Comparative efficacy of different combinations of natural enemies for the biological control of California red scale in citrus groves

The California red scale (CRS), Aonidiella aurantii, a worldwide citrus pest, has the ectoparasitoid Aphytis melinus as its main natural control agent. Other natural enemies can complement A. melinus in the pest control. For 3 years we studied the incidence of the parasitoids and predators on CRS populations of 19 citrus groves divided in four groups according to its parasitoid composition to determine which combination of natural enemies reaches higher effectiveness in the biological control of CRS in field conditions. The parasitoids species preferred different scale instars and different periods of the year for parasitism. In the groves where A. melinus was present in high numbers, either alone or coexisting with Aphytis chrysomphali, parasitism rates reached 22.4% on average, whereas parasitism rates were much lower (11.5%) when A. chrysomphali was the dominant parasitoid. The best parasitism level was achieved when these ectoparasitoids occurred together with the endoparasitoid Encarsia perniciosi. The average annual mortality rate of A. aurantii was 73.6%. The analysis of dead scales killed by Aphytis confirms the results obtained in parasitism of live scales. The more abundant predators were Lestodiplosis aonidiellae and Rhyzobius lophantae. The incidence of predators on the CRS populations was comparatively much lower.