Bj. Vanderkamp et Pv. Blenis, A MODEL OF HYPERPARASITE REGULATION OF THE GALL RUST - LODGEPOLE PINEPATHOSYSTEM, Canadian journal of forest research, 26(7), 1996, pp. 1256-1265
Endocronartium harknessii (J.P. Moore) Hirat, populations never approa
ch the level where all susceptible Pinus contorta Dougl. ex Loud var.
latifolia Engelm. tissue is infected, even in years when environmental
conditions are favourable for infection. A simple simulation model wa
s developed to determine whether a hyperparasite could regulate the ru
st population and maintain it at an equilibrium level far below host s
aturation. The model assumed that galls begin sporulating and first be
come susceptible to parasitism 2 years after formation and requires sp
ecification of infection rates for the rust and the hyperparasite, mor
tality rates for normal and parasitized galls, and the degree to which
aeciospore production is reduced following hyperparasite infection. A
nalysis of tile model showed that the hyperparasite could regulate the
rust population, producing a stable equilibrium, but only if the vari
ous rates were such that healthy galls, in their lifetime, produced en
ough aeciospores to give rise to more than one new gall, while galls t
hat were parasitized during the first year of aeciospore production pr
oduced,in their lifetime, fewer than one new gall. The model of hyperp
arasite regulation provides one possible explanation of the dynamics o
f the gall rust pathosystem. It shows that control measures such as sa
nitation and breeding for resistance may reduce the effectiveness of t
he hyperparasite in regulating the system and, thus, may fail to achie
ve the anticipated goals.