The effects of fir coneworm, Dioryctria abietivorella (Grote) (Lepidoptera: Pyralidae), on seed production in small, isolated populations of red pine, Pinus resinosa Ait.

Abstract

Red pine ( Pinus resinosa Ait.) is a rare endemic species in Newfoundland, where it occurs in small, isolated stands at the northeastern extreme of its geographic range. During 1989 and 1990, the fir coneworm, Dioryctria abietivorella (Grote), infested the entire cone crop in two of six natural red pine stands in eastern Newfoundland while the average incidence of coneworm in the remaining four stands was 89% in 1989 and 83% in 1990. Incidence of fir coneworm averaged 25% (1989) and 22% (1990) of the cone crop in five natural stands from a population in western Newfoundland. Following a bumper cone crop in all conifers in 1988, high numbers of fir coneworm became concentrated in red pine which has produced consistently good cone crops for 3 consecutive years, while cone production has been sporadic in other conifers. The coneworm infestation reduced the number of full seeds per cone by 93%, and cone size by 17% in severely infested trees of the eastern Newfoundland red pine population. High seed losses documented in 1989 and 1990 demonstrate the effects of stochastic events on reproductive success in rare populations, and the potential adaptive value of sporadic cone crops in limiting seed losses. The number of full seeds per cone was reduced by only 11%, with no significant reduction in cone size, in the lightly infested trees in western Newfoundland. However, trees from the eastern population compensated for low numbers of full seeds per cone by producing significantly larger seeds, thereby compensating for losses in seed number by increasing the average fitness or quality of the remaining full seeds. If coneworm infestations continue at current high levels for an extended time, reproductive success in the small, fragmented red pine population of eastern Newfoundland may be adversely affected.