Petter Öhrn

Fungi Vectored by the Bark Beetle Ips typographus Following Hibernation Under the Bark of Standing Trees and in the Forest Litter

The bark beetle Ips typographus has different hibernation environments, under the bark of standing trees or in the forest litter, which is likely to affect the beetle-associated fungal flora. We isolated fungi from beetles, standing I. typographus-attacked trees, and forest litter below the attacked trees. Fungal identification was done using cultural and molecular methods. The results of the two methods in detecting fungal species were compared. Fungal communities associated with I. typographus differed considerably depending on the hibernation environment. In addition to seven taxa of known ophiostomoid I. typographus-associated fungi, we detected 18 ascomycetes and anamorphic fungi, five wood-decaying basidomycetes, 11 yeasts, and four zygomycetes. Of those, 14 fungal taxa were detected exclusively from beetles that hibernated under bark, and six taxa were detected exclusively from beetles hibernating in forest litter. The spruce pathogen, Ceratocystis polonica, was detected occasionally in bark, while another spruce pathogen, Grosmannia europhioides, was detected more often from beetles hibernating under the bark as compared to litter. The identification method had a significant impact on which taxa were detected. Rapidly growing fungal taxa, e.g. Penicillium, Trichoderma, and Ophiostoma, dominated pure culture isolations; while yeasts dominated the communities detected using molecular methods. The study also demonstrated low frequencies of tree pathogenic fungi carried by I. typographus during its outbreaks and that the beetle does not require them to successfully attack and kill trees.

Seasonal flight patterns of Ips typographus in southern Sweden and thermal sums required for emergence

The spruce bark beetle Ips typographus is the major tree‐killing bark beetle in Eurasia. To increase knowledge about its seasonal flight patterns and about the thermal sums required for emergence, a study was conducted in southern Sweden from 2006 to 2010. Seasonal flight patterns were recorded by pheromone traps and development was recorded by felling trees three times during each season. Flight began, on average, on 27 April [after 47 degree‐days (dd) > 5 °C]. More than 50% of flight activity occurred after mid‐June, and this continued to mid‐August. Re‐emergence of parental beetles after they had produced the first brood started, on average, on 24 May (after 122 dd). Continued flight and oviposition demonstrated that sister broods were frequent. A higher proportion of parental beetles re‐emerged from trees colonized in May (95%) than in July (20%). Beetles that colonized trees late had to accumulate a higher thermal sum before re‐emerging (400 dd). Filial beetles began to emerge, on average, on 29 June (after 437 dd) and started to fly in early July, giving rise to at least a partial second generation in each year. A higher proportion of filial beetles had emerged from trees colonized in May (75%) than in July (15%). Knowledge of these region‐specific flight patterns and the associated thermal sums required for emergence will facilitate efficient pest management by enabling timely removal of fallen and standing weakened host trees. The obtained data will also be useful for improving models that predict the population dynamics in a warmer climate.

Two non-destructive techniques for determining the sex of live adult Hylobius warreni

Two non-destructive sexing techniques suitable for use in the field and laboratory are described, and tested with the Warren root collar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae). On the second visible abdominal sternite of males is a longitudinal depression that is absent on females. In addition, setae on the last visible abdominal sternite of females are arranged longitudinally; setae on males are arranged radially. For the first character, accuracy was 90% and sex could be determined without the aid of magnification. The latter character was slightly more reliable, at 95% accuracy, but required at least 12× magnification.

Occurrence, performance and shoot damage of Tomicus piniperda in pine stands in southern Sweden after storm-felling

The pine shoot beetle, Tomicus piniperda (L.), is considered one of the most destructive pests of Scots pine, Pinus sylvestris (L.), in Europe. At high population densities, its feeding in the shoots of living pine trees may lead to substantial shoot and subsequent growth losses. After a storm‐felling in southern Sweden in January 2005, there were high amounts of breeding material and a subsequent risk for bark beetle outbreaks. To study the beetles reproductive success, population levels and risks for growth losses, we analysed bark samples of colonized trees, and counted fallen pine shoots. During the first season after the storm‐felling, the pine shoot beetle population level was low. However, due to high reproductive success beetle numbers markedly increased in the second season, and there were high rates of successful colonization of available host material in following years. Shoot damage levels concomitantly rose in 2005–2006, then declined in 2007 and 2008. However, the accumulated shoot losses do not indicate any subsequent growth losses, as the recorded shoot damage levels were below those earlier seen in connection with growth reductions in damaged pine stands.