Homogeneous Linewidths in the Optical Spectrum of a Single Gallium Arsenide Quantum Dot

The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution. The energies and linewidths of the homogeneous spectrum provide a new perspective on the dephasing dynamics of the exciton in a quantum-confined, solid-state system. The origins of the linewidths are discussed in terms of the dynamics of the exciton in zero dimensions, in particular, in terms of lifetime broadening through the emission or absorption of phonons and photons.     

Laboratory evaluation of two novel strategies to control first-instar gypsy moth larvae with spinosad applied to tree trunks

Two strategies for controlling first-instar larvae of gypsy moth (Lymantria dispar (L)), insecticidal bait and contact insecticide applied directly to the tree trunk, were evaluated in the laboratory. Spinosad was selected as a candidate natural-product insecticide that is active both by contact and ingestion. Incorporated into artificial diet-based bait, spinosad was toxic to neonate larvae with a minimal 10-s feeding period, with an LC50 value of 20 (15-26, 95% confidence interval) mg liter-1. It was significant that neonate larvae did not discriminate between spinosad-treated and control diet. Efficacy of diet-based bait in the laboratory, however, was significantly impacted by previous exposure to diet; fed larvae did not stop at the bait and did not incur mortality, as compared to unfed larvae. Oak bark was a suitable substrate from which neonate larvae could contact spinosad residues. Spinosad applied directly to oak bark resulted in significant mortality after 1- and 4-min crawling contact exposure times (LC50 = 24 [20-29, 95% CI] and 8.7 [6.9-11, 95% CI] mg liter-1, respectively) and contact activity persisted for 2 weeks. While contact activity was more potent on glass surfaces than on oak bark, the LC50 values differed only by factors of 2.4 and 3.6, for 1- and 4-min exposures respectively.     

The impacts of season and livestock management strategy on the quality of diets selected by goats and sheep in the semi-arid rangelands of Namaqualand,South Africa

Access to good-quality forages is one of the major limitations to livestock production in semi-arid pastoral systems. This study aimed to determine whether there are differences in the nutritional quality of diets selected by herded and free-ranging goat and sheep flocks utilising Namaqualand Granite Renosterveld vegetation during the wet and dry seasons. Plant samples collected along the grazing routes of livestock were dried and analysed for their fibre, condensed tannin, total phenolic and mineral nutrient contents. The study showed that a large variety of forages were on offer and livestock groups selected different diets of which some were different to the total diet on offer. In general, significant deficiencies in phosphate, protein and energy in the diets selected by herded and free-ranging goats and sheep were observed in both wet and dry season. The quality of the diets selected by herded and free-ranging livestock was also found to be different from each other, with herded livestock generally selecting more nutrient-dense diets. Herding, therefore, allows livestock to access better-quality forage in the Namaqualand Granite Renosterveld rangeland, where it is generally poor.     

Detection and quantification of airborne inoculum of Hymenoscyphus pseudoalbidus using real‐time PCR assays

A method based on real‐time polymerase chain reaction (PCR) and the use of rotating‐arm spore traps was developed for quantifying airborne Hymenoscyphus pseudoalbidus ascospores. The method was sensitive and reproducible, and the collection efficiency was 10% of the spores present in the air. The temporal ascospore dispersal pattern was studied over 3 years by collecting spores every 15 days for a 24 h air‐sampling period during the ash‐growing season. The highest production was detected from the end of June to the beginning of September. The overall ascospore production did not differ significantly among stands within a specific year but there were differences from year to year. There was a positive correlation between air temperature and the number of ascospores trapped, with most of the positive samples being observed at temperatures above 12°C. The vertical profile of ascospore dispersal showed a strong decrease in ascospore density within a height of 3 m, regardless of date of collection. An analysis of the spore traps installed at increasing distances from an infected stand showed that most of the ascospores were deposited downwind within 50 m of the stand. These data are discussed in context of the epidemiology of the disease.     

Brassica campestris L.: Floral Induction by One Long Day

A strain of Brassica campestris L. responds to a single photoinductive cycle 4 days after sowing. Extending the photoperiod from 8 to 22 or 24 hours, with incandescent light of 538-lux intensity, induced inflorescence in 90 percent of the plants. Inflorescence development was visible on dissection 5 or 6 days after photoinduction. Floral induction increased with duration and intensity of the supplementary light.