Augmentative releases of a parasitoid (Metaphycus sp. nr. flavus) against citricola scale (Coccus pseudomagnoliarum) on oranges in the San Joaquin Valley of California

Augmentative release trials with Metaphycus sp. nr. flavus (Howard), an encyrtid parasitoid of citricola scale, Coccus pseudomagnoliarum (Kuwana), were conducted in two orange groves in the southern San Joaquin Valley of California. Between mid-February and early May 1998, over 4000 female parasitoids were released per experimental tree. Control trees, where no parasitoids were released, were at least eight trees (45 m) distant from release trees. Samples taken between 18 April and 20 May indicated that levels of live citricola scales on release trees were significantly reduced on twigs, greater numbers of female M. sp. nr. flavus were recovered from scales, and the fraction of scales parasitized by Metaphycus spp. was significantly higher. These data support the hypothesis that parasitism by the released wasps suppressed the scale population. By mid-May, more M. helvolus (Compere) were recovered from control than from release trees, suggesting that released M. sp. nr. flavus had depleted the scales available to M. helvolus. Additionally, in May, more male Coccophagus lycimnia (Walker) were recovered from release trees. C. lycimnia produces male offspring by heterospecifically or conspecifically hyperparasitizing parasitoids of citricola scale. The implications of these results for developing augmentative parasitoid release strategies against citricola scale in California citrus are discussed.