Environmental and genetic influences on the dispersal propensity of spruce budworm (Choristoneura fumiferana)

Abstract

1 For many species, dispersal among populations has profound impacts on local dynamics and the spread of outbreaks. Understanding the environmental and genetic triggers of density-dependent dispersal is important for improving population models and developing reliable management strategies. 2 We hypothesized that moth dispersal in the spruce budworm (Choristoneura fumiferana Clem.) is triggered by reductions in larval food availability and mediated by the expression of the for gene, which affects movement and dispersal activity in Drosophila and other species. Late-stage larvae were reared under different food-limitation treatments. Dispersal of adults was assessed using three measures of flight performance on flight mills: maximum velocity, 1-h flight distance and maximum sustained flight time. Accumulation of for transcripts was measured by a quantitative polymerase chain reaction on moths from each treatment. 3 Flight activity was positively related to moth size and, although food limitation caused reductions in moth size, it also had an independent and positive effect on maximum velocities, sustained flight times and flight distances. Food limitation had no effect on expression of the for gene. 4 We conclude that reductions in food availability will produce moths that are smaller but exhibit increased flight activity, potentially increasing the population of dispersing individuals. The physiological basis for this effect remains unknown.

Modeling Migratory Flight in the Spruce Budworm: Temperature Constraints

“…However, females from severely defoliated stands are smaller, lighter, and have lower fecundity than well-fed females. Those lighter females can fly soon after emergence without laying any eggs [15,16], an observation also consistent with our model formulation. Simulated vertical density profiles (Figure 9a) are further consistent with recent radar observations of SBW mass migration events [19].…”

“…Observations indicate that fully gravid females are generally too heavy to fly, and thus lay part of their eggs locally prior to undertaking long-distance flight [13,14]. Exceptions can occur in conditions of highly depleted food resources, where starved females carrying smaller egg complements may emigrate without first laying eggs [15,16].…”

Density Dependence of Egg Recruitment and Moth Dispersal in Spruce Budworms

“…However, fully-fecund, well-nourished adult females appear less capable of sustained flight, presumably as a result of wing loading, so some portion of their fecundity is realized at the natal location before migration [22,23]. On the other hand, food limitation resulting from severe defoliation reduces the size and fecundity of budworm moths with a commensurate positive effect of their propensity to disperse [24,25].…”

“…On the other hand, large, fully-fed females may not be able to fly upon emergence and so do not migrate until they have laid at least a portion of their eggs at the natal site [23]. This suggests α, the Many authors contend budworm moths that are small as a result of food limitation have a greater propensity to fly and may even emigrate without first laying eggs [13,24,25,32,33]. On the other hand, large, fully-fed females may not be able to fly upon emergence and so do not migrate until they have laid at least a portion of their eggs at the natal site [23].…”

Effects of tebufenozide on the assemblage of moths (Lepidoptera) in an operational spruce budworm (Lepidoptera: Tortricidae) suppression programme

“…Newly emerged females usually mate within 24 hours (Outram 1971) but, unless food-deprived larvae, cannot fly from their natal stand until they have reduced their body mass through oviposition (Wellington 1948;Van Hezewijk et al 2018) of about 50% of their eggs (Rhainds and Kettela 2013). These phenomena are probably responsible for the Rhainds and Kettela (2014) observation of correlation of numbers of eggs and catches of moths in light traps located in the tree canopy.…”