CITRICOLA SCALE (HOMOPTERA, COCCIDAE) ABUNDANCE ON CHINESE HACKBERRY AND SCALE CONTROL WITH SPRAY OIL OR ACEPHATE TRUNK IMPLANTS

Citricola scale, Coccus pseudomagnoliarum (Kuwana), infesting Chinese hackberry, Celtis sinensis Persoon, was studied during 1991-1994 in Da vis, CA. Female scale and crawler densities on untreated trees increas ed each year in comparison with previous years; populations of this in troduced subtropical species were recovering from a population decline possibly induced by cold temperatures in northern California during t he winter of 1990-1991. In California, European fruit lecanium, Parthe nolecanium corni (Bouche). P. pruinosum (Coquillett), and Calico scale , Eulecanium cerasorum (Cockerell), also infest Chinese hackberry. How ever, citricola scale was 5-25 times more abundant than the Parthenole canium species combined, and no calico scale were found on sample bran ches. Citricola scale was more abundant in the east and north tree can opy in comparison with tile sunnier south canopy; abiotic mortality fr om hot, dry conditions may help to reduce scale populations. Transpare nt sticky tape traps helped monitor scale crawler populations and were used to time foliar-season control actions. The number of crawlers tr apped depended on scale density, not sticky trap size. Crawler density peaked at 353 DD (SD = 43) above 11 degrees C accumulated from 1 Marc h, but laboratory development rate and threshold temperature data and sampling from other locations are needed to validate this empirical mo del. Thr ee control methods were equally effective: a single foliar sp ray of 2% superior oil, acephate implants during the foliar season, or a single application of 3% supreme oil to bark during the dormant sea son. Each method reduced scale populations by approximate to 50% durin g the season of treatment, but there was no difference among treatment s 1 yr after control actions. Apparent parasitism of female citricola scale in Davis, CA, was only approximate to 1%. Parasitism was signifi cantly lower on treated trees.