Pheromone identification of Dioryctria abietivorella (Lepidoptera: Pyralidae) from an eastern North American population: geographic variation in pheromone response

The fir coneworm, Dioryctria abietivorella (Groté), is a transcontinental pest of coniferous seed cones. Recently, the attractive pheromone components and lure blend for the fir coneworm in western Canada were identified as a 200 µg : 2000 µg ratio of (9Z,11E)-tetradecadienyl acetate (9Z,11E-14:Ac) and a polyunsaturated hydrocarbon, (3Z,6Z,9Z,12Z,15Z)-pentacosapentaene (C25 pentaene). A potential third component, (Z)-9-tetradecenyl acetate (9Z-14:Ac), which was detected in pheromone gland extracts, had no effect on males of the western population when added to the binary blend. In contrast, in eastern Canada (Quebec) we found that the 200 µg : 2000 µg binary blend was unattractive to male fir coneworms until 9Z-14:Ac was added. By means of several field experiments we established that a 67 µg : 200 µg : 2000 µg ratio of 9Z-14:Ac, 9Z,11E-14:Ac, and the C25 pentaene was attractive to fir coneworms in Quebec. Gas chromatography - mass spectrometry analysis of pheromone gland extracts of fir coneworm from Quebec confirmed the presence of the three components in extracts in an approximately 1 µg : 4 µg : 10 µg ratio of 9Z-14:Ac, 9Z,11E-14:Ac, and the C25 pentaene. Our results provide evidence that the eastern and western populations of D. abietivorella are distinct geographic pheromone races, with 9Z-14:Ac being required for attracting males of the eastern population but not males of the western population.

DIAPAUSE INDUCTION AND OVERWINTERING STAGE IN THE FIR CONEWORM (LEPIDOPTERA: PYRALIDAE)

A laboratory experiment was conducted to identify the overwintering stage of the fir coneworm, Dioryctria abietivorella (Grote), in eastern Canada and determine the influence of photoperiod on diapause induction. In another experiment, different developmental stages were exposed to field conditions to evaluate their capacity to survive the overwintering period. Insects were either placed in the duff or exposed to ambient (above ground) conditions to assess the importance of overwintering site on winter survival. Exposure of the fir coneworm to constant short-days or a daily decreasing photoperiod during larval development induced almost all insects to initiate diapause at the fifth instar. Third-, fourth-, and fifth-instar larvae survived the overwintering period when placed in the duff. Because the fir coneworm must leave its host tree and drop to the ground to avoid rigorous winter conditions, we concluded that only fifth-instar larvae could resume development in spring using such a strategy.

VULNERABILITY OF THE FIR CONEWORM, DIORYCTRIAABIETIVORELLA (GROTE) (LEPIDOPTERA: PYRALIDAE), IN DIFFERENT LARVAL STAGES TO THE HD-1 STRAIN OF BACILLUS THURINGIENSIS

The fir coneworm, Dioryctria abietivorella (Grote), is a major insect pest in seed orchards across Canada and the adjoining eastern and western United States. Larvae feed principally on cones, but they can also feed on needles and occasionally on the bark of young tree trunks (Hedlin et al. 1980; Ruth 1980; Martineau 1985). The potential for a population of D. abietivorella to build up in seed orchards may be greater than in natural stands (Hedlin et al. 1980; Ruth et al. 1982). The use of entomopathogen in the management of fir coneworm could be an adequate measure to reduce the impact of this insect. Moreover, Bacillus thuringiensis ssp. kurstaki has a specific effect on Lepidoptera (Aronson et al. 1986; Gill et al. 1992). The purpose of our study was to determine the activity of the HD-1 strain of B. thuringiensis ssp. kurstaki (serotype H-3a:3b) to larvae D. abietivorella. Bioassays were conducted with first-, third-, and fifth-instar larvae of fir coneworm to determine whether or not the insect's vulnerability to B. thuringiensis varies with larval age.

FIR CONEWORM, DIORYCTRIA ABIETIVORELLA (GROTÉ) (LEPIDOPTERA: PYRALIDAE), PREFER CONES PREVIOUSLY EXPLOITED BY THE SPRUCE CONE MAGGOTS STROBILOMYIA NEANTHRACINA MICHELSEN AND STROBILOMYIA APPALACHENSIS MICHELSEN (DIPTERA: ANTHOMYIIDAE)

We tested the prediction that larvae of the fir coneworm, Dioryctria abietivorella (Groté), preferentially exploit cones previously damaged by cone maggots, Strobilomyia spp. In most years sampled, fir coneworm attacked a significantly greater proportion of maggot-damaged than healthy cones of both white spruce and black spruce. The ecological implications for pest management are briefly discussed.

EFFICACY OF ESFENVALERATE FOR CONTROL OF INSECTS HARMFUL TO SEED PRODUCTION IN DISEASE-RESISTANT WESTERN WHITE PINES

We tested the pyrethroid insecticide esfenvalerate in single, double, and triple applications for control of insects affecting seed production of blister rust-resistant western white pine, Pinus monticola Douglas. All treatments increased the proportion of normal seed produced and reduced the proportion of seed damaged by the western conifer seed bug, Leptoglossus occidentalis Heidemann. Only the triple application reduced the proportion of cones killed by the pine cone beetle, Conophthorus ponderosae Hopkins. Other seed-damaging insect species [seed chalcids, Megastigmus sp.; the fir coneworm, Dioryctria abietivorella (Grote); and seedworms, Cydia sp.] were present but in numbers too low to test for insecticide efficacy.