feeding tendencies of two sibling species in the Anopheles gambiae complex

A DNA–DNA hybridization method, reverse dot blot analysis (RDBA), was used to identify Anopheles gambiae s.s. and Anopheles arabiensis (Diptera: Culicidae) hosts. Of 299 blood‐fed and semi‐gravid An. gambiae s.l. collected from Kisian, Kenya, 244 individuals were identifiable to species; of these, 69.5% were An. arabiensis and 29.5% were An. gambiae s.s. Host identifications with RDBA were comparable with those of conventional polymerase chain reaction (PCR) followed by direct sequencing of amplicons of the vertebrate mitochondrial cytochrome b gene. Of the 174 amplicon‐producing samples used to compare these two methods, 147 were identifiable by direct sequencing and 139 of these were identifiable by RDBA. Anopheles arabiensis bloodmeals were mostly (94.6%) bovine in origin, whereas An. gambiae s.s. fed upon humans more than 91.8% of the time. Tests by RDBA detected that two of 112 An. arabiensis contained blood from more than one host species, whereas PCR and direct sequencing did not. Recent use of insecticide‐treated bednets in Kisian is likely to have caused the shift in the dominant vector species from An. gambiae s.s. to An. arabiensis. Reverse dot blot analysis provides an opportunity to study changes in host‐feeding by members of the An. gambiae complex in response to the broadening distribution of vector control measures targeting host‐selection behaviours.     

Effects of Concentration and Time of Exposure on the Phytotoxicity of Linuron

When seedlings of lettuce and turnip were grown in nutrientsolutions containing different concentrations of linuron, theconcentration in the shoot at the time when toxicity symptomsappeared was related to the solution concentration. With lettuce,for example, symptoms were recorded after 7 d at 0.15 µg/mland the shoot concentration was 2.7 µg/g fresh wt. At0.06 µg/ml, symptoms appeared after 10 d and the shootconcentration was then 1.1 µg/g fresh wt. If grown fordifferent periods in solutions containing linuron and then transferredto fresh nutrient solutions containing no herbicide, turnipor lettuce seedlings which had accumulated 0.7–0.8 µglinuron/g fresh wt developed toxicity symptoms 4 to 6 d later.Seedlings were also treated with linuron after they had grownfor different periods in control nutrient solutions. The shootconcentrations attained before toxicity symptoms appeared werehigher in those seedlings which were larger when herbicide treatmentbegan. These results show that the herbicide concentration insolution, time of exposure, and age of seedling are interrelatedin determining linuron phytotoxicity.     

A note on Yersinia enterocolitica in a swine farm watershed

Swine faeces from three pig farms in the La Crosse River watershed near La Crosse, Wisconsin, were sampled for Yersinia enterocolitica ; 19 presumptive isolates were recovered and biochemically confirmed as Y. enterocolitica. Simultaneously, during a 2mD2 cm rainfall, the confluences of runoff water flowing from the swine holding pens and of nearby streams also were sampled; a single isolate was obtained from one holding pen runoff-stream confluence. Biochemical analysis showed that the water isolate was a biotype identical with that of a swine isolate from the adjacent farm. These results demonstrate one possible mechanism for the introduction of Y. enterocolitica into water supplies; faecal material from swine, a suspected natural reservoir of the bacterium, is transported via runoff water to streams.