RELATIVE ACTIVITIES OF GLUCOSINOLATES AS OVIPOSITION STIMULANTS FOR PIERIS-RAPAE AND P-NAPI-OLERACEA

The relative activities of 10 glucosinolates in stimulating oviposition by P. rapae and P. napi oleracea were compared under the same conditions. When tested at the same concentration, the structurally different glucosinolates stimulated both butterfly species to widely varying degrees. In most cases, P. rapae was more sensitive to aromatic and indole glucosinolates than to aliphatic representatives. This species responded even less to alkyl thio and sulfinyl glucosinolates. However, P. napi oleracea responded strongly to these aliphatic and sulfur-containing members of the group, and the relative activities of aromatic and aliphatic glucosinolates did not show a clear pattern for this species. P. napi oleracea was much more sensitive to low concentrations of sinigrin than was P. rapae. The threshold concentration for response of P. napi oleracea to sinigrin was 10(-8) M, which was 100 times lower than for P. rapae, but P. rapae was more sensitive than P. napi oleracea to changes in glucosinolate concentrations. For both Pieris species, an optimal concentration was reached, above which the response remained constant or tended to decrease.