White pine weevil performances in relation to budburst phenology and traumatic resin duct formation in Norway spruce

Abstract

Abstract1 As the phenological window hypothesis was reported to be significant in influencing the fitness of many herbivores feeding on tree foliage, could it also explain the performance of an insect such as the white pine weevil Pissodes strobi mainly attacking the bark phloem of conifers?2 Under field conditions, adult weevils were caged on Norway spruce trees presenting a natural variation in their shoot growth phenology.3 We evaluated white pine weevil biological performances, including oviposition, the number of emerged insects, survival, adult mean weight and tree defense responses as reflected by the production of induced resin canals.4 None of the white pine weevil biological parameters was significantly affected by Norway spruce phenology.5 The number of eggs per hole, the number of oviposition holes per leader, the number of emerged adults and their mean weight were not affected by host phenology.6 The intensity of the traumatic response observed was variable and not correlated with budburst phenology.7 Trees with higher traumatic responses, forming two or more layers of traumatic ducts, had lower adult emergence and estimated survival.8 The distance between the first layer of traumatic resin ducts and the start of the annual ring was not correlated with the number of emerged weevils.9 Norway spruce, which is an exotic tree in North America and a relatively recent host for the white pine weevil, might not possess the defense mechanisms necessary to fight off the white pine weevil.