Seasonal flight patterns of the Spruce bark beetle (Ips typographus) in Sweden : phenology, voltinism and development

• The major bark beetle threat to Norway spruce (Picea abies (L.) Karst.) in Eurasia is the spruce bark beetle Ips typographus. Beetles cause damage after population build-up in defenseless trees. To minimize attacks, timely removal of these trees is important. This is practiced by clearing of wind throws and sanitation felling. Thus, knowledge about the region-specific flight pattern and voltinism of I. typographus is necessary for efficient pest management. This thesis focuses on the flight initiation and the variation in flight pattern of I. typographus over the season, which we have studied using pheromone traps during a seven year period in Sweden. Additionally, logs, that became colonized, were used to determine thermal sums required for the re-emergence of parental beetles and the emergence of filial beetles in southern Sweden. Swarming began in the end of April (51 degree-days (dd) >5°C; daytime temp. >18°C). More than 50% of the flight activity occurred after mid-June and it continued until mid-August. That is a longer flight period than has been recorded previously. At least partly, this discrepancy with previous observations may be explained by our results that the temperature requirement for flight commencement is fulfilled more than two weeks earlier now than 30 years ago. Re-emergence of parental beetles from the first brood started in the end of May (122 dd >5°C). A much higher proportion of parental beetles had re-emerged from trees colonized in May (95%) compared to in June (60%) or July (20%). This verifies that sister broods is an important part of the beetles' reproductive biology. The high proportion of beetles that re-emerged together with a significant continued beetle flight and oviposition showed that a high proportion of the beetles initate at least one sister brood. Filial beetles began to emerge in the end of June (437 dd >5°C) and were caught in flight traps in early July and at least a partial second generation was started in each year. A much higher proportion of filial beetles had emerged from trees colonized in May (75%) than in June (50%) and July (15%). We have shown that the temperature requirement for flight initiation are met earlier in the present climate which gives more time for the development of several sister broods and a potential second generation. This together with an expected increase in severe storm fellings indicates that the need for efficient pest management will increase with time. Timely removal of wind-felled trees is the main pest management option and in this thesis I present results of when the critical time periods occurs.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

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