Jan Pettersson

Resource Curse or not : A Question of Appropriability

This paper shows that whether natural resources are good or bad for a country’s development crucially depends on the interaction between institutional setting and the type of resources possessed by the country. Some natural resources are, for economical and technical reasons, more likely to cause problems such as rent-seeking and conflicts than others. This potential problem can, however, be countered by good institutional quality. In contrast to the traditional resource curse hypothesis, we show the impact of natural resources on economic growth to be non-monotonic in institutional quality. Countries rich in minerals are cursed only if they have low quality institutions, while the curse is reversed if institutions are sufficiently good.

Normal-phase high-performance liquid chromatography of tocopherols and tocotrienols Comparison of different chromatographic columns

Natural vitamin E is composed of eight different vitamers (alpha-, beta-, gamma- and delta-tocopherols and alpha-, beta-, gamma- and delta-tocotrienols). As these eight vitamers have different antioxidant and biological activities, it is necessary to have quantitative data on each substance separately. The aim of this study was to find universal HPLC columns for the separation of all eight components and to test if a few columns of the same material (different batches) will give reproducible results. Normal-phase HPLC separations of vitamin E compounds in a prepared mixture (containing oat extracts, palm oil and tocopherol standards) were tried on six silica, three amino and one diol columns. As shown by calculations of retention factors (k), separation factors (alpha), numbers of theoretical plates (N) and resolutions (Rs), the best separations were obtained on three silica columns and two amino columns using 4 or 5% dioxane in hexane as the mobile phase as well as on a diol column using 4% tert.-butyl methyl ether in hexane as the mobile phase.

Winter host component reduces colonization by bird-cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera, Aphididae), and other aphids in cereal fields.

Methyl salicylate, a volatile component ofPrunus padus, the winter host ofRhopalosiphum padi, was found to reduce colonization of the summer host by this aphid. The compound was identified by gas chromatographic analysis coupled with recordings from cells in the primary rhinarium on the sixth antennal segment of the aphid. Methyl salicylate eliminated the attractancy of oat leaves to spring migrants in olfactometer tests. In Sweden, this compound significantly decreased colonization of field grown cereals byR. padi and in the U.K., populations ofSitobion avenae andMetopolophium dirhodum were significantly lower on treated plots.

Response of the Seven-spot Ladybird to an Aphid Alarm Pheromone and an Alarm Pheromone Inhibitor is Mediated by Paired Olfactory Cells

Electrophysiological responses of adult seven-spot ladybirds, Coccinella septempunctata, to (E)-β-farnesene, an aphid alarm pheromone, and (−)-β-caryophyllene, a plant-derived alarm pheromone inhibitor, were investigated by recording from single olfactory cells (neurons) on the antenna. Cells having high specificity for each of the two compounds were identified. Furthermore, these two cell types were frequently found in close proximity, with a larger amplitude consistently recorded for the cell responding specifically to (E)-β-farnesene. Preliminary behavioral studies in a two-way olfactometer showed that walking adults were significantly attracted to (E)-β-farnesene; this activity was inhibited with increasing proportions of (−)-β-caryophyllene. The possible ecological significance of colocation or pairing of olfactory cells for semiochemicals with different behavioral roles is discussed.

Semiochemicals mediating spacing behavior of bird cherry-oat aphid, Rhopalosiphum padi feeding on cereals.

Olfactometry using an apterous individual of Rhopalosiphum padi (L.) showed an arresting effect by volatiles from a wheat seedling and a repellent effect by volatiles from a wheat seedling infested with aphids at a high population density (ca. 9 aphids/cm2). Four compounds, 6-methyl-5-hepten-2-one, (−)- and (+)-6-methyl-5-hepten-2-ol, and 2-tridecanone, were identified by GC-MS in air entrainments from the wheat seedlings with high aphid density but not from the wheat seedlings alone. The mixture of the four compounds in the natural proportion counteracted the attractivity of the volatiles from the intact uninfested wheat seedling. The likely role of these compounds in the spacing behavior of this aphid species, when present in high densities on wheat, is discussed.

Ladybird beetle odour identified and found to be responsible for attraction between adults

Abstract. The distinctive odour of the seven-spot ladybird beetle, Coccinella septempunctata, had not previously been identified unequivocally, although it was considered likely to arise from olfactorily potent pyrazines. The component responsible was located by human organoleptic evaluation of the gas chromatography effluent from ladybird volatiles and was fully characterized as 2-isopropyl-3-methoxypyrazine. Although insects may not be expected to have similar olfactory sensitivities to human beings, this compound was found to fulfil a pheromonal role in the attraction between adult C. septempunctata, typical of many ladybird species. Thus, in a behavioural assay, both males and females were attracted by amounts of this pyrazine equivalent to the ladybird volatiles.

Sex attractant pheromone of damson-hop aphid Phorodon humuli (Homoptera, aphididae)

Behavioral studies using an olfactometer demonstrated that sexual females (oviparae) of the damson-hop aphid,Phorodon humuli, release a pheromone to which males respond. Volatiles produced by the oviparae were analyzed by coupled gas chromatography-single cell recording from the secondary rhinaria on the male antenna and showed the presence of one peak with major activity. Coupled gas chrornatography-mass spectrometry suggested a nepetalactol, which was shown to have the 4aR, 7S, 7aS stereochemistry by synthesis from the corresponding nepetalactone isolated from the labiate plantNepeta mussinii. Although the stereochemistry at carbon-1 is not yet established, a synthetic sample comprising ca. 70% 1S and 30% 1R attracted highly significant numbers of males to water traps placed within and adjacent to a hop garden. Initial studies also indicated attraction of males in both the olfactometer and in the field by volatiles from the primary host.

Why do migrating robins, Erithacus rubecula, captured at two nearby stop-over sites orient differently?

Abstract The orientation of robins captured during autumn and spring migration at two different sites, Falsterbo and Ottenby, in southern Sweden was investigated by cage experiments during the twilight period after sunset. The robins were tested under clear skies with skylight from sunset visible, and under simulated total overcast. The robins from the two sites differed in orientation, especially during autumn migration. While robins from Ottenby generally oriented in their expected migratory direction, the birds from Falsterbo under clear skies oriented towards the sunset direction with a narrow scatter in individual mean headings. Under simulated total overcast the robins from Falsterbo perferred northerly directions in autumn. Short-distance recoveries, one or only a few days after ringing, show that robins in autumn regularly fly 20–80 km from Falsterbo on northerly courses, indicating that they have temporarily reoriented from their normal migratory direction when confronted with the Baltic Sea. In contrast, most robins arrive at Ottenby by extensive flights across the Baltic Sea, and rapidly continue their sea crossing in the normal migratory directions. Mean fat deposits in autumn robins were significantly larger at Ottenby than at Falsterbo. These results indicate that migrating birds may show markedly different orientational dispositions depending on body condition and on their situation with respect to preceding and impending migration over land and sea, respectively.

Mixing barley cultivars affects aphid host plant acceptance in field experiments

Four barley varieties with no significant difference in aphid acceptance were sown in pure stands and in pairwise combinations with varieties side by side in separate rows. Settling tests were done in situ in the field plots with apterae of Rhopalosiphum padi (L.) (Homoptera:Aphididae) and showed that aphid acceptance was changed in some combinations of cultivars. In a laboratory test, in which plants of one cultivar were exposed to air from the other cultivars, aphid acceptance was significantly reduced in three of the four cultivars when treated with air from certain other cultivars. Two of these three cultivars showed the same reduction under field conditions. This supports the hypothesis that plant/plant communication may release responses in neighbouring plants that change aphid host plant acceptance. The results also show that this mechanism is not restricted to optimal growing conditions in the laboratory, although it may be modified under field conditions depending on plant genotype.

Effects of two types of semiochemical on population development of the bird cherry oat aphid Rhopalosiphum padi in a barley crop

1 Field experiments were performed in barley using volatile semiochemicals affecting population density (density‐related substances – DRS) and spring migration (methyl salicylate) in bird cherry oat aphid Rhopalosiphum padi (L.). Natural infestations of aphids were used, and semiochemical dosages were chosen to be biologically relevant based on previous studies. A simple formulation method for active substances using wax pellets was developed.