• Cunningham, J.C.
  Canadian Forestry Service
  
• Kaupp, W.J.
  Canadian Forestry Service
  
• Howse, G.M.
  Canadian Forestry Service
  
• McPhee, J.R.
  Canadian Forestry Service
  
• de Groot, P.
  Canadian Forestry Service
  

Five plots with a total area of 148 ha were treated with spruce budworm, Choristoneura fumiferana, nuclear polyhedrosis virus to test 3 formulations, 2 dosages and 2 strains of virus. The application was made with a Grumman Agcat equipped with boom and nozzle spray equipment calibrated to deliver 9.4 l/ha. Larvae were mainly in the fourth and fifth instar in 4 of the plots and fifth instar with some sixth instar present in the other plot.

The efficacy of the treatments was assessed by 5 methods. (i) Larvae collected from the plots 5 days after the application were reared in the laboratory until death or pupation occurred. (ii) Samples of larvae from treated and check plots, taken at weekly intervals, were examined microscopically to determine if they were infected with virus. (iii) Pupal survival in treated areas was compared to check areas. (iv) Population reduction estimates due to the treatment were made by comparing prespray larval and postspray pupal samples from treated and check areas. (v) Defoliation estimates were made in treated and check areas.

Generally the results indicated that a formulation containing 250 ml/l molasses, 60 g.l IMC 90-001 UV protectant and 1.25 ml/l Chevron sticker was superior to a polymer bound carbon formulation or a virus adjuvant manufactured by Sandoz Inc., SAN 285 wettable powder. Subsequent laboratory tests showed that considerable inactivation of the virus had occurred as a result of preparing the polymer bound carbon formulation. The SAN 285 wettable powder was compatible with the virus.

The efficacy of virus isolates obtained from Choristoneura fumiferana and C. occidentalis were similar. When two dosages of the C. fumiferana nuclear polyhedrosis virus were compared, 750 billion polyhedra/ha gave considerably better results than 250 billion. The former dosage gave a population reduction of 92% which is the best result obtained to date with a nuclear polyhedrosis virus treatment on spruce budworm.