Pear sawfly (Caliroa cerasi) (Hymenoptera: Tenthredinidae) host preference and larval development on six Pyrus genotypes

Abstract The larvae of the sawfly Caliroa cerasi can cause serious damage to pear (Pyrus sp.) foliage particularly in organic or reduced‐spray orchards. Six pear cultivars and selections, three with low susceptibility to pear slug damage and three with high susceptibility, were subjected to oviposition choice tests in the field and subsequent larval development rates were monitored to clarify the nature of the variable susceptibility. Observed differences in oviposition rates corresponded with the low and high susceptibility categories of the genotypes. Larval development rates differed among genotypes and were inversely related to density of hatched eggs (a surrogate measure of leaf damage). These results confirm that host oviposition preference is a key factor influencing susceptibility to pear slug. It is further argued that feeding‐induced plant resistance and larval migration could be important factors influencing pear sawfly populations on pear trees.