Lethal and sublethal effects of single and double applications of Bacillus thuringiensis variety kurstaki on spruce budworm (Lepidoptera: Tortricidae) larvae.
We conducted laboratory experiments to examine the effects of single versus double exposures of spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) female larvae to various concentrations of a Bacillus thuringiensis variety kurstaki (Btk) commercial formulation (Foray 48B). Our main objective was to document the vulnerability to Btk and the sublethal responses of fifth-instar larvae that survived from a first ingestion of Btk during their fourth stadium and to compare them with insects treated either during their fifth or fourth stadium only. As reported in the literature, fifth-instar larvae were more vulnerable than fourth-instar larvae, but only at low and medium concentrations. Fifth-instar larvae that had survived Btk ingestion during their fourth stadium were more vulnerable to a high concentration of Btk and had a shorter feeding inhibition period than those that had not been exposed during their fourth stadium. Compared with a single treatment at the fourth stadium, a double exposure to Btk further reduced the population by 20-30%, depending on the concentration applied. The second treatment also induced another feeding inhibition period and increased larval development time by 14%. The impact of the different treatments on pupal weight depended on whether treated insects exhibited supernumerary instars. In the absence of developmental polymorphism, a higher concentration, a late, or a double exposure to Btk significantly reduced pupal weight.
Moreau
Gaétan
G
Centre de Recherche en Biologie Forestière, Département des Sciences du Bois et de la Forêt, Faculté de Foresterie et de Géomatique, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4.
Bauce
Eric
E
D000818:Animals; D001413:Bacillus thuringiensis / Q000502:physiology*; D007814:Larva / Q000254:growth & development; D009036:Moths / Q000254:growth & development; D010572:Pest Control, Biological / Q000379:methods*; D011679:Pupa / Q000254:growth & development