Arne C. Nilssen

Diapause, embryo growth and supercooling capacity of Epirrita autumnata eggs from northern Fennoscandia

The supercooling point (SCP) of individual Epirrita autumnata eggs (approx. 60 eggs batch−1) was tested each month from September (eggs newly laid) to April under laboratory conditions simulating winter temperatures in the field (from + 4 to −30 °C). Parallel to each test, one batch of eggs was transferred from the acclimation treatment to room temperature (∼22 °C) and the incubation duration to the first 50% hatch was recorded, giving a measure of embryo growth at the time of the SCP test. Data also give information on egg mortality, which generally was low.

Primary attraction and host tree selection in deciduous and conifer living Coleoptera : Scolytidae, Curculionidae, Cerambycidae and Lymexylidae

Abstract: Primary attraction and host tree selection among bark and wood living Coleoptera were investigated in this research. The experiments were carried out in Dividalen, Troms County, and lasted from May to August, in 1993 and 1994. Beetles living in deciduous trees were the main objects of the present study. Trap type used excluded pheromones in the host tree selection. The traps were placed in areas dominated by Scots pine (Pinus sylvestis) and birch (Betula pubescens), and areas that contained both tree species. The traps were baited with billets of Betula pubescens, Alnus incana and Pinus sylvestris. Empty traps were used as controls. Beetle species found to have both primary attraction and host tree selection prior to landing were the conifer living Tomicus piniperda, Hylastes brunneus, Pityogenes quadridens, Pissodes pini, Hylobius abietis, Magdalis phlegmatica, and the deciduous living Magdalis carbonaria, Hylecoetes dermestoides and Rhagium mordax. Also, Scolytus ratzeburgi and Trypodendron signatum were able to distinguish between suitable and unsuitable host tress prior to landing. Ips acuminatus was found to have neither primary attraction nor host tree selection prior to landing, probably because pheromones were excluded in the attraction. According to the literature, the mechanism used in the host selection is mainly olfactory sensing and vision.

Primary attraction in host recognition of coniferous bark beetles and bark weevils (Col., Scolytidae and Curculionidae)

The hypothesis of primary attraction in Scolytidae and Curculionidae was tested in the field from late May throughout June 1979 and 1980 with 20 and 14 flight traps, respectively. The traps, designed especially to exclude the possibility of secondary attraction, were baited with billets of Scots pine (Pinus sylvestris) or Norway spruce (Picea abies), and empty controls. Tomicus piniperda, Hylastes brunneus, Hylastes cunicularius, Pityogenes bidentatus, Pityogenes chalcographus, Hylobius abietis and Pissodes pini were significantly more frequently caught in traps baited with pine or spruce than to empty controls, and the random flight hypothesis was rejected. The same species, except P. chalcographus, were also able to discriminate significantly between pine and spruce before landing. H. cunicularius was exclusively attracted to traps baited with Norway spruce, whereas the rest of the species preferred the traps baited with Scots pine. The mechanism used by the beetles in their host selection is olfactory sensing of chemical compounds. Host acceptance and nonhost rejecting starts before landing, implying the ability the perceive plant characteristics at a distance (primary attraction).

Do reindeer aggregate on snow patches to reduce harassment by parasitic flies or to thermoregulate

During warm, sunny days (Max. temp. 22 °C to 25 °C) C02-baited traps operated at sites on and off snow patches (SPs) in subarctic Norway caught significantly fewer culicids, simuliids and tabanids on snow in both 1985 and 1987. However, for overnight catches (18.30 - 07.30 h) there was no significant difference in the number of culicids caught on versus off SPs. Analysis of videotapes taken in 1987 showed that defensive anti-fly behaviors of reindeer on and off SPs remained low ( 150 animals often occupied the entire surface of a snow patch. At the fly densities and climatic conditions encountered it seemed apparent that reindeer intermittently used SPs primarily to thermoregulate following periods of foraging. Almost all reindeer remained on SPs from 11.00 to 12.30 h, but at other times between 08.00 and 19 00 h about half the herd (ca. 800 animals) foraged for about an hour while the other half aggregated on SPs. However, by 20.00 h, during the cooler period when trap catches of mosquitoes were increasing, almost all reindeer had moved off SPs. The small decreases in anti-fly defensive behaviors observed for reindeer on SPs versus animals foraging in snow-free areas indicated that their presence on SPs may have resulted in a minor, coincidental reduction in harassment. Significantly more tabanids were caught during the morning trapping period than at other times, and significantly more mosquitoes were caught during the evening/overnight trapping period than at other times.

Dimethyl trisulphide is a strong attractant for some calliphorids and a muscid but not for the reindeer oestrids Hypoderma tarandi and Cephenemyia trompe

A field test with synthetic dimethyl trisulphide as attractant in flight traps was carried out in Finnmark, northern Norway, in July 1992 and 1994. The reindeer oestrids Hypoderma (= Oedemagena) tarandi (L.) and Cephenemyia trompe (Modeer) (Diptera: Oestridae), previously shown to react positively to dimethyl trisulphide on the olfactory receptor level, were only caught in small numbers, with no significant differences between baited and unbaited traps. In both years, however, the baited traps caught significantly more individuals of Calliphoridae and Hydrotaea anxia (Zetterstedt) (Diptera: Muscidae) than unbaited control traps. In 1992, Protophormia terraenovae (Robineau‐Desvoidy) (Diptera: Calliphoridae) and H. anxia were the predominant species (78.5% and 20.5%, respectively). In 1994, H. anxia was the most prevalent species (73.6%). Seven species of Calliphoridae were caught, with P. terraenovae, Calliphora vomitoria (L.), C. uralensis (Villeneuve) and C. loewi (Enderlain) as the most numerous ones. Dimethyl trisulphide is probably a decomposition product from bacterial activity and may be one of the major cues for calliphorid host finding. The significance of the reaction for oestrids on the receptor level, but evidently not on a behavioural level, remains unclear.

Geometrid outbreak waves travel across Europe

We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year(-1) and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

Late autumn eclosion in the winter moth Operophtera brumata : compromise of selective forces in life-cycle timing

Abstract.1. In eclosion experiments at constant temperatures (6, 9, 12, 15, 18, 21, and 25 °C), Operophtera brumata (L.) pupae were found to respond nonlinearly to temperature, with 9 °C giving the highest developmental rate.

Trapping oestrid parasites of reindeer: the response of Cephenemyia trompeand Hypoderma tarandi tobaited traps

Abstract. At 340–360 km North of the Arctic Circle in Norway, Hypoderma tarandi(L.) and Cephenemyia trompe(Modeer) females were caught in baited traps from 10 July to 21 August. During three summers, adverse climatic conditions inhibited flight activity of these oestrids on 56–68% of the days. Flies were not caught prior to or after these dates, nor at winds above 8 m/s, temperatures below 10d̀C, light intensities below 20,000 lux, or during periods of rain or snow. C02‐baited insect flight traps caught significantly more H. tarandifemales than non‐baited traps. However, neither a white reindeer hide or reindeer interdigital pheromone glands enhanced the attraction of C02to H. tarandior C. trompe. Hypoderma tarandifemales also were attracted to mobile people, but not to stationary individuals. There were no significant differences in the numbers of C.trompeor H.tarandicaught in C02‐baited traps in a birch/willow woods, on the treeless vidda (=tundra‐like biome), or at woodsrvidda ecotone sites. Flies were caught in traps on days when the nearest reindeer herds were 25–100 km away. Significantly more H.tarandiand C.trompewere caught from 09.30 to 14.30 hours than from 14.30 to 19.30 hours; no flies were caught from 20.00 to 07.00 hours (Norwegian Standard Time = NST). Because COz‐baited traps caught from hundreds to thousands of mosquitoes, blackflies and Culicoidesmidges, when climatic conditions inhibited oestrid activity, reindeer aggregations and movements attributed to insect attacks during warm sunny days may be largely in response to attacks by H.tarandiand C.trompe.

Ophthalmomyiasis caused by the reindeer warble fly larva.

Two boys with ophthalmomyiasis caused by the first instar larva of the reindeer warble fly Hypoderma tarandi are reported. Both were 9 years old and came from the coast of northern Norway. One had ophthalmomyiasis interna posterior and one eye had been removed because of progressive pain and blindness. Histological examination showed the remains of a fly larva. The second boy had ophthalmomyiasis externa with a tumour in the upper eyelid, and histological examination showed a warble with a well preserved larva. Identification of the parasite in the histological material was based on the finding of cuticular spines and parts of the cephalopharyngeal skeleton identical with those of the first instar larva of H tarandi.

Mating behavior and thermoregulation of the reindeer warble fly,Hypoderma tarandi L. (Diptera: Oestridae)

Hypoderma (=Oedemagena) tarandi L. (Diptera: Oestridae) is characterized by a mating strategy in which both sexes meet and mate at two types of distinct topographical landmarks. In the expansive, treeless vidda (= tundra-like) biome, mating places are unique, rocky areas located along rivers and streams or in rocky areas of drying river and stream beds. In wooded valleys below the vidda, flies mated at certain topographical areas along dirt road tracks/paths. Thermoregulatory activities of males occupying perches at mating places included selection of substratum at perch site, orientation of body to suns rays, crouching, stilting, and flights into upper cooler air. On warm sunny days males perched for just 1–2 min before flying up into cooler air to promote cooling. Laboratory and field studies revealed that flies could not metabolically cool down when held at 25–38°C. Time spent at mating places depended on temperature, duration of sunshine, and wind velocity. Males were very aggressive in pursuing allHypoderma-sized objects that passed by them or that landed near them, but they did not defend specific perch sites. Males either pursued and caught females in flight, or they hopped onto females that landed near them. During 5 years, 74 males and 14 females were seen at mating places. Dissection of six females caught at mating places revealed them to be recently eclosed flies full of fat body and with all eggs intact; two not paired with males were non-inseminated. Three experimentally paired females remainedin copulo for 10, 13, and 19.5 min.