Suitability of citricola scale Coccus pseudomagnoliarum (Hemiptera: Coccidae) as host of Metaphycus helvolus (Hymenoptera: Encyrtidae): Influence of host size and encapsulation

Citricola scale Coccus pseudomagnoliarum (Kuwana) (Hemiptera: Coccidae), a widespread citrus pest in California and Europe, has been recently found in Spain. A preliminary survey suggests that Metaphycus helvolus (Compere) (Hymenoptera: Encyrtidae) is its main parasitoid. This parasitoid has been also documented in other citrus areas where its efficiency as biological control agent seems to be limited. Several hypotheses have been previously proposed to explain its lack of success. In this paper we study the relationship between citricola scale and M. helvolus in both field and laboratory to elucidate some of these hypotheses. According to our data, M. helvolus may play an important role as a biological agent when the scale length ranges from 1 to 2 mm. For those scale sizes, M. helvolus develops as a solitary parasitoid and its sex allocation pattern appears to be host size dependent. Once the scale length reaches 2 mm at the end of the spring, high encapsulation levels reduce M. helvolus efficiency as a citricola scale parasitoid. During that time, as well as in summer and fall, when citricola scale is too small to be parasitized, M. helvolus may survive parasitizing alternative soft scales present in Mediterranean groves.