A 2-YEAR STUDY OF THE EFFICACY OF BACILLUS THURINGIENSIS – CHITINASE COMBINATIONS IN SPRUCE BUDWORM (CHORISTONEURA FUMIFERANA) CONTROL

Abstract

AbstractSpruce budworm infested balsam fir trees were aerially sprayed with Bacillus thuringiensis – chitinase combinations at the rate of 4 Billion International Units of B.t. and 18 mg of enzyme in 0.5 gal/acre. Larvae were peak third instar at spray time. Deposit rates ranged from 1.07 to 3.26 BIU/acre. Efficacy of the treatments was assessed in the year of treatment and carry-over effects were assessed 1 year later.Results in the year of treatment indicated that: (1) Residual activity of B. thuringiensis was drastically reduced after 15 days’ exposure to weathering. (2) Larval mortality alone is not a suitable criterion of efficacy. (3) Dipel and Dipel + chitinase (but not Thuricide 16B or Thuricide + chitinase) were highly effective in reducing budworm densities. (4) Thuricide + chitinase treatment resulted in significant foliage protection. The treatments inhibited feeding in the following order of efficiency: Thuricide + chitinase > Dipel + chitinase > Dipel alone > chitinase alone > Thuricide alone. (5) There was no direct relationship between larval mortality and foliage protection in any of the treatments, likely due to delayed mortality effects. (6) No direct relationship exists between viable spore deposits and deposit of active ingredient (IUs). (7) B.t. treatments retarded development of the spruce budworm and reduced pupal weights, oviposition rates, and egg viability.Assessment of the plots 1 year after spray showed that the treatments apparently gave no long term protection from defoliation, but this was likely due in part to mass invasion of the test plots by moths from immediately surrounding untreated areas.