Secondary effects of the pesticide Bacillus thuringiensis kurstaki on chicks of spruce grouse (Dendragapus canadensis)

The objective of this study was to determine if application of the biologic al pesticide Bacillus thuringiensis kurstaki (B.t.k.) had secondary effects on spruce grouse (Dendragaptis canadensis) chicks in the southern boreal f orest of Ontario, Canada. B.t.k. kills larvae of Lepidoptera that ir-light otherwise be food. This may affect types of food ingested and influence chi ck growth rates by reducing the availability of a high-protein food. Amount of ingested grit, which is diet-dependent, may also be influenced, which c ould alter exposure to anthropogenic toxic metals, such as cadmium (Cd) and lead (Pb), associated with the grit. Chick growth rate from 0 to 14 days o f age was determined, and gizzard contents were analyzed for types of foods and levels of macronutrients and trace metals in chicks raised in a plot t reated with B.t.k. compared to chicks raised on a control plot. Chick growt h rates were significantly different (p < 0.05); chicks from the treatment plot increased body mass 30% less as compared to chicks raised on the contr ol plot. Control chicks contained on average 2.5-fold the mass (in g) of gr it and nearly twofold the mass of food, which included larvae, in their giz zards compared to those exposed to B.t.k. whose diets were dominated by spi ders and ants. Concentrations of magnesium (Mg), calcium (Ca), phosphorous (P), iron (Fe), manganese (Mn), sulfur (S) and the trace metals zinc (Zn), copper (Cu), nickel (Ni), and chromium (Cr) did not differ between experime ntal and control birds (p > 0.05). In contrast, control chicks had higher l evels of aluminum (Al), Cd, cobalt (Co), and Pb in their gizzards than chic ks from the sprayed area (p < 0.05), attributed to greater amounts of consu med grit. Although birds from the sprayed area had lower levels of the toxi c metals Pb and Cd in their gizzards, a protein-deficient diet could have b een a factor that contributed to decreased rates of growth in B.t.k.-expose d birds as compared to those birds held on nonsprayed sites. Reduced growth during the first 2 weeks of avian development has important consequences a t the population level, and it is recommended that this secondary effect be considered for all species who rely on Lepidoptera larvae as a food resour ce prior to wide spread application of B.t.k. for insect control.