Seasonal flight patterns of <i>Ips typographus</i> in southern <scp>S</scp> weden and thermal sums required for emergence

Abstract

Abstract The spruce bark beetle Ips typographus is the major tree‐killing bark beetle in E urasia. To increase knowledge about its seasonal flight patterns and about the thermal sums required for emergence, a study was conducted in southern S weden 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 A pril [after 47 degree‐days (dd) &gt; 5 °C]. More than 50% of flight activity occurred after mid‐ J une, and this continued to mid‐ A ugust. Re‐emergence of parental beetles after they had produced the first brood started, on average, on 24 M ay (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 M ay (95%) than in J uly (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 J une (after 437 dd) and started to fly in early J uly, giving rise to at least a partial second generation in each year. A higher proportion of filial beetles had emerged from trees colonized in M ay (75%) than in J uly (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.