The glassy-winged sharpshooter, Homalodisca coagulata (Say) is the focus of a major classical biological 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-inhabiting bacterium Xylella fastidiosa, the causative organism of “scorch like” diseases such as Pierce’s Disease of grapes and oleander leaf scorch, a serious malady of oleanders (Purcell & Saunders 1999). Homalodisca coagulata is an invasive pest in California and its native range is the southeastern and northeastern regions of the USA and Mexico, respectively (Triapitsyn & Phillips 2000). Homalodisca coagulata probably was translocated to southern California as egg masses via the movement of ornamental plants in the late 1980s (Sorensen & 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 receipt vouchers for H. coagulata were provided that had been sent in for identification by lay people, ornamental, horticultural, and agricultural growers from around Florida. A total of 229 receipts were catalogued for adult H. coagulata over the period 1958-2001 inclusive, and chits contained information on date of collection, locality, host plant, and sex of specimens. These data were used to determine possible host plant records, distribution 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 common plants from which adult H. coagulata were captured (Table 1). Of these plant association records in Table 1 it is uncertain which can support development of H. coagulata from egg to adulthood. Adult H. coagulata are vagile and known to be highly polyphagous while the relatively immobile immature stages have a narrower host range (Turner & Pollard 1959). Citrus may be over-represented in this dataset because of regular pest surveys in this economically important 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 according 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 χ2 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 (χ2 = 11.03; df = 2; P = 0.004). Significantly more specimens were received for identification from north Florida, intermediate numbers from central Florida, and fewest specimens came from south Florida (Fig. 1). No significant differences (χ2 = 3.23; df = 2; P = 0.20) in frequency of submissions from each region were observed (Fig. 1).
When taken together, these data suggest that more H. coagulata were caught and submitted for each identification event from North and Central Florida but the rate of submission was similar across the entire state. These data support MSH and SVT’s observations that H. coagulata is more abundant and easier to collect in northern Florida in comparison to central and southern Florida. Possible constraints on the southern distribution of H. coagulata could be related to temperature, humidity, and rainfall clines or interspecific competition with other proconiine sharpshooters (e.g., Oncometopia nigricans [Walker] [Hemiptera: Cicadellidae: Cicadellinae: Proconiini]) that have similar habitat requirements.
This work was supported in part by the California Department of Food and Agriculture. We thank Ruth Vega (UCR) for assistance with data entry. Susan Halbert at the Florida State Collection of Arthropods, Bureau of Entomology, Florida Department of Agriculture and Consumer Services in Gainesville helped with locating H. coagulata identification records.
Information from identification receipt vouchers prepared by the Florida State Collection of Arthropods, Bureau of Entomology, Florida Department of Agriculture and Consumer Services in Gainesville over the period 1958-2001 for Homalodisca coagulata were analyzed for information on host plants and distribution in Florida. Homalodisca coagulata was recorded from at least 72 plant species in 37 families and greater numbers of H. coagulata were sent in for identification from northern Florida even though there were no significant difference in specimen submission frequencies from north, central, and south Florida.