Jg. Fidgen et al., INTRA-CROWN AND INTER-CROWN DISTRIBUTION OF THE EASTERN SPRUCE GALL ADELGID, ADELGES ABIETIS (L.), ON YOUNG WHITE SPRUCE, Canadian Entomologist, 126(5), 1994, pp. 1105-1110
Intra- and inter-crown distribution of eastern spruce gall adelgid, Ad
elges abietis (L.) (Homoptera: Adelgidae), on young white spruce, Pice
a glauca (Moench) Voss., was studied at three sites in New Brunswick,
Canada. Within a branch, the majority of galls were found on lateral s
hoots. Similar distributions of galls within trees were observed regar
dless of whether 20 or 30 lateral shoots or all shoots on a branch wer
e sampled. Gall densities were highest on mid-crown branches of open-g
rown trees 1-4 m tall and were not influenced by cardinal direction. A
fter crown closure, most galls were found in the upper crown, above th
e point of branch overlap. In all circumstances, gall distributions we
re strongly clumped within trees. Inter-tree distribution of A. abieti
s galls differed significantly from a Poisson but not a negative binom
ial distribution, indicating a high degree of aggregation among trees.
Therefore, a stratified random sampling plan using 20 lateral shoots
of a mid-crown branch as a sampling unit would be adequate for monitor
ing A. abietis populations. If the mid-crown branches are undergoing c
rown closure, we suggest sampling in the lowest open-grown branch abov
e the point of crown overlap.