The response of sensitive and tolerant clones of Populus tremuloides to dynamic ozone exposure under controlled environmental conditions

Both sensitive and tolerant clones of aspen ( Populus tremuloides ) were exposed to ozone using four different exposure regimes under controlled environmental conditions. Based on data on ambient ozone from 10 cities in the USA, three treatments of 4-wk exposure to the same SUM06 (an accumulation of hourly O₃ concentrations greater than 0.06 ml l⁻¹) were constructed. The regimes allowed us to investigate: (a) the importance of long (3 wk, treatment 1) versus short (1 wk, treatment 2) duration of regimes with high peaks; (b) the effect of treatments with variable peak occurrence (treatments 1 and 2) versus uniform peak occurrence (treatment 3) during the exposure period. Nonfumigated control plants were maintained at ozone concentrations <10 nl l⁻¹. Bifacial black necrosis, a typical symptom of ozone injury on aspen leaves, occurred on both clones after 2 wk exposure. Up to 60% of the leaves on the sensitive clone were injured, with an average of 6% of total leaf area injured. In the tolerant clone only 10% of the leaves were injured, with less than 1% of the total leaf area symptomatic. The severity of injury was consistently greatest in treatment 2, followed by treatments 1 and 3, respectively. The interval between peak exposures was less important than the occurrence of peaks versus a stable maximum concentration. Premature leaf abscission occurred in the sensitive clone. Measures of gas exchange demonstrated reduced photosynthesis under ozone fumigation, but exposure regime was not a significant factor. Concentrations of two antioxidants, ascorbic acid and glutathione, were almost always greater in the resistant than in the sensitive clone, but the differences were not statistically significant. The levels of these antioxidants in aspen leaves did not change with ozone fumigation or leaf age.     

Novel high‐throughput screens of Anopheles gambiae odorant receptors reveal candidate behaviour‐modifying chemicals for mosquitoes

Despite many decades of multilateral global efforts, a significant portion of the world population continues to be plagued with one or more mosquito‐vectored diseases. These include malaria and filariasis, as well as numerous arboviral‐associated illnesses, such as dengue and yellow fevers. The dynamics of disease transmission by mosquitoes is complex, and involves both vector competence and vectorial capacity. One area of intensive effort is the study of chemosensory‐driven behaviours in the malaria vector mosquito Anopheles gambiae Giles, the modulation of which is likely to provide opportunities for disease reduction. In this context, recent studies characterize a large divergent family of An. gambiae odorant receptors (AgORs) that play critical roles in olfactory signal transduction. This work facilitates high‐throughput, cell‐based calcium mobilization screens of AgOR‐expressing human embryonic kidney cells identifying a large number of conventional AgOR ligands, as well as the first nonconventional Orco (olfactory receptor co‐receptor) family agonist. As such, ligand‐mediated modulation serves as a proof‐of‐concept demonstration that AgORs represent viable targets for high‐throughput screening and for the eventual development of behaviour‐modifying olfactory compounds. Such attractants or repellents could foster malaria reduction programmes.     

A comparison of queen oviposition rates from monogyne and polygyne fire ant, Solenopsis invicta, colonies

Abstract. The oviposition rate of individual queens of Solenopsis invicta Buren (Hymenoptera: Formicidae) in relation to their weight and number of queens present in the colony was investigated by direct 2 h observations. There is a strong positive correlation between the weight of a queen and its oviposition rate in both monogyne and polygyne colonies. However, the number of eggs laid per mg queen is higher for moonogyne queens than for polygyne queens. This difference is more evident when the total weight of queens present in a colony is considered. The individual queen oviposition rate is negatively correlated with the number of queens in the colony. In addition, the weight loss per egg laid is significantly greater for polygyne than for monogyne queens, probably due to differences in egg size. These data suggest that oviposition is more efficient in monogyne than in polygyne queens at the individual level; however, at the colony level, polygyne colonies produce significantly more eggs. Comparison of colony level efficiency predicts that polygyne colonies must have at least nine queens to compete reproductively with a mature monogyne queen. Therefore, oligogyny does not appear to be a viable strategy for S.invicata.     

Phylogenetic relationships within the genus Desmothrips (Thysanoptera,Aeolothripidae), an Australian genus of facultative flower‐living predators

A phylogenetic analysis of the Australian Aeolothripidae genus Desmothrips Hood is presented. A data matrix with 27 species is analysed under parsimony criteria. The monophyly of Desmothrips is recovered. Continuous and discrete characters were analysed separately and in combination, and continuous characters were rescaled and analysed under equal weights. Three new species from the northwestern and one from the southeastern areas of Australia are described and illustrated. A key to the 18 species of Desmothrips is provided.