Effects of seasonal changes in host tree quality on gonad maturation and breeding activity of the spruce bark beetle, Ips typographus from different climate regions

Abstract of projects aims/goals, materials & methods and (available) resultsThere is evidence that seasonal changes in brood tree quality also have – together with microclimatic and day length conditions - a crucial effect on emergence and the reproductive behaviour of young adults of the spruce bark beetle Ips typographus, the main important central European forest pest. In the submitted project, bark beetles from three different origins (lowland population, montane-subalpine pop.; north-Scandinavian pop.) will be tested for their stage of gonad maturation and breeding activity after developing on logs of host trees felled either in spring or autumn. In order to study beetles from the same generation synchronously under long- and short-day conditions at 20°C on both types of host tree quality, we will compare their emergence rate and fecundity on either freshly cut logs from May with deep frozen logs cut in September of the last year or vice versa, on freshly cut logs from September with deep frozen logs cut in May of the same year. The quality of the brood material will be checked by biochemical analyses of the main nutritional compounds (carbohydrates, protein and amino acids, nitrogen) and by measuring the water content of the phloem at the time of tree felling, start of beetles’ breeding activity and after ending of the breeding experiments. The stage of gonad maturation will be analysed by histo-chemical methods after dissection of emerged and non-emerged beetles. The fecundity of young emerged beetles developed on logs of different brood quality will be tested in brood experiments under controlled conditions. Therefore, male and female beetles will be attached in pairs to brood logs by capsular pits and reared for two weeks. After this period the brood systems will be checked for length of the developed mother galleries, number of egg niches and number of larval galleries. The combined variations of brood tree quality and photoperiod conditions will allow to differentiate between the importance of photoperiod and host tree quality on sexual maturity and breeding behaviour of Ips typographus from different origins. This again is important to gain more insight into factors driving the population dynamics of this bark beetle species in different regions and to understand the influence of external factors in its diapause induction and breeding activity during the late summer period.