Populations of sharpshooters in two citrus groves in east-central Florida as indicated by yellow sticky card traps

Sharpshooter infestations in Florida citrus are a concern due to potential introduction of citrus variegated chlorosis (CVC), a serious disease of citrus caused by a strain of the bacterium Xylella fastidiosa Wells et al. 1987. The disease is trans mitted by some sharpshooter species (Redak et al. 2004) and is present in citrus in Brazil (Lacava et al. 2001). We recently surveyed two citrus groves in east-central Florida for sharpshooters. One of the citrus groves was near Fort Pierce (27?26'08"N, 80?25'50"W), and the other was near Vero Beach (27?39'02"N, 80?28'02"W). One yellow sticky card trap (7.62 x 12.7 cm, sticky on both sides) (Great Lakes IPM, Vestaburg, MI) was placed in each of 10 trees randomly se lected within each block of trees. The traps were suspended 1 to 1.5 m above ground in each tree near the outside of the canopy from a branch by a twist tie and replaced weekly. The Fort Pierce grove contained many blocks of trees of various va rieties and ages, all regularly irrigated. The partic ular block sampled contained 'Marsh' grapefruit (Citrus paradise Macf.) trees (2.5 yr old, -1.3 m tall). Sampling was conducted from Jan 2005 to Jul 2006, when the young trees had to be removed due to discovery of citrus canker disease. The Vero Beach grove was a non-irrigated block of 'Temple' orange [C. reticulata Blanco x C. sinensis (L.) Os beck] trees (36 years old, -3.4 m tall). Sampling was conducted from Jan 2005 to the end of Dec 2007. Petroleum spray oil was periodically applied for plant disease control (twice to the young trees, 1 or 2 times each year to the mature trees). No other pesticides were applied. Three sharpshooter species were captured dur ing the study: Homalodisca ins?lita (Walker), H. vitripennis (Germar) and Oncometopia nigricans (Walker). These species had previously been shown to occur in citrus (Timmer et al. 1982), and H. vitripennis and O. nigricans are known to transmit CVC (Brlansky et al. 2002, Damsteegt et al. 2006). Only 2 H. ins?lita adults were captured during the study, a single adult at each grove dur ing Aug 2005. Greater numbers of this species might have been collected if traps had been posi tioned lower to the ground, as Ball (1979) re ported that H. ins?lita is a low flying species. Only 1 adult H. vitripennis was captured in the young trees; this individual was collected during Mar 2005. However, H. vitripennis was often relatively abundant in the mature trees. Differences in veg etation surrounding the 2 blocks may have been responsible for the near absence of H. vitripennis on traps in the young trees and its abundance on traps in the mature trees. The block of young trees was imbedded near the edge of a large, well manicured citrus grove surrounded by a wide ex panse of fallow ground. The block of mature trees frequently needed mowing and was surrounded in close proximity by many different plant species including grasses, herbaceous vegetation, various tree species, and ornamental plants. Low num bers of O. nigricans were frequently captured on traps in the mature trees, but only a single indi vidual was trapped in the young trees (Jun 2006). Applications of insecticides were made during the study to some blocks of trees in the vicinity of the young trees, which could have negatively influ enced the number of sharpshooters captured in the young trees. Increases in numbers of H. vitripennis cap tured on traps in the mature citrus trees generally occurred each year when air temperatures began to exceed 30?C and increases in rainfall occurred (Fig. 1). Peak means of 0.01, 0.004, and 0.01 adult H. vitripennis per cm2 per trap per week (2.0, 0.8, and 1.9 adults per trap per week) were observed in the mature trees during 2005, 2006, and 2007, re spectively. Mean populations of only 0.0003 and 0.001 adults per cm2 per trap per week were re ported in citrus groves during Apr-Jul (1980) in east-central Florida (Vero Beach and Indiantown, respectively) (extrapolations of data from Timmer et al. 1982). We observed a mean of 0.014 H. vitrip ennis per cm2 per trap per week during these months in the mature trees. Homalodisca vitrip ennis has been reported to be more abundant in northern than southern areas of Florida (Timmer et al. 1982). However, data comparisons indicated that appreciable population levels of if. vitripen nis may sometimes develop in citrus in east-cen tral Florida. Differences between population lev els of H. vitripennis we observed and those re ported by Timmer et al. (1982) could have been an artifact of environmental differences and/or differ ences in alternate host plant species used by H. vitripennis in the vicinity of the groves sampled. Numbers of H. vitripennis captured on traps in the mature citrus trees indicated that populations were abundant during Jul through Sep with large peaks during Jul and Aug (Fig. 1). Seasonal trends in population levels of adult H. vitripennis on traps at our mature-tree study site were simi lar to those reported in other areas of Florida (Timmer et al. 1982), although the largest popula tion peaks occurred somewhat later than previ ously reported. Oncometopia nigricans was cap tured on traps nearly every month of the year in