Studies on rearing Metaphycus helvolus (Hymenoptera: Encyrtidae) for augmentative release against black scale (Homoptera: Coccidae) on citrus in California

We conducted an evaluation of insectary production of black scale, Saissetia oleae (Olivier), and the encyrtid parasitoid Metaphycus helvolus (Compere) at the Fillmore Insectary in Fillmore, CA. Insectary scale, reared on 3-year-old oleander plants, tended to be smaller on leaves than those on stems and largest on green stems greater-or-equal, slanted3 mm in diameter. Many scale were below the optimal size range for parasitization when M. helvolus were first released to “sting” them. The majority of parasitoids (79%) were produced from scale on large green stems. Plants we evaluated produced a mean of 231 female M. helvolus and the sex ratio was near 1:1. When M. helvolus were allowed to oviposit only during discrete 3-day periods (days 0–3, 3–6, 6–9, or 9–12) on 33 day-old scale (at day 0), there were no significant differences in the mean numbers of parasitoid progeny produced among the four treatment periods; however, there appeared to be a trend towards higher production later in the “stinging” process. Female parasitoids emerged from larger scale than male parasitoids. We suggest that insectary production might be improved by delaying the normal “stinging” process until scales are 36 days old. Other methods of reducing per unit parasitoid cost are suggested that might be optimized if alternative methods of rearing black scale could be developed.