Positive Results of an Early Intervention Strategy to Suppress a Spruce Budworm Outbreak after Five Years of Trials

David A Maclean,Luke Amos-Binks,Peter Amirault,Jacques Régnière,Rob Johns,Drew Carleton,Chris Hennigar

doi:10.3390/f10050448

Abstract

Spruce budworm (Choristoneura fumiferana Clem.; SBW) outbreaks are one of the dominant natural disturbances in North America, having killed balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea sp.) trees over tens of millions of hectares. Responses to past SBW outbreaks have included the aerial application of insecticides to limit defoliation and keep trees alive, salvage harvesting of dead and dying trees, or doing nothing and accepting the resulting timber losses. We tested a new ‘early intervention strategy’ (EIS) focused on suppressing rising SBW populations before major defoliation occurs, from 2014 to 2018 in New Brunswick, Canada. The EIS approach included: (1) intensive monitoring of overwintering SBW to detect ‘hot spots’ of low but rising populations; (2) targeted insecticide treatment to prevent spread; and (3) proactive public communications and engagement on project activities and results. This is the first attempt of area-wide (all areas within the jurisdiction of the province of New Brunswick) management of a native forest insect population. The project was conducted by a consortium of government, forest industry, researchers, and other partners. We developed a treatment priority and blocking model to optimize planning and efficacy of EIS SBW insecticide treatment programs. Following 5 years of over 420,000 ha of EIS treatments of low but increasing SBW populations, second instar larvae (L2) SBW levels across northern New Brunswick were found to be considerably lower than populations in adjacent Québec. Treatments increased from 4500 ha in 2014, to 56,600 ha in 2016, and to 199,000 ha in 2018. SBW populations in blocks treated with Bacillus thuringiensis or tebufenozide insecticide were consistently reduced, and generally did not require treatment in the subsequent year. Areas requiring treatment increased up to 2018, but SBW L2 populations showed over 90% reductions in that year. Although this may be a temporary annual decline in SBW population increases, it is counter to continued increases in Québec. Following 5 years of tests, the EIS appears to be effective in reducing the SBW outbreak.

Highlights

The spruce budworm (Choristoneura fumiferana Clem.; SBW) outbreak in eastern Canada andMaine from 1967 to 1993 was the dominant natural disturbance in the region, peaking at over 50 million hectares of defoliation [1]
In the Early Intervention Strategy (EIS) trials conducted from 2014 to 2018, SBW populations in blocks treated with Bacillus thuringiensis var. Kurstaki (Btk) or tebufenozide were consistently reduced and generally did not require treatment in the subsequent years
Following 5 years of EIS treatments of low but increasing SBW populations, L2 populations across northern New Brunswick are considerably lower than SBW populations across the border in adjacent

Summary

Introduction

The spruce budworm (Choristoneura fumiferana Clem.; SBW) outbreak in eastern Canada andMaine from 1967 to 1993 was the dominant natural disturbance in the region, peaking at over 50 million hectares of defoliation [1]. Outbreaks (repeated annual defoliation typically lasting up to 10 years) results in growth reduction of up to 90% [2], tree mortality in balsam fir (Abies balsamea (L.) Mill.)-spruce (Picea sp.) forests often exceeding 85% [3,4], and changes in regeneration patterns [5]. To limit timber supply shortfalls and the economic impact of SBW, at the peak of the last outbreak, 6.9 million hectares of forest was treated with insecticide in Canada in 1976, primarily in the provinces of Québec and New Brunswick [14]. In Québec, mortality losses during the 1967 to 1992 SBW outbreak were estimated at 238 million m3 of spruce and balsam fir, with an estimated similar additional amount of reduced growth [15]. The total losses from the SBW outbreak in Québec had an estimated commercial value of $12.5 billion [16]

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Discussion

Conclusion