Henderson, Deborah

The influence of oviposition experience on response to host pheromone in Trichogramma sibericum (Hymenoptera: Trichogrammatidae)

Digital Document

Searching times and residence times of Trichogramma sibericum Sorokina were measured in the laboratory on individual cranberry leaves that had been treated with the sex pheromone of blackheaded fireworm [Rhopobota naevana (Hübner)] and on leaves that were left untreated. Mean searching time was higher on leaves treated by passive diffusion with either 50 or 100 μg of the main component of fireworm pheromone, (Z)-11-tetradecen-1-ol acetate (Z11-14: Ac), than on control leaves. Mean residence times were also higher on leaves treated by passive diffusion with 50 μg of Z11-14: Ac than on leaves untreated with pheromone. Pretrial oviposition experience in either the presence or the absence of host pheromone did not influence variation in searching time or residence time. This indicates that neither associative learning of the odor of host pheromone nor a more generalized increase in response to chemical stimuli after oviposition (priming) affects retention responses of T. sibericum to pheromone. Results are discussed in the context of current theories on the evolution of learning in insect parasitoids and as they relate to the concurrent use of pheromone-based mating disruption and releases of T. sibericum for pest management of the blackheaded fireworm.

Digital Document

Field isolates of threeTrichogrammaspecies were collected and tested in the laboratory for host acceptance and suitability of oblique-banded leafroller (Choristoneura rosaceana(Harris) (OBLR) andEphestia kuehniellaZeller eggs. An isolate ofTrichogramma minutumRiley 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 ofTrichogrammasp. nr.pretiosumRiley, and four isolates ofTrichogramma sibericumSorokina, were collected from leafroller and cutworm eggs found in commercial raspberry and blueberry fields in British Columbia. All of these isolates and an additional isolate ofT. sibericum,originally collected from blackheaded fireworm on cranberries, accepted and successfully parasitized OBLR eggs, but at a very low level. In contrast, all eightTrichogrammaisolates had a high level of acceptance of the rearing hostE. kuehniella.All isolates ofT. sibericumappear to be completely thelytokous. Thelytokous isolates reverted to sexual reproduction on treatment with tetracycline indicating that thelytoky was caused by microorganisms.

Digital Document

Inundative releases of Trichogramma minutum Riley were made in a commercial blueberry field in British Columbia, Canada, to determine the extent of dispersal of adult wasps, and to determine whether complete parasitism of eggs within egg masses of the target host [oblique-bandedleafroller (OBLR), Choristoneura rosaceana(Harris)] occurred. Three weekly releases of wasps were made from a single release point in the center of each field during the flight of first generation OBLR adults. Sticky trap, sentinel egg mass and target-host egg mass data all indicated only a limited range of dispersal of T. minutum within the field. In addition, only partial parasitism of egg masses of the target host occurred even in close proximity to the release point. We discuss the importance of determining the response of Trichogramma females to previously-parasitized eggs when using Trichogramma wasps for biological control of lepidopterous species that oviposit large egg masses. [Publisher abstract]

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