Collection and evaluation of Trichogramma species (Hymenoptera: Trichogrammatidae) as biological controls of the oblique-banded leafroller Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) in raspberries and blueberries

Field isolates of three Trichogramma species were collected and tested in the laboratory for host acceptance and suitability of oblique-banded leafroller Choristoneura rosaceana (Harris) (OBLR) and Ephestia kuehniella Zeller eggs. An isolate of Trichogramma minutum Riley that was collected from OBLR eggs found on birch trees in Ontario had a much higher level of acceptance of OBLR eggs than any of the other strains that were tested. Two isolates of Trichogramma sp. nr. pretiosum Riley, and four isolates of Trichogramma sibericum Sorokina, were collected from leaf-roller and cutworm eggs found in commercial raspberry and blueberry fields in British Columbia. All of these isolates and an additional isolate of T. sibericum, originally collected from blackheaded fireworm on cranberries, accepted and successfully parasitized OBLR eggs, but at a very low level. In contrast, all eight Trichogramma isolates had a high level of acceptance of the rearing host E. kuehniella. All isolates of T. sibericum appear to be completely thelytokous. Thelytokous isolates reverted to sexual reproduction on treatment with tetracycline indicating that thelytoky was caused by microorganisms