The Role of Climate and Dispersal in the Initiation of Outbreaks of the Spruce Budworm in New Brunswick: Ii. The Role of Dispersal

Abstract

In Part I of this papcr consideration was given to the role of c!imate in the initiation of outbreaks of the spruce budworm in New Brunsv~ick. Analysis of the avai!able \\;eather data sho\\:ed that the 1912 and 1949 outbreaks developed after several consec~rtive dry summcrs. Support was given to thc theory of climatic release, which csplains thc time and place of outbreaks 011 n climatic basis. Howevcr, the recorcletl history of the sprucc bucl\\rorm also sho\vs that high populations appeared ill New Brunswick shortly after "sprcading" through Quebec, and this suggests that the New Bruns\vick outbreaks are also a continuation of this spread. I n the prcserlt part of the paper coi~sideration is given to the role of dispersal. ;\loth dispersal is a morc effective agent of spread than larval clispersal. 5 1 0 t h~ may be transportetl by convectional and turbulent air currents for l o n~ dista~lces. Light traps uscd to detcct the incidence of moth mo\:ernents, sho\\;ccl that large segments of a pop~rlation may bc transfcrrecl frorn onc area to another. Unspent fenlales often pretlominate in thcse no\-cments. hloth invasion \\;as not detected bcforc the 1949 outbreak although thcre is e\:iclence fro111 other sources that it occurrecl in 1948. \\'hen deposited in dense, mature, softwoocl stancls, the moths can crcate outbreaks, but \\-hen deposited in young, opcn, or mised-\\rood stancls thc ensuing high populations so011 dcclinc unlcss I,olstcretl by repeated invasions. Populations i11 Ncw Bruns\\~icl; sho\\;cd gradual and general increases as early as 1917. I t is thought probable that these increases rcsultccl from thc I~uilcl-up of local populations through clirnatic relcase. The nearest highly-populated celitel-s were over 100 rnilcs to the \\:est in 1947. Latcr, in\.asio11 of moths from centers outside of the I~'ro\.i~~cc nla!-have hastcnecl the proccss.

Population dynamics of the major North American needle-eating budworms.

“…Greenbank (1957), for example, noted that dense eastern budworm populations "...in young, open, or mixed-wood stands...soon decline unless bolstered by repeated invasions. "…”

Population Ecology of Some Warblers of Northeastern Coniferous Forests

“…More recent information confirms this. To correlate with the fact (Greenbank 1956) that there have been continuously high budworm populations since 1909, there is the statement of Forbush (1929) that the Cape May warbler became more common about 1909. and the statement of Bond ( pers. comm.…”

GENETICS OF NATURAL POPULATIONS. XXVII.: THE GENETIC CHANGES IN POPULATIONS OFDROSOPHILA PSEUDOOBSCURAIN THE AMERICAN SOUTHWEST

“…Ch. L. Remington has kindly called my attention to the work of Henson (1951) and Greenbank (1957) on the spruce budworm moth, Choristoneura fumiferana. Large numbers of these moths are sometimes drawn into the updrafts of air which occur during the passage of cold frontal air masses, and then deposited by the downdrafts at considerable distances from their places of origin.…”