Lars Monrad Hansen

Efficacy of mineral oil combined with insecticides for the control of aphid virus vectors to reduce potato virus Y infections in seed potatoes (Solanum tuberosum)

Abstract Aphids are major vectors of plant viruses. Potato virus Y (PVY) is the most important aphid-transmitted virus affecting potato crops in Denmark. Because of a changed seed potato growing strategy, the seed potato area in Denmark is changing from regions with a low average temperature to regions with a higher average temperature. This means that the aphids may infest the potato crops earlier and the population development of the aphids may be faster, and consequently PVY may more easily become epidemic in seed potato crops. With a view to reducing the spread of PVY a 3-year experiment was carried out with a combination of mineral oil and insecticides. In 2005 and 2007 when a very high number of aphids were present, nearly all plants were infected with PVY. In 2006 with a lower number of aphids a smaller proportion of the plants were infected, and a tendency to a lower PVY incidence in mineral-oil treated plots was found, but more than the 8% threshold value. Even in plots where systemic neonicotinoids were applied and very few aphids were recorded, no significant reduction in infestation level of PVY was found. The present experiment shows that mineral oil and insecticides applied to potato crops each week for a 6-week period as protection against aphid transmission of PVY did not significantly reduce the level of PVY infestations in potatoes.

Cold tolerance and freeze-induced glucose accumulation in three terrestrial slugs.

Cold tolerance and metabolic responses to freezing of three slug species common in Scandinavia (Arion ater, Arion rufus and Arion lusitanicus) are reported. Autumn collected slugs were cold acclimated in the laboratory and subjected to freezing conditions simulating likely winter temperatures in their habitat. Slugs spontaneously froze at about -4 °C when cooled under dry conditions, but freezing of body fluids was readily induced at -1 °C when in contact with external ice crystals. All three species survived freezing for 2 days at -1 °C, and some A. rufus and A. lusitanicus also survived freezing at -2 °C. (1)H NMR spectroscopy revealed that freezing of body fluids resulted in accumulation of lactate, succinate and glucose. Accumulation of lactate and succinate indicates that ATP production occurred via fermentative pathways, which is likely a result of oxygen depletion in frozen tissues. Glucose increased from about 6 to 22 μg/mg dry tissue upon freezing in A. rufus, but less so in A. ater and A. lusitanicus. Glucose may thus act as a cryoprotectant in these slugs, although the concentrations are not as high as reported for other freeze tolerant invertebrates.

Low temperature survival in different life stages of the Iberian slug, Arion lusitanicus☆

The slug Arion lusitanicus Mabille (Gastropoda: Pulmonata: Arionidae) is an invasive species which has spread to most parts of Europe. The area of origin is unknown, but A. lusitanicus seems to cope well with the local conditions in the countries to which it has migrated. It spreads rapidly, occurs often in high densities and has become a serious pest in most European countries. Therefore there is an urgent need for better knowledge of the ecophysiology of A. lusitanicus, such as the influence of climatic conditions, in order to develop prognostic models and strategies for novel pest management practises. The aim of our study was to investigate the influence of subzero temperatures in relation to winter survival. A. lusitanicus is shown to be freeze-tolerant in some life stages. Most juveniles and some adult slugs survived being frozen at -1.3°C for 3days, but none of the slugs survived freezing at -3°C. The eggs survived subzero temperatures (down to -2°C) probably by supercooling. Juveniles and adults may also survive in a supercooled state (down to -3°C) but are generally poor supercoolers. Therefore, the winter survival of A. lusitanicus depends to a high degree on migration to habitats protected from low winter temperatures, e.g. under plant litter, buried in the soil or in compost heaps.

Effect of Weather During Spring on the Time of Arrival of Bird Cherry-oat Aphid (Rhopalosiphum padi L.) in Spring Barley (Hordeum vulgare L.) Fields

Bird cherry-oat aphid is the principal pest of spring barley in Denmark. The time of arrival in the fields is an important element in deciding whether chemical control is needed. This paper describes a regression model managed by climate variables, which incorporate the biology of the bird cherry-oat aphid on its primary host, the bird cherry (Prunus padus L.). In the period 1987-1998, three to nine spring barley fields were monitored annually for the first occurrence of bird cherry-oat aphid. Different climatic variables were analysed in relation to the time of arrival, with a view to constructing a model. The analysis showed good correlation between the date of arrival into the fields after 1 May (D), day-degrees (DD) in February (TF), DD in March (TM), DD in April (TA), precipitation in April (PA) and precipitation in May until 15th (PM) according to the following model: D = 0.61TF - 0.17TM + 0.30TA - 0.46PA + 1.85PM (r 2=0.98, P<0.001, df=51). DD were calculated with a threshold temperature of 3°C. It...