THE SELECTION BY CERTAIN SMALL MAMMALS OF DEAD, PARASITIZED, AND HEALTHY PREPUPAE OF THE EUROPEAN PINE SAWFLY, NEODIPRION SERTIFER (GEOFF.)

Abstract

Caged Sorex cinereus cinereus Kerr, Blarina brevicauda talpoides Gapper, and Peromyscus maniculatus bairdii Hoy and Kenicott opened more cocoons containing healthy, living sawfly prepupae than ones containing prepupae attacked by fungus. In the field and in the laboratory, S.c.cinereus opened more healthy cocoons than cocoons containing parasites. The reverse appeared to be true for B.b.talpoides. P.m.bairdii opened equal numbers of healthy and parasitized cocoons. The more insectivorous animals exhibited the greatest selective ability. Pretreatment to cocoons of one category affected the selective ability. Pretreating P.m.bairdii to fungus cocoons lowered the ability to select healthy cocoons over fungus cocoons. Pretreating animals to healthy cocoons raised the selective ability. Selection occurred in the digging, removing, opening, and eating phases in the search for cocoons. The closer the phase to the consummatory action, the greater was the degree of selection. The selective ability in the first three phases was acquired with experience. In the final, eating, phase it was innate.