Abundance and emergence of spruce cone insects in different parts of Switzerland.
In 1989 a total of 4471 cones from Picea abies was harvested at 29 locations distributed over the 5 main geographic regions of Switzerland, i.e. Jura, Central Plateau, North, Central and South Alps. The cones were incubated in a controlled environment chamber and the emerging insects were collected and identified. This analysis excluded parasitoids except for the most abundant Torymus spp. Twelve insect species and some 14 000 individuals in total were identified. On the average, every cone was inhabited by 3 insects. The most numerous species were Kaltenbachiola strobi, Cydia strobilella and Torymus spp., amounting together to 95% of the total insect number. Though the abundance of peaks varied for different species, most insects were reared from cones from the alpine area. Vegetation type (alliance) was related to the abundance of several species but did not correlate with total infestation rate. For 2 species their number was related to sampling site altitude. Likewise, a positive, linear correlation was found between the frequencies of the parasitoid Torymus spp. and its host K. strobi, the ratio between the 2 species averaging 0.7. Cone setting did not correlate with infestation level, but tree age was positively related to total insect number/cone. In the laboratory C. strobilella and K. strobi were the earliest species to emerge; they had the shortest emergence period as well. The percentage of K. strobi with prolonged diapause (emergence in 2nd year after cone sampling) was 51%, while the corresponding values for all the other species were lower than 20%. Neither sampling site elevation nor cone setting affected diapause length.