Parasitism of cranberry fruitworm (Acrobasis vaccinii; Lepidoptera: Pyralidae) by endemic or released Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

Two levels of commercially-reared Trichogramma pretiosum were released during the oviposition period of the cranberry fruitworm (Acrobasis vaccinii) in eight Massachusetts (U.S.A.) cranberry bog sites. Release levels of 4.8 x 10 super(5) T. pretiosum per ha or 1.9 x 10 super(6) T. pretiosum per ha were made at 3-5 day intervals, with a total of nine releases. Parasitism was estimated by collecting cranberry fruits and examining them for the presence of A. vaccinii eggs and T. pretiosum. Eggs were classified as unhatched, hatched, parasitized or emergent parasite. Collections of cranberries from four 'neglected' bog sites (not currently under cultivation) were examined and classified similarly, but T. pretiosum were not released, to determine the level of parasitism from endemic populations. Cumulative parasitism from the neglected sites was consistently higher than levels recorded from the release sites throughout the season. Parasitism in the neglected sites was determined to be from natural populations of T. pretiosum. Comparisons of cranberries damaged by A. vaccinii showed that damage was greatest in the neglected sites, but was not significantly different from fruit damage within either the low release or high release level. Collections of cranberries were also made within bog sites managed under current Massachusetts Cooperative Extension IPM guidelines. Damage to cranberries was lowest in the IPM-managed sites; although this value was less than the other bog sites, it did not differ significantly.