MATERIALS AND METHODS
Environmental ConditionsStock cultures of the host and parasite were maintained in an insectary room at 26.7±1°C and 50% RH. Light was supplied by eight 40-watt, cool, fluorescent tubes, and was reg ulated by an automatic time switch set for alternating periods of 12 hours of light and 12 hours of darkness. A fan circulated air in the room to prevent stratification of air.
Cultures of hostCultures of P. operculella were maintained in the insectary on White Rose and Russett potato tubers, using techniques developed by Plainer and Oatman (1968). Adult P. operculella were placed in cages which held muslin cloth that had been soaked in potato juice to stimulate oviposition thereon. These u egg cloths" were removed daily and the eggs used to establish subcultures of the parasites or for various experiments.
Cultures of parasiteChelonus kellieae and C. phthorimaeae were handled identically throughout these studies. Studies of both species were conducted concurrently in separate spaces with identical conditions and repeated for replication. A culture of C. kellieae has been maintained in the insectary since its release from quarantine in June 1973. The culture of C. phthorimaeae was obtained in 1977 from host material collected from potato plants grown on the University of California's field station at Moreno.The parasite colonies were maintained in wooden cage "emergence units" (41.9 X 41.9 X 35.6 cm) with glass tops, lateral panels of organdy cloth for ventilation, and a detachable section on one side to facilitate manipulation of the material inside the emergence unit without letting the insects escape. White sand was distributed evenly over the bottom of the emergence units for pupation of the larvae. To maintain the culture, female parasites, newly emerged from hosts, were removed daily and placed in a wooden cage "sting unit" (30.5 X 35.6 X 27.9 cm). The sting unit was similar in construction to the emergence unit, except that its top was covered with black cloth to eliminate light. The back organdy panel also was covered with black cloth, except for a 10.2 X 10.2 cm area which permitted light to penetrate. An egg cloth (ca. 10 X 10 cm) with newly oviposited host eggs was fastened to the inside of this lighted area of the sting unit. Female parasites were attracted to this lighted area and, upon contact with the egg cloth, oviposited in the host egg. After a 24-hour exposure, the host egg cloth was removed and placed on punctured tubers on an inverted galvanized wire tray (12 X 12 cm) within the emergence unit. These procedures were repeated periodically, using one emergence unit and one sting unit for each species.When needed, virgin female or male parasites were obtained by isolating cocoons in clear gelatin capsules (size 000) and holding them until the parasite emerged.