Sh. Dreistadt, CITRICOLA SCALE (HOMOPTERA, COCCIDAE) ABUNDANCE ON CHINESE HACKBERRY AND SCALE CONTROL WITH SPRAY OIL OR ACEPHATE TRUNK IMPLANTS, Journal of economic entomology, 89(2), 1996, pp. 481-487
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.