DISTRIBUTION AND PLANT ASSOCIATION RECORDS FOR HOMALODISCA COAGULATA (HEMIPTERA: CICADELLIDAE) IN FLORIDA

Abstract

Scientific Notes DISTRIBUTION AND PLANT ASSOCIATION RECORDS FOR HOMALODISCA COAGULATA (HEMIPTERA: CICADELLIDAE) IN FLORIDA M ARK S. H ODDLE 1 , S ERGUEI V. T RIAPITSYN 1 AND D AVID J. W. M ORGAN 2 Department of Entomology, University of California, Riverside, CA 92521 California Department of Food and Agriculture, Mt. Rubidoux Field Station 4500 Glenwood Drive, Riverside, CA 92501 The glassy-winged sharpshooter, Homalodisca coagulata (Say) is the focus of a major classical bi- ological control program in California. This insect presents a serious threat to several agricultural commodities and potentially native plants as well because of its ability to vector the xylem-inhabit- ing bacterium Xylella fastidiosa, the causative or- ganism of “scorch like” diseases such as Pierce’s Disease of grapes and oleander leaf scorch, a seri- ous malady of oleanders (Purcell & Saunders 1999). Homalodisca coagulata is an invasive pest in California and its native range is the southeast- ern and northeastern regions of the USA and Mex- ico, respectively (Triapitsyn & Phillips 2000). Homalodisca coagulata probably was translocated to southern California as egg masses via the move- ment of ornamental plants in the late 1980’s (So- rensen & Gill 1996) and without an accompanying natural enemy fauna; inordinate populations of glassy-winged sharpshooters have resulted. During foreign exploration by MSH and SVT for H. coagulata and associated egg parasitoids in Florida in August 2001, the authors visited the Florida State Collection of Arthropods, Bureau of Entomology, Florida Department of Agriculture and Consumer Services in Gainesville. Following discussion with colleagues there, specimen re- ceipt vouchers for H. coagulata were provided that had been sent in for identification by lay peo- ple, ornamental, horticultural, and agricultural growers from around Florida. A total of 229 re- ceipts were catalogued for adult H. coagulata over the period 1958-2001 inclusive, and chits con- tained information on date of collection, locality, host plant, and sex of specimens. These data were used to determine possible host plant records, dis- tribution densities, and submission frequencies for H. coagulata for different areas of Florida. Homalodisca coagulata was collected from at least 72 plant species in 71 genera contained in 37 families and Citrus spp. were the most com- mon plants from which adult H. coagulata were captured (Table 1). Of these plant association records in Table 1 it is uncertain which can sup- port development of H. coagulata from egg to adulthood. Adult H. coagulata are vagile and known to be highly polyphagous while the rela- tively immobile immature stages have a nar- rower host range (Turner & Pollard 1959). Citrus may be over-represented in this dataset because of regular pest surveys in this economically im- portant crop. To determine if regional differences in numbers of H. coagulata specimens sent in for identification existed, Florida was divided into thirds: (1) top third was north of 29° Latitude; (2) middle third was 27°-29°; and (3) the bottom third was south of 29°. Specimen receipts for each county in each section of the state were assumed to have been submitted for identification accord- ing to a poisson distribution and proportions were compared using a Log-likelihood Ratio Test (i.e., G-test). Pair-wise comparisons between regions from which specimens were received were made using χ 2 as sample sizes were large (Sokal & Rohlf 1995). The G-test was also used to determine if the frequency with which samples were submitted from each region significantly differed. Significant differences in the number of specimens received by region existed ( χ 2 = 11.03; df = 2; P = 0.004). Sig- nificantly more specimens were received for iden- tification from north Florida, intermediate numbers from central Florida, and fewest speci- mens came from south Florida (Fig. 1). No signifi- Fig. 1. Proportion (±95% CI) of specimens and sub- missions of adult Homalodisca coagulata from north, central, and south Florida to the Florida State Collec- tion of Arthropods in Gainesville for identification over the period 1958-2001. Bars with the same letters (upper case [specimen comparisons] or lower case [submission comparisons]) are not significantly different from each other at the 0.05 level of significance.