two counties is quite diverse, consisting of a cool coastal zone, a warm southern zone, and a mild midpeninsula zone. Data for 10 locations throughout the two counties during November through Previously imported February 1975-78 were processed using daily maximum and minimum tempera- tures obtained from National Oceanic parasite may control and Atmospheric Administration Cli- matology Reports. Results show a large range in chill-hour estimates, from 150 hours in San Francisco in 1975-76 to invading whitefly 1,403 in Woodside in 1977-78 (table 2). The chill-hour map constructed from these values shows that chilling is great- Mike Rose James B. Woolley est in the hot-summer/cool-winter, south peninsula zone (approximately 900 to 1,200 hours). The cool-summer/ mild-winter coastal zone had the lowest Duringurban grid surveys in Septem- Several other species of Tetraleurodes number of chill hours (200 to 600), while ber 1982, San Diego County biologists are found in southern California, in- the midpeninsula zone had an interme- discovered a new invading whitefly on cluding the mulberry whitefly, T. mori diate number of chill hours (600 to 800). avocado. Ray Gill, insect taxonomist for (Quaintance), acacia whitefly, T. aca- Both the midpeninsula and south penin- the California Department of Food and ciae (Quaintance), and Stanford white- sula zones can be considered climatical- Agriculture (CDFA), identified the new fly, T. stanfordi (Bemis). The red-band- ly closer to the inland locations of Davis invader as Tetraleurodes sp. Steve Na- ed whitefly can be distinguished from and Blackwell's Corner than to the kahara of the United States National these three species in southern Califor- coastal sites of Santa Maria and Watson- Museum then confirmed both the iden- nia by both adult and larval characters. ville. Therefore, the values calculated tification and the fact that the whitefly The red patterns on the wings are using the Aron equation should be a was new to California. Gill and Naka- unique to the red-banded whitefly and reliable indication of actual chill hours hara agree that this whitefly is the same are readily visible. Late larval stages of received. However, values calculated undescribed species known from the all four species are a characteristic jet for the coastal zone may not closely Caribbean, Central America, Florida, black, surrounded by a white marginal reflect the amount of chilling received: and Mexico. fringe. However, red-banded whitefly they are likely to be somewhat less than larvae, which develop on the under- actual values. These estimates are an The whitefly sides of maturing avocado leaves, pro- indication, nonetheless, that chilling The adults of both sexes of the invad- duce a copious white marginal fringe hours in this coast zone are probably not ing Tetraleurodes sp. bear red wing pat- that curls up and partially covers the sufficient to meet the requirements of terns, prompting the common name, dorsum. The white fringe of mulberry, high-chill fruit species. red-banded whitefly. acacia, and Stanford whitefly larvae The estimated value for the city of generally lies flat on the leaf surface and San Mateo also appears low in compari- is not as prominent. son with Burlingame and Redwood Additionally, of the three named spe- City. However, since the thermograph cies of Tetraleurodes previously in for San Mateo was adjacent to a wall, southern California, only mulberry heat from the wall may have increased whitefly has been recorded from avoca- night temperatures and resulted in the do. Therefore, host plant association is a low chill-hour estimate. A more likely partially reliable means of identifying value for San Mateo is suggested to be the red-banded whitefly. between 800 and 900 hours. In conclusion, this equation offers a History quick, economical means of estimating Following the original detections in chill hours for inland areas, and can be San Diego, we were asked to examine used to construct a chill-hour map. the newly discovered infestations. A Such a map can be useful when evaluat- preliminary search indicated that the ing an area for either commercial or Wing patterns of adult give red-banded red-banded whitefly infestation was home fruit, nut, and berry production. whitefly its common name. Also shown more widespread than had been known. Varieties can be selected for areas in here is black fourth-stage larva. A subsequent survey of avocado trees which they will receive adequate chill- by the County Department of Agricul- ing, and those with high-chill require- ture showed some 100 square miles in- ments can be avoided in zones with low fested in southern San Diego County. chilling. The extent of infestation in California and plant host range are as yet un- known. The California Department of Laurence R. Costello is Farm Advisor, University of California Cooperative Extension, San Mateo Food and Agriculture has determined County. The author thanks Ellen Gates. Statisti- that eradication programs against other cian. and Richard Snvder. Eioclimatoloeist. both whitefly species have generally failed. with' UC Cooperotive'Extension, for th& 'assis- tance. Thus, attaining biological control is Adult female Cales noacki wasp parasi- critical, particularly because avocado tizes both red-banded and woolly whitefly. growers rely extensively or completely

24 CALIFORNIA AGRICULTURE, MARCH-APRIL 1984 White curly fringe that partially covers dorsum characterizes late-stage red-banded Exit hole on red-banded larva at left indi- whitefly larva. Fringes of late-stage mulberry whitefly larvae lie nearly flat. cates parasitization by Cales noacki. on natural enemies to control other enemies (parasites) have been discov- of parasitization during the winter re- pests. Pesticide applications against an ered, imported, and established in sulted in an overall red-banded whitefly invading foliar pest on avocado could southern California. mortality of about 92 percent. create secondary outbreaks of mites, Of the many parasites imported dur- These trends proved to be wide- Lepidoptera, scale, and mealybug, all of ing the biological control project on spread. Our continuing field searches which are usually under complete bio- woolly whitefly, Amitus spiniferus and parasite recovery samples all logical control. Brethes and Cales noacki Howard are showed evidence of C. noacki. San Initial searches for evidence of hy- now established and have proved very Diego County biologists provided 27 menopterous parasites attacking the effective. The tiny wasp C. noacki is parasite recovery samples collected red-banded whitefly in San Diego were now the most abundant woolly whitefly from avocado on nine sites throughout negative. Parasites of red-banded white- parasite in southern California. the infested area from November 24, fly are known to exist in Mexico, how- Over the past several years, we have 1982, to February 17,1983. Cales noacki ever, where this species had previously found that C. noacki successfully parasi- was recovered in 25 of the 27 samples. been observed. In Uruapan, Michoacan, tizes both mulberry whitefly and acacia Most importantly, C. noacki was found Mexico, the red-banded whitefly re- whitefly. Although no evidence of para- to be active, and rates of parasitization cently attained pest status on avocado, sitization of the red-banded whitefly by were high (from about 50 percent to apparently as a result of a pesticide- C. noacki was found initially in San nearly 100 percent in all 25 samples induced upset. The avocado treehopper, Diego, there was a good probability that from all sites), even though red-banded Metcalfiella monogramma (German), it would occur because of the demon- whitefly populations were very small has been treated with a pyrethroid in- strated ability of C. noacki to parasitize (averaging 3 to 15 larvae per sample secticide in Michoacan for the past sev- two other Tetraleurodes spp. leaf). Sample leaves were those which eral years and new pest problems, in- Parasite recovery samples were col- bore larvae of the red-banded whitefly. cluding Tetraleurodes sp., have lected throughout the known infested occurred during this period. Untreated area in San Diego to determine if C. Conclusion avocado groves in Uruapan were found noacki would parasitize the red-banded Cales noacki has rapidly achieved to be nearly free of the red-banded whitefly. During November 1982, we high rates of parasitization resulting in whitefly because three species of para- selected several varieties of avocado substantial mortality to overwintering sites - two Encarsia spp. and an Eret- trees for study in a small grove harbor- populations of the invading red-banded mocerus sp. - were maintaining satis- ing the largest observed populations of whitefly, Tetraleurodes sp. in San Dicgo factory biological control. red-banded whitefly in San Diego. We County. Such high rates of parasitiza- began preliminary analyses of the biol- tion when red-banded whitefly popula- Fortuitous biological control ogy, behavior, and phenology of the new tions were low indicate that complete California has been invaded three whitefly, along with determination of biological control may be occurring other times by exotic whitefly species mortality imposed by any naturally oc- throughout the known infested area and since the early 1900s. The citrus white- curring parasites on this site. The infor- that importation of additional parasite fly, Dialeurodes citri Ashmead, was the mation was needed to plan a biological species may not be required. Addition- first of these to be discovered when it control research project that would ally, the rate of dispersal of the red- was found in Marysville in 1906 (see stress parasite importations from Mexi- banded whitefly to uninfested areas has California Agriculture, July-August co, followed by rapid field colonization, undoubtedly greatly decreased as a re- 1981). Woolly whitefly, Aleurothrixus establishment, and measurement of the sult of population regulation by C. floccosus (Maskell), was detected 60 effect of the imported natural enemies noa cki. years later in nearly the same areas of on red-banded whitefly populations. Mike Rose and James B. Woolley. formerly with the San Diego County that now harbor the Although it was no great surprise to Division of Biological Control, Department o Ento red-banded whitefly (California Agricul- find C. noacki parasitizing the red-band- mology. University of California, Riverside. ar, ture, May 1976). The bayberry whitefly, ed whitefly during November 1982, it now Staff Research Associate and Assistant Profes- sor of Entomology, respectively, Texas A 6 M Parabemisia myricae (Kuwana), was was surprising to find that rates of para- Universitv. Collene Station. Texas. Rav Gill. Cali- found in California in 1978 (California sitization very rapidly reached nearly fornia Departmegt of Food and Agriculture, pro- vided taxonomic information and the photo raph Agriculture, March-April 1981). All of 50 percent on the study site within three of the adult red-banded whitefly. George Opef, San these whitefly species attack citrus and weeks. Rates of parasitization by C. Diego County Department of Agriculture, provided parasite recovery samples. The authors especiall have been subjects of biological control noacki reached 82 percent on this site thank Paul DeBach, Division of Biological Control research, during which effective natural by mid-January 1983. These high rates UC Riverside.

CALIFORNIA AGRICULTURE, MARCH-APRIL 1984 25