Host Discrimination by Adult and Larval European Apple Sawflies Hoplocampa testudinea (Klug) (Hymenoptera: Tenthredinidae)

Abstract

Adult and larval European apple sawflies (EAS), Hoplocampa testudinea (Klug), were assayed for propensity to avoid resource sites (apple blossoms and growing apples, respectively) already occupied by conspecifics (i.e., assayed for host discrimination). Under laboratory conditions, adults oviposited significantly less frequently in blossoms containing oviposition wounds and eggs than in healthy, uninfested ones. Similarly, significantly fewer adults attempted oviposition in blossoms containing artificial oviposition wounds than in intact blossoms. These results suggest that wound tissue exudates provide information to EAS adults on the infestation state of individual blossoms. EAS larvae, following emigration from their first hosts, invaded uninfested apples significantly more often than apples harboring living conspecifics. Similar results were obtained when resident larvae were killed before testing. We were unable to determine the stimulus(i) larvae employ in the hostdiscrimination process.