E.G. Kettela, C. Lucarotti, S.E. Holmes, R. Feng, W. Bowers and Shiyou Li
SERG Project # 1998/06 (1999)
The balsam fir sawfly (BFS), Neodiprion abietis, has become increasingly important as a pest of thinned and unthinned balsam fir, Abies balsamea, stands in Atlantic Canada. The affected areas have expanded to include extensive areas in western Newfoundland and Nova Scotia, and the population appears to be growing rapidly in other areas of Nova Scotia. The only insecticide presently available, under temporary registration, is the chemical Dylox® 420. Since 1996, alternatives to chemicals have been requested by the forest industry to cope with this pest to protect stands. This compendium presents studies on alternatives to chemical insecticides for use against the BFS.
The search for an effective, affordable, and acceptable pest management product for use in BFS management led to experiments on Abietivirus (NaNPV), and Vectobac®1200 L (Bacillus thuringiensis israelensis) (B.t.i.). Test blocks to assess lower dosage treatments of Dylox® 420 were included as a condition of the operational spray permit. The final field test program included trials of the virus, B.t.i., and Dylox® (reduced dosage). The virus application provided encouraging results and it was recommended that its development proceed as rapidly as possible. The results achieved with B.t.i. were positive, although a better formulation or strain is needed. Dylox® 420 is an effective control agent, but at 125 g/ha, the efficacy decreases when sprayed on mature larvae. Trials that explore this rate on early instar larvae should be conducted. For maximum benefit, the products should be applied early and as near to 100% egg hatch as possible.
In the 1999 laboratory study, VectoBac® 12AS, Neemix® 4.5 EC, and Dylox® insecticides were bioassayed in the laboratory against field-collected second, third, and fourth instar balsam fir sawfly larvae. The results indicated that VectoBac® had little toxicity to the larvae while Neemix® was toxic. The LC50 values against second, third, and fourth instar larvae were 1.73, 5.03, and 13.37 ppm azadirachtin, respectively, for Neemix® and 1.06, 1.30, and 5.73 ppm trichlorfon for Dylox®. Early instar larvae are more susceptible to both Neemix® and Dylox® than later instar larvae, which means that sprays for the control of this sawfly should be targeted against early larval stages. B.t.i. was marginally toxic to balsam fir sawfly, and a different approach is needed to evaluate this product. Neemix® showed promising results in killing sawfly larvae in the laboratory.
The impacts of Dylox® on non-target arthropod species in a balsam fir forest ecosystem in western Newfoundland were monitored in 1999. There were no significant differences in total wet and dry biomasses of samples collected from light traps between Dylox® treated and untreated blocks either before or after spray application. The major species captured in light traps were Lepidoptera moths, whose populations were reduced by 50% 1 day after Dylox® application. However, the knockdown effect of Dylox® spray was decreased approximately three-fold 3 days postspray and almost five-fold 7 days postspray. At the end of the sampling season, the knockdown effect was reduced by almost ten-fold. Dylox® applied in the field did not have significant impact on key forest health indicators such as spiders, carabids, and parasitic wasps.
A progress report on a preliminary study is included as an appendix. The 1998 ad hoc trial against the yellowheaded spruce sawfly, Pikonema alaskensis, concluded that VectoBac® provided the highest level of insect mortality of three B.t.i. products tested.