Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract

1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir-white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray. 2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/ tannins ratio, which might have induced inactivation of Btk toxins. 3 Larval mortality due to Btk did not depend on spruce budworm larval age. 4 Foliage protection of both host trees was similar in plots treated with Btk:larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production. 5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir-white spruce stands).

Life‐history consequences and disease resistance of western tent caterpillars in response to localised, herbivore‐induced changes in alder leaf quality

“…De Vos et al , 2005; Pieterse & Dicke, 2007) and entomopathogens (e.g. Hunter & Schultz, 1993; Carisey et al , 2004) led us to predict that plant induction could also reduce the impact of other disease‐causing organisms found on the phylloplane and/or carried sublethally by the herbivore.…”

“…Similarly, tannins were negatively correlated with the efficacy of a bacterial pathogen ( Bacillus thuringiensis var. kurstaki Berliner) against Pieris brassicae L. (Lüthy et al , 1985), Heliothis virescens Fabricius (Navon et al , 1993), L. dispar (Appel & Schultz, 1994) and Choristoneura fumiferana (Clemens) (Carisey et al , 2004). Moreover, alpha‐tomatine in the diet of Heliothis zea (Boddie) inhibited larval infections by a pathogenic fungus, Nomuraea rileyi (Farlow) Samson (Gallardo et al , 1990).…”

“…The induced responses of plants can also indirectly benefit herbivores if they cascade up to the trophic web and negatively impact herbivore natural enemies and entomopathogens (e.g. Krischik et al , 1991; Hunter & Schultz, 1993; Mayer et al , 2002; Carisey et al , 2004; De Vos et al , 2005; Cory & Hoover, 2006; Pieterse & Dicke, 2007; De Roode et al , 2011). We tested the hypothesis that localised induced defences in red alder trees have deleterious effects on entomopathogenic organisms and that herbivorous insects may indirectly benefit from this through increased resistance to their pathogens.…”

Aerial spraying of bacterial insecticides to control spruce budworm defoliation leads to reduced carbon losses

“…The main objective of Btk application is to maintain 50% or more of current‐year foliage on trees in order to reduce timber losses during outbreaks (Carisey et al. , Fuentealba et al. ).…”

Adaptation of an outbreaking insect defoliator to chronic nutritional stress

“…Many studies on forest pests focus on ecological aspects such as tree age (Bauce et al ., ), host plant phenology (Lawrence et al ., ; Carisey et al ., ) and natural enemies (Royama, ; Venier & Holmes, ), even if it has been observed that quality of food affects performance of forest pests (Carisey & Bauce, ; Carisey et al ., ). The adaptive processes related to selection pressure caused by the nutritional quality of the host have been widely neglected.…”