Allee effects can cause populations to decline due to decreasing population growth rates with decreasing density and play a major role in population dynamics. Mate-finding failure, a common mechanism contributing to demographic Allee effects, is usually difficult to demonstrate because of the arduous nature of sampling individuals at very low densities. In a rising outbreak of the eastern spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), we used caged and tethered virgin females in traps to measure mating success over population densities ranging from deep endemic to outbreak conditions. We found that mating success increased with increasing population density, and that at endemic population densities, females experienced difficulties attracting males and mating, demonstrating for the first time a mate-finding Allee effect in the spruce budworm. The relationship between population density and mating success is nonlinear. As population density increased, the proportion of mated females eventually reached a plateau and mating success was not 100% even at the highest moth densities, probably due to female reluctance to mate and perhaps interference competition by males for access to females. Both laboratory-reared and wild females were equally effective in synthesizing pheromone, attracting males, and mating. Our results strongly suggest that a mate-finding Allee effect is involved in maintaining low-density spruce budworm populations below an Allee threshold where they fail to grow. Factors such as changes in predation pressure and immigration could help populations overcome this Allee threshold.

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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.

Reproductive processes in female Pissodes strobi (Peck) fed with a 5% ground bark artificial diet following summer emergence were studied. Females exposed to different temperature and photoperiod regimes were dissected every other week and their reproductive organs were observed to evaluate the maturation time according to the treatments. After 12 weeks, half the females were transferred onto lateral branch sections of white pine and the other half onto artificial diet supplemented with 10% ground bark of white pine, and their realized fecundity was determined. During the first 12 weeks, ovary development was detected but very few mature oocytes were found. No significant differences were observed for the maturation times between the different abiotic conditions used, but significant differences were observed in female egg-laying response on natural and artificial diets. Females that completed their sexual maturation at 24 °C and 16L: 8D laid over a 3-week period 14.4 ± 8.8 (mean ± SE) and 2.6 ± 2.6 eggs per female on white pine sections and artificial diet, respectively. Oviposition behaviour was compared with results from an earlier experiment conducted with spring-emerging white pine weevils on natural and artificial substrates. The egg-laying responses on white pine seedlings and on an artificial diet with a concentration of 15% ground white pine bark were 0.892 ± 0.124 and 0.171 ± 0.394 eggs per female per day, respectively.

Aerial applications of a registered formulation of synthetic spruce budworm female sex pheromone were made in 2008, 2013 and 2014 to disrupt mating in populations of this forest insect pest in Quebec, Canada. Each year, the applications resulted in a 90% reduction in captures of male spruce budworm moths in pheromone-baited traps. A commensurate reduction in mating success among virgin females held in individual cages at mid-crown of host trees was also obtained. However, there was no reduction in the populations of eggs or overwintering larvae in the following generation (late summer and fall). The failure of this approach as a viable tactic for spruce budworm population reduction could have resulted from considerable immigration of mated females, as evidenced by high rates of immigration and emigration that caused steep negative relationships between apparent fecundity and the density of locally emerged adults.