NO EVIDENCE OF GENETIC SPECIALIZATION TO DIFFERENT NATURAL HOST PLANTS WITHIN OR AMONG POPULATIONS OF A POLYPHAGOUS GEOMETRID MOTH EPIRRITA-AUTUMNATA

Possible food plant specialization of larvae of a polyphagous geometrid, Epirrita autumnata, with cyclic outbreaks in density, was studied in four populations. Moths originating from within or outside the outbreak range of E. autumnata were not differently specialized on the two birch species, nor among the populations. Pupal masses or performance on different host species did not vary among populations. In the within-population study, pupal mass of field-collected E. autumnata deviated significantly among larvae fed on the three host species, which indicates variation in the relative suitability of the hosts. There were significant differences among the host species also in the next (laboratory) generation. However, parental food plant in the field did not affect pupal mass, nor did it interact with the food plant of the laboratory generation. Different broods did not vary in their performance on different hosts which suggests that there is little genetic variation in E. autumnata populations in respect to their ability to utilize the hosts. However, lack of specialization on different food plants among and within E. autumnata populations can better be understood by large variation in foliage quality within a host species, high dispersal of adults and larvae relative to patch size of host plants, as well as by matings taking place among individuals originating from different host species.